Chromatography controlled by light

Abstract

The present invention relates to means and methods for the one-step affinity purification of a polypeptide of interest controlled by light. Accordingly, the present invention relates to a polypeptide comprising an N-terminal or C-terminal light-responsive affinity tag, wherein said N-terminal or C-terminal light-responsive affinity tag may comprise a non-natural light-responsive amino acid. Accordingly, the present invention further relates to such light-responsive affinity tags. Further provided herein are means and methods for the recombinant coupling of such non-natural light-responsive amino acids and / or light-responsive affinity tags to a polypeptide of interest. Provided herein is also a solid (stationary) phase to be employed with said light-responsive affinity tag in a method for the purification of said polypeptide of interest. Further provided is a kit comprising any of the above.

Description

[0001]New PCT-patent application Technische Universität München Vossius Ref.: AG2706 PCT S3 Chromatography controlled by light The present invention relates to means and methods for the one-step affinity purification of a polypeptide of interest controlled by light. Accordingly, the present invention relates to a polypeptide comprising an N- terminal or C-terminal light-responsive affinity tag, wherein said N-terminal or C-terminal light-responsive affinity tag may comprise a non-natural light-responsive amino acid. Accordingly, the present invention further relates to such light-responsive affinity tags. Further provided herein are means and methods for the recombinant coupling of such non-natural light-responsive amino acids and / or light-responsive affinity tags to a polypeptide of interest. Provided herein is also a solid phase (or stationary phase) to be employed with said light-responsive affinity tag in a method for the purification of said polypeptide of interest. Further provided is a kit comprising any of the above. Bioaffinity chromatography has revolutionized protein purification in many areas, from fundamental research up to biotechnological and biopharmaceutical applications. In this technique, a specific ligand or binding partner (also including a specific antibody) of the protein of interest (POI) is covalently immobilized onto a stationary phase, usually a biocompatible hydrophilic polymer such as agarose or polyacrylamide. The POI is applied as a mixed solution with various contaminants – typically from a cell extract or culture supernatant – in the aqueous mobile phase whereby it forms a non-covalent complex with the immobilized ligand. After thoroughly washing out the contaminants via buffer flow, the POI gets specifically eluted in a following step. This can be achieved either with a solution of a competing ligand or by changing the buffer conditions of the mobile phase, for example to high or low pH, elevated salt concentration, or by applying a chemical denaturant, detergent, or chelating agent. Bioaffinity or, simply, affinity chromatography emerged more than 50 years ago as a technique mainly for the purification of enzymes, but also of antibodies or antigens as well as binding proteins such as avidin, from natural sources (Cuatrecasas & Wilchek, 1968; Lowe & Dean, 1974). More recently, after the advent of gene technology and the possibility of overexpressing recombinant proteins in a host cell of choice, the concept of the affinity tag emerged. In this advanced embodiment, the immobilized ligand does not primarily interact with the POI itself – e.g. by targeting an enzyme active site, a ligand-binding site or an immunological paratope or epitope – but with a distinct peptide sequence that is fused to its N- or C- terminus and enables specific engagement. The first example was the myc-tag (Munro & Pelham, 1986), a short epitope peptide used in combination with a monoclonal antibody (MAb) immobilized to the stationary phase, allowing elution under acid conditions. This was followed by the His-tag in conjunction with immobilized metal ion affinity chromatography (IMAC), initially applied under strongly denaturing conditions (6 M GdnHCl) with acid elution (Hochuli et al., 1988) and, subsequently, under physiological buffer conditions using competitive elution with imidazole (Skerra et al., 1991). Further examples include the FLAG peptide tag (DYKDDDDK), utilizing a MAb that binds the peptide only in the presence of CaII, allowing elution in the presence of EDTA (Hopp et al., 1988), and the Strep-tag (AWRHPQFGG or WSHPQFEK for the Strep- tag II), which targets the widely applied protein reagent streptavidin, whose binding activity can be competed with biotin derivatives (Schmidt & Skerra, 1993). Despite wide application, including the industrial use of protein A affinity chromatography for the purification of antibody-based biopharmaceuticals (Ramos-de-la-Peña et al., 2019; Uhlén, 2008), there is a general disadvantage associated with bioaffinity chromatography: the eluted POI is usually contaminated with a ligand, or denaturant, detergent, chelator, which may interfere with subsequent use for biochemical or in vivo experiments. Furthermore, its functional integrity can be affected by the application of extreme pH, high salt concentration, depletion of metal ions or action of the denaturant or detergent. Therefore, the affinity-purified protein normally has to undergo an additional purification step, often size exclusion chromatography (SEC) or ion exchange chromatography (IEC), but at least a buffer exchange (e.g. by dialysis or cross-flow filtration) before it is ready for experimental study or practical use. Accordingly, an elution method that does not involve any addition of reagents, or change of buffer conditions, is highly desirable as it would directly yield the isolated protein in the mobile phase in which it was applied – or in a suitable buffer of choice. WO 2018 / 206738 describes a method for the light-controlled isolation of a protein of interest comprising a Strep-tag. In particular, the protein reagent streptavidin was engineered to comprise the light-responsive amino acid 4’-carboxyphenylazophenylalanine in proximity to the biotin binding pocket (i.e., in proximity to the active site of streptavidin). Irradiation of said light- responsive amino acid with a specific wavelength is described to alter the protein conformation and consequently its affinity to the ligand (i.e., the Strep-tag). Here, coupling of the engineered streptavidin to a chromatography matrix is described to allow for light-dependent elution of the protein of interest carrying the Strep-tag (II). Light-responsive polymers (such as light-responsive amino acids) are well known in the art. Such light-responsive compounds may comprise light-responsive azo-benzene groups as described in Shimoboji (2002) disclosing site-specific conjugation of light-responsive polymers (namely N,N- dimethylacrylamide (DMA)-co-4-phenylazophenyl acrylate (AZAA) copolymer (DMAA) and DMA-co- N-4-phenylazophenyl acrylamide (AZAAm) copolymer (DMAAm)) near the biotin-binding pocket of streptavidin, thereby providing control of ligand (e.g., biotin) binding affinity in response to irradiation with UV and visible light. Parisot (2009) discloses the engineering of a FLAG-tag that comprises N-Fmoc- AMPB as light-responsive polymer, however, concludes that their approach does not present a practical solution for bio-separation (i.e., for affinity purification). Accordingly, the technical problem underlying the present invention is the provision of improved means and methods for the one-step affinity purification of a polypeptide of interest, wherein contamination(s) and / or biochemical modification(s) of the eluted molecule of interest are reduced. The technical problem is solved by provision of the embodiments as defined herein and as characterized in the claims. Accordingly, the present invention relates to a polypeptide comprising an N-terminal or a C-terminal light- responsive affinity tag. In particular, the present invention relates to a polypeptide comprising a structure of formula (I) or of formula (II): X-[L-]lP (I) P[-L]l-X (II) wherein X is a light-responsive affinity tag, L is a linker, l is 1 or 0, so that L can be present or absent, P is a polypeptide of interest, wherein in formula (I) X-[L-]l is linked to the amino-terminus of P, and wherein in formula (II) [-L]l-X is linked to the carboxy-terminus of P. In particular, wherein [X-] of formula (I) may comprise a structure of [A-]aB-[C-]c so that the polypeptide of formula (I) may be a polypeptide with a structure according to formula (III) [A-]aB-[C-]c[L-]lP (III), wherein [-X] of formula (II) may comprise a structure of [-A]a-B[-C]c, so that said polypeptide of formula (II) may be a polypeptide with a structure according to formula (IV) P[-L]l[-C]c-B[-A]a (IV), wherein A may comprise one or more amino acid(s), a may be 1 or 0, so that A can be present or absent, B may be a non-natural light-responsive amino acid, C may comprise one or more amino acid(s), c may be 1 or 0, so that C can be present or absent, wherein in formula (III) X-[L-]l may be linked to the amino-terminus of P, and wherein in formula (IV) [-L]l-X may be linked to the carboxy-terminus of P. In particular said non-natural light-responsive amino acid (i.e., a non-natural light-responsive α-amino acid) may be selected from benzazo-phenylalanine (Baf; commonly also referred to p-(phenylazo)-L- phenylalanine or Pap), p-amino-benzazo-phenylalanine, and p-carboxy-benzazo-phenylalanine, preferably Baf. Thus, herein provided is a polypeptide of interest (also referred to as protein of interest; POI) comprising an N-terminal or a C-terminal light-responsive affinity tag (also referred to as light-responsive affinity tag, affinity tag, or tag), which paves the way for the one-step affinity purification of said polypeptide of interest using means and methods also detailed hereinbelow. In particular, the herein provided polypeptide of interest may be comprised in a liquid phase (also herein referred to as mobile phase) and may be applied to the chromatography column of a chromatography apparatus / device. As further detailed herein below, when in the ground state the light-responsive affinity tag (in particular, a non-natural light-responsive amino acid comprised in said light-responsive affinity tag) may be in a first configuration (in particular the trans-configuration). The (non-natural) light-responsive amino acid can be brought into the trans-configuration by irradiation with a particular wavelength of light (e.g., 405 nm to about 470 nm and / or daylight). When in the ground state (i.e., in the trans-configuration), the light-responsive amino acid has particularly and surprisingly high affinity to a solid phase also provided herein (in particular to a solid phase comprising α-cyclodextrin / α-cyclodextrin groups). Accordingly, when applying a liquid phase comprising the polypeptide of interest comprising the light-responsive affinity tag in a ground state (i.e., comprising said light-responsive amino acid in the trans-configuration) to a suitable solid phase (e.g., comprising α-cyclodextrins), the light-responsive affinity tag has particularly high affinity to said solid phase and may cause the polypeptide of interest to be retained on the solid phase. In contrast, any other polypeptide (or other molecule that does not comprise the light-responsive affinity tag) may not be retained on said solid phase. Accordingly, any contaminant or unwanted molecule (that does not comprise said affinity tag and / or that does not have affinity to α-cyclodextrin) may be separated from the polypeptide of interest by, e.g., washing of the chromatography column. Washing of the chromatography column (e.g., with a washing buffer) may cause any contaminant to elute with the buffer flow, resulting in highly pure protein of interest in association with the solid phase. Subsequent irradiation of the polypeptide of interest with a different wavelength (e.g., UV-light, in particular UV-light having a wavelength of about 310 nm to about 370 nm) causes the light-responsive affinity tag to change its conformation. In particular, irradiation with such wavelengths of light may cause the light-responsive amino acid to switch from the trans-configuration to the cis-configuration, thereby changing (i.e., reducing / abolishing) its affinity to the solid phase. Accordingly, when in the cis- configuration the light-responsive essentially does not bind to the solid phase and may be eluted with any desired buffer or solution (herein also referred to as elution buffer). In particular, the composition of this elution buffer is not particularly limited as, in contrast to state of the art chromatography procedures inter alia discussed herein above, the elution buffer of the present invention is not responsible for altering the affinity of the affinity tag to the solid phase. Thus, this elution buffer does not need to comprise any ligand, denaturant, detergent, chelator, or the like in order to alter the (light-responsive affinity tags) affinity to the solid phase (e.g., to α-cyclodextrin). This allows for the purification of a POI without the introduction of any contaminant (such as ligands, denaturants, detergents, chelators, or the like) during the elution. Accordingly, a technical advantage of the herein provided means and methods is the inexpensive and facile purification of a polypeptide of interest (comprising a light-responsive affinity tag according to the present invention) in a single purification step (i.e., without the need for any additional purification steps) as: - no additional contaminants need to be introduced to / included in the elution buffer (see, inter alia, Example 6), and - most / essentially all contaminants that are present in the liquid phase (i.e., the solution comprising the POI) are removed by washing the chromatography column (see, inter alia, Example 6). A further advantage of the present invention may be the small size of the herein provided light-responsive affinity tag. It is well known in the art that larger affinity tags may (negatively) affect the structure and / or the function of a protein of interest (i.e., the protein comprising said affinity tag). Sizes of state of the art affinity tags range from multiple hundred amino acids (for example, the glutathione S-transferase (GST) affinity tag comprises 211 amino acids while the maltose binding protein (MBP) affinity tag comprises 370 or 371 amino acids) to about or less than about 10 amino acids (for example the FLAG-tag comprises 8 amino acids). As is further detailed herein below, the herein provided light-responsive affinity tag (i.e., the affinity tag that may be linked to the polypeptide of interest in accordance with the present invention) may comprise varying sizes, however, as is shown in the enclosed examples (in particular in Example 9), an affinity tag with a sizes of only few (e.g., about 5 to about 2) amino acids is sufficient to allow for the one- step purification of a polypeptide of interest. In accordance with the present invention, even an N-terminal or a C-terminal light-responsive affinity tag comprising only a single amino acid residue (i.e., a single light-responsive amino acid, such as Baf), when in the trans-configuration, may have sufficient affinity to the solid phase to enable the successful purification of a polypeptide of interest. Accordingly, such light-responsive affinity tags may be particularly small in size and, as result, may cause low or reduced sterical hinderance of the polypeptide of interest. Hence, it is conceivable that the herein provided affinity tags may have particularly low / reduced (negative) effects on the structure and / or the function of a protein of interest (as compared to state of the art affinity tags comprising a larger number of amino acids). The above mentioned advantages of the present invention are, inter alia, further detailed in the enclosed examples. In particular, Examples 5 and 6 illustratively show that the herein provided light-responsive affinity tag (comprising a non-natural light-responsive amino acid) may be (e.g., as part of a recombinant protein) coupled to various proteins of interest and may, accordingly, be used for the successful, facile and time and cost efficient purification of such proteins of interest. Accordingly, the present invention further relates to a light-responsive affinity tag as comprised in the protein of interest disclosed herein above. Accordingly, the present invention relates to a light-responsive affinity tag wherein said light-responsive affinity tag comprises a structure of formula (V) or formula (VI) [A-]aB-[C]c (V) [C]c-B[-A]a, (VI) wherein A comprises one or more amino acid(s), a is 1 or 0, so that A can be present or absent, B is a non-natural light-responsive amino acid, C comprises one or more amino acid(s), c is 1 or 0, so that C can be present or absent. In particular said non-natural light-responsive amino acid may be selected from benzazo-phenylalanine (Baf), p-amino-benzazo-phenylalanine, and p-carboxy-benzazo-phenylalanine, preferably Baf. As detailed herein above and below, the herein provided light-responsive affinity tag may be coupled to the N-terminus or to the C-terminus of polypeptide of interest and may thus pave the way for the light- controlled affinity purification of the same. While the enclosed examples illustratively show that both N- terminal and C-terminal coupling of a herein provided light-responsive affinity tag to such a polypeptide of interest allow for the efficient purification thereof (see, inter alia, Examples 4 to 6), the present inventors have surprisingly found that coupling of such an affinity tag to the N-terminus of a POI may be particularly advantageous in the context of the present invention. This is further detailed in the enclosed Example 5. Furthermore, in the context of the present invention, it was found that the amino acid sequence of the regions N-terminally or C-terminally flanking the non-natural light-responsive amino acid in the light- responsive affinity tag (i.e., [A-]a and [C-]c in formula (III), [-C]c and [-A]a in formula (IV), [A-]a and [C]c in formula (V) and [C]c and [-A]a in formula (VI)) may by particularly beneficial with regard to the binding affinity of the affinity tag to α-cyclodextrin. For example, in the enclosed Example 9 it is illustratively shown that various sequences of the herein provided light-responsive affinity tag (i.e., [A-]aB-[C-]c in formula (III), [-C]c-B[-A]a in formula (IV), [A-]aB-[C]c in formula (V), or [C]c-B[-A]a in formula (VI)) are particularly advantageous (i.e., when the non-natural light-responsive amino acid is in the trans- configuration, the respective affinity tag sequences leads to particularly strong affinity to an α-cyclodextrin matrix, as can be observed by the low or reduced migration of a band corresponding to the tagged protein of interest under day light irradiation; Figure 15). In the context of the present invention such flanking amino acid regions may be preferably selected from the group of (natural) amino acids consisting of glycine, proline, alanine, and serine. This is the result of extensive experimentation and could not have been predicted by the skilled artisan merely based on the knowledge provided by the prior art. In particular, Table 1 details several non-limiting amino acid sequences of the herein provided N-terminal or C-terminal light-responsive affinity tags that are particularly useful in the context of the present invention (inter alia, due to their improved / strong affinity to α- cyclodextrin, for example when irradiated with day light). As is detailed herein above and below, such N-terminal or C-terminal light-responsive affinity tags are particularly useful in the purification of a polypeptide of interest comprising the same / being linked to the same. Accordingly, the present invention also relates to a method for the isolation and / or purification of a polypeptide comprising an N-terminal or a C-terminal light-responsive affinity tag from a liquid phase, wherein the method comprises the steps of: (a) contacting said liquid phase with a solid phase, wherein said light-responsive affinity tag comprises a non-natural light-responsive amino acid, and wherein said non-natural light-responsive amino acid is in a first configuration so that it has high affinity to said solid phase; and (b) irradiating the light-responsive affinity tag with a wavelength of light that changes said non- natural light-responsive amino acid to a second configuration such that it has a decreased affinity to said solid phase as compared to the affinity thereof in step (a) and eluting said polypeptide comprising the N-terminal or the C-terminal light-responsive affinity tag. In particular, the polypeptide comprising an N-terminal or C-terminal may comprise a structure as detailed in any one of formula (I), (II), (III), or (IV) and the solid phase may be a solid phase comprising an α- cyclodextrin group (also referred to as α-cyclodextrin herein). In the context of the present invention, the binding of the protein of interest comprising the N-terminal or C-terminal light-responsive affinity tag (in particular the binding of the non-natural light-responsive amino acid) to the solid phase (in particular to a solid phased comprising α-cyclodextrin) may be particularly effective when the liquid phase comprises particular salt compositions and / or concentrations. This is illustratively shown in the enclosed Figure 17 and Example 10. The herein above and below detailed advantages of the means being employed in such a method for the purification of a polypeptide comprising an N-terminal or a C-terminal light-responsive affinity tag from a liquid phase also apply to such a method mutatis mutandis. The herein provided means and methods (in particular certain embodiments of the herein provided method for the isolation and / or purification of a polypeptide comprising an N-terminal or a C-terminal light-responsive affinity tag) are illustratively and non-limiting summarized in the schematic representation of Figure 23. The present invention further relates to a solid phase comprising α-cyclodextrin groups. Further provided herein are means and methods for the manufacture of such solid phases comprising α-cyclodextrin groups. As detailed herein above and below, the present inventors have surprisingly found that the herein provided light-responsive affinity tag (in particular the non-natural light-responsive amino acid comprised in the same) has particularly high affinity to α-cyclodextrin. In particular, the non-natural light-responsive amino acid benzazo-phenylalanine (Baf), when in the trans-configuration (i.e., when illuminated with e.g., daylight) has high affinity to the hydrophobic cavity of α-cyclodextrin. Namely, when contacted with α- cyclodextrin, Baf comprises a remarkably low equilibrium dissociation constant (KD or Kd, also referred to as dissociation constant herein) of about 91.0 µM. Illumination with e.g., UV-light effectively alters the configuration of Baf (from the trans-configuration to the cis-configuration), thereby altering (i.e., reducing if not abolishing) its affinity to α-cyclodextrin (here, no equilibrium dissociation constant could be determined). This is illustratively shown, inter alia, in the enclosed Figure 2 and Example 2. Accordingly, the herein provided α-cyclodextrin solid phase (e.g., when housed or comprised in a chromatography column) further paves the way for the one-step affinity chromatography purification of a polypeptide of interest comprising an N-terminal or a C-terminal light-responsive affinity tag in accordance with the present invention. As is evident from the enclosed examples, the herein provided stationary phase (or solid phase) itself is translucent, functionally inert and chemically robust, which is particularly useful for its use in light-controlled chromatography approaches (also provided herein). It was further surprisingly found that the switch of the configuration of the non-natural light-responsive amino acid (e.g., benzazo-phenylalanine; Baf) from the trans-configuration (for example referred to herein as trans-Baf) to the cis-configuration (for example referred to herein as cis-Baf) depends on the specific wavelength employed. The state of the art would have routinely employed a wavelength corresponding to the absorption maximum for trans-Baf (i.e., 326 nm) and a wavelength corresponding to the largest absorption maximum for cis-Baf in the visible light region (i.e., 426 nm). However, the present inventors have surprisingly found that a wavelength corresponding to the biggest difference in the extinction coefficient of trans-Baf and cis-Baf is particularly useful in switching the confirmation of Baf from trans to cis. Namely, it was found that a wavelength of about 355 nm is particularly useful in switching trans- Baf to cis-Baf, resulting in at least about 90% of all Baf molecules to comprise the cis-configuration (see also Figure 19). Similarly, it was found that a wavelength of about 430 nm was particularly useful in switching cis-Baf to trans-Baf, resulting in at least about 80% molecules comprising the trans- configuration. In the context of the present invention, it is particularly relevant to establish conditions that allow for a highly efficient switch between the configurations of the herein utilized non-natural light- responsive amino acid (from cis-configuration to trans-configuration, and vice-versa), as this switch alters the binding affinity to the herein provided solid phase (e.g., a solid phase comprising α-cyclodextrin) and thereby enables light-regulated affinity chromatography (i.e., without the need for an additional elution buffer that alters the binding of the affinity tag to the solid phase). In this context, it was further surprisingly found that after irradiation with a wavelength of light of about 405 nm to about 470 nm and / or daylight for about or less than about 30 min, at least 80% of the light- responsive amino acid (in particular Baf) stably remained in the trans-configuration even when subsequently kept in the dark for at least about 60 min. Similarly, when irradiated with a wavelength of light of about 310 nm to about 370 nm for about or less than about 30 min and subsequently not irradiated with visible light, at least 90% of the light-responsive amino acid (in particular Baf) stably remained in the cis-configuration even when subsequently kept in the dark for at least about 60 min (see also Figure 20C). Collectively, this demonstrates that the herein provided means and methods for the purification of a polypeptide of interest do not require continuous illumination of said polypeptide of interest with the above mentioned wavelengths in order to allow for the maintenance of the trans-configuration or the cis- configuration of the light-responsive amino acid (in particular of Baf). Hence, this further facilitates one-step purification of a polypeptide of interest by reducing the illumination duration required and allowing for upscaling of the purification procedure. The latter is particularly useful in the context of, inter alia, high-throughput purification approaches aiming at purifying various polypeptides comprised in many (i.e., dozens, hundreds, if not thousands) different samples in parallel. As will be further detailed herein below, the purified polypeptides (comprising the N-terminal or C-terminal light-responsive affinity tag) may be comprised in a composition (for examples in a buffer, such as an elution buffer, or a composition comprising further suitable reagents). Accordingly, the present invention further relates to a composition comprising the polypeptide comprising the N-terminal or the C-terminal light-responsive affinity tag. It was surprisingly found that such a composition (resulting, for example, from the elution of a polypeptide of interest from the herein provided solid phase, such as a solid phase comprising α-cyclodextrin) comprises primarily the protein of interest. Accordingly, the polypeptide comprising the N-terminal or the C-terminal light-responsive affinity tag may constitute at least about 90 mol% of the total polypeptide content of such a composition. The remarkable purity of compositions resulting from the herein provided affinity chromatography methods is, inter alia, detailed in the enclosed Figure 5. In the context of the present invention, the integration of non-natural light-responsive amino acids (such as benzazo-phenylalanine, p-amino-benzazo-phenylalanine, and p-carboxy-benzazo-phenylalanine) into a light-responsive affinity tag may be performed by means and methods of recombinant DNA technology. In general, the biosynthesis of proteins with non-natural (i.e. non-proteinogenic) amino acids has been established since several years and has opened the way to novel biomolecular reagents for biophysical, structural and biochemical research as well as biotechnological and biopharmaceutical applications (Wals & Ovaa 2014 Front. Chem.2: 15). A versatile method for the site-specific incorporation of non-natural (i.e. non-proteinogenic) amino acids exploits a nucleic acid codon that is less frequently used by the genetic code of the host cell. Thus, the amber stop codon (UAG), which also is subject to natural nonsense suppression mechanisms, has been recruited as an additional coding triplet for novel amino acids to provide new side chain chemistries in recombinant proteins. Initially developed for in vitro translation systems employing synthetic aminoacyl- tRNAs, this general approach has been adapted to the heterologous overexpression of proteins in live cells by utilizing an artificial aminoacyl-tRNA synthetase (aaRS) with the desired amino acid substrate specificity (Young & Schultz 2010 J. Biol. Chem.285: 11039-11044). Importantly, such an aaRS must not aminoacylate any endogenous cellular tRNA, whereas the cognate suppressor tRNA, which is co- overexpressed in vivo, must not be aminoacylated with a natural amino acid by any endogenous aminoacyl- tRNA synthetase. In other words, suppressor tRNA and the foreign or engineered aaRS must be orthogonal to their endogenous counterparts in the host cell of choice. The first efficient orthogonal pair of tRNA and aaRS suitable for in vivo translation in E. coli was found in the tyrosyl-tRNA synthetase (TyrRS) from the archaebacterium Methanococcus jannaschii (Mj) and its cognate tRNATyr, which was mutated to specifically recognize and suppress the amber stop codon (Wang & Schultz 2001 Chem. Biol. 8: 883-890). Later, the toolbox for incorporation of non-natural amino acids was expanded by a system based on the 22nd proteinogenic amino acid, L-pyrrolysine (Pyl), which is translated in response to an amber stop codon by the action of pyrrolysyl-tRNA synthetase (PylRS) together with its cognate natural suppressor tRNAPyl(Fekner & Chan 2011 Curr. Opin. Chem. Biol. 15: 387-391). This system was originally found in the methanogenic archaeon Methanosarcina barkeri (Mb) and Methanosarcina mazei (James et al.2001 J. Biol. Chem.276: 34252-34258) and is now increasingly used as a genetic code expansion tool (Wan at al. 2014 Biochem. Biophys. Acta 1844: 1059-1070). Due to its rather low selectivity towards the natural substrate Pyl, PylRS has (in part after protein engineering) permitted the genetic incorporation of more than 100 non-natural amino acids (Wan et al.2014 Biochem. Biophys. Acta 1844: 1059-1070). Nonetheless, it was found herein that the incorporation of non-natural light-responsive amino acids (such as Baf or p-amino-benzazo-phenylalanine) using PylRS did not allow the efficient recombinant production of proteins comprising a light-responsive affinity tag. Accordingly, only by extensive experimentation the present inventors have surprisingly identified means and methods to improve the incorporation efficiency of non-natural light-responsive amino acids into the herein provided affinity tags. It was initially found that while the solubility of Baf was low in the culture medium of a cell expressing the heterologous polypeptide comprising the N-terminal or C-terminal light-responsive affinity tag, the addition of β-cyclodextrin (also referred to as (2-hydroxypropyl)-β-cyclodextrin) increased the solubility of Baf. Further, the present inventors have improved the PylRS enzyme by incorporating various mutations that could not have been foreseen and surprisingly result in an enzyme having improved Baf-incorporation activity (hence, herein referred to as “BafRS”) as compared to a reference PylRS (such as an PylRS of SEQ ID NO: 14 or an PylRS of SEQ ID NO: 13). This is further detailed in the enclosed Example 7. Accordingly, the present invention also relates to an aminoacyl tRNA synthetase (aaRS) with substrate specificity for benzazo-phenylalanine or a derivative thereof, wherein said aaRS is characterized in that: it comprises enzymatic activity for charging a cognate suppressor tRNA with benzazo-phenylalanine (Baf) or a derivate thereof, preferably wherein said derivate is a non-natural light-responsive amino acid selected from the group consisting of p-amino-benzazo-phenylalanine and p-carboxy-benzazo-phenylalanine, and it comprises an amino acid sequence with at least 95% amino acid sequence identity to SEQ ID NO: 14, wherein: (a) the amino acid at position 295 in the amino acid sequence of SEQ ID NO: 14 or a position corresponding to this position is substituted with an amino acid selected from the group consisting of L; (b) the amino acid at position 304 in the amino acid sequence of SEQ ID NO: 14 or a position corresponding to this position is substituted with an amino acid selected from the group consisting of S; and / or (c) the amino acid at position 346 in the amino acid sequence of SEQ ID NO: 14 or a position corresponding to this position is substituted with an amino acid selected from the group consisting of A. Thus, the aaRS with substrate specificity for Baf or a derivate thereof (i.e., BafRS) provided herein paves the way for the efficient (recombinant) incorporation of non-natural light-responsive amino acids into the light-responsive affinity tag comprised in the polypeptides of interest provided herein. Accordingly, said aaRS is particularly advantageous in the recombinant expression of such polypeptides (comprising an N- terminal or a C-terminal light-responsive affinity tag). Accordingly, the present invention further relates to a method for the recombinant expression and / or the recombinant production of a polypeptide comprising the N-terminal or the C-terminal light-responsive affinity tag as detailed herein above and below. However, said aaRS may also be of relevance in the recombinant expression and / or the recombinant production of other proteins and / or polypeptides comprising non-natural light-responsive amino acids (such as Baf or derivates thereof). Accordingly, the present invention also relates to a method for the recombinant expression and / or the recombinant production of a polypeptide of comprising a non-natural light-responsive amino acid, wherein said method comprises the recombinant expression of a polypeptide comprising a non- natural light-responsive amino acid in the presence of the aaRS of the present invention (i.e., BafRS), a cognate suppressor tRNA, and a non-natural light-responsive amino acid. Further, the present invention relates to nucleic acid molecules and nucleic acid vectors encoding the herein provided aaRS, as well as host cells comprising such nucleic acid molecules or nucleic acid vectors. In the context of the present invention it is envisaged that the herein provided polypeptide comprising an N- terminal or a C-terminal light-responsive affinity tag may be expressed from the same nucleic acid molecules or the same nucleic acid vectors as the herein provided aaRS (and, preferably, as the cognate suppressor tRNA). It is further envisaged that the expression of genetic elements (such as a nucleic acid molecule encoding the herein provided aaRS) from such vectors is regulated by one or more inducible promoter(s), as it was surprisingly shown that the introduction of such inducible promotors improved the enzymatic incorporation activity of non-natural light-responsive amino acids (such as, inter alia, Baf) by approx. two-fold. This is further detailed in the enclosed Example 7. Accordingly, the present invention further relates to a nucleic acid molecule encoding the polypeptide comprising the N-terminal or the C-terminal light-responsive affinity tag. Further, the present invention relates to a nucleic acid vector comprising said nucleic acid molecule encoding the polypeptide comprising the N-terminal or the C-terminal light-responsive affinity tag. As is further detailed herein below, the present invention in particular also relates to such nucleic acid vectors in which the nucleic acid sequence encoding the protein of interest (POI, or P in, inter alia, formula I) is replaced by a (multiple) cloning site (see also Figure 22 illustrating such cloning approaches and an exemplary vector). This allows for the efficient and simple introduction of nucleic acid sequences encoding various proteins of interest into such vectors and subsequently facilitates recombinant expression of such proteins. Further provided herein are host cells comprising said nucleic acid vectors for the recombinant expression of such polypeptides comprising the N-terminal or the C-terminal light-responsive affinity tag. It was surprisingly found that (prokaryotic) host cells (such as Escherichia coli) are particularly useful for the recombinant expression of the herein provided polypeptides comprising the N-terminal or the C-terminal light-responsive affinity tag, in particular Escherichia coli strains that do not encode a functional ribosomal release factor 1 (RF1 or RF-1) or that are characterized by reduced expression of RF1 as compared to a E. coli wildtype strain, as RF1 counteracts amber stop codon suppression in certain bacteria. This is detailed in the non-limiting Example 8 and Example 1S. Further, it was surprisingly found that the maltose binding protein (MBP) encoded by the malE gene in, for example, E. coli may bind to α-cyclodextrin (as for example comprised in the herein provided solid phase) and, as such, may cause (minor) impurities in the elution fractions of the polypeptide comprising the N-terminal or the C-terminal light-responsive affinity tag. Accordingly, in the context of the present invention it may be preferred that (prokaryotic) host cells (such as Escherichia coli) do not encode a functional maltose binding protein. The invention is also characterized by the following items: 1. A polypeptide comprising an N-terminal or a C-terminal light-responsive affinity tag. 2. The polypeptide of item 1, wherein said polypeptide comprises a structure of formula (I) or of formula (II): X-[L-]lP (I) P[-L]l-X (II) wherein X is a light-responsive affinity tag, L is a linker, l is 1 or 0, so that L can be present or absent, P is a polypeptide of interest, wherein in formula (I) X-[L-]lis linked to the amino-terminus of P, and wherein in formula (II) [-L]l-X is linked to the carboxy-terminus of P. A method for the isolation and / or purification of a polypeptide comprising an N-terminal or a C- terminal light-responsive affinity tag from a liquid phase, wherein the method comprises the steps of: (a) contacting said liquid phase with a solid phase, wherein said light-responsive affinity tag comprises a non-natural light-responsive amino acid, and wherein said non-natural light-responsive amino acid is in a first configuration so that it has high affinity to said solid phase; and (b) irradiating the light-responsive affinity tag with a wavelength of light that changes said non- natural light-responsive amino acid to a second configuration such that it has a decreased affinity to said solid phase as compared to the affinity thereof in step (a) and eluting said polypeptide comprising the N-terminal or the C-terminal light-responsive affinity tag. The method of item 3, wherein said polypeptide comprises a structure of formula (I) or of formula (II): X-[L-]lP (I) P[-L]l-X (II) wherein X is a light-responsive affinity tag, L is a linker, l is 1 or 0, so that L can be present or absent, P is a polypeptide of interest, wherein in formula (I) X-[L-]l is linked to the amino-terminus of P, and wherein in formula (II) [-L]l-X is linked to the carboxy-terminus of P. 5. The polypeptide of item 2, or the method of item 4, wherein [X-] of formula (I) comprises a structure of [A-]aB-[C-]cso that the polypeptide of formula (I) is a polypeptide with a structure according to formula (III) [A-]aB-[C-]c[L-]lP (III), wherein [-X] of formula (II) comprises a structure of [-A]a-B[-C]c, so that said polypeptide of formula (II) is a polypeptide with a structure according to formula (IV) P[-L]l[-C]c-B[-A]a(IV), wherein A comprises one or more amino acid(s), a is 1 or 0, so that A can be present or absent, B is a non-natural light-responsive amino acid, C comprises one or more amino acid(s), c is 1 or 0, so that C can be present or absent, wherein in formula (III) X-[L-]l is linked to the amino-terminus of P, and wherein in formula (IV) [-L]l-X is linked to the carboxy-terminus of P. 6. The polypeptide of item 5, wherein said non-natural light-responsive amino acid is in a first configuration or in a second configuration. 7. The polypeptide of item 6, or the method to item 5, wherein said first configuration is the trans- configuration of an azo-group comprised in said non-natural light-responsive amino acid and wherein said second configuration is the cis-configuration of said azo-group. 8. The polypeptide of any one of items 5 to 7, or the method of any one of items 5 and 7, wherein said non-natural light-responsive amino acid is selected from the group consisting of benzazo- phenylalanine (Baf), p-amino-benzazo-phenylalanine, and p-carboxy-benzazo-phenylalanine. 9. The polypeptide of any one of items 5 to 8, or the method of any one of items 5, 7, and 8, wherein said non-natural light-responsive amino acid is Baf. 10. The polypeptide of any one of items 5 to 9, or the method of any one of items 5 and 7 to 9, wherein a is 1. 11. The polypeptide of item 10, or the method of item 10, wherein A comprises one or more natural amino acid(s). 12. The polypeptide of item 10 or 11, or the method of item 10 or 11, wherein A comprises less than about 10 amino acid(s). 13. The polypeptide of any one of items 10 to 12, or the method of any one of items 10 to 12, wherein A comprises one or more amino acid(s) selected from the group consisting of Gly, Pro, Ala, and Ser. 14. The polypeptide of any one of items 10 to 13, or the method of any one of items 10 to 13, wherein A comprises one or more Gly residue(s). 15. The polypeptide of any one of items 10 to 14, or the method of any one of items 10 to 14, wherein A comprises one or two amino acid(s) selected from the group consisting of Gly, Pro, Ala, and Ser, preferably one amino acid. 16. The polypeptide of any one of items 10 to 15, or the method of any one of items 10 to 15, wherein A comprises one or two Gly residue(s), preferably one Gly residue. 17. The polypeptide of any one of items 5 to 9, or the method of any one of items 5 and 7 to 9, wherein a is 0. 18. The polypeptide of any one of items 5 to 17, or the method of any one of items 5 and 7 to 17, wherein c is 1. 19. The polypeptide of item 18, or the method of item 18, wherein C comprises one or more natural amino acid(s). 20. The polypeptide of item 18 or 19, or the method of item 18 or 19, wherein C comprises less than about 10 amino acids. 21. The polypeptide of any one of items 18 to 20, or the method of any one of items 18 to 20, wherein C comprises one or more amino acid(s) selected from the group consisting of Gly, Pro, Ala, and Ser. 22. The polypeptide of any one of items 18 to 21, or the method of any one of items 18 to 21, wherein C comprises one or more Gly residue(s). 23. The polypeptide of any one of items 18 to 22, or the method of any one of items 18 to 22, wherein C comprises one or two amino acid(s) selected from the group consisting of Gly, Pro, Ala, and Ser, preferably Gly and Pro. 24. The polypeptide of any one of items 18 to 23, or the method of any one of items 18 to 23, wherein C comprises one or two Gly residue(s), preferably one Gly residue. 25. The polypeptide of any one of items 5 to 17, or the method of any one of items 5 and 7 to 17, wherein c is 0. 26. The polypeptide of any one of items 5 to 9, or the method of any one of items 5 and 7 to 9, wherein X consists of 1 to 5 amino acids. 27. The polypeptide of item 26, or the method of item 26, wherein X consists of about 4 amino acids. 28. The polypeptide of item 26, or the method of item 26, wherein X consists of about 3 amino acids. 29. The polypeptide of item 26, or the method of item 26, wherein X consists of about 2 amino acids, preferably wherein X consists of Baf-Gly or Gly-Baf. 30. The polypeptide of item 26, or the method of item 26, wherein in formula (I) X comprises an amino acid sequence selected from the group consisting of B-Gly-Gly, Gly-B-Gly-Gly (SEQ ID NO: 23 to 25), Ala-B-Gly-Gly (SEQ ID NO: 26 to 28), Gly-B-Gly-Pro (SEQ ID NO: 29 to 31), Ala-B-Gly-Pro (SEQ ID NO: 32 to 34), Gly-B-Gly, Ala-B-Gly, Gly-B-Ala, Gly-Gly-B, Gly-Gly-B-Gly (SEQ ID NO: 35 to 37), and Pro-Gly-B-Gly (SEQ ID NO: 38 to 40). 31. The polypeptide of item 26, or the method of item 26, wherein in formula (II) X comprises an amino acid sequence selected from the group consisting of B-Gly-Gly, Gly-B-Gly-Gly (SEQ ID NO: 23 to 25), Ala-B-Gly-Gly (SEQ ID NO: 26 to 28), Gly-B-Gly-Pro (SEQ ID NO: 29 to 31), Ala-B-Gly-Pro (SEQ ID NO: 32 to 34), Gly-B-Gly, Ala-B-Gly, Gly-B-Ala, Gly-Gly-B, Gly-Gly-B-Gly (SEQ ID NO: 35 to 37), and Pro-Gly-B-Gly (SEQ ID NO: 38 to 40). 32. The polypeptide of item 26 or 28, or the method of item 26 or 28, wherein X in formula (I) or in formula (II) comprises an amino acid sequence consisting of Gly-B-Gly. 33. The polypeptide of item 26 or 28, or the method of item 26 or 28, wherein X in formula (I) or in formula (II) comprises an amino acid sequence consisting of Gly-B-Gly, and wherein B is Baf. 34. The polypeptide of any one of items 7 to 33, or the method of any one of items 7 to 33, wherein the configuration of B can be switched from the trans-configuration to the cis-configuration by irradiation with a specific wavelength of light, preferably wherein said wavelength of light is selected from one or more wavelength(s) of light from about 310 nm to about 370 nm, more preferably from about 345 nm to about 365 nm, more preferably from about 350 nm to about 355 nm. 35. The polypeptide of any one of items 7 to 34, or the method of any one of items 7 to 34, wherein the configuration of B can be switched from the cis-configuration to the trans-configuration by irradiation with a specific wavelength of light, preferably wherein said wavelength of light is selected from one or more wavelength(s) of light from about 405 nm to about 470 nm and / or daylight, preferably from about 420 nm to about 430 nm and / or daylight. 36. The polypeptide of item 34 or 35, or the method of item 34 or 35, wherein the switch of said configuration alters its affinity towards α-cyclodextrin. 37. The polypeptide of any one of items 7 to 36, or the method of any one of items 7 to 36, wherein when in the trans-configuration, B forms or is capable of forming a complex with α-cyclodextrin, preferably as determined by spectroscopic analysis during titration of B in the trans-configuration with α-cyclodextrin. 38. The polypeptide of any one of items 7 to 37, or the method of any one of items 7 to 37, wherein when in the cis-configuration, B does not form a stable complex with α-cyclodextrin, preferably as determined by spectroscopic analysis during titration of B in the cis-configuration with α- cyclodextrin. 39. The polypeptide of any one of items 7 to 38, or the method of any one of items 7 to 38, wherein when in the trans-configuration, B comprises an equilibrium dissociation constant (KD) of about or less than about 91 µM ± 5 µM when contacted with α-cyclodextrin, preferably wherein KD is determined by spectroscopic analysis during titration of B in the trans-configuration with α-cyclodextrin. 40. The polypeptide of any one of items 7 to 39, or the method of any one of items 7 to 39, wherein when irradiated with visible light having about 405 nm to about 470 nm and / or daylight, at least about 80% of the polypeptide of formula (I) or (II) comprise B in the trans-configuration. 41. The polypeptide of any one of items 7 to 40, or the method of any one of items 7 to 40, wherein when irradiated with visible light having about 405 nm to about 470 nm and / or daylight for about or less than about 30 min, at least about 80% of the polypeptide of formula (III) or (IV) comprise B in the trans-configuration which is maintained for at least about 60 min under daylight or in the dark. 42. The polypeptide of any one of items 7 to 41, or the method of any one of items 7 to 41, wherein when irradiated with UV light having about 310 nm to about 370 nm, at least about 90% of the polypeptide of formula (III) or (IV) comprise B in the cis-configuration. 43. The polypeptide of any one of items 7 to 42, or the method of any one of items 7 to 42, wherein when irradiated with UV light having about 310 nm to about 370 nm for about or less than about 30 min and subsequently not irradiated with visible light, at least about 90% of the polypeptide of formula (III) or (IV) comprise B in the cis-configuration which is maintained for at least about 60 min in the dark. 44. The polypeptide of any one of items 7 to 43, or the method of any one of items 7 to 43, wherein P is selected from the group consisting of an oligopeptide, a polypeptide, a protein, an immunoglobulin or an antigen-binding fragment thereof, a binding protein, a growth factor, a signaling protein, an enzyme, and / or a complex thereof. 45. The polypeptide of any one of items 2 and 5 to 44, or the method of any one of items 4, 5, and 7 to 44, wherein said polypeptide further comprises a signal peptide, preferably selected from the group consisting of OmpA, OmpF, PhoA, MalE, PelB, stII, DsbC. 46. The polypeptide of any one of items 2 and 5 to 45, or the method of any one of items 4, 5, and 7 to 45, wherein l is 1. 47. The polypeptide of item 46, or the method of item 46, wherein L comprises an amino acid sequence selected from the group consisting of the following: Glu-Asn-Leu-Tyr-Phe-Gln-Ser-Gly (SEQ ID NO: 41), Glu-Asn-Leu-Tyr-Phe-Gln-Ser-Ala (SEQ ID NO: 42), Leu-Val-Pro-Arg-Gly-Ser (SEQ ID NO: 43), Ile-Glu-Gly-Arg (SEQ ID NO: 44), Leu-Glu-Val-Leu-Phe-Gln-Gly-Pro (SEQ ID NO: 45). 48. The polypeptide of item 46, or the method of item 46, wherein L is a cleavable linker. 49. The polypeptide of item 48, or the method of item 48, wherein L comprises a cleavable amino acid sequence selected from the group consisting of the following: Tobacco Etch Virus (TEV) protease, thrombin, factor Xa, human rhinovirus type 143C protease (HRV 3C). The polypeptide of any one of items 2 and 5 to 45, or the method of any one of items 4, 5, and 7 to 45, wherein l is 0. The method of any one of items 4, 5, and 7 to 50, wherein during step (a) said N-terminal or C- terminal light-responsive affinity tag is irradiated with a wavelength of light that is capable of switching the configuration of said non-natural light-responsive amino acid from the cis- configuration to the trans-configuration, preferably wherein said wavelength of light is selected from one or more wavelength(s) of light from about 405 nm to about 470 nm and / or daylight, preferably from about 410 nm to about 440 nm, more preferably from about 420 nm to about 430 nm and / or daylight. The method of any one of items 4, 5, and 7 to 50, wherein during step (a) said N-terminal or C- terminal light-responsive affinity tag is not irradiated with light. The method of any one of items 4, 5, and 7 to 52, wherein during step (b) said N-terminal or C- terminal light-responsive affinity tag is irradiated with a wavelength of light that changes said non- natural light-responsive amino acid to a second configuration for about or less than about 30 min and subsequently is not irradiated with light. The method of any one of items 4, 5, and 7 to 53, wherein said solid phase comprises α-cyclodextrin groups. The method of item 54, wherein said solid phase further comprises a structural matrix, preferably wherein said structural matrix is selected from the group consisting of agarose, a cross-linked form of agarose, cellulose, starch, dextran, polymethacrylate, polystyrene, polyacrylamide, and silica gel, more preferably agarose or a cross-linked form of agarose. The method of item 55, wherein said structural matrix is transparent or translucent. The method of item 55 or 56, wherein said α-cyclodextrin is covalently linked to said structural matrix. The method of any one of items 54 to 56, wherein said α-cyclodextrin is covalently linked to said structural matrix via a linker. The method of item 58, wherein said linker is derived from 1,4-bis(2,3-epoxypropoxy)butane, 1- chloro-acetylchloride, or cyanogen bromide, preferably from 1,4-bis(2,3-epoxypropoxy)butane. 60. The method of any one of items 54 to 59, wherein said solid phase is light-resistant, at least in the wavelength range from about 300 nm to about 500 nm. 61. The method of any one of items 54 to 60, wherein said solid phase is light-transmissive at least for UV light in the wavelength range from about 310 nm to about 370 nm. 62. The method of any one of items 54 to 61, wherein said solid phase can be reused at least 10 times for affinity chromatography. 63. The method of any one of items 54 to 62, wherein said solid phase is a matrix, a hydrogel, a bead, a chip, a glass surface, a plastic surface, a gold surface, a silver surface, or a plate such as a microtiter well plate. 64. The method of any one of items 54 to 63, wherein said matrix, said hydrogel, or said bead is the affinity matrix of an affinity chromatography column. 65. A polypeptide comprising the N-terminal or the C-terminal light-responsive affinity tag as obtained by and / or obtainable by the method of any one of items 4, 5, and 7 to 64. 66. A composition comprising the polypeptide comprising the N-terminal or the C-terminal light- responsive affinity tag of any one of items 1, 2, and 5 to 50. 67. The composition of item 66, wherein said polypeptide comprising the N-terminal or the C-terminal light-responsive affinity tag constitutes at least about 90 mol% of the total polypeptide content of said composition. 68. A method for cleaving the light-responsive affinity tag from the polypeptide of interest of item 48 or 49, wherein the method comprises the steps of: (a) cleaving said cleavable linker; and (b) purifying the polypeptide of interest. 69. The method of item 68, wherein the step of cleaving said cleavable linker comprises contacting said cleavable linker with a cleaving reagent. 70. The method of item 69, wherein said cleaving reagent is selected from the group consisting of one or more enzyme(s), preferably Tobacco Etch Virus (TEV) protease, thrombin, factor Xa, human rhinovirus type 143C protease (HRV 3C) preferably TEV protease. 71. A polypeptide of interest as obtained by and / or obtainable by the method of any one of items 68 to 70. 72. A nucleic acid molecule encoding the polypeptide comprising the N-terminal or the C-terminal light- responsive affinity tag of any one of items 1, 2, and 5 to 50. 73. The nucleic acid molecule of item 72, wherein B is encoded by a stop codon. 74. The nucleic acid molecule of item 73, wherein said stop codon is selected from the group consisting of UAG, UGA, and UAA, preferably UAG. 75. The nucleic acid molecule of any one of items 72 to 74, wherein the nucleic acid sequence encoding for P is replaced with a multiple cloning site. 76. A nucleic acid vector comprising the nucleic acid molecule of any one of items 72 to 75. 77. The nucleic acid vector of item 76, wherein said nucleic acid vector further comprises one or more nucleic acid sequence(s) encoding one or more selected from the group consisting of the following: (a) an aminoacyl tRNA synthetase (aaRS); (b) a suppressor tRNA; and (c) an antibiotic selection marker. 78. The nucleic acid vector of item 77, wherein said nucleic acid molecule encoding the aaRS is selected from the group consisting of the following: (a) a nucleic acid molecule comprising a nucleic acid sequence of SEQ ID NO: 60 to SEQ ID NO: 67; (b) a nucleic acid molecule that hybridizes with a nucleic acid molecule comprising a nucleic acid sequence complementary to the nucleotide sequence of SEQ ID NO: 60 to SEQ ID NO: 67 and that encodes a polypeptide with aaRS activity; (c) a nucleic acid molecule encoding a polypeptide comprising an amino acid sequence of SEQ ID NO: 15 to SEQ ID NO: 22; (d) a nucleic acid molecule encoding a polypeptide comprising an amino acid sequence of SEQ ID NO: 15 to SEQ ID NO: 22 with a deletion, substitution, insertion, and / or addition of one or more amino acid(s), and wherein said polypeptide comprises aaRS activity; and (e) a nucleic acid molecule encoding a polypeptide comprising an amino acid sequence with at least about 80% amino acid sequence identity to the amino acid sequence of SEQ ID NO: 15 to SEQ ID NO: 22, and wherein said polypeptide comprises aaRS activity. 79. The nucleic acid vector of item 77 or 78, wherein said nucleic acid molecule encoding the suppressor tRNA is selected from the group consisting of the following: (a) a nucleic acid molecule comprising a nucleic acid sequence of SEQ ID NO: 70; and (b) a nucleic acid molecule that hybridizes with a nucleic acid molecule comprising a nucleic acid sequence complementary to the nucleotide sequence of SEQ ID NO: 70 and that encodes a suppressor tRNA, wherein said suppressor tRNA forms or is capable of forming a cloverleaf structure and comprises an anticodon, and wherein said anticodon is complementary to a stop codon selected from the group consisting of UAG, UGA, and UAA, preferably UAG. 80. The nucleic acid vector of any one of items 76 to 79, wherein said nucleic acid vector comprises a nucleic acid sequence of SEQ ID NO: 68,SEQ ID NO: 69, SEQ ID NO: 72 or SEQ ID NO: 73. 81. A host cell or a host comprising the nucleic acid molecule of any one of items 72 to 75, and / or the nucleic acid vector of any one of items 76 to 80. 82. The host cell or the host of item 81, wherein said host cell or said host is eukaryotic. 83. The host cell or the host of item 82, wherein said host cell or said host is selected from the group consisting of cultivated mammalian cells, cultivated insect cells, yeast. 84. The host cell or the host of item 81, wherein said host cell or said host is prokaryotic. 85. The host cell or the host of item 82, wherein said host cell or said host is selected from the group consisting of Escherichia coli (E. coli), Bacillus subtilis, Corynebacterium glutamicum and Pseudomonas fluorescens, preferably E. coli. 86. The host cell or the host of item 85, wherein said host cell or said host is an E. coli B strain or an E. coli K12 strain, preferably an E. coli B strain. 87. The host cell or the host of item 86, wherein said E. coli B strain is NEBExpress. 88. The host cell or the host of any one of items 84 to 87, wherein said host cell or said host does not encode a functional ribosomal release factor 1 (RF1 alias PrfA) or is a RF1 knockdown strain that expresses a functional RF1. 89. The host cell or the host of any one of items 84 to 88, wherein said host cell or said host does not encode a functional maltose binding protein (MBP) or is a MBP knockdown strain. 90. An aminoacyl tRNA synthetase (aaRS) with substrate specificity for benzazo-phenylalanine or a derivative thereof, wherein said aaRS is characterized in that: it comprises enzymatic activity for charging a cognate suppressor tRNA with benzazo- phenylalanine (Baf) or a derivate thereof, preferably wherein said derivate is a non-natural light- responsive amino acid selected from the group consisting of p-amino-benzazo-phenylalanine and p- carboxy-benzazo-phenylalanine, and it comprises an amino acid sequence with at least 95% amino acid sequence identity to SEQ ID NO: 14, wherein: (a) the amino acid at position 295 in the amino acid sequence of SEQ ID NO: 14 or a position corresponding to this position is substituted with an amino acid selected from the group consisting of L and R; (b) the amino acid at position 304 in the amino acid sequence of SEQ ID NO: 14 or a position corresponding to this position is substituted with an amino acid selected from the group consisting of S; and / or (c) the amino acid at position 346 in the amino acid sequence of SEQ ID NO: 14 or a position corresponding to this position is substituted with an amino acid selected from the group consisting of A. 91. The aaRS of item 90, wherein said aaRS further comprises one or more deletion(s), substitution(s), insertion(s), and / or addition(s) of one or more amino acid(s), and wherein: (a) the amino acid at position 295 in the amino acid sequence of SEQ ID NO: 14 or a position corresponding to this position is substituted with an amino acid selected from the group consisting of L and R; (b) the amino acid at position 304 in the amino acid sequence of SEQ ID NO: 14 or a position corresponding to this position is substituted with an amino acid selected from the group consisting of S; and / or (c) the amino acid at position 346 in the amino acid sequence of SEQ ID NO: 14 or a position corresponding to this position is substituted with an amino acid selected from the group consisting of A. 92. A method for the recombinant expression and / or the recombinant production of a polypeptide comprising the N-terminal or the C-terminal light-responsive affinity tag according to any one of items 1, 2, and 5 to 50. 93. The method of item 92, wherein said method comprises the recombinant expression of the polypeptide of formula (I) or the polypeptide of formula (II) in the presence of an aminoacyl tRNA synthetase (aaRS), a cognate suppressor tRNA, and a non-natural light-responsive amino acid as defined in item 8 or 9. 94. The method of item 93, wherein said aaRS is the aaRS of item 90 or 91. 95. A method for the recombinant expression and / or the recombinant production of a polypeptide of comprising a non-natural light-responsive amino acid, wherein said method comprises the recombinant expression of a polypeptide comprising a non-natural light-responsive amino acid in the presence of the aaRS of item 90 or 91, a cognate suppressor tRNA, and a non-natural light-responsive amino acid. 96. The method of any one of items 92 to 94, or the method of item 95, wherein said non-natural light- responsive amino acid is Baf or a derivate thereof, wherein said derivate is a non-natural light- responsive amino acid selected from the group consisting of p-amino-benzazo-phenylalanine and p- carboxy-benzazo-phenylalanine. 97. The aaRS of item 90 or 91, the method of any one of items 92 to 94, and 96, or the method of item 95 or 96, wherein said cognate suppressor tRNA comprises an anticodon, and wherein said anticodon is complementary to a stop codon. 98. The aaRS of item 97, or any of the methods of item 97, wherein said stop codon is selected from the group consisting of UAG, UGA, and UAA, preferably UAG. 99. The aaRS of any one of items 90, 91, 97, and 98, the method of any one of items 92 to 94 and 96 to 98, or the method of any one of items 95 to 98, wherein said cognate suppressor tRNA is selected from the group consisting of: (a) a nucleic acid molecule comprising a nucleic acid sequence of SEQ ID NO: 70; and (b) a nucleic acid molecule that hybridizes with a nucleic acid molecule comprising a nucleic acid sequence complementary to the nucleotide sequence of SEQ ID NO: 70 and that encodes a suppressor tRNA, wherein said suppressor tRNA forms or is capable of forming a cloverleaf structure and comprises an anticodon, and wherein said anticodon is complementary to said stop codon, as defined in item 98. 100. The aaRS of any one of items 90, 91, and 97 to 99, the method of any one of items 92 to 94 and 96 to 99, or the method of any one of items 95 to 99, wherein said non-natural light-responsive amino acid is Baf. 101. The aaRS of any one of items 90, 91, and 97 to 100, the method of any one of items 92 to 94 and 96 to 100, or the method of any one of items 95 to 100, wherein said non-natural light-responsive amino acid is in the trans-configuration. 102. The aaRS of any one of items 90, 91, and 97 to 101, the method of any one of items 92 to 94 and 96 to 101, or the method of any one of items 95 to 101, wherein said non-natural light-responsive amino acid is complexed and / or solubilized using β-cyclodextrin. 103. The aaRS of any one of items 90, 91, and 97 to 102, the method of any one of items 92 to 94 and 96 to 102, or the method of any one of items 95 to 102, wherein said aaRS comprises an amino acid sequence selected from the group consisting of SEQ ID NO: 15 to SEQ ID NO: 22. 104. The aaRS of any one of items 90, 91, and 97 to 103, the method of any one of items 92 to 94 and 96 to 103, or the method of any one of items 95 to 103, wherein said aaRS has increased enzymatic activity for charging said cognate suppressor tRNA with a non-natural light-responsive amino acid selected from the group consisting of Baf, p-amino-benzazo-phenylalanine, and p-carboxy-benzazo- phenylalanine as compared to the reference aaRS with an amino acid sequence of SEQ ID NO: 14. 105. The aaRS of any one of items 90, 91, and 97 to 104, the method of any one of items 92 to 94 and 96 to 104, or the method of any one of items 95 to 104, wherein said aaRS has at least about 10-fold increased enzymatic activity for charging said cognate suppressor tRNA with an amino acid selected from the group consisting of Baf, p-amino-benzazo-phenylalanine, and p-carboxy-benzazo- phenylalanine as compared to the reference aaRS with an amino acid sequence of SEQ ID NO: 14. 106. A nucleic acid molecule encoding the aaRS of any one of items 90, 91, and 97 to 105. 107. The nucleic acid molecule of item 106, wherein said nucleic acid molecule is selected from the group consisting of the following: (a) a nucleic acid molecule comprising a nucleic acid sequence of SEQ ID NO: 60 to SEQ ID NO: 67; and (b) a nucleic acid molecule that hybridizes with a nucleic acid molecule comprising a nucleic acid sequence complementary to the nucleotide sequence of SEQ ID NO: 60 to SEQ ID NO: 67 and that encodes a polypeptide with aaRS activity. 108. A nucleic acid vector comprising the nucleic acid molecule of item 106 or 107. 109. The nucleic acid vector of item 108, wherein said nucleic acid vector further comprises a suppressor tRNA, and wherein said suppressor tRNA forms a suitable orthogonal tRNA / aaRS pair with the aaRS of any one of items 90, 91, and 97 to 105. 110. The nucleic acid vector of item 109, wherein expression of said aaRS is inducible. 111. A host cell or a host comprising the aaRS of any one of items 90, 91, and 97 to 105, the nucleic acid molecule of item 106 or 107, and / or the nucleic acid vector of any one of items 108 to 110. 112. A method for the cloning of the nucleic acid molecule of any one of items 72 to 75, the nucleic acid vector of any one of items 76 to 80, the nucleic acid molecule of item 106 or 107, or the nucleic acid vector of any one of items 108 to 110. 113. A method for the amplification of the nucleic acid molecule of any one of items 72 to 75, the nucleic acid vector of any one of items 76 to 80, the nucleic acid molecule of item 106 or 107, or the nucleic acid vector of any one of items 108 to 110. 114. A method for the sequencing of the nucleic acid molecule of any one of items 72 to 75, the nucleic acid vector of any one of items 76 to 80, the nucleic acid molecule of item 106 or 107, or the nucleic acid vector of any one of items 108 to 110. 115. A light-responsive affinity tag, as defined in any one of items 2, and 5 to 43. 116. A light-responsive affinity tag, wherein said light-responsive affinity tag comprises a structure of formula (V) or formula (VI): [A-]aB-[C]c (V) [C]c-B[-A]a, (VI) wherein A comprises one or more amino acid(s), a is 1 or 0, so that A can be present or absent, B is a non-natural light-responsive amino acid, C comprises one or more amino acid(s), c is 1 or 0, so that C can be present or absent. 117. The light-responsive affinity tag of item 116, wherein said non-natural light-responsive amino acid is in a first configuration or in a second configuration. 118. The light-responsive affinity tag of item 117, wherein said first configuration is the trans- configuration of an azo-group comprised in said non-natural light-responsive amino acid and wherein said second configuration is the cis-configuration of said azo-group. 119. The light-responsive affinity tag of item 118, wherein said non-natural light-responsive amino acid is selected from the group consisting of benzazo-phenylalanine (Baf), p-amino-benzazo- phenylalanine, and p-carboxy-benzazo-phenylalanine. 120. The light-responsive affinity tag of item 118 or 119, wherein said non-natural light-responsive amino acid is Baf. 121. The light-responsive affinity tag of any one of items 116 to 120, wherein a is 1. 122. The light-responsive affinity tag of item 121, wherein A comprises one or more natural amino acid(s). 123. The light-responsive affinity tag of item 121 or 122, wherein A comprises less than about 10 amino acid(s). 124. The light-responsive affinity tag of any one of items 121 to 123, wherein A comprises one or more amino acid(s) selected from the group consisting of Gly, Pro, Ala, and Ser. 125. The light-responsive affinity tag of any one of items 121 to 124, wherein A comprises one or more Gly residue(s). 126. The light-responsive affinity tag of any one of items 121 to 125, wherein A comprises one or two amino acid(s) selected from the group consisting of Gly, Pro, Ala, Ser, preferably one amino acid. 127. The light-responsive affinity tag of any one of items 121 to 126, wherein A comprises one or two Gly residue(s), preferably one Gly residue. 128. The light-responsive affinity tag of any one of items 116 to 120, wherein a is 0. 129. The light-responsive affinity tag of any one of items 116 to 128, wherein c is 1. 130. The light-responsive affinity tag of item 129, wherein C comprises one or more natural amino acid(s). 131. The light-responsive affinity tag of item 129 or 130, wherein C comprises less than about 10 amino acid(s). 132. The light-responsive affinity tag of any one of items 129 to 131, wherein C comprises one or more amino acid(s) selected from the group consisting of Gly, Pro, Ala, and Ser. 133. The light-responsive affinity tag of any one of items 129 to 132, wherein C comprises one or more Gly residue(s). 134. The light-responsive affinity tag of any one of items 129 to 133, wherein C comprises one or two amino acid(s) selected from the group consisting of Gly, Pro, Ala, and Ser, preferably Gly and Pro. 135. The light-responsive affinity tag of any one of items 129 to 134, wherein C comprises one or two Gly residue(s), preferably one Gly residue. 136. The light-responsive affinity tag of any one of items 116 to 128, wherein c is 0. 137. The light-responsive affinity tag of any one of items 116 to 120, wherein said light-responsive affinity tag consists of about 1 to about 5 amino acids. 138. The light-responsive affinity tag of item 137, wherein said light-responsive affinity tag consists of about 4 amino acids. 139. The light-responsive affinity tag of item 137, wherein said light-responsive affinity tag consists of about 3 amino acids. 140. The light-responsive affinity tag of item 137, wherein said light-responsive affinity tag consists of about 2 amino acids. 141. The light-responsive affinity tag of item 137, wherein in formula (V) said light-responsive affinity tag comprises an amino acid sequence selected from the group consisting of B-Gly-Gly, Gly-B-Gly- Gly (SEQ ID NO: 23 to 25), Ala-B-Gly-Gly (SEQ ID NO: 26 to 28), Gly-B-Gly-Pro (SEQ ID NO: 29 to 31), Ala-B-Gly-Pro (SEQ ID NO: 32 to 34), Gly-B-Gly, Ala-B-Gly, Gly-B-Ala, Gly-Gly-B, Gly-Gly-B-Gly (SEQ ID NO: 35 to 37), and Pro-Gly-B-Gly (SEQ ID NO: 38 to 40). 142. The light-responsive affinity tag of item 137, wherein in formula (VI) said light-responsive affinity tag comprises an amino acid sequence selected from the group consisting of B-Gly-Gly, Gly-B-Gly- Gly (SEQ ID NO: 23 to 25), Ala-B-Gly-Gly (SEQ ID NO: 26 to 28), Gly-B-Gly-Pro (SEQ ID NO: 29 to 31), Ala-B-Gly-Pro (SEQ ID NO: 32 to 34), Gly-B-Gly, Ala-B-Gly, Gly-B-Ala, Gly-Gly-B, Gly-Gly-B-Gly (SEQ ID NO: 35 to 37), and Pro-Gly-B-Gly (SEQ ID NO: 38 to 40). 143. The light-responsive affinity tag of item 137 or 139, wherein said light-responsive affinity tag comprises an amino acid sequence consisting of Gly-B-Gly. 144. The light-responsive affinity tag of item 137 or 139, wherein said light-responsive affinity tag comprises an amino acid sequence consisting of Gly-B-Gly, and wherein B is Baf. 145. The light-responsive affinity tag of any one of items 118 to 144, wherein the configuration of B can be switched from the trans-configuration to the cis-configuration by irradiation with a specific wavelength of light, preferably wherein said wavelength of light is selected from one or more wavelength(s) of light from about 310 nm to about 370 nm, more preferably from about 345 nm to about 365 nm, more preferably from about 350 nm to about 355 nm. 146. The light-responsive affinity tag of any one of items 118 to 145, wherein the configuration of B can be switched from the cis-configuration to the trans-configuration by irradiation with a specific wavelength of light, preferably wherein said wavelength of light is selected from one or more wavelength(s) of light from about 405 nm to about 470 nm and / or daylight. 147. The light-responsive affinity tag of items 145 or 146, wherein the switch of said configuration alters its affinity towards α-cyclodextrin. 148. The light-responsive affinity tag of any one of items 145 to 147, wherein when in the trans- configuration, forms or is capable of forming a complex with α-cyclodextrin, preferably as determined by spectroscopic analysis during titration of B in the trans-configuration with α- cyclodextrin. 149. The light-responsive affinity tag of any one of items 118 to 148, wherein when in the cis- configuration, B does not form a complex with α-cyclodextrin, preferably as determined by spectroscopic analysis during titration of B in the cis-configuration with α-cyclodextrin. 150. The light-responsive affinity tag of any one of items 118 to 149, wherein when in the trans- configuration, B comprises an equilibrium dissociation constant (KD) of about or less than about 91 µM ± 5 µM when contacted with α-cyclodextrin, wherein KDis determined by spectroscopicanalysis during titration of B in the trans-configuration with α-cyclodextrin. 151. The light-responsive affinity tag of any one of items 118 to 150, wherein when irradiated with visible light having about 405 nm to about 470 nm and / or daylight, at least about 80% of the light-responsive affinity tag of formula (V) or (VI) comprise B in the trans-configuration. 152. The light-responsive affinity tag of any one of items 118 to 151, wherein when irradiated with a visible light having about 405 nm to about 470 nm and / or daylight for about or less than about 30 min, at least about 80% of the light-responsive affinity tag of formula (V) or (VI) comprise B in the trans-configuration which is maintained for at least about 60 min under daylight or in the dark. 153. The light-responsive affinity tag of any one of items 118 to 152, wherein when irradiated with UV light having about 310 nm to about 370 nm, at least about 90% of the light-responsive affinity tag of formula (V) or (VI) comprise B in the cis-configuration. 154. The light-responsive affinity tag of any one of items 118 to 153, wherein when irradiated with visible light having about 310 nm to about 370 nm for about or less than about 30 min and subsequently not irradiated with visible light, at least about 90% of the light-responsive affinity tag of formula (V) or (VI) comprise B in the cis-configuration which is maintained for at least about 60 min in the dark. 155. A nucleic acid molecule encoding the light-responsive affinity tag of any one of items 115 to 154. 156. The nucleic acid molecule of item 155, wherein B is encoded by a stop codon. 157. The nucleic acid molecule of item 156, wherein said stop codon is selected from the group consisting of UAG, UGA, and UAA, preferably UAG. 158. A nucleic acid vector comprising the nucleic acid molecule of any one of items 155 to 157. 159. A host cell or a host comprising the nucleic acid molecule of any one of items 155 to 157, and / or the nucleic acid vector of item 158. 160. A solid phase comprising α-cyclodextrin groups. 161. The solid phase of item 160, wherein said solid phase further comprises a structural matrix, preferably wherein said structural matrix is selected from the group consisting of agarose, a cross- linked form of agarose, cellulose, starch, dextran, polymethacrylate, polystyrene, polyacrylamide, and silica gel, more preferably agarose or a cross-linked form of agarose. 162. The solid phase of item 161, wherein said structural matrix is transparent or translucent. 163. The solid phase of item 162, wherein said α-cyclodextrin is covalently linked to said structural matrix. 164. The solid phase of any one of items 161 to 163, wherein said α-cyclodextrin is covalently linked to said structural matrix via a linker. 165. The solid phase of item 164, wherein said linker is derived from 1,4-bis(2,3-epoxypropoxy)butane, 1-chloro-acetylchloride, or cyanogen bromide, preferably from 1,4-bis(2,3-epoxypropoxy)butane. 166. The solid phase of any one of items 160 to 165, wherein said solid phase is light-resistant at least in the wavelength range from about 300 nm to about 500 nm. 167. The solid phase of any one of items 160 to 166, wherein said solid phase is light-transmissive at least for UV light in the wavelength range from about 310 nm to about 370 nm. 168. The solid phase of any one of items 160 to 167, wherein said solid phase can be reused at least 10- times for affinity chromatography. 169. The solid phase of any one of items 160 to 168, wherein said solid phase is a matrix, a hydrogel, a bead, a chip, a glass surface, a plastic surface, a gold surface, a silver surface, or a plate such as a microtiter well plate. 170. The solid phase of item 169, wherein said matrix, said hydrogel, or said bead is the affinity matrix of an affinity chromatography column. 171. A kit comprising one or more selected from the group consisting of the following (a) to (e); wherein (a) is selected from one or more of the group consisting of the following (a1) to (a6): (a1) the polypeptide comprising the N-terminal or C-terminal light-responsive affinity tag of any one of items 1, 2, and 5 to 50, (a2) the nucleic acid molecule of any one of items 72 to 75, (a3) the nucleic acid vector of any one of items 76 to 80, (a4) the light-responsive affinity tag of any one of 115 to 154, (a5) the nucleic acid molecule of any one of items 155 to 157, (a6) the nucleic acid of item 158; (b) is selected from one or more of the group consisting of the following (b1) to (b3): (b1) the aaRS of any one of items 90, 91, and 97 to 105, (b2) the nucleic acid molecule of item 106 or 107, (b3) the nucleic acid vector of any one of item 108 to 110; (c) is selected from one or more of the group consisting of the following (c1) to (c3): (c1) the cognate suppressor tRNA as defined in any one of items 97 to 99, (c2) a nucleic acid molecule encoding the suppressor tRNA as defined in any one of items 97 to 99, (c3) the nucleic acid vector comprising the nucleic acid molecule of (c2); (d) is a host cell selected from one or more of the group consisting of (d1) to (d2): (d1) a host cell for the recombinant expression of the herein above provided polypeptide comprising the N-terminal or C-terminal light-responsive affinity tag, wherein said host cell comprises or harbors the herein above provided nucleic acid molecule of (a2), (b2), and / or (c2) and / or the herein above provided nucleic acid vector of (a3), (b3), and / or (c3), (d2) a host cell for the recombinant expression of the herein above provided light-responsive affinity tag, wherein said host cell comprises or harbors the herein above provided nucleic acid molecule of (a5), (b2), and / or (c2) and / or the herein above provided nucleic acid vector of (a6), (b3), and / or (c3); (e) is selected from one or more of the group consisting of the following (e1) to (e3): (e1) benzazo-phenylalanine (Baf), (e2) p-amino-benzazo-phenylalanine, and (e3) p-carboxy-benzazo-phenylalanine;and (f) is the solid phase of any one of items 160 to 170. 172. The kit of item 171, wherein said kit comprises one or more selected from the group defined as (a1) to (a3) in item 171, preferably wherein said kit further comprises one or more selected from the group defined as (b) to (f) in item 171, even more preferably wherein said kit comprises (b), (c), (d1), (e), and (f) in item 171. 173. The kit of item 171, wherein said kit comprises one or more selected from the group defined as (a4) to (a6), preferably wherein said kit further comprises one or more selected from the group defined as (b) to (f) in item 171, even more preferably wherein said kit comprises (b), (c), (d2), (e), and (f) in item 168. 174. The kit of any one of item 171to 173, wherein said kit further comprises a UV light source, preferably one or more LED light sources emitting one or more wavelength(s) of light selected from one or more wavelength(s) of light from about 310 nm to about 370 nm, more preferably from about 345 nm to about 365 nm, more preferably from about 350 nm to about 355 nm and, optionally, a second light source, preferably wherein said second light source is selected from one or more LED light sources emitting one or more wavelength(s) of light from about 405 nm to about 470 nm, preferably from about 420 nm to about 430 nm. 175. Use of the kit of any one of items 171to 174, the polypeptide comprising the N-terminal or the C- terminal light-responsive affinity tag of any one of items 1, 2, and 5 to 50, the polypeptide of interest of item 71, and / or the light-responsive affinity tag of item 115 to 154 in an in vitro or an in vivo assay. 176. The use of item 175, wherein said in vitro or said in vivo assay is a binding assay, an enzyme assay, and / or a cell culture assay. In a first aspect, the present invention relates to a polypeptide comprising an N-terminal or a C-terminal light-responsive affinity tag. In particular, said polypeptide may comprise a structure of formula (I) or of formula (II): X-[L-]lP (I) P[-L]l-X (II) wherein X is a light-responsive affinity tag, L is a linker, l is 1 or 0, so that L can be present or absent, P is a polypeptide of interest, wherein in formula (I) X-[L-]lis linked to the amino-terminus of P, and wherein in formula (II) [-L]l-X is linked to the carboxy-terminus of P. The polypeptide comprising an N-terminal or a C-terminal light-responsive affinity tag according to the present invention is particularly useful in the fields of biology, biochemistry, biotechnology, medicine and the like as such polypeptides are particularly useful in the context of affinity purification. Accordingly, the identity of the polypeptide of interest (POI or P in, inter alia, formulas (I) and (II)) is not particularly limited and may be selected from any polypeptide, protein, peptide, enzyme, antibody, antibody fragment and the like that may be of relevance in, for example, any area of academic, medical or industrial research or manufacturing. Further, the present invention also allows for the coupling of the herein provided light- responsive affinity tag (X in formulas (I) and (II)) to other molecules of interest (i.e., molecules, reagents, medicaments and the like that are not of proteinaceous nature, in other words that are no polypeptides). As will be detailed further herein below, the herein provided light-responsive affinity tag may be a (poly)peptide and, accordingly, may comprise a C-terminus and / or an N-terminus. The prior art describes means and methods that allow for the linkage or (chemical) coupling of various molecules to the C-terminus, the N-terminus or amino acid side chains of (poly)peptides. Accordingly, in the context of the present invention, the polypeptide of interest may also be a molecule of interest, whereas the nature of such molecules of interest is not particularly limited, as long as the person skilled in the art may couple the herein provided light-responsive affinity tag to such molecules. It is further envisaged that the herein below detailed linker (L in, inter alia, formulas (I) and (II)) may be comprised between the herein provided light-responsive affinity tag and such a molecule of interest. In the context of the present invention, it is also envisaged that the herein provided light-responsive affinity tag may not only be attached / linked / coupled (optionally via the linker L, inter alia, formulas (I) and (II)) either to the C-terminus or the N-terminus of the polypeptide of interest. Instead, it is envisaged that also multiple herein provided light-responsive affinity tags may be (recombinantly) coupled to a polypeptide of interest. Accordingly, the present invention also relates to a polypeptide comprising a structure of formula (VII): X1-[L1-]l1P-[L2-]l2X2 (VII) wherein X1 is a light-responsive affinity tag, X2 is a light-responsive affinity tag, L1 is a linker, l1 is 1 or 0, so that L1 can be present or absent, L2 is a linker, l2 is 1 or 0, so that L2 can be present or absent, P is a polypeptide of interest, wherein X1-[L1-]l1 is linked to the amino-terminus of P, and -[L2-]l2X2 is linked to the carboxy-terminus of P. X1 and X2 (in formula (VII)) may independently comprise identical or different sequences and / or structures. Both X1 and X2 may be defined according to the definitions of the light-responsive affinity tag X, herein below. L1 and L2 (in formula (VII)) may be independent from each other and may comprise sequences that are defined similarly to L herein below. L1 and L2 may further be independently present or absent from each other. The present invention further envisages more than two light-responsive affinity tags being linked to a polypeptide of interest. Said light-responsive affinity tags may be recombinantly linked (via a linker) to the C-terminus and / or the N-terminus of the polypeptide of interest or may be linked (via a linker) to the C- terminus and / or the N-terminus and / or any suitable amino acid side chain of the polypeptide of interest. The light-responsive affinity tag may comprise a structure and / or sequence as defined in any of the aspects of the present invention. Generally, any definition and / or specification of a certain aspect of the present invention may also apply mutatis mutandis to any other aspect of the present invention. In particular, in the context of the first aspect (i.e., the polypeptide comprising an N-terminal or a C-terminal light-responsive affinity tag) any definition and / or specification that applies to said N-terminal or C-terminal light- responsive affinity tag comprising in said polypeptide may, for example, also apply to the light-responsive affinity tag detailed in another aspect, any method detailed herein below and vice versa. Accordingly, in the context of the herein provided polypeptide comprising an N-terminal or a C-terminal light-responsive affinity tag, [X-] of formula (I) may comprise a structure of [A-]aB-[C-]c so that the polypeptide of formula (I) may be a polypeptide with a structure according to formula (III) [A-]aB-[C-]c[L-]lP (III), wherein [-X] of formula (II) may comprise a structure of [-A]a-B[-C]c, so that said polypeptide of formula (II) may be a polypeptide with a structure according to formula (IV) P[-L]l[-C]c-B[-A]a (IV), wherein A may comprise one or more amino acid(s), a may be 1 or 0, so that A can be present or absent, B may be a non-natural light-responsive amino acid, C may comprise one or more amino acid(s), c may be 1 or 0, so that C can be present or absent, wherein in formula (III) X-[L-]l may be linked to the amino-terminus of P, and wherein in formula (IV) [-L]l-X may be linked to the carboxy-terminus of P. Accordingly, the herein provided polypeptide comprising an N-terminal or a C-terminal light-responsive affinity tag may comprise a structure according to formula (III) or according to formula (IV): [A-]aB-[C-]c[L-]lP (III) P[-L]l[-C]c-B[-A]a (IV) wherein A may comprise one or more amino acid(s), a may be 1 or 0, so that A can be present or absent, B may be a non-natural light-responsive amino acid, C may comprise one or more amino acid(s), c may be 1 or 0, so that C can be present or absent, L may be a linker, l may be 1 or 0, so that L can be present or absent, P may be a polypeptide of interest, wherein in formula (III) [A-]aB-[C-]c[L-]l may be linked to the amino-terminus of P, and wherein in formula (IV) [-L]l[-C]c-B[-A]a may be linked to the carboxy-terminus of P. In the context of the present invention, it is further envisaged that the light-responsive affinity tag (comprised in the herein provided polypeptide) may comprise more than one non-natural light-responsive amino acid (i.e., non-natural light-responsive α-amino acid; B in, inter alia, formula (III) and formula (IV)). Whereas, said more than one non-natural light-responsive amino acids may for example be about 2, about 3, about 4, and so on, non-natural light-responsive amino acids. These amino acids may be selected independently of each other, for example, from the group consisting of benzazo-phenylalanine (Baf), p- amino-benzazo-phenylalanine, and p-carboxy-benzazo-phenylalanine. Further, it is also conceivable in the context of the present invention that said more than one non-natural light-responsive amino acids may be separated by one or more amino acid residue(s), whereas the identity of such one or more amino acid residue(s) is not particularly limited. In the context of the present invention the non-natural light-responsive amino acid may be in a first configuration or in a second configuration. As is detailed herein below and above, this is particularly useful in the context of light-controlled affinity chromatography approaches also provided herein, as the switch of said non-natural light-responsive amino acid from a first to a second configuration (or vice versa) may alter the affinity of said amino acid to a solid phase (such as a solid phase comprising α-cyclodextrin groups also provided herein). The non-natural light-responsive amino acid may be an azo-compound and, accordingly, comprise an azo- group, also known as diazenyl group (comprising a structure of R−N=N−R′, in which R and R’ may be (aromatic) aryl groups or derivates thereof). The non-natural light-responsive amino acid may comprise any structure as long as it allows for the light-responsive switch of its configuration from a first to a second configuration and vice versa and one of these preferentially binds to cyclodextrin. Accordingly, the first configuration of the non-natural light-responsive amino acid may be the trans- configuration of an azo-group comprised in said non-natural light-responsive amino acid and the second configuration may be the cis-configuration of said azo-group. In other words, the first configuration of the non-natural light-responsive amino acid may be the trans-configuration of an azo-group as part of said non- natural light-responsive amino acid and the second configuration may be the cis-configuration of said azo- group. In particular, the non-natural light-responsive amino acid in accordance with the present invention may comprise azobenzene or derivates thereof. As such, amino acid derivates of azobenzene (such as for example benzazo-phenylalanine) are particularly envisaged. Accordingly, the non-natural light-responsive amino acid may be selected from the group consisting of benzazo-phenylalanine (Baf), p-amino-benzazo-phenylalanine (NH2-Baf), and p-carboxy-benzazo- phenylalanine (COOH-Baf). The synthesis of these compounds is further detailed in the enclosed Examples 1J and 1L. It is particularly preferred in the context of the present invention that the non-natural light-responsive amino acid is benzazo-phenylalanine (Baf). Accordingly, the present invention may also relate to a polypeptide comprising an N-terminal or a C- terminal light-responsive affinity tag having a structure according to formula (III) or according to formula (IV): [A-]aB-[C-]c[L-]lP (III) P[-L]l[-C]c-B[-A]a (IV) wherein A may comprise one or more amino acid(s), a may be 1 or 0, so that A can be present or absent, B is benzazo-phenylalanine (Baf), C may comprise one or more amino acid(s), c may be 1 or 0, so that C can be present or absent, L may be a linker, l may be 1 or 0, so that L can be present or absent, P may be a polypeptide of interest, wherein in formula (III) [A-]aB-[C-]c[L-]l may be linked to the amino-terminus of P, and wherein in formula (IV) [-L]l[-C]c-B[-A]a may be linked to the carboxy-terminus of P. In the context of the present invention the N-terminal or the C-terminal light-responsive affinity tag may in its smallest embodiment solely comprise the above detailed non-natural light-responsive amino acid (e.g., benzazo-phenylalanine). However, the size of said light-responsive affinity tag is not particularly limited. Accordingly, said non-natural light-responsive amino acid may be flanked by one or more amino acid residues (A and / or C in, inter alia, formula (III) and (IV)). Accordingly, in the context of the present invention, a may be 1, so that A (in formula (III) or (IV)) may be present. While A (in formula (III) or (IV)) is not particularly limited, it may be one or more natural amino acid(s). Preferably, wherein A comprises less than about 100, less than about 50, less than about 20, more preferably less than about 10, even more preferably less than about 9, even more preferably less than about 8, even more preferably less than about 7, even more preferably less than about 6, even more preferably less than about 5, even more preferably less than about 4, even more preferably less than about 3, most preferably less than about 2 or about 1 (natural) amino acid(s). As also demonstrated in the illustrative and non-limiting Example 6, the present inventors have surprisingly found that the light-responsive affinity tag is particularly advantageous (for example in regard to its binding to a solid phase comprising α-cyclodextrin) if A (in, inter alia, formula (III) and (IV)) comprises specific amino acids (or combinations thereof). Namely, Gly, Pro, Ala, and Ser were found to be of particular advantage in this respect. Accordingly, in the context of the present invention A may comprise one or more amino acid(s) selected from the group consisting of Gly, Pro, Ala, and Ser. Preferably, wherein A comprises one or more Gly residue(s). In the context of the present invention it may be particularly advantageous if A comprises one or two amino acid(s) selected from the group consisting of Gly, Pro, Ala, and Ser, preferably one amino acid selected from the group consisting of Gly, Pro, Ala, and Ser. Preferably, wherein A comprises one or two Gly residue(s), more preferably one Gly residue. Alternatively, A may be absent and accordingly, a may be 0. As mentioned above, the non-natural light-responsive amino acid may be flanked by one or more amino acid residues (A and / or C in, inter alia, formula (III) and (IV)). Accordingly, in the context of the present invention, c may be 1, so that C (in formula (III) or (IV)) may be present. While C (in formula (III) or (IV)) is not particularly limited, it may be one or more natural amino acid(s). Preferably, wherein C comprises less than about 100, less than about 50, less than about 20, more preferably less than about 10, even more preferably less than about 9, even more preferably less than about 8, even more preferably less than about 7, even more preferably less than about 6, even more preferably less than about 5, even more preferably less than about 4, even more preferably less than about 3, most preferably less than about 2 or about 1 (natural) amino acid(s). As also demonstrated in the illustrative and non-limiting Example 6, the present inventors have surprisingly found that the light-responsive affinity tag is particularly advantageous (for example in regard to its binding to a solid phase comprising α-cyclodextrin) if C (in, inter alia, formula (III) and (IV)) comprises specific amino acids (or combinations thereof). Namely, Gly, Pro, Ala, and Ser were found to be of particular advantage in this respect. Accordingly, in the context of the present invention C may comprise one or more amino acid(s) selected from the group consisting of Gly, Pro, Ala, and Ser. Preferably, wherein C comprises one or more Gly residue(s). In the context of the present invention it may be particularly advantageous if C comprises one or two amino acid(s) selected from the group consisting of Gly, Pro, Ala, and Ser, preferably one or two amino acid selected from the group consisting of Gly and Pro. Preferably, wherein C comprises one or two Gly residue(s), more preferably one Gly residue. Alternatively, C may be absent and accordingly, c may be 0. As detailed herein above, the light-responsive affinity tag may be particularly small (i.e., comprise a low number of amino acid residues) and, consequently, may result in low / reduced sterical hindrance of a polypeptide of interest (said light-responsive affinity tag may be coupled to). Accordingly, in the context of the present invention the (N-terminal or C-terminal) light-responsive affinity tag may consist of about 1 to about 20 amino acid(s), preferably about 1 to about 10 amino acid(s), more preferably about 1 to about 9 amino acid(s), more preferably about 1 to about 8 amino acid(s), more preferably about 1 to about 7 amino acid(s), more preferably about 1 to about 6 amino acid(s), more preferably about 1 to about 5 amino acid(s), such as about 1 to about 4 amino acid(s), about 1 to about 3 amino acid(s), about 1 to about 2 amino acid(s), about 1 amino acid. Accordingly, the light-responsive affinity tag may consist of about 1 to about 5 amino acids. Accordingly, the light-responsive affinity tag may consist of about 5 amino acids, of about 4 amino acids, of about 3 amino acids, of about 2 amino acids, or of about 1 amino acid. In the context of the present invention, if the tag consists merely of a single amino acid (in other words of 1 amino acid or of about 1 amino acid), said amino acid is a non-natural light-responsive amino acid as defined herein above and below. Preferably, said non-natural light-responsive amino acid is benzazo- phenylalanine (Baf). In a preferred embodiment of the herein provided polypeptide comprising an N-terminal or a C-terminal light-responsive affinity tag, said light-responsive affinity tag consists of about 2 amino acids, preferably wherein X (i.e., the light-responsive affinity tag) consists of Baf-Gly or Gly-Baf. In particular, in formula (I) X consists of Gly-Baf and / or in formula (II) X consists of Baf-Gly. Herein below, Table 1 illustratively and non-limitingly highlights specific embodiments of the herein provided light-responsive affinity tag comprised in the herein provided polypeptides. Table 1: Illustrative and non-limiting examples of the herein provided (N-terminal or C-terminal) light- responsive affinity tag in accordance with the present invention. Exemplary light-responsive affinity tags comprising 2, 3, or 4 amino acids (AAs) are shown. Natural amino acids are shown in the three-letter code, “B” represents a non-natural light-responsive amino acid as defined herein above or below (such as B in, inter alia, formula III or IV). In particular, “B” can be selected from benzazo-phenylalanine (Baf), p-amino- benzazo-phenylalanine, and p-carboxy-benzazo-phenylalanine. In the context of the present invention, it is preferred that the light-responsive affinity tag does not comprise the sequence of a routinely employed proteinaceous affinity tag comprising a non-natural light-responsive amino acid (such as a FLAG-tag comprising a non-natural light-responsive amino acid, a Strep-tag comprising a non-natural light-responsive amino acid, a His-tag comprising a non-natural light-responsive amino acid, and the like). The herein provided polypeptides comprising an N-terminal or a C-terminal light-responsive affinity tag may, however, further comprise any other affinity tags (such as a Strep-tag or the like). When the herein provided light-responsive affinity tag is coupled to the C-terminus, it may be preferred that any further (e.g., non-light-responsive) affinity tag may be coupled to the N-terminus of said POI. The present inventors have found that the addition of a further affinity tag (in particular the addition of a further Strep-tag II) does not interfere with the herein provided means and methods for the purification of a polypeptide. In a particularly preferred embodiment, in formula (I) X (i.e., the N-terminal light-responsive affinity tag) comprises an amino acid sequence selected from the group consisting of B-Gly, B-Gly-Gly, Gly-B-Gly, Gly-B-Gly-Gly (SEQ ID NO: 23 to 25), Ala-B-Gly-Gly (SEQ ID NO: 26 to 28), Gly-B-Gly-Pro (SEQ ID NO: 29 to 31), Ala-B-Gly-Pro (SEQ ID NO: 32 to 34), Gly-B-Gly, Ala-B-Gly, Gly-B-Ala, Gly-Gly-B, Gly-Gly-B-Gly (SEQ ID NO: 35 to 37), and Pro-Gly-B-Gly (SEQ ID NO: 38 to 40). In a particularly preferred embodiment, in formula (II) X (i.e., the C-terminal light-responsive affinity tag) comprises an amino acid sequence selected from the group consisting of B-Gly-Gly, Gly-B-Gly-Gly (SEQ ID NO: 23 to 25), Ala-B-Gly-Gly (SEQ ID NO: 26 to 28), Gly-B-Gly-Pro (SEQ ID NO: 29 to 31), Ala-B- Gly-Pro (SEQ ID NO: 32 to 34), Gly-B-Gly, Ala-B-Gly, Gly-B-Ala, Gly-Gly-B, Gly-B, Gly-Gly-B-Gly (SEQ ID NO: 35 to 37), and Pro-Gly-B-Gly (SEQ ID NO: 38 to 40). In a more preferred embodiment, X in formula (I) (i.e., the N-terminal light-responsive affinity tag) or in formula (II) (i.e., the C-terminal light-responsive affinity tag) comprises an amino acid sequence consisting of Gly-B-Gly. In an even more preferred embodiment, X in formula (I) (i.e., the N-terminal light-responsive affinity tag) or in formula (II) (i.e., the C-terminal light-responsive affinity tag) comprises an amino acid sequence consisting of Gly-B-Gly, and wherein B is Baf. Accordingly, X may comprise a sequence consisting of Gly-Baf-Gly. As detailed herein above, the configuration of the light-responsive affinity tag (in particular the configuration of the non-natural light-responsive amino acid comprised in said affinity tag) may, in the context of the present invention, be switched from the trans-configuration to the cis-configuration, and vice versa. Accordingly, the configuration of B (i.e., said non-natural light-responsive amino acid) can be switched from the trans-configuration to the cis-configuration by irradiation with a specific wavelength of light, preferably wherein said wavelength of light is selected from one or more wavelength(s) of light from about 310 nm to about 370 nm, preferably from about 340 nm to about 365 nm, preferably from about 345 nm to about 360 nm, more preferably from about 350 nm to about 355 nm, most preferably about 355 nm. Figure 19 illustratively shows that a wavelength of about 355 nm is particularly advantageous when aiming at obtaining a high ratio of cis-Baf (i.e., for effecting efficient elution of the light-responsive amino acid comprised in the light-responsive affinity tag from a solid phase that may comprise α- cyclodextrin). This is particularly surprising as the prior art often employed a wavelength of 365 nm in order to induce the transition from trans-Baf to cis-Baf. However, in the context of the present invention, the wavelength for inducing a switch of the non-natural light-responsive amino acid from trans- configuration to the cis-configuration can be adapted depending on, e.g., the polypeptide of interest that is to be isolated. For example, when aiming at isolating a protein that has an absorption maximum for light having 355 nm, it may be preferred to employ a wavelength that does not fall within said absorption maximum and, however, is still able to induce the transition of the non-natural light-responsive amino acid from the trans- to the cis-configuration. Such a wavelength may be selected from the above-mentioned ranges, such as, for example about 365 nm. Accordingly, the configuration of B (i.e., said non-natural light-responsive amino acid) can be switched from the cis-configuration to the trans-configuration by irradiation with a specific wavelength of light, preferably wherein said wavelength of light is selected from one or more wavelength(s) of light from about 405 nm to about 470 nm and / or daylight, preferably from about 410 nm to about 440 nm, more preferably from about 420 nm to about 430 nm and / or daylight. As detailed herein above, and as illustratively shown in the enclosed and non-limiting Figure 2, the present inventors have surprisingly found that only when in the trans-configuration (as opposed to the cis- configuration), the non-natural light-responsive amino acid has high affinity towards α-cyclodextrin. Accordingly, the switch of said configuration (of non-natural light-responsive amino acid) alters its affinity (i.e., the affinity of said non-natural light-responsive amino acid) towards α-cyclodextrin. The person skilled in the art is aware of means and methods to determine whether two (or more) compounds (such as, for example, Baf and α-cyclodextrin) form a complex and is furthermore able to determine the stability of such complexes. Particular means and methods are exemplarily detailed in the enclosed examples, such as Example 1B. The skilled person is aware that the equilibrium dissociation constant (KD) can provide an indication regarding the stability of a given complex. In the context of the present invention, a complex having an equilibrium dissociation constant (as for example determined by spectroscopic analysis during titration experiments, as exemplified in Example 1B) of KD ≤ 1 mM is considered a stable complex, whereas any complex having an equilibrium dissociation constant (as for example determined by spectroscopic analysis during titration experiments, as exemplified in Example 1B) of KD ≥ 1 mM is considered an unstable complex. As shown in the illustrative and non-limiting Figure 2, the complex of trans-Baf and α-cyclodextrin comprises an equilibrium dissociation constant (KD) of about or less than about 91 µM ± 5 µM. Accordingly, when in the trans-configuration, B (i.e., the non-natural light- responsive amino acid) forms or is capable of forming a (stable) complex with α-cyclodextrin, preferably as determined by spectroscopic analysis during titration of B in the trans-configuration with α-cyclodextrin. Accordingly, when in the trans-configuration, B may comprise an equilibrium dissociation constant (KD) of less than about 1 mM, of about or less than about 900 µM, of about or less than about 800 µM, of about or less than about 700 µM, of about or less than about 600 µM, of about or less than about 500 µM, of about or less than about 400 µM, of about or less than about 350 µM, of about or less than about 300 µM, of about or less than about 250 µM, of about or less than about 200 µM, of about or less than about 150 µM, of about or less than about 140 µM, of about or less than about 130 µM, of about or less than about 120 µM, of about or less than about 110 µM, of about or less than about 105 µM, of about or less than about 104 µM, of about or less than about 103 µM, of about or less than about 102 µM, of about or less than about 101 µM, of about or less than about 100 µM, of about or less than about 99 µM, of about or less than about 98 µM, of about or less than about 97 µM, of about or less than about 96 µM, of about or less than about 95 µM, of about or less than about 94 µM, of about or less than about 93 µM, of about or less than about 92 µM, of about or less than about 91 µM, preferably wherein KD is determined by spectroscopic analysis during titration of B in the trans-configuration with α-cyclodextrin. Accordingly, when in the trans-configuration, B comprises an equilibrium dissociation constant (KD) of about or less than about 91 µM ± 5 µM when contacted with α-cyclodextrin, preferably wherein KD is determined by spectroscopic analysis during titration of B in the trans-configuration with α-cyclodextrin in solution. The illustrative and non-limiting Figure 2 further demonstrates that contacting cis-Baf with α-cyclodextrin does not allow for the determination and / or quantification of an equilibrium dissociation constant (KD) using spectroscopic titration. Accordingly, when in the cis-configuration, B does not form a stable complex with α-cyclodextrin, preferably as determined by spectroscopic analysis during titration of B in the cis- configuration with α-cyclodextrin. As further detailed, inter alia, in the enclosed examples, irradiating the non-natural light-responsive amino acids of the present invention with specific wavelengths alters the configuration of a fraction of these non- natural light-responsive amino acids. Accordingly, when irradiated with visible light having about 405 nm to about 470 nm and / or daylight, at least about 50%, at least about 60%, at least about 70%, at least about 75%, at least about 80%, at least about 85%, at least about 90%, at least about 95% of the polypeptide of formula (III) or (IV) comprise B in the trans-configuration, preferably at least about 80% of the polypeptide of formula (III) or (IV) comprise B in the trans-configuration. Accordingly, when irradiated with visible light having about 405 nm to about 470 nm and / or daylight for about or less than about 30 min, at least about 50%, at least about 60%, at least about 70%, at least about 75%, at least about 80%, at least about 85%, at least about 90%, at least about 95% of the polypeptide of formula (I) or (II) comprise B in the trans-configuration which is maintained for at least about 60 min under daylight or in the dark, preferably at least about 80% of the polypeptide of formula (III) or (IV) comprise B in the trans-configuration which is maintained for at least about 60 min under daylight or in the dark. As also demonstrated in Figure 20 A and B, in the context of the present invention it was surprisingly found that contacting a solid phase (e.g., comprising α-cyclodextrin) with a POI coupled to the herein provided light-responsive affinity tag (as well as the optional subsequent washing step) can be performed in the presence of light having a wavelength that induces the switch from the cis- to the trans-configuration of said non-natural light-responsive amino acid (e.g., in the presence of light having a wavelength of about 430 nm). Alternatively, said contacting step (as well as the optional subsequent washing step) can be performed in the dark. As illustrated in Figure 20 and discussed herein above, a wavelength of e.g., 430 nm results in a higher quantity / yield as compared to darkness. See also Figure 23 providing a schematic and non-limiting illustration of the herein provided means and method. Accordingly, the herein provided polypeptide comprising a light-responsive affinity tag is particularly advantageous as it can, depending on the need, either be contacted to a herein provided solid phase the in the dark (resulting particularly in a remarkably high purity of the to be purified polypeptide) or at e.g., 430 nm (resulting particularly in a remarkably high quantity / yield of the to be purified polypeptide). Accordingly, when irradiated with UV light having about 310 nm to about 370 nm, at least about 50%, at least about 60%, at least about 70%, at least about 75%, at least about 80%, at least about 85%, at least about 90%, at least about 95% of the polypeptide of formula (III) or (IV) comprise B in the cis- configuration, preferably at least about 90% of the polypeptide of formula (III) or (IV) comprise B in the cis-configuration. Accordingly, when irradiated with UV light having about 310 nm to about 370 nm for about or less than about 30 min and subsequently not irradiated with visible light, at least about 50%, at least about 60%, at least about 70%, at least about 75%, at least about 80%, at least about 85%, at least about 90%, at least about 95% of the polypeptide of formula (III) or (IV) comprise B in the cis-configuration which is maintained for at least about 60 min in the dark, preferably at least about 90% of the polypeptide of formula (III) or (IV) comprise B in the cis-configuration which is maintained for at least about 60 min in the dark. The present inventors could surprisingly show that after an (initial) irradiation for about 3 or even about 1 min with UV light having about 355 nm, and when subsequently not irradiated with visible light or subsequently kept in the dark, at least about 50%, at least about 60%, at least about 70%, at least about 75%, at least about 80%, at least about 85%, at least about 90%, at least about 95% of said non-natural light-responsive amino acid remains in the cis-configuration. Such an initial irradiation (with e.g., a wavelength of 355 nm) may be about or less than about 30 min. The present inventors could surprisingly demonstrate that e.g., an (initial) irradiation for about 3 min or even about 1 min with UV light having a wavelength of about 355 nm and when subsequently not irradiated with visible light or subsequently kept in the dark is sufficient to allow for efficient elution of the herein provided polypeptide comprising an N- terminal or a C-terminal light-responsive affinity tag (see also Figure 20 C). Accordingly, when irradiated with UV light having about 310 nm to about 370 nm for about or less than about 30 min, for about or less than about 20 min, for about or less than about 10 min, for about or less than about 9 min, for about or less than about 8 min, for about or less than about 7 min, for about or less than about 6 min, for about or less than about 5 min, for about or less than about 4 min, for about or less than about 3 min, for about or less than about 2 min, or for about or less than about 1 min, and subsequently not irradiated with visible light, at least about 50%, at least about 60%, at least about 70%, at least about 75%, at least about 80%, at least about 85%, at least about 90%, at least about 95% of the polypeptide of formula (III) or (IV) comprise B in the cis-configuration which is maintained for at least about 60 min in the dark, preferably at least about 90% of the polypeptide of formula (III) or (IV) comprise B in the cis-configuration which is maintained for at least about 60 min in the dark. As indicated herein above, the identity of P (i.e., the protein of interest in the context of the present invention) is not particularly limited and, as such, any polypeptide or the like may be employed in this context. Accordingly, P may be selected from the group consisting of an oligopeptide, a polypeptide, a protein, an immunoglobulin or an antigen-binding fragment thereof, a binding protein, a growth factor, a signaling protein, an enzyme, and / or a complex thereof. Furthermore, P may be selected from the group consisting of intracellular, cytosolic, cytoplasmic, periplasmic, secreted, membrane or plasma proteins. In the field of affinity chromatography, protein purification and the like it may be advantageous to express a recombinant protein of interest coupled to a signal peptide that may affect the translocation of said polypeptide of interest to a certain organelle, compartment or the extracellular space of a host cell expressing said protein or polypeptide of interest. Accordingly, in the context of the present invention the polypeptide of interest may further comprise a signal peptide. The identity of such signal peptides is not particularly limited and the skilled artisan is aware of signal peptides that may be employed in order to target (recombinant) expression of a polypeptide of interest to e.g., a specific cellular compartment. In the context of the present invention, signal peptides are preferably selected from the group consisting of OmpA, OmpF, PhoA, MalE, PelB, stII, DsbC. In the context of the present invention, it may be advantageous to couple the herein provided light- responsive affinity tag (for example, X in formula (I) and formula (II)) to the polypeptide of interest via a linker. As illustratively shown in, inter alia, the enclosed Examples 5 and 6 such a linker is not essential, for example, for the efficient purification of a polypeptide comprising an N-terminal or a C-terminal light- responsive affinity tag. However, it is conceivable that such a linker may, depending on the identity of a polypeptide of interest and its structural characteristics, be advantageous for the accessibility of the light- responsive affinity tag to α-cyclodextrin (as, for example, comprised in the stationary or solid phase of a chromatography column). Accordingly, in the context of the present invention, l (in, for example, formula (I), formula (II), formula (III), or formula (IV)) may be 1, so that L (in, for example, formula (I), formula (II), formula (III), or formula (IV)) may be present. In the context of the present invention, the identity of the linker (L) is not particularly limited. Exemplary linkers may for example comprise any kind and combinations of (natural) amino acids. However, also non- proteinogenic linkers (such as, for example, polyethylene glycol-based linkers and the like) are envisaged herein. In particular, a linker of the present invention may preferably comprise one or more amino acids selected from the group consisting of Gly, Pro, Ala, and Ser. A particularly preferred linker (L) in the context of the present invention may comprise an amino acid sequence selected from the group consisting of the following: Glu-Asn-Leu-Tyr-Phe-Gln-Ser-Gly (SEQ ID NO: 41), Glu-Asn-Leu-Tyr-Phe-Gln-Ser-Ala (SEQ ID NO: 42), Leu-Val-Pro-Arg-Gly-Ser (SEQ ID NO: 43), Ile-Glu-Gly-Arg (SEQ ID NO: 44), Leu-Glu-Val-Leu-Phe-Gln-Gly-Pro (SEQ ID NO: 45). In the context of the present invention it may be advantageous to cleave the N-terminal or C-terminal light- responsive affinity tag of the polypeptide of interest (for example after successful affinity purification thereof using the herein provided means and methods). Accordingly, the linker (L in, for example, formula (I), formula (II), formula (III), or formula (IV)) may be a cleavable linker. The identity of such a cleavable linker (L) is not particularly limited. Exemplary linkers may for example comprise any kind and combinations of (natural) amino acids, as long as they are cleavable by, for example, enzymatic, chemical, or other suitable means and methods. A particularly preferred linker (L) in the context of the present invention may comprise a cleavable amino acid sequence. Preferably, wherein said cleavable amino acid sequence is selected from the group consisting of the following: Tobacco Etch Virus (TEV) protease, thrombin, factor Xa, human rhinovirus type 143C protease (HRV 3C). Alternatively, l (in, for example, formula (I), formula (II), formula (III), or formula (IV)) may be 0, so that L (in, for example, formula (I), formula (II), formula (III), or formula (IV)) may be absent (and the N- terminal or C-terminal light-responsive affinity tag (X) is directly coupled to the N-terminus or the C- terminus of the polypeptide of interest (P), respectively. The present invention further relates to a method for cleaving the (N-terminal or C-terminal) light- responsive affinity tag from the polypeptide of interest (comprising said N-terminal or C-terminal light- responsive affinity tag) as defined herein above, wherein the method comprises the steps of: (a) cleaving said cleavable linker; and (b) purifying the polypeptide of interest. The skilled person is aware, that in the context of the present invention, said method is only applicable to a polypeptide comprising an N-terminal or C-terminal light-responsive affinity tag, wherein said polypeptide (e.g., according to, for example, formula (I) or formula (II)) comprises a polypeptide of interest (P, as detailed herein above), a cleavable linker (L, as detailed herein above) and a light-responsive affinity tag (for example X, as detailed herein above). In other words, the skilled person is aware that said method is only applicable to a polypeptide of the present invention (e.g., according to formula (I) or formula (II)) wherein the linker L is present (i.e., when l is 1) and wherein said linker L is a cleavable linker as defined herein above. The skilled person is furthermore aware of cleavable linkers and suitable cleaving reagents. In the context of the present invention a (suitable) cleaving reagent may be, for example, an enzyme, such as a protease or peptidase, with specificity to a (poly)peptide sequence and capability to cleave said sequence (i.e., the cleavable linker detailed herein above). Accordingly, in the context of the herein provided method for cleaving the (N-terminal or C-terminal) light- responsive affinity tag from the polypeptide of interest, the step of cleaving the cleavable linker (i.e., step (a)) may comprise contacting said cleavable linker with a cleaving reagent. In the context of the present invention, said cleaving reagent is not particularly limited and any cleaving reagent that is capable of cleaving a given cleavable linker (comprised in the herein provided polypeptide) may be employed herein. In particular, said cleaving reagent may, for example, be selected from the group consisting of one or more enzyme(s), preferably Tobacco Etch Virus (TEV) protease, thrombin, factor Xa, human rhinovirus type 143C protease (HRV 3C) preferably TEV protease (Zhou et al., (2014) Microb. Cell Fact.13:44.). The present invention further relates to a polypeptide of interest as obtained by and / or obtainable by the method for cleaving the (N-terminal or C-terminal) light-responsive affinity tag from the polypeptide of interest, as detailed herein above. The present invention further relates to a nucleic acid molecule encoding the polypeptide comprising the N-terminal or the C-terminal light-responsive affinity tag as detailed herein above. Any definition and / or specification relating to nucleic acid molecules provided herein also apply to the nucleic acid molecule encoding the polypeptide comprising the N-terminal or the C-terminal light- responsive affinity tag. Accordingly, the present invention relates to a nucleic acid encoding a polypeptide comprising the N- terminal or the C-terminal light-responsive affinity tag, wherein said polypeptide may comprise a structure of formula (I) or of formula (II): X-[L-]lP (I) P[-L]l-X (II) wherein X is a light-responsive affinity tag, L is a linker, l is 1 or 0, so that L can be present or absent, P is a polypeptide of interest, wherein in formula (I) X-[L-]l is linked to the amino-terminus of P, and wherein in formula (II) [-L]l-X is linked to the carboxy-terminus of P. Accordingly, the present invention relates to a nucleic acid encoding a polypeptide comprising the N- terminal or the C-terminal light-responsive affinity tag, wherein said polypeptide may comprise a structure according to formula (III) or according to formula (IV): [A-]aB-[C-]c[L-]lP (III) P[-L]l[-C]c-B[-A]a (IV) wherein A may comprise one or more amino acid(s), a may be 1 or 0, so that A can be present or absent, B may be a non-natural light-responsive amino acid, preferably wherein B is benzazo-phenylalanine (Baf), C may comprise one or more amino acid(s), c may be 1 or 0, so that C can be present or absent, L may be a linker, l may be 1 or 0, so that L can be present or absent, P may be a polypeptide of interest, wherein in formula (III) [A-]aB-[C-]c[L-]l may be linked to the amino-terminus of P, and wherein in formula (IV) [-L]l[-C]c-B[-A]a may be linked to the carboxy-terminus of P. As detailed herein above, A and C (in formula (III) and (IV)) may, in the context of the present invention, preferably be natural amino acids. Accordingly, in the context of said nucleic acid molecule encoding the herein provided polypeptide comprising the N-terminal or the C-terminal light-responsive affinity tag, the amino acids comprised in A and / or C may be encoded by the respective codons amply known in the art. In contrast, B (in formula (III) and (IV)) is a non-natural light-responsive amino acid (such as Baf). The skilled person is aware that non-natural (light-responsive) amino acids are naturally not encoded by any of the 64 codons known in the art. As detailed above and below, the present inventors have identified means and methods for the (recombinant) expression of a herein provided light-responsive affinity tag (comprising a non-natural light-responsive amino acid) from a nucleic acid. In this context, the non-natural light-responsive amino acid (B) may be encoded by a stop codon. Said stop codon may be selected from the group consisting of UAG, UGA, and UAA, preferably UAG (i.e., the amber stop codon). In the context of the present invention, the nucleic acid sequence encoding P (i.e., the polypeptide of interest in any one of formulas (I) to (IV)) may be replaced with a (multiple) cloning site. This allows for the efficient and simple introduction of nucleic acid sequences encoding various proteins of interest into such vectors and subsequently facilitates recombinant expression of such proteins. The present invention further relates to a nucleic acid vector comprising said nucleic acid molecule (encoding the herein provided polypeptide comprising the N-terminal or the C-terminal light-responsive affinity tag). Any definition and / or specification relating to nucleic acid vectors provided herein also apply to the nucleic acid vector comprising the nucleic acid molecule encoding the light-responsive affinity tag detailed above. As is detailed herein above and below, the present inventors have found means and methods for the efficient (recombinant) expression of a polypeptide comprising an N-terminal or a C-terminal light-responsive affinity tag. This includes the provision of an aminoacyl tRNA synthetase (aaRS) (and a cognate suppressor tRNA) that paves the way for the efficient incorporation of non-natural light-responsive amino acids (such as benzazo-phenylalanine). It may be particularly advantageous to express such an aaRS and the cognate suppressor tRNA from the same nucleic acid vector as the polypeptide comprising the N-terminal or C- terminal light-responsive affinity tag. Accordingly, in the context of the present invention, said nucleic acid vector further comprises one or more nucleic acid sequence(s) encoding one or more selected from the group consisting of the following: (a) an aminoacyl tRNA synthetase (aaRS); (b) a suppressor tRNA; and (c) (optionally) an antibiotic selection marker. The person skilled in the art is aware of suitable antibiotic section markers and respective antibiotics. Such antibiotic selection markers can, in the context of the present invention, for example, be nucleic acid sequences that when expressed confer resistance towards an antibiotic and thereby allows survival of a host cell comprising a vector encoding said antibiotic selection marker when said host cell is cultured in the presence of or contacted with the respective antibiotic. It is envisaged that such an aaRS and the suppressor tRNA may be as defined in any other aspect of the present invention. In the context of the present invention, it is preferred that the nucleic acid molecule encoding the aaRS is selected from the group consisting of the following: (a) a nucleic acid molecule comprising a nucleic acid sequence of SEQ ID NO: 60 to SEQ ID NO: 67; (b) a nucleic acid molecule that hybridizes with a nucleic acid molecule comprising a nucleic acid sequence complementary to the nucleotide sequence of SEQ ID NO: 60 to SEQ ID NO: 67 and that encodes a polypeptide with aaRS activity; (c) a nucleic acid molecule encoding a polypeptide comprising an amino acid sequence of SEQ ID NO: 15 to SEQ ID NO: 22; (d) a nucleic acid molecule encoding a polypeptide comprising an amino acid sequence of SEQ ID NO: 15 to SEQ ID NO: 22 with a deletion, substitution, insertion, and / or addition of one or more amino acid(s), and wherein said polypeptide comprises aaRS activity; and (e) a nucleic acid molecule encoding a polypeptide comprising an amino acid sequence with at least about 80% amino acid sequence identity to the amino acid sequence of SEQ ID NO: 15 to SEQ ID NO: 22, and wherein said polypeptide comprises aaRS activity. In the context of the present invention, the aaRS activity may refer to the (enzymatic) activity of a polypeptide of charging a (cognate) suppressor tRNA with a non-natural light-responsive amino acid, preferably wherein said non-natural light-responsive amino acid is selected from the group consisting of benzazo-phenylalanine (Baf), p-amino-benzazo-phenylalanine, and p-carboxy-benzazo-phenylalanine, most preferably Baf. Accordingly, in the context of the present invention, it is preferred that the nucleic acid molecule encoding the aaRS is selected from the group consisting of the following: (a) a nucleic acid molecule comprising a nucleic acid sequence of SEQ ID NO: 60 to SEQ ID NO: 67; (b) a nucleic acid molecule that hybridizes with a nucleic acid molecule comprising a nucleic acid sequence complementary to the nucleotide sequence of SEQ ID NO: 60 to SEQ ID NO: 67 and that encodes a polypeptide with aaRS activity; (c) a nucleic acid molecule encoding a polypeptide comprising an amino acid sequence of SEQ ID NO: 15 to SEQ ID NO: 22; (d) a nucleic acid molecule encoding a polypeptide comprising an amino acid sequence of SEQ ID NO: 15 to SEQ ID NO: 22 with a deletion, substitution, insertion, and / or addition of one or more amino acid(s), and wherein said polypeptide comprises aaRS activity; and (e) a nucleic acid molecule encoding a polypeptide comprising an amino acid sequence with at least about 80% amino acid sequence identity to the amino acid sequence of SEQ ID NO: 15 to SEQ ID NO: 22, and wherein said polypeptide comprises aaRS activity, wherein, said aaRS activity is the (enzymatic) activity of charging a (cognate) suppressor tRNA with a non- natural light-responsive amino acid, preferably wherein said non-natural light-responsive amino acid is selected from the group consisting of benzazo-phenylalanine (Baf), p-amino-benzazo-phenylalanine, and p-carboxy-benzazo-phenylalanine, most preferably Baf. In the context of the present invention, the suppressor tRNA is not particularly limited, as long as it forms a (suitable) orthogonal tRNA / aaRS pair with the herein provided aaRS, and wherein it comprises an anticodon which is complementary to a stop codon selected from the group consisting of UAG, UGA, and UAA, preferably UAG. In the context of the present invention, the nucleic acid molecule encoding the suppressor tRNA is preferably selected from the group consisting of the following: (a) a nucleic acid molecule comprising a nucleic acid sequence of SEQ ID NO: 70; and (b) a nucleic acid molecule that hybridizes with a nucleic acid molecule comprising a nucleic acid sequence complementary to the nucleotide sequence of SEQ ID NO: 70 and that encodes a suppressor tRNA, wherein said suppressor tRNA forms or is capable of forming a cloverleaf structure and comprises an anticodon, and wherein said anticodon is complementary to a stop codon selected from the group consisting of UAG, UGA, and UAA, preferably UAG. In the context of the present invention, said nucleic acid vector preferably comprises a nucleic acid sequence of SEQ ID NO: 68,SEQ ID NO: 69, SEQ ID NO: 72 or SEQ ID NO: 73. The present invention further relates to a host cell or a host comprising the herein above provided nucleic acid molecule encoding the polypeptide comprising the N-terminal or the C-terminal light-responsive affinity tag, and / or the herein above provided nucleic acid vector comprising said nucleic acid molecule. Such host cells or hosts may, in accordance with the present invention, be particularly useful in the recombinant production of a herein provided polypeptide comprising an N-terminal or a C-terminal light- responsive affinity tag. In other words, the present invention also provides for an expression system for the recombinant expression of a polypeptide comprising an N-terminal or a C-terminal light-responsive affinity tag. The skilled person is aware that certain expression systems (i.e., hosts or host cells) may be particularly advantageous for the expression depending on the polypeptide of interest to be expressed. Further, the skilled artisan can readily select suitable hosts and / or host cells for the expression of a given polypeptide of interest being linked to a light-responsive affinity tag in accordance with the present invention. Such expression systems may be prokaryotic or eukaryotic. Accordingly, said host cell or said host may be eukaryotic, preferably wherein said host cell or said host is selected from the group consisting of cultivated mammalian cells, cultivated insect cells, yeast. The skilled artisan is aware of suitable eukaryotic host or host cells. Exemplary and non-limiting (cultivated) mammalian cells are CHO, HEK, COS or insect cells such as Sf9 from Spodoptera frugiperda. In the context of the present invention, hosts are not human. Accordingly, the herein provided host cell or the herein provided host is prokaryotic, preferably said host cell or said host is selected from the group consisting of Escherichia coli (E. coli), Bacillus subtilis, Corynebacterium glutamicum and Pseudomonas fluorescens, preferably E. coli. As detailed herein above, the present inventors have surprisingly found that E. coli expression systems may be particularly advantageous in the context of the present invention. In particular, it was found that E. coli B strains and E. coli K12 strains are advantageous for the (recombinant) expression of the herein provided polypeptides comprising an N-terminal or a C-terminal light-responsive affinity tag. Accordingly, the present invention relates to a (prokaryotic) host cell or host, preferably wherein said (prokaryotic) host cell or host is E. coli, more preferably wherein said host cell or said host is an E. coli B strain or an E. coli K12 strain, even more preferably an E. coli B strain. In the context of the present invention, said E. coli B strain may be NEBExpress. The present inventors have surprisingly found that (prokaryotic) host cells (such as Escherichia coli) are particularly useful for the recombinant expression of the herein provided polypeptides comprising the N- terminal or the C-terminal light-responsive affinity tag if they do not encode a functional ribosomal release factor 1 (RF1) or that are characterized by reduced expression of RF1 as compared to a E. coli wildtype strain as RF1 counteracts amber stop codon suppression. Accordingly, the host cell or host of the present invention does preferably not encode a functional ribosomal release factor 1 (RF1 alias PrfA) or is a RF1 knockdown strain. Further, it was surprisingly found that maltose binding protein (MBP) encoded by the malE gene in, for example, E. coli may bind to α-cyclodextrin (as for example comprised in the herein provided solid phase), and as such, may cause (minor) impurities in the elution fractions of the polypeptide comprising the N- terminal or the C-terminal light-responsive affinity tag. Accordingly, in the context of the present invention it may be preferred that (prokaryotic) host cells (such as Escherichia coli) do not encode a functional maltose binding protein (MBP). The skilled person is readily capable to assess whether a host cell or a host (such as, for example, an E. coli strain) encodes a functional ribosomal release factor 1 (RF1 alias PrfA) and / or encode a functional maltose binding protein (MBP). Further, the person skilled in the art is aware of means and methods to generate, for example, a RF1 and / or MBP knockout or knockdown mutant. In a further aspect, the present invention relates to a method for the recombinant expression and / or the recombinant production of a polypeptide comprising an N-terminal or a C-terminal light-responsive affinity tag as detailed herein above. Said method may comprise culturing the herein provided host and / or the host cell as detailed herein above. Accordingly, the present invention relates to a method for the recombinant expression and / or the recombinant production of a polypeptide comprising an N-terminal or a C-terminal light-responsive affinity tag, wherein said polypeptide may comprise a structure of formula (I) or of formula (II): X-[L-]lP (I) P[-L]l-X (II) wherein X is a light-responsive affinity tag, L is a linker, l is 1 or 0, so that L can be present or absent, P is a polypeptide of interest, wherein in formula (I) X-[L-]l is linked to the amino-terminus of P, and wherein in formula (II) [-L]l-X is linked to the carboxy-terminus of P. Accordingly, the present invention relates to a method for the recombinant expression and / or the recombinant production of a polypeptide comprising an N-terminal or a C-terminal light-responsive affinity tag, wherein said polypeptide may comprise a structure according to formula (III) or according to formula (IV): [A-]aB-[C-]c[L-]lP (III) P[-L]l[-C]c-B[-A]a (IV) wherein A may comprise one or more amino acid(s), a may be 1 or 0, so that A can be present or absent, B may be a non-natural light-responsive amino acid, preferably benzazo-phenylalanine, C may comprise one or more amino acid(s), c may be 1 or 0, so that C can be present or absent, L may be a linker, l may be 1 or 0, so that L can be present or absent, P may be a polypeptide of interest, wherein in formula (III) [A-]aB-[C-]c[L-]l may be linked to the amino-terminus of P, and wherein in formula (IV) [-L]l[-C]c-B[-A]a may be linked to the carboxy-terminus of P. In the context of the present invention, said method may comprise the recombinant expression of the polypeptide of formula (I), the polypeptide of formula (II), the polypeptide of formula (III), or the polypeptide of formula (IV) in the presence of an aminoacyl tRNA synthetase (aaRS), a cognate suppressor tRNA, and a non-natural light-responsive amino acid, preferably wherein said non-natural light-responsive amino acid is selected from of benzazo-phenylalanine (Baf), p-amino-benzazo-phenylalanine, and p- carboxy-benzazo-phenylalanine, more preferably of benzazo-phenylalanine. In the context of the present invention said aaRS may be the herein provided aaRS as defined herein below. Accordingly, in the context of the present invention, said method may comprise the recombinant expression of the polypeptide of formula (I), the polypeptide of formula (II), the polypeptide of formula (III), or the polypeptide of formula (IV) in the presence of an aminoacyl tRNA synthetase (aaRS), a cognate suppressor tRNA, and a non-natural light-responsive amino acid, preferably wherein said non-natural light-responsive amino acid is selected from of benzazo-phenylalanine (Baf), p-amino-benzazo-phenylalanine, and p- carboxy-benzazo-phenylalanine, more preferably of benzazo-phenylalanine, wherein said aaRS may be characterized in that: it comprises enzymatic activity for charging a cognate suppressor tRNA with benzazo- phenylalanine (Baf) or a derivate thereof, preferably wherein said derivate is a non-natural light- responsive amino acid selected from the group consisting of p-amino-benzazo-phenylalanine and p- carboxy-benzazo-phenylalanine, and it comprises an amino acid sequence with at least 70%, at least 80%, at least 85%, at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, preferably at least 95%, more preferably at least 96%, even more preferably at least 97%, even more preferably at least 98%, even more preferably at least 99%, even more preferably 100% amino acid sequence identity to SEQ ID NO: 14, wherein: (a) the amino acid at position 295 in the amino acid sequence of SEQ ID NO: 14 or a position corresponding to this position is substituted with an amino acid selected from the group consisting of L and R; and / or (b) the amino acid at position 304 in the amino acid sequence of SEQ ID NO: 14 or a position corresponding to this position is substituted with an amino acid selected from the group consisting of S; and / or (c) the amino acid at position 346 in the amino acid sequence of SEQ ID NO: 14 or a position corresponding to this position is substituted with an amino acid selected from the group consisting of A; and / or (d) the amino acid at position 221 in the amino acid sequence of SEQ ID NO: 14 or a position corresponding to this position is substituted with an amino acid selected from the group consisting of R. In the context of the present invention said cognate suppressor tRNA may be as defined herein below. Accordingly, in the context of the herein provided method for the recombinant expression and / or the recombinant production of a polypeptide comprising an N-terminal or a C-terminal light-responsive affinity tag, said cognate suppressor tRNA may comprise an anticodon, wherein said anticodon is complementary to a stop codon, preferably wherein said stop codon is selected from the group consisting of UAG, UGA, and UAA, more preferably UAG. Accordingly, in the context of the present invention, said method may comprise the recombinant expression of the polypeptide of formula (I), the polypeptide of formula (II), the polypeptide of formula (III), or the polypeptide of formula (IV) in the presence of an aminoacyl tRNA synthetase (aaRS), a cognate suppressor tRNA, and a non-natural light-responsive amino acid, preferably wherein said non-natural light-responsive amino acid is selected from the group consisting of benzazo-phenylalanine (Baf), p-amino-benzazo- phenylalanine, and p-carboxy-benzazo-phenylalanine, more preferably of benzazo-phenylalanine, wherein said cognate suppressor tRNA may preferably be selected from the group consisting of: (a) a nucleic acid molecule comprising a nucleic acid sequence of SEQ ID NO: 70; and (b) a nucleic acid molecule that hybridizes with a nucleic acid molecule comprising a nucleic acid sequence complementary to the nucleotide sequence of SEQ ID NO: 70 and that encodes a suppressor tRNA, wherein said suppressor tRNA forms or is capable of forming a cloverleaf structure and comprises an anticodon, and wherein said anticodon is complementary to said stop codon (e.g., UAG, UGA or UAA). In the context of the method for the recombinant expression and / or the recombinant production of a polypeptide comprising an N-terminal or a C-terminal light-responsive affinity tag, the non-natural light- responsive amino acid (preferably comprised in said light-responsive affinity tag) may be Baf or a derivate thereof, wherein said derivate may be a non-natural light-responsive amino acid selected from the group consisting of p-amino-benzazo-phenylalanine and p-carboxy-benzazo-phenylalanine. Preferably, wherein said non-natural light-responsive amino acid is Baf. Example 1J and Example 1L provide illustrative means and methods for the synthesis of said non-natural light-responsive amino acids. As detailed herein below, in the context of the present invention an aaRS may preferably incorporate non- natural light-responsive amino acids (such as Baf) when they are in the trans-configuration. Accordingly, in the context of the present invention, an aaRS may have substrate specificity for trans-benzazo- phenylalanine, trans-p-amino-benzazo-phenylalanine, and / or trans-p-carboxy-benzazo-phenylalanine. Accordingly, the non-natural light-responsive amino acid to be incorporated in the context of the herein provided method may preferably be trans-benzazo-phenylalanine, trans-p-amino-benzazo-phenylalanine, and / or trans-p-carboxy-benzazo-phenylalanine. Benzazo-phenylalanine or derivates thereof may be particularly hydrophobic, which may limit the efficiency of their incorporation into a suppressor tRNA, due to limited solubility of such non-natural light- responsive amino acids. As detailed in the enclosed Example 7, the present inventors have surprisingly found means and methods to increase the solubility of such non-natural light-responsive amino acids (such as, in particular, Baf). Namely, it was found that such non-natural light-responsive amino acids (such as, in particular, Baf) may be complexed and / or solubilized using β-cyclodextrin. In a preferred embodiment of the herein provided method, said aaRS comprises an amino acid sequence selected from the group consisting of SEQ ID NO: 15 to SEQ ID NO: 22, preferably SEQ ID NO: 21. As mentioned herein below and as detailed in the illustrative Example 7 and Figure 9, an aaRS in accordance with the present invention (such as, for example, an aaRS comprising an amino acid sequence selected from the group consisting of SEQ ID NO: 15 to SEQ ID NO: 22) may have improved enzymatic activity regarding the incorporation of a non-natural light-responsive amino acid. Accordingly, in the context of the herein provided method, such an aaRS may have increased enzymatic activity for charging said cognate suppressor tRNA with a non-natural light-responsive amino acid selected from the group consisting of Baf, p-amino-benzazo-phenylalanine, and p-carboxy-benzazo-phenylalanine as compared to the reference aaRS with an amino acid sequence of SEQ ID NO: 14. Accordingly, in the context of the herein provided method, an aaRS in accordance with the present invention (such as, for example, an aaRS comprising an amino acid sequence selected from the group consisting of SEQ ID NO: 15 to SEQ ID NO: 22) may have at least about 1.5-fold, at least about 2-fold, at least about 3-fold, at least about 4-fold, at least about 5-fold, at least about 6-fold, at least about 7-fold, at least about 8-fold, at least about 9-fold, preferably at least about 10-fold increased enzymatic activity for charging said cognate suppressor tRNA with an amino acid selected from the group consisting of Baf, p- amino-benzazo-phenylalanine, and p-carboxy-benzazo-phenylalanine as compared to the reference aaRS with an amino acid sequence of SEQ ID NO: 14. In a further aspect the present invention relates to a light-responsive affinity tag. The light-responsive affinity tag may be as defined in any of the above or below detailed aspects, in particular, the light-responsive affinity tag may be the N-terminal or C-terminal light-responsive affinity tag comprised in the polypeptide detailed in the preceding aspect. In the context of the present invention, the light-responsive affinity tag may comprise a structure of formula (V) or formula (VI): [A-]aB-[C]c (V) [C]c-B[-A]a, (VI) wherein A may comprise one or more amino acid(s), a may be 1 or 0, so that A can be present or absent, B may be a non-natural light-responsive amino acid, C may comprise one or more amino acid(s), c may be 1 or 0, so that C can be present or absent. The light-responsive affinity tag according to the present invention is particularly useful in the fields of biology, biochemistry, biotechnology, medicine and the like as it is particularly useful in the context of affinity purification, preferably the affinity purification of recombinant proteins. Accordingly, the light- responsive affinity tag of the present invention may be coupled to, for example, a polypeptide of interest or other molecules of interest by (recombinant) means and methods know to the person skilled in the art and further detailed herein below or above. The light-responsive affinity tag according to the present invention may be a (poly)peptide, and as such comprise an N-terminus and / or a C-terminus. It is understood that in the context of formula (V), A (if present) is part of or comprised in the N-terminal region, and C (if present) is part of or comprised in the C-terminal region of said light-responsive affinity tag. In the context of formula (VI), A (if present) is part of or comprised in the C-terminal region, and C (if present) is part of the N-terminal region of said light- responsive affinity tag. Accordingly, depending on the structure of said light-responsive affinity tag, the later may be either preferably coupled to a polypeptide (of interest) via its C-terminus or its N-terminus in the form of a recombinant fusion protein. It is further understood that if A and C are absent, the light- responsive affinity tag may consist of B (i.e., a light-responsive amino acid), which may nonetheless comprise an N-terminus or a C-terminus suitable for the (recombinant) coupling to e.g., a polypeptide. It is further understood that in the context of the present invention the light-responsive affinity tag of formula (V) may preferably be coupled, as a recombinant fusion protein, via its C-terminus (for example the C-terminus of C, if C is present) to the N-terminus of a polypeptide (of interest), whereas the light- responsive affinity tag of formula (VI) may preferably be coupled, as a recombinant fusion protein, via its N-terminus (for example the N-terminus of C, if C is present) to the C-terminus of a polypeptide (of interest). However, the present invention envisages coupling of the herein provided light-responsive affinity tag to any molecule of interest by means and methods detailed in, inter alia, the non-limiting enclosed examples and / or by means and methods known to the skilled person. In the context of the present invention said non-natural light-responsive amino acid may be in a first configuration or in a second configuration. As is detailed herein below and above, this is particularly useful in the context of light-controlled affinity chromatography approaches, also provided herein, as the switch of said non-natural light-responsive amino acid from a first to a second configuration (or vice versa) may alter the affinity of said amino acid to a solid phase (such as a solid or stationary phase comprising α- cyclodextrin groups also provided herein). The non-natural light-responsive amino acid may be an azo-compound and, accordingly, comprise an azo- group, also known as diazenyl group (comprising a structure of R−N=N−R′, in which R and R’ may be (aromatic) aryl groups or derivates thereof). The non-natural light-responsive amino acid may comprise any structure as long as it allows for the light-responsive switch of its configuration from a first to a second configuration and vice versa. Accordingly, the first configuration of the non-natural light-responsive amino acid may be the trans- configuration of an azo-group comprised in said non-natural light-responsive amino acid and the second configuration may be the cis-configuration of said azo-group. In other words, the first configuration of the non-natural light-responsive amino acid may be the trans-configuration of an azo-group as part of said non- natural light-responsive amino acid and the second configuration may be the cis-configuration of said azo- group. In particular, the non-natural light-responsive amino acid (i.e., a non-natural light-responsive α-amino acid) in accordance with the present invention may comprise azobenzene or derivates thereof. As such, amino acid derivates of azobenzene (such as, for example, benzazo-phenylalanine) are particularly envisaged. Accordingly, the non-natural light-responsive amino acid may be selected from the group consisting of benzazo-phenylalanine (Baf), p-amino-benzazo-phenylalanine (NH2-Baf), and p-carboxy-benzazo- phenylalanine (COOH-Baf). The synthesis of these compounds is further detailed in the enclosed Examples 1J and 1L. It is particularly preferred in the context of the present invention that the non-natural light-responsive amino acid is benzazo-phenylalanine (Baf). Accordingly, the present invention may also relate to a light-responsive affinity tag comprising a structure of formula (V) or formula (VI): [A-]aB-[C]c (V) [C]c-B[-A]a, (VI) wherein A may comprise one or more amino acid(s), a may be 1 or 0, so that A can be present or absent, B is benzazo-phenylalanine (Baf), C may comprise one or more amino acid(s), c may be 1 or 0, so that C can be present or absent. In the context of the present invention the light-responsive affinity tag may, in its smallest embodiment, solely comprise the above detailed non-natural light-responsive amino acid (e.g., benzazo-phenylalanine). However, the size of said light-responsive affinity tag is not particularly limited. Accordingly, said non- natural light-responsive amino acid may be flanked by one or more amino acid residues (A and / or C in, inter alia, formula (V) and (VI)). Accordingly, in the context of the present invention, a may be 1, so that A (in formula (V) or (VI)) may be present. While A (in formula (V) or (VI)) is not particularly limited, it may be one or more natural amino acid(s). Preferably, wherein A comprises less than about 100, less than about 50, less than about 20, more preferably less than about 10, even more preferably less than about 9, even more preferably less than about 8, even more preferably less than about 7, even more preferably less than about 6, even more preferably less than about 5, even more preferably less than about 4, even more preferably less than about 3, most preferably less than about 2 or about 1 (natural) amino acid(s). As also demonstrated in the illustrative and non-limiting Example 6, the present inventors have surprisingly found that the light-responsive affinity tag is particularly advantageous (for example in regard to its binding to a solid phase comprising α-cyclodextrin) if A (in, inter alia, formula (V) and (VI)) comprises specific amino acids (or combinations thereof). Namely, Gly, Pro, Ala, and Ser were found to be of particular advantage in this respect. Accordingly, in the context of the present invention A may comprise one or more amino acid(s) selected from the group consisting of Gly, Pro, Ala, and Ser. Preferably, wherein A comprises one or more Gly residue(s). In the context of the present invention it may be particularly advantageous if A comprises one or two amino acid(s) selected from the group consisting of Gly, Pro, Ala, and Ser, preferably one amino acid selected from the group consisting of Gly, Pro, Ala, and Ser. Preferably, wherein A comprises one or two Gly residue(s), more preferably one Gly residue. Alternatively, A may be absent and accordingly, a may be 0. As mentioned above, the non-natural light-responsive amino acid may be flanked by one or more amino acid residues (A and / or C in, inter alia, formula (V) and (VI)). Accordingly, in the context of the present invention, c may be 1, so that C (in formula (V) or (VI)) may be present. While C (in formula (V) or (VI)) is not particularly limited, it may be one or more natural amino acid(s). Preferably, wherein C comprises less than about 100, less than about 50, less than about 20, more preferably less than about 10, even more preferably less than about 9, even more preferably less than about 8, even more preferably less than about 7, even more preferably less than about 6, even more preferably less than about 5, even more preferably less than about 4, even more preferably less than about 3, most preferably less than about 2 or about 1 (natural) amino acid(s). As also demonstrated in the illustrative and non-limiting Example 6, the present inventors have surprisingly found that the light-responsive affinity tag is particularly advantageous (for example in regard to its binding to a solid phase comprising α-cyclodextrin) if C (in, inter alia, formula (V) and (VI)) comprises specific amino acids (or combinations thereof). Namely, Gly, Pro, Ala, and Ser were found to be of particular advantage in this respect. Accordingly, in the context of the present invention C may comprise one or more amino acid(s) selected from the group consisting of Gly, Pro, Ala, and Ser. Preferably, wherein C comprises one or more Gly residue(s). In the context of the present invention it may be particularly advantageous if C comprises one or two amino acid(s) selected from the group consisting of Gly, Pro, Ala, and Ser, preferably one or two amino acid selected from the group consisting of Gly and Pro. Preferably, wherein C comprises one or two Gly residue(s), more preferably one Gly residue. Alternatively, C may be absent and accordingly, c may be 0. As is detailed herein above, the light-responsive affinity tag may be particularly small (i.e., comprise a remarkable low number of amino acid residues) and, consequently, may result in low / reduced sterical hindrance of a polypeptide (of interest) said light-responsive affinity tag may be coupled to. Accordingly, in the context of the present invention the light-responsive affinity tag may consists of about 1 to about 20 amino acid(s), preferably about 1 to about 10 amino acid(s), more preferably about 1 to about 9 amino acid(s), more preferably about 1 to about 8 amino acid(s), more preferably about 1 to about 7 amino acid(s), more preferably about 1 to about 6 amino acid(s), more preferably about 1 to about 5 amino acid(s), such as about 1 to about 4 amino acid(s), about 1 to about 3 amino acid(s), about 1 to about 2 amino acid(s), about 1 amino acid. Accordingly, the light-responsive affinity tag may consist of about 1 to about 5 amino acids. Accordingly, the light-responsive affinity tag may consist of about 5 amino acids, of about 4 amino acids, of about 3 amino acids, of about 2 amino acids, or of about 1 amino acid. In the context of the present invention, if the tag consists merely of a single amino acid (in other words of 1 amino acid or of about 1 amino acid), said amino acid is a non-natural light-responsive amino acid as defined herein above and below. Preferably, said non-natural light-responsive amino acid is benzazo- phenylalanine (Baf). In a preferred embodiment, the light-responsive affinity tag consists of about 2 amino acids, preferably wherein X (i.e., the light-responsive affinity tag) of consists of Baf-Gly or Gly-Baf. In particular, in formula (I) X consists of Gly-Baf and / or in formula (II) X consists of Baf-Gly. Table 1 illustratively and non-limitingly highlights specific embodiments of the herein provided light- responsive affinity tag. In the context of the present invention, it is preferred that the light-responsive affinity tag does not comprise the sequence of a routinely employed proteinaceous affinity tag comprising a non-natural light-responsive amino acid (such as a FLAG-tag comprising a non-natural light-responsive amino acid, a Strep-tag comprising a non-natural light-responsive amino acid, a His-tag comprising a non-natural light-responsive amino acid, and the like). In a particularly preferred embodiment, the light-responsive affinity tag of formula (V) comprises an amino acid sequence selected from the group consisting of B-Gly-Gly, Gly-B-Gly-Gly (SEQ ID NO: 23 to 25), Ala-B-Gly-Gly (SEQ ID NO: 26 to 28), Gly-B-Gly-Pro (SEQ ID NO: 29 to 31), Ala-B-Gly-Pro (SEQ ID NO: 32 to 34), Gly-B-Gly, Ala-B-Gly, Gly-B-Ala, Gly-Gly-B, Gly-Gly-B-Gly (SEQ ID NO: 35 to 37), and Pro-Gly-B-Gly (SEQ ID NO: 38 to 40). In a particularly preferred embodiment, the light-responsive affinity tag of formula (VI) comprises an amino acid sequence selected from the group consisting of B-Gly-Gly, Gly-B-Gly-Gly (SEQ ID NO: 23 to 25), Ala-B-Gly-Gly (SEQ ID NO: 26 to 28), Gly-B-Gly-Pro (SEQ ID NO: 29 to 31), Ala-B-Gly-Pro (SEQ ID NO: 32 to 34), Gly-B-Gly, Ala-B-Gly, Gly-B-Ala, Gly-Gly-B, Gly-Gly-B-Gly (SEQ ID NO: 35 to 37), and Pro-Gly-B-Gly (SEQ ID NO: 38 to 40). In a more preferred embodiment, the light-responsive affinity tag of formula (V) or of formula (VI) comprises an amino acid sequence consisting of Gly-B-Gly. In an even more preferred embodiment, the light-responsive affinity tag of formula (V) or of formula (VI) comprises an amino acid sequence consisting of Gly-B-Gly, and wherein B is Baf. Accordingly, the light- responsive affinity tag of formula (V) or of formula (VI) may comprise a sequence consisting of Gly-Baf- Gly. As detailed herein above, the configuration of the light-responsive affinity tag (in particular the configuration of the non-natural light-responsive amino acid comprised in said affinity tag) may, in the context of the present invention, be switch from the trans-configuration to the cis-configuration and vice versa. Accordingly, the configuration of B (i.e., said non-natural light-responsive amino acid) can be switched from the trans-configuration to the cis-configuration by irradiation with a specific wavelength of light, preferably wherein said wavelength of light is selected from one or more wavelength(s) of light from about 310 nm to about 370 nm, more preferably from about 345 nm to about 365 nm, more preferably from about 350 nm to about 355 nm. Accordingly, the configuration of B (i.e., said non-natural light-responsive amino acid) can be switched from the cis-configuration to the trans-configuration by irradiation with a specific wavelength of light, preferably wherein said wavelength of light is selected from one or more wavelength(s) of light from about 405 nm to about 470 nm and / or daylight, preferably from about 420 nm to about 430 nm and / or daylight. As detailed herein above, and as illustratively shown in the enclosed and non-limiting Figure 2, the present inventors have surprisingly found that only when in the trans-configuration (as opposed to the cis- configuration), the non-natural light-responsive amino acid has high affinity towards α-cyclodextrin. Accordingly, the switch of said configuration (of the non-natural light-responsive amino acid) alters its affinity (i.e., the affinity of said non-natural light-responsive amino acid) towards α-cyclodextrin. The person skilled in the art is aware of means and methods to determine whether two (or more) compounds (such as, for example, Baf and α-cyclodextrin) form a complex and is furthermore able to determine the stability of such complexes. Particular means and methods are exemplarily detailed in the enclosed examples, such as Example 1B. The skilled person is aware that the equilibrium dissociation constant (KD) can provide an indication regarding the stability of a given complex. In the context of the present invention, a complex having an equilibrium dissociation constant (as for example determined by spectroscopic analysis during titration experiments, as exemplified in Example 1B) of KD ≤ 1 mM is considered a stable complex, whereas any complex having an equilibrium dissociation constant (as for example determined by spectroscopic analysis during titration experiments, as exemplified in Example 1B) of KD ≥ 1 mM is considered an unstable complex. As shown in the illustrative and non-limiting Figure 2, the complex of trans-Baf and α-cyclodextrin comprises an equilibrium dissociation constant (KD) of about 91 µM ± 5 µM. Accordingly, when in the trans-configuration, B (i.e., the non-natural light-responsive amino acid) forms or is capable of forming a (stable) complex with α-cyclodextrin, preferably as determined by spectroscopic analysis during titration of B in the trans-configuration with α-cyclodextrin. Accordingly, when in the trans-configuration, B may comprise an equilibrium dissociation constant (KD) of less than about 1 mM, of about or less than about 900 µM, of about or less than about 800 µM, of about or less than about 700 µM, of about or less than about 600 µM, of about or less than about 500 µM, of about or less than about 400 µM, of about or less than about 350 µM, of about or less than about 300 µM, of about or less than about 250 µM, of about or less than about 200 µM, of about or less than about 150 µM, of about or less than about 140 µM, of about or less than about 130 µM, of about or less than about 120 µM, of about or less than about 110 µM, of about or less than about 105 µM, of about or less than about 104 µM, of about or less than about 103 µM, of about or less than about 102 µM, of about or less than about 101 µM, of about or less than about 100 µM, of about or less than about 99 µM, of about or less than about 98 µM, of about or less than about 97 µM, of about or less than about 96 µM, of about or less than about 95 µM, of about or less than about 94 µM, of about or less than about 93 µM, of about or less than about 92 µM, of about or less than about 91 µM, preferably wherein KD is determined by spectroscopic analysis during titration of B in the trans-configuration with α-cyclodextrin. Accordingly, when in the trans-configuration, B comprises an equilibrium dissociation constant (KD) of about or less than about 91 µM ± 5 µM when contacted with α-cyclodextrin, preferably wherein KD is determined by spectroscopic analysis during titration of B in the trans-configuration with α-cyclodextrin in solution. The illustrative and non-limiting Figure 2 further demonstrates that contacting cis-Baf with α-cyclodextrin does not allow for the determination and / or quantification of an equilibrium dissociation constant (KD). Accordingly, when in the cis-configuration, B does not form a stable complex with α-cyclodextrin, preferably as determined by spectroscopic analysis during titration of B in the cis-configuration with α- cyclodextrin. As further detailed, inter alia, in the enclosed examples, irradiating the non-natural light-responsive amino acids of the present invention with specific wavelengths alters the configuration of a major fraction of these non-natural light-responsive amino acids. Accordingly, when irradiated with visible light having about 405 nm to about 470 nm and / or daylight, at least about 50%, at least about 60%, at least about 70%, at least about 75%, at least about 80%, at least about 85%, at least about 90%, at least about 95% of the light- responsive affinity tag of formula (V) or (VI) comprise B in the trans-configuration, preferably at least about 80% of the light-responsive affinity tag of formula (V) or (VI) comprise B in the trans-configuration. Accordingly, when irradiated with visible light having about 405 nm to about 470 nm and / or daylight for about or less than about 30 min, at least about 50%, at least about 60%, at least about 70%, at least about 75%, at least about 80%, at least about 85%, at least about 90%, at least about 95% of the light-responsive affinity tag of formula (V) or (VI) comprise B in the trans-configuration which is maintained for at least about 60 min under daylight or in the dark, preferably at least about 80% of the light-responsive affinity tag of formula (V) or (VI) comprise B in the trans-configuration which is maintained for at least about 60 min under daylight or in the dark. As also demonstrated in Figure 20 A and B, in the context of the present invention it was surprisingly found that contacting a solid phase (e.g., comprising α-cyclodextrin) with a POI coupled to the herein provided light-responsive affinity tag (as well as the optional subsequent washing step) can be performed in the presence of light having a wavelength that induces the switch from the cis- to the trans-configuration of said non-natural light-responsive amino acid (e.g., in the present of light having a wavelength of about 430 nm). Alternatively, said contacting step (as well as the optional subsequent washing step) can be performed in the dark. As illustrated in Figure 20 and discussed herein above, a wavelength of e.g., 430 nm results in a higher quantity / yield as compared to darkness. See also Figure 23 providing a schematic and non-limiting illustration of the herein provided means and method. Accordingly, the herein provided light-responsive affinity tag is particularly advantageous as it can, depending on the need, either be contacted to a herein provided solid phase the in the dark (resulting particularly in a remarkably high purity of a to be purified polypeptide that may be coupled to said light-responsive affinity tag) or at e.g., 430 nm (resulting particularly in a remarkably high quantity / yield of a to be purified polypeptide that may be coupled to said light-responsive affinity tag). Accordingly, when irradiated with UV light having about 310 nm to about 370 nm, at least about 50%, at least about 60%, at least about 70%, at least about 75%, at least about 80%, at least about 85%, at least about 90%, at least about 95% of the light-responsive affinity tag of formula (V) or (VI) comprise B in the cis-configuration, preferably at least about 90% of the light-responsive affinity tag of formula (V) or (VI) comprise B in the cis-configuration. Accordingly, when irradiated with UV light having about 310 nm to about 370 nm for about or less than about 30 min and subsequently not irradiated with visible light, at least about 50%, at least about 60%, at least about 70%, at least about 75%, at least about 80%, at least about 85%, at least about 90%, at least about 95% of the light-responsive affinity tag of formula (V) or (VI) comprise B in the cis-configuration which is maintained for at least about 60 min in the dark, preferably at least about 90% of the light- responsive affinity tag of formula (V) or (VI) comprise B in the cis-configuration which is maintained for at least about 60 min in the dark. The inventors could surprisingly show that after an (initial) irradiation for about 3 or even about 1 min with UV light having about 355 nm and, when subsequently not irradiated with visible light or subsequently kept in the dark, at least about 50%, at least about 60%, at least about 70%, at least about 75%, at least about 80%, at least about 85%, at least about 90%, at least about 95% of said non-natural light-responsive amino acid remains in the cis-configuration. Such an initial irradiation (with e.g., a wavelength of 355 nm) may be about or less than about 30 min. The present inventors could surprisingly demonstrate that e.g., an (initial) irradiation for about 3 min or even about 1 min with UV light having about 355 nm wavelength and when subsequently not irradiated with visible light or subsequently kept in the dark is sufficient to allow for efficient elution of a polypeptide comprising the herein provided N-terminal or C-terminal light- responsive affinity tag (see also Figure 20 C). Accordingly, when irradiated with UV light having about 310 nm to about 370 nm for about or less than about 30 min, for about or less than about 20 min, for about or less than about 10 min, for about or less than about 9 min, for about or less than about 8 min, for about or less than about 7 min, for about or less than about 6 min, for about or less than about 5 min, for about or less than about 4 min, for about or less than about 3 min, for about or less than about 2 min, or for about or less than about 1 min, and subsequently not irradiated with visible light, at least about 50%, at least about 60%, at least about 70%, at least about 75%, at least about 80%, at least about 85%, at least about 90%, at least about 95% of the light-responsive affinity tag of formula (V) or (VI) comprise B in the cis- configuration which is maintained for at least about 60 min in the dark, preferably at least about 90% of the light-responsive affinity tag of formula (V) or (VI) comprise B in the cis-configuration which is maintained for at least about 60 min in the dark. The present invention further relates to a nucleic acid molecule encoding the light-responsive affinity tag detailed herein above. Any definition and / or specification relating to nucleic acid molecules provided herein also apply to the nucleic acid molecule encoding the light-responsive affinity tag detailed above. As detailed herein above, A and C (in formula (V) and (VI)) may in the context of the present invention preferably be natural amino acids. Accordingly, in the context of said nucleic acid molecule encoding the herein provided light-responsive affinity tag, the amino acids comprised in A and / or C may be encoded by the respective codons amply known in the art. In contrast, B (in formula (V) and (VI)) is a non-natural light- responsive amino acid (such as Baf). The skilled person is aware that non-natural (light-responsive) amino acids are naturally not encoded by any of the 64 codons known in the art. As detailed above and below, the present inventors have identified means and methods for the (recombinant) expression of a herein provided light-responsive affinity tag (comprising a non-natural light-responsive amino acid) from a nucleic acid. In this context, the non-natural light-responsive amino acid (B) may be encoded by a stop codon. Said stop codon may be selected from the group consisting of UAG, UGA, and UAA, preferably UAG (i.e., the amber stop codon). The present invention further relates to a nucleic acid vector comprising said nucleic acid molecule (encoding the light-responsive affinity tag detailed above). Any definition and / or specification relating to nucleic acid vectors provided herein also apply to the nucleic acid vector comprising the nucleic acid molecule encoding the light-responsive affinity tag detailed above. The present invention further relates to a host cell or a host comprising the nucleic acid molecule (encoding the light-responsive affinity tag detailed above) or the nucleic acid vector (comprising said nucleic acid molecule encoding the light-responsive affinity tag detailed above). In a further aspect, the present invention relates to a method for the isolation and / or purification of a polypeptide comprising an N-terminal or a C-terminal light-responsive affinity tag from a liquid (mobile) phase. Said polypeptide (comprising an N-terminal or a C-terminal light-responsive affinity tag) may be a polypeptide as defined anywhere herein above and said light-responsive affinity tag may be any light- responsive affinity tag defined herein above. As detailed herein above and below, the present inventors have surprisingly found that the herein provided non-natural light-responsive amino acid (such as, for example, benzazo-phenylalanine (Baf)) comprised in the herein provided light-responsive affinity tag has a particularly high affinity to the herein provided solid (stationary) phase comprising α-cyclodextrin groups or to α-cyclodextrin per se when in a first configuration (i.e., for example, the trans-configuration). When in a second configuration (i.e., for example, the cis-configuration), said non-natural light-responsive amino acid does not have affinity to said solid phase comprising α-cyclodextrin groups or to α-cyclodextrin per se. This is, inter alia, shown in the illustrative and non-limiting Figure 2. As detailed herein above, the switch of said first to said second configuration (and vice versa) may be achieved via irradiation with light of specific wavelength (such as, for example, light having a wavelength of about 355 nm or light having a wavelength of about 430 nm). Accordingly, this paves the way for a method for the isolation and / or purification of a polypeptide comprising an (N-terminal or C-terminal) light-responsive affinity tag that comprises such a non-natural light-responsive amino acid (such as, for example, Baf). Accordingly, the present invention relates to a method for the isolation and / or purification of a polypeptide comprising an N-terminal or a C-terminal light-responsive affinity tag from a liquid phase, the method comprises the steps of: (a) contacting said liquid phase with a solid phase, wherein said light-responsive affinity tag comprises a non-natural light-responsive amino acid, and wherein said non-natural light-responsive amino acid is in a first configuration so that it has high affinity to said solid phase; and (b) irradiating the light-responsive affinity tag with a wavelength of light that changes said non- natural light-responsive amino acid to a second configuration such that it has a decreased affinity to said solid phase as compared to the affinity thereof in step (a) and eluting said polypeptide comprising the N-terminal or the C-terminal light-responsive affinity tag with a buffer or mobile phase. In the context of the present invention, the elution of a polypeptide comprising an N-terminal or a C- terminal light-responsive affinity tag can be achieved by irradiating said polypeptide (and / or said light- responsive affinity tag) with a wavelength of light that changes the affinity of said light-responsive affinity tag to said solid phase and applying a buffer (mobile phase) to said solid phase, resulting in the elution of said polypeptide with the buffer flow. It may be advantageous in the context of the herein provided method for the isolation and / or purification of a polypeptide comprising an N-terminal or a C-terminal light-responsive affinity tag that all steps (except of the irradiation steps with the specified wavelengths of light) are performed in the dark. As illustratively demonstrated in the enclosed examples, said light-responsive affinity tag (particularly said non-natural light-responsive amino acid) may be irradiated with a wavelength of light that is capable of switching the configuration of said non-natural light-responsive amino acid from the trans-configuration to the cis-configuration, thereby reducing the affinity of said light-responsive affinity tag to a solid phase. Preferably wherein said wavelength of light is selected from one or more wavelength(s) of light from about 310 nm to about 370 nm, preferably from about 340 nm to about 365 nm, preferably from about 345 nm to about 360 nm, more preferably from about 350 nm to about 355 nm. The present inventors could surprisingly show that after an initial irradiation with such a wavelength (e.g., 355nm) and when subsequently not irradiated with visible light or subsequently kept in the dark, at least about 50%, at least about 60%, at least about 70%, at least about 75%, at least about 80%, at least about 85%, at least about 90%, at least about 95% of said non-natural light-responsive amino acid remains in the cis-configuration. Such an initial irradiation (with e.g., a wavelength of 355 nm) may be about or less than about 30 min. The present inventors could surprisingly demonstrate that e.g., an initial irradiation of about 3 min, even about 1 min is sufficient to allow for efficient elution of a polypeptide comprising an N-terminal or a C-terminal light-responsive affinity tag (see also Figure 20 C). Accordingly, in the context of the herein provided method for the isolation and / or purification of a polypeptide comprising an N-terminal or a C-terminal light-responsive affinity tag, during step (b) said N- terminal or C-terminal light-responsive affinity tag may be irradiated with a wavelength of light that changes said non-natural light-responsive amino acid to a second configuration for about or less than about 30 min and subsequently is not irradiated with light. In a preferred embodiment of the herein provided method for the isolation and / or purification of a polypeptide comprising an N-terminal or a C-terminal light-responsive affinity tag, irradiating the light- responsive affinity tag (during step (b)) with a wavelength of light that changes said non-natural light- responsive amino acid to a second configuration (the cis-configuration) comprises irradiation of the light- responsive affinity tag (with a herein above detailed wavelength, such as, 355 nm) for about or for less than about 30 mins, for about or for less than about 20 mins, for about or for less than about 10 mins, for about or for less than about 9 mins, for about or for less than about 8 mins, for about or for less than about 7 mins, for about or for less than about 6 mins, for about or for less than about 5 mins, for about or for less than about 4 mins, for about or for less than about 3 mins, for about or for less than about 2 mins, for about or for less than about 1 min, wherein subsequent to said (initial) irradiation the light-responsive affinity tag is not irradiated with visible light / kept in the dark. It was also surprisingly found that an irradiation with pulsed light (with a herein above detailed wavelength, such as, 355 nm) comprising 10% pulses (i.e., 0.1 sec illumination followed by 0.9 sec darkness, continuously repeating for 20 min) were sufficient to induce the above-mentioned switch from the trans- to the cis-conformation of said non-natural light-responsive amino acid. Accordingly, in another preferred embodiment of the herein provided method for the isolation and / or purification of a polypeptide comprising an N-terminal or a C-terminal light-responsive affinity tag, irradiating the light-responsive affinity tag (during step (b)) with a wavelength of light that changes said non-natural light-responsive amino acid to a second configuration (the cis-configuration) comprises irradiation of the light-responsive affinity tag (with a herein above detailed wavelength, such as, 355 nm) with one or more pulse(s) of light. Said pulse may be a 100% pulse (i.e., continuous illumination), a 90% pulse, a 80% pulse, a 70% pulse, a 60% pulse, a 50% pulse, a 40% pulse, a 30% pulse, a 20% pulse, a 10% pulse, a 9% pulse, a 8% pulse, a 7% pulse, a 6% pulse, a 5% pulse, a 4% pulse, a 3% pulse, a 2% pulse, a 1% pulse, preferably a 10% pulse. In the context of the present invention an, e.g., 10% pulse comprises 10% illumination (e.g., 0.1 sec illumination) followed by 90% darkness / no illumination (e.g., 0.9 sec darkness). In the context of the present invention, at least one pulse is required to induce a change in conformation, preferably however, more than one pulse is employed. For example, Figure 20C illustrates that illumination with 10% pulses for about 20 min can be readily employed (i.e., 0.1 sec illumination followed by 0.9 sec darkness, continuously repeating for 20 min). Accordingly, the present invention provides for a method for the isolation and / or purification of a polypeptide comprising an N-terminal or a C-terminal light-responsive affinity tag from a liquid phase, the method comprises the steps of: (a) contacting said liquid phase with a solid phase, wherein said light-responsive affinity tag comprises a non-natural light-responsive amino acid, and wherein said non-natural light-responsive amino acid is in a first configuration so that it has high affinity to said solid phase; and (b) irradiating the light-responsive affinity tag with a wavelength of light that changes said non- natural light-responsive amino acid to a second configuration such that it has a decreased affinity to said solid phase as compared to the affinity thereof in step (a) and eluting said polypeptide comprising the N-terminal or the C-terminal light-responsive affinity tag under or with the chromatography buffer flow. In the context of the herein provided method for the isolation and / or purification of a polypeptide comprising an N-terminal or a C-terminal light-responsive affinity tag, step (a) may further comprise washing said solid phase with a suitable (washing) buffer (i.e., said method may further comprise a washing step). The skilled person is aware that applying a (washing) buffer to a solid phase (such as a solid phase comprising α-cyclodextrin groups) comprising a bound ligand (such as a polypeptide comprising an N- terminal or a C-terminal light-responsive affinity tag) may preferably wash out any undesired contaminants / molecules that do not specifically bind to said solid phase from said solid phase, whereas said ligand (specifically binding to said solid phase, here a polypeptide comprising an N-terminal or a C-terminal light-responsive affinity tag) remains (entirely, essentially, mostly, or at least partially) bound to said solid phase. As also demonstrated in Figure 20 A and B, in the context of the present invention it was surprisingly found that contacting a solid phase (e.g., comprising α-cyclodextrin) with a POI coupled to the herein provided light-responsive affinity tag (i.e., step (a) of the herein provided method for the isolation and / or purification of a polypeptide comprising an N-terminal or a C-terminal light-responsive affinity tag; as well as the optional subsequent washing step) can be performed in the presence of light having a wavelength that induces the switch from the cis- to the trans-configuration of said non-natural light-responsive amino acid (e.g., in the present of light having a wavelength of about 430 nm). Alternatively, said contacting step (i.e., step (a); as well as the optional subsequent washing step) can be performed in the dark. As illustrated in Figure 20 and discussed herein above, a wavelength of e.g., 430 nm results in a higher quantity / yield as compared to darkness. See also Figure 23 providing a schematic and non-limiting illustration of the herein provided means and methods. Accordingly, in a preferred embodiment of the herein provided method for the isolation and / or purification of a polypeptide comprising an N-terminal or a C-terminal light-responsive affinity tag, during step (a) (and optionally also during the optional washing step) said light-responsive affinity tag (particularly said non- natural light-responsive amino acid) is irradiated with a wavelength of light that is capable of switching the configuration of said non-natural light-responsive amino acid from the cis-configuration to the trans- configuration, preferably wherein said wavelength of light is selected from one or more wavelength(s) of light from about 405 nm to about 470 nm and / or daylight, preferably from about 410 nm to about 440 nm, more preferably from about 420 nm to about 430 nm and / or daylight. As discussed herein above, this embodiment allows for the purification of the POI in particular high quantities / yields (i.e., in a ‘high concentration mode’ of the herein provided method). In another preferred embodiment of the herein provided method for the isolation and / or purification of a polypeptide comprising an N-terminal or a C-terminal light-responsive affinity tag, during step (a) (and optionally also during the optional washing step) said light-responsive affinity tag (particularly said non- natural light-responsive amino acid) is kept in the dark (i.e., is not irradiated with light). As discussed herein above, this embodiment allows for the purification of the POI in particular high purity (i.e., in a ‘high purity mode’ of the herein provided method). Accordingly, it is envisaged that the polypeptide of interest stays within the column or bound to the solid phase during this washing step. Such a washing buffer is not particularly limited in the context of the present invention. Non-limiting washing buffers are exemplified in the enclosed Example 1G. As is evident from enclosed Figure 17, a washing buffer corresponding to phosphate buffered saline (PBS) or to 25 mM Tris / Cl pH 8.0, 150 mM NaCl, comprising K2SO4, or the zwitterionic osmolyte trimethylamine N-oxide (TMAO; e.g., a washing buffer comprising 50 mM Tris pH 8.0, 0.5 M TMAO), may be particularly advantageous in the context of the present invention, as such a washing buffer further improves the binding of the herein provided polypeptide comprising an N-terminal or a C-terminal light-responsive affinity tag to said α- cyclodextrin groups comprised in the solid phase. Herein preferred is a washing buffer comprising NaCl (e.g., 25 mM Tris / Cl pH 8.0, 150 mM NaCl) or K2SO4 (e.g., 50 mM Tris / Cl pH 8.0, 100 mM K2SO4), with K2SO4 being particularly preferred. Accordingly, the present invention provides for a method for the isolation and / or purification of a polypeptide comprising an N-terminal or a C-terminal light-responsive affinity tag from a liquid phase, the method comprises the steps of: (a) contacting said liquid phase with a solid phase, wherein said light-responsive affinity tag comprises a non-natural light-responsive amino acid, and wherein said non-natural light-responsive amino acid is in a first configuration so that it has high affinity to said solid phase applying a washing buffer to said solid phase; and (b) irradiating the light-responsive affinity tag with a wavelength of light that changes said non- natural light-responsive amino acid to a second configuration such that it has a decreased affinity to said solid phase as compared to the affinity thereof in step (a) and eluting said polypeptide comprising the N-terminal or the C-terminal light-responsive affinity tag under or with the chromatography buffer flow. In the context of the herein provided method for the isolation and / or purification of a polypeptide, said polypeptide may comprise a structure of formula (I) or of formula (II): X-[L-]lP (I) P[-L]l-X (II) wherein X may be a light-responsive affinity tag, L may be a linker, l may be 1 or 0, so that L can be present or absent, P may be a polypeptide of interest, wherein in formula (I) X-[L-]l may be linked to the amino-terminus of P, and wherein in formula (II) [-L]l-X may be linked to the carboxy-terminus of P. Accordingly, the present invention relates to a method for the isolation and / or purification of a polypeptide comprising an N-terminal or a C-terminal light-responsive affinity tag from a liquid phase, the method comprises the steps of: (a) contacting said liquid phase with a solid phase, wherein said light-responsive affinity tag comprises a non-natural light-responsive amino acid, and wherein said non-natural light-responsive amino acid is in a first configuration so that it has high affinity to said solid phase; and (b) irradiating the light-responsive affinity tag with a wavelength of light that changes said non- natural light-responsive amino acid to a second configuration such that it has a decreased affinity to said solid phase as compared to the affinity thereof in step (a) and eluting said polypeptide comprising the N-terminal or the C-terminal light-responsive affinity tag (for example, with the chromatography buffer), wherein said polypeptide may comprise a structure of formula (I) or of formula (II): X-[L-]lP (I) P[-L]l-X (II) wherein X may be a light-responsive affinity tag, L may be a linker, l may be 1 or 0, so that L can be present or absent, P may be a polypeptide of interest, wherein in formula (I) X-[L-]l may be linked to the amino-terminus of P, and wherein in formula (II) [-L]l-X may be linked to the carboxy-terminus of P. The identity of the polypeptide of interest (P in, inter alia, formulas (I) and (II)) is not particularly limited and may be selected from any polypeptide, protein, enzyme, antibody, and the like that may be of relevance in, for example, any industrial area. Further, the present invention also allows for the coupling of the herein provided light-responsive affinity tag (X in formulas (I) and (II)) to other molecules of interest (i.e., molecules, reagents, medicaments, and the like that are not of proteinaceous nature, in other words, that are no polypeptides). As is detailed herein above, the herein provided light-responsive affinity tag may be a (poly)peptide and, accordingly, may comprise a C-terminus and / or an N-terminus. The prior art describes means and methods that allow for the linkage / (chemical) coupling of various molecules to the C-terminus, the N-terminus, or amino acid side chains of (poly)peptides. Accordingly, in the context of the present invention, the polypeptide of interest may also be a molecule of interest, whereas the nature of such molecules of interest is not particularly limited, as long as the person skilled in the art may couple the herein provided light-responsive affinity tag to such molecules. It is further envisaged that the herein below detailed linker (L in, inter alia, formulas (I) and (II)) may be comprised between the herein provided light- responsive affinity tag and such a molecule of interest. Accordingly, the present invention also relates to a method for the isolation and / or purification of a molecule of interest comprising a light-responsive affinity tag from a liquid phase, the method being any one of the ones detailed herein. In the context of the present invention, it is also envisaged that the herein provided light-responsive affinity tag may not only be attached / linked / coupled (optionally via the linker L, inter alia, formulas (I) and (II)) either to the C-terminus or the N-terminus of the polypeptide of interest. Instead, it is envisaged that also multiple herein provided light-responsive affinity tags may be (recombinantly) coupled to a polypeptide of interest. Accordingly, in the context of the herein provided method for the isolation and / or purification of a polypeptide comprising an N-terminal or a C-terminal light-responsive affinity tag from a liquid phase said polypeptide may comprise a structure of formula (VII): X1-[L1-]l1P-[L2-]l2X2 (VII) wherein X1 is a light-responsive affinity tag, X2 is a light-responsive affinity tag, L1 is a linker, l1 is 1 or 0, so that L1 can be present or absent, L2 is a linker, l2 is 1 or 0, so that L2 can be present or absent, P is a polypeptide of interest, wherein X1-[L1-]l1 is linked to the amino-terminus of P, and -[L2-]l2X2 is linked to the carboxy-terminus of P. X1 and X2 (in formula (VII)) may independently comprise identical or different sequences and / or structures. Both X1 and X2 may be defined according to the definitions of the light-responsive affinity tag X, herein above. L1 and L2 (in formula (VII)) may be independent from each other and may comprise sequences that are defined similarly to L herein below. L1 and L2 may further be independently present or absent from each other. The present invention further envisages more than two light-responsive affinity tags being linked to a polypeptide of interest. Said light-responsive affinity tags may be recombinantly linked (via a linker) to the C-terminus and / or the N-terminus of the polypeptide of interest or may be linked (via a linker) to the C- terminus and / or the N-terminus and / or any suitable amino acid side chain of the polypeptide of interest. In the context of the herein provided method for the isolation and / or purification of a polypeptide, said polypeptide of formula (I) or formula (II) may comprise a light-responsive affinity tag (X), wherein [X-] of formula (I) may comprise a structure of [A-]aB-[C-]c so that the polypeptide of formula (I) may be a polypeptide with a structure according to formula (III) [A-]aB-[C-]c[L-]lP (III), wherein [-X] of formula (II) may comprise a structure of [-A]a-B[-C]c, so that said polypeptide of formula (II) may be a polypeptide with a structure according to formula (IV) P[-L]l[-C]c-B[-A]a (IV), wherein A may comprise one or more amino acid(s), a may be 1 or 0, so that A can be present or absent, B may be a non-natural light-responsive amino acid, C may comprise one or more amino acid(s), c may be 1 or 0, so that C can be present or absent, wherein in formula (III) X-[L-]l may be linked to the amino-terminus of P, and wherein in formula (IV) [-L]l-X may be linked to the carboxy-terminus of P. In the context of the herein provided method for the isolation and / or purification of a polypeptide, said polypeptide comprising an N-terminal or a C-terminal light-responsive affinity tag may comprise a structure according to formula (III) or according to formula (IV): [A-]aB-[C-]c[L-]lP (III) P[-L]l[-C]c-B[-A]a (IV) wherein A may comprise one or more amino acid(s), a may be 1 or 0, so that A can be present or absent, B may be a non-natural light-responsive amino acid, C may comprise one or more amino acid(s), c may be 1 or 0, so that C can be present or absent, L may be a linker, l may be 1 or 0, so that L can be present or absent, P may be a polypeptide of interest, wherein in formula (III) [A-]aB-[C-]c[L-]l may be linked to the amino-terminus of P, and wherein in formula (IV) [-L]l[-C]c-B[-A]a may be linked to the carboxy-terminus of P. In the context of the present invention, it is further envisaged that the light-responsive affinity tag may comprise more than one non-natural light-responsive amino acid (B in, inter alia, formula (III) and formula (IV)). Whereas, said more than one non-natural light-responsive amino acids may for example be about 2, about 3, about 4, and so, non-natural light-responsive amino acids. These amino acids may be selected independently of each other, for example, from the group consisting of benzazo-phenylalanine (Baf), p- amino-benzazo-phenylalanine, and p-carboxy-benzazo-phenylalanine. Further, it is also conceivable in the context of the present invention that said more than one non-natural light-responsive amino acids may be separated by one or more amino acid residue(s), whereas the identity of such one or more amino acid residue(s) is not particularly limited. In the context of the present invention the non-natural light-responsive amino acid may be in a first configuration or in a second configuration. As is detailed herein below and above, this is particularly useful in the context of light-controlled affinity chromatography approaches also provided herein as the switch of said non-natural light-responsive amino acid from a first to a second configuration (or vice versa) may alter the affinity of said amino acid to a solid phase (such as a solid phase comprising α-cyclodextrin groups also provided herein). The non-natural light-responsive amino acid may be an azo-compound and accordingly comprise an azo- group, also known as diazenyl group (comprising a structure of R−N=N−R′, in which R and R’ may be (aromatic) aryl groups or derivates thereof). The non-natural light-responsive amino acid may comprise any structure as long as it allows for the light-responsive switch of its configuration from a first to a second configuration and vice versa. Accordingly, the first configuration of the non-natural light-responsive amino acid may be the trans- configuration of an azo-group comprised in said non-natural light-responsive amino acid and the second configuration may be the cis-configuration of said azo-group. In other words, the first configuration of the non-natural light-responsive amino acid may be the trans-configuration of an azo-group as part of said non- natural light-responsive amino acid and the second configuration may be the cis-configuration of said azo- group. Preferably, the non-natural light-responsive amino acid in accordance with the present invention may comprise azobenzene or derivates thereof. As such, amino acid derivates of azobenzene (such as for example benzazo-phenylalanine) are particularly envisaged. Accordingly, the non-natural light-responsive amino acid (i.e., the non-natural light-responsive α-amino acid) may be selected from the group consisting of benzazo-phenylalanine (Baf), p-amino-benzazo- phenylalanine (NH2-Baf), and p-carboxy-benzazo-phenylalanine (COOH-Baf). The synthesis of these compounds is further detailed in the enclosed Examples 1J and 1L. It is most preferred in the context of the present invention that the non-natural light-responsive amino acid is benzazo-phenylalanine (Baf). Accordingly, the present invention relates to a method for the isolation and / or purification of a polypeptide comprising an N-terminal or a C-terminal light-responsive affinity tag from a liquid phase, the method comprises the steps of: (a) contacting said liquid phase with a solid phase, wherein said light-responsive affinity tag comprises a non-natural light-responsive amino acid, and wherein said non-natural light-responsive amino acid is in a first configuration so that it has high affinity to said solid phase; and (b) irradiating the light-responsive affinity tag with a wavelength of light that changes said non- natural light-responsive amino acid to a second configuration such that it has a decreased affinity to said solid phase as compared to the affinity thereof in step (a) and eluting said polypeptide comprising the N-terminal or the C-terminal light-responsive affinity tag (for example, with the chromatography buffer), wherein said polypeptide may comprise a structure according to formula (III) or according to formula (IV): [A-]aB-[C-]c[L-]lP (III) P[-L]l[-C]c-B[-A]a (IV) wherein A may comprise one or more amino acid(s), a may be 1 or 0, so that A can be present or absent, B may be a non-natural light-responsive amino acid, preferably benzazo-phenylalanine (Baf), C may comprise one or more amino acid(s), c may be 1 or 0, so that C can be present or absent, L may be a linker, l may be 1 or 0, so that L can be present or absent, P may be a polypeptide of interest, wherein in formula (III) [A-]aB-[C-]c[L-]l may be linked to the amino-terminus of P, and wherein in formula (IV) [-L]l[-C]c-B[-A]a may be linked to the carboxy-terminus of P. In the context of the present invention the N-terminal or the C-terminal light-responsive affinity tag may in its smallest embodiment solely comprise the above detailed non-natural light-responsive amino acid (e.g., benzazo-phenylalanine). However, the size of said light-responsive affinity tag is not particularly limited. Accordingly, said non-natural light-responsive amino acid may be flanked by one or more amino acid residues (A and / or C in, inter alia, formula (III) and (IV)). Accordingly, in the context of the present invention, a may be 1, so that A (in formula (III) or (IV)) may be present. While A (in formula (III) or (IV)) is not particularly limited, it may be one or more natural amino acid(s). Preferably, wherein A comprises less than about 100, less than about 50, less than about 20, more preferably less than about 10, even more preferably less than about 9, even more preferably less than about 8, even more preferably less than about 7, even more preferably less than about 6, even more preferably less than about 5, even more preferably less than about 4, even more preferably less than about 3, most preferably less than about 2 or about 1 (natural) amino acid(s). As also demonstrated in the illustrative and non-limiting Example 6, the present inventors have surprisingly found that the light-responsive affinity tag is particularly advantageous (for example with regard to its binding to a solid phase comprising α-cyclodextrin) if A (in, inter alia, formula (III) and (IV)) comprises specific amino acids (or combinations thereof). Namely, Gly, Pro, Ala, and Ser were found to be of particular advantage in this respect. Accordingly, in the context of the present invention A may comprise one or more amino acid(s) selected from the group consisting of Gly, Pro, Ala, and Ser. Preferably, wherein A comprises one or more Gly residue(s). In the context of the present invention it may be particularly advantageous if A comprises one or two amino acid(s) selected from the group consisting of Gly, Pro, Ala, and Ser, preferably one amino acid selected from the group consisting of Gly, Pro, Ala, and Ser. Preferably, wherein A comprises one or two Gly residue(s), more preferably one Gly residue. Alternatively, A may be absent and accordingly, a may be 0. As mentioned above, the non-natural light-responsive amino acid may be flanked by one or more amino acid residues (A and / or C in, inter alia, formula (III) and (IV)). Accordingly, in the context of the present invention, c may be 1, so that C (in formula (III) or (IV)) may be present. While C (in formula (III) or (IV)) is not particularly limited, it may be one or more natural amino acid(s). Preferably, wherein C comprises less than about 100, less than about 50, less than about 20, more preferably less than about 10, even more preferably less than about 9, even more preferably less than about 8, even more preferably less than about 7, even more preferably less than about 6, even more preferably less than about 5, even more preferably less than about 4, even more preferably less than about 3, most preferably less than about 2 or about 1 (natural) amino acid(s). As also demonstrated in the illustrative and non-limiting Example 6, the present inventors have surprisingly found that the light-responsive affinity tag is particularly advantageous (for example with regard to its binding to a solid phase comprising α-cyclodextrin) if C (in, inter alia, formula (III) and (IV)) comprises specific amino acids (or combinations thereof). Namely, Gly, Pro, Ala, and Ser were found to be of particular advantage in this respect. Accordingly, in the context of the present invention C may comprise one or more amino acid(s) selected from the group consisting of Gly, Pro, Ala, and Ser. Preferably, wherein C comprises one or more Gly residue(s). In the context of the present invention it may be particularly advantageous if C comprises one or two amino acid(s) selected from the group consisting of Gly, Pro, Ala, and Ser, preferably one or two amino acid selected from the group consisting of Gly and Pro. Preferably, wherein C comprises one or two Gly residue(s), more preferably one Gly residue. Alternatively, C may be absent and accordingly, c may be 0. As is detailed herein above, the light-responsive affinity tag may be particularly small (i.e., comprise a remarkable low number of amino acid residues) and, consequently, may result in low / reduced sterical hinderance of a polypeptide of interest (said light-responsive affinity tag may be coupled to). Accordingly, in the context of the present invention the (N-terminal or C-terminal) light-responsive affinity tag may consist of about 1 to about 20 amino acid(s), preferably about 1 to about 10 amino acid(s), more preferably about 1 to about 9 amino acid(s), more preferably about 1 to about 8 amino acid(s), more preferably about 1 to about 7 amino acid(s), more preferably about 1 to about 6 amino acid(s), more preferably about 1 to about 5 amino acid(s), such as about 1 to about 4 amino acid(s), about 1 to about 3 amino acid(s), about 1 to about 2 amino acid(s), about 1 amino acid. Accordingly, the light-responsive affinity tag may consist of about 1 to about 5 amino acids. Accordingly, the light-responsive affinity tag may consist of about 5 amino acids, of about 4 amino acids, of about 3 amino acids, of about 2 amino acids, or of about 1 amino acid. In the context of the present invention, if the tag consists merely of a single amino acid (in other words of 1 amino acid or of about 1 amino acid), said amino acid is a non-natural light-responsive amino acid as defined herein above and below. Preferably, said non-natural light-responsive amino acid is benzazo- phenylalanine (Baf). In a preferred embodiment of the herein provided method for the isolation and / or purification of a polypeptide comprising an N-terminal or a C-terminal light-responsive affinity tag from a liquid phase, the light-responsive affinity tag consists of about 2 amino acids, preferably wherein X (i.e., the light-responsive affinity tag) consists of Baf-Gly or Gly-Baf. In particular, wherein in formula (I) X consists of Gly-Baf and / or in formula (II) X consists of Baf-Gly. Table 1 illustratively and non-limitingly highlights specific embodiments of the light-responsive affinity tag, for example, to be employed in the herein provided method. In the context of the herein provided method, it is preferred that the light-responsive affinity tag does not comprise the sequence of a routinely employed proteinaceous affinity tag comprising a non-natural light- responsive amino acid (such as a FLAG-tag comprising a non-natural light-responsive amino acid, a Strep- tag comprising a non-natural light-responsive amino acid, a His-tag comprising a non-natural light- responsive amino acid, and the like). In a particularly preferred embodiment of the herein provided method, in formula (I) X (i.e., the N-terminal light-responsive affinity tag) comprises an amino acid sequence selected from the group consisting of B- Gly-Gly, Gly-B-Gly-Gly (SEQ ID NO: 23 to 25), Ala-B-Gly-Gly (SEQ ID NO: 26 to 28), Gly-B-Gly-Pro (SEQ ID NO: 29 to 31), Ala-B-Gly-Pro (SEQ ID NO: 32 to 34), Gly-B-Gly, Ala-B-Gly, Gly-B-Ala, Gly- Gly-B, Gly-Gly-B-Gly (SEQ ID NO: 35 to 37), and Pro-Gly-B-Gly (SEQ ID NO: 38 to 40). In a particularly preferred embodiment of the herein provided method, in formula (II) X (i.e., the C-terminal light-responsive affinity tag) comprises an amino acid sequence selected from the group consisting of B- Gly-Gly, Gly-B-Gly-Gly (SEQ ID NO: 23 to 25), Ala-B-Gly-Gly (SEQ ID NO: 26 to 28), Gly-B-Gly-Pro (SEQ ID NO: 29 to 31), Ala-B-Gly-Pro (SEQ ID NO: 32 to 34), Gly-B-Gly, Ala-B-Gly, Gly-B-Ala, Gly- Gly-B, Gly-Gly-B-Gly (SEQ ID NO: 35 to 37), and Pro-Gly-B-Gly (SEQ ID NO: 38 to 40). In a more preferred embodiment of the herein provided method, X in formula (I) (i.e., the N-terminal light- responsive affinity tag) or in formula (II) (i.e., the C-terminal light-responsive affinity tag) comprises an amino acid sequence consisting of Gly-B-Gly. In an even more preferred embodiment of the herein provided method, X in formula (I) (i.e., the N-terminal light-responsive affinity tag) or in formula (II) (i.e., the C-terminal light-responsive affinity tag) comprises an amino acid sequence consisting of Gly-B-Gly, and wherein B is Baf. Accordingly, X may comprise a sequence consisting of Gly-Baf-Gly. As detailed herein above, the configuration of the light-responsive affinity tag (in particular the configuration of the non-natural light-responsive amino acid comprised in said affinity tag) may, in the context of the herein provided method, be switch from the trans-configuration to the cis-configuration, and vice versa. Accordingly, the configuration of B (i.e., said non-natural light-responsive amino acid) can be switched from the trans-configuration to the cis-configuration by irradiation with a specific wavelength of light, preferably wherein said wavelength of light is selected from one or more wavelength(s) of light from about 310 nm to about 370 nm, preferably from about 340 nm to about 365 nm, preferably from about 345 nm to about 360 nm, more preferably from about 350 nm to about 355 nm. Accordingly, the configuration of B (i.e., said non-natural light-responsive amino acid) can be switched from the cis-configuration to the trans-configuration by irradiation with a specific wavelength of light, preferably wherein said wavelength of light is selected from one or more wavelength(s) of light from about 405 nm to about 470 nm and / or daylight, preferably from about 410 nm to about 440 nm, more preferably from about 420 nm to about 430 nm and / or daylight. As detailed herein above, and as illustratively shown in the enclosed and non-limiting Figure 2, the present inventors have surprisingly found that only when in the trans-configuration (as opposed to the cis- configuration), the non-natural light-responsive amino acid has high affinity towards α-cyclodextrin. Accordingly, the switch of said configuration (of non-natural light-responsive amino acid) alters its affinity (i.e., the affinity of said non-natural light-responsive amino acid) towards α-cyclodextrin. The person skilled in the art is aware of means and methods to determine whether two (or more) compounds (such as, for example, Baf and α-cyclodextrin) form a complex and is furthermore able to determine the stability of such complexes. Particular means and methods are exemplarily detailed in the enclosed examples, such as Example 1B. The skilled person is aware that the equilibrium dissociation constant (KD) can provide an indication regarding the stability of a given complex. In the context of the present invention, a complex having an equilibrium dissociation constant (as for example determined by spectroscopic analysis during titration experiments, as exemplified in Example 1B) of KD ≤ 1 mM is considered a stable complex, whereas any complex having an equilibrium dissociation constant (as for example determined by spectroscopic analysis during titration experiments, as exemplified in Example 1B) of KD ≥ 1 mM is considered an unstable complex. As shown in illustrative and non-limiting Figure 2, the complex of trans- Baf and α-cyclodextrin comprises an equilibrium dissociation constant (KD) of about or less than about 91 µM ± 5 µM. Accordingly, when in the trans-configuration, B (i.e., the non-natural light-responsive amino acid) forms or is capable of forming a (stable) complex with α-cyclodextrin, preferably as determined by spectroscopic analysis during titration of B in the trans-configuration with α-cyclodextrin. Accordingly, when in the trans-configuration, B may comprise an equilibrium dissociation constant (KD) of less than about 1 mM, of about or less than about 900 µM, of about or less than about 800 µM, of about or less than about 700 µM, of about or less than about 600 µM, of about or less than about 500 µM, of about or less than about 400 µM, of about or less than about 350 µM, of about or less than about 300 µM, of about or less than about 250 µM, of about or less than about 200 µM, of about or less than about 150 µM, of about or less than about 140 µM, of about or less than about 130 µM, of about or less than about 120 µM, of about or less than about 110 µM, of about or less than about 105 µM, of about or less than about 104 µM, of about or less than about 103 µM, of about or less than about 102 µM, of about or less than about 101 µM, of about or less than about 100 µM, of about or less than about 99 µM, of about or less than about 98 µM, of about or less than about 97 µM, of about or less than about 96 µM, of about or less than about 95 µM, of about or less than about 94 µM, of about or less than about 93 µM, of about or less than about 92 µM, of about or less than about 91 µM, preferably wherein KD is determined by spectroscopic analysis during titration of B in the trans-configuration with α-cyclodextrin. Accordingly, when in the trans-configuration, B comprises an equilibrium dissociation constant (KD) of about or less than about 91 µM ± 5 µM when contacted with α-cyclodextrin, preferably wherein KD is determined by spectroscopic analysis during titration of B in the trans-configuration with α-cyclodextrin in solution. Illustrative and non-limiting Figure 2 further demonstrates that contacting cis-Baf with α-cyclodextrin does not allow for the determination and / or quantification of an equilibrium dissociation constant (KD) using spectroscopic titration. Accordingly, when in the cis-configuration, B does not form a stable complex with α-cyclodextrin, preferably as determined by spectroscopic analysis during titration of B in the cis- configuration with α-cyclodextrin. As further detailed, inter alia, in the enclosed examples, irradiating the non-natural light-responsive amino acids of the present invention with specific wavelengths alters the configuration of a major fraction of these non-natural light-responsive amino acids. Accordingly, when irradiated with visible light having about 405 nm to about 470 nm and / or daylight, at least about 50%, at least about 60%, at least about 70%, at least about 75%, at least about 80%, at least about 85%, at least about 90%, at least about 95% of the polypeptide of formula (III) or (IV) comprise B in the trans-configuration, preferably at least about 80% of the polypeptide of formula (III) or (IV) comprise B in the trans-configuration. Accordingly, when irradiated with visible light having about 405 nm to about 470 nm and / or daylight for about or less than about 30 min, at least about 50%, at least about 60%, at least about 70%, at least about 75%, at least about 80%, at least about 85%, at least about 90%, at least about 95% of the polypeptide of formula (I) or (II) comprise B in the trans-configuration which is maintained for at least about 60 min under daylight or in the dark, preferably at least about 80% of the polypeptide of formula (III) or (IV) comprise B in the trans-configuration which is maintained for at least about 60 min under daylight or in the dark. Accordingly, when irradiated with UV light having about 310 nm to about 370 nm, at least about 50%, at least about 60%, at least about 70%, at least about 75%, at least about 80%, at least about 85%, at least about 90%, at least about 95% of the polypeptide of formula (III) or (IV) comprise B in the cis- configuration, preferably at least about 90% of the polypeptide of formula (III) or (IV) comprise B in the cis-configuration. Accordingly, when irradiated with UV light having about 310 nm to about 370 nm for about or less than about 30 min and subsequently not irradiated with visible light, at least about 50%, at least about 60%, at least about 70%, at least about 75%, at least about 80%, at least about 85%, at least about 90%, at least about 95% of the polypeptide of formula (III) or (IV) comprise B in the cis-configuration which is maintained for at least about 60 min in the dark, preferably at least about 90% of the polypeptide of formula (III) or (IV) comprise B in the cis-configuration which is maintained for at least about 60 min in the dark. The present inventors could surprisingly show that after an (initial) irradiation for about 3 or even about 1 min with UV light having about 355 nm and when subsequently not irradiated with visible light / subsequently kept in the dark, at least about 50%, at least about 60%, at least about 70%, at least about 75%, at least about 80%, at least about 85%, at least about 90%, at least about 95% of said non-natural light-responsive amino acid remains in the cis-configuration. Such an initial irradiation (with e.g., a wavelength of 355 nm) may be about or less than about 30 min. The present inventors could surprisingly demonstrate that e.g., an (initial) irradiation for about 3 min or even about 1 min with UV light having about 355 nm and when subsequently not irradiated with visible light / subsequently kept in the dark is sufficient to allow for efficient elution of the herein provided polypeptide comprising an N-terminal or a C-terminal light-responsive affinity tag (see also Figure 20 C). Accordingly, when irradiated with UV light having about 310 nm to about 370 nm for about or less than about 30 min, for about or less than about 20 min, for about or less than about 10 min, for about or less than about 9 min, for about or less than about 8 min, for about or less than about 7 min, for about or less than about 6 min, for about or less than about 5 min, for about or less than about 4 min, for about or less than about 3 min, for about or less than about 2 min, or for about or less than about 1 min, and subsequently not irradiated with visible light, at least about 50%, at least about 60%, at least about 70%, at least about 75%, at least about 80%, at least about 85%, at least about 90%, at least about 95% of the polypeptide of formula (III) or (IV) comprise B in the cis- configuration which is maintained for at least about 60 min in the dark, preferably at least about 90% of the polypeptide of formula (III) or (IV) comprise B in the cis-configuration which is maintained for at least about 60 min in the dark. As indicated herein above, the identity of P (i.e., the protein of interest in the context of the present invention) is not particularly limited and, as such, any polypeptide or the like may be employed in this context. Accordingly, P may be selected from the group consisting of an oligopeptide, a polypeptide, a protein, an immunoglobulin or an antigen-binding fragment thereof, a binding protein, a growth factor, a signaling protein, an enzyme, and / or a complex thereof. Furthermore, P may be selected from the group consisting of intracellular, cytosolic, cytoplasmic, periplasmic, secreted, membrane or plasma proteins. In the field of affinity chromatography, protein purification, and the like it may be advantageous to express, using recombinant DNA technology, a protein of interest coupled to a signal peptide that may affect the translocation of said polypeptide of interest to a certain organelle, compartment, or the extracellular space of a host cell expressing said polypeptide of interest. Accordingly, in the context of the present invention the polypeptide of interest may further comprise a signal peptide. The identity of such signal peptides is not particularly limited and the skilled artisan is aware of signal peptides that may be employed in order to target (recombinant) expression of a polypeptide of interest to e.g., a specific cellular compartment. In the context of the present invention, signal peptides are preferably selected from the group consisting of OmpA, OmpF, PhoA, MalE, PelB, stII, DsbC. In the context of the present invention, it may be advantageous to couple the herein provided light- responsive affinity tag (for example, X in formula (I) and formula (II)) to the polypeptide of interest via a linker. As illustratively shown in, inter alia, enclosed Examples 5 and 6 such a linker is not essential, for example, for the efficient purification of a polypeptide comprising an N-terminal or a C-terminal light- responsive affinity tag. However, it is conceivable that such a linker may, depending on the identity of a polypeptide of interest and its structural specificities be advantageous for the accessibility of the light- responsive affinity tag to α-cyclodextrin (as, for example, comprised in the solid phase of a chromatography column). Accordingly, in the context of the present invention, l (in, for example, formula (I), formula (II), formula (III), or formula (IV)) may be 1, so that L (in, for example, formula (I), formula (II), formula (III), or formula (IV)) may be present. In the context of the present invention, the identity of the linker (L) is not particularly limited. Exemplary linkers may for example comprise any kind and combinations of (natural) amino acids. However, also non- proteinogenic linkers (such as, for example, polyethylene glycol-based linkers and the like) are envisaged herein. In particular, a linker of the present invention may preferably comprise one or more amino acids selected from the group consisting of Gly, Pro, Ala, and Ser. A particularly preferred linker (L) in the context of the present invention may comprise an amino acid sequence selected from the group consisting of the following: Glu-Asn-Leu-Tyr-Phe-Gln-Ser-Gly (SEQ ID NO: 41), Glu-Asn-Leu-Tyr-Phe-Gln-Ser-Ala (SEQ ID NO: 42), Leu-Val-Pro-Arg-Gly-Ser (SEQ ID NO: 43), Ile-Glu-Gly-Arg (SEQ ID NO: 44), Leu-Glu-Val-Leu-Phe-Gln-Gly-Pro (SEQ ID NO: 45). In the context of the present invention it may be advantageous to cleave the N-terminal or C-terminal light- responsive affinity tag of the polypeptide of interest (for example after successful affinity purification thereof using the herein provided means and methods). Accordingly, the linker (L in, for example, formula (I), formula (II), formula (III), or formula (IV)) may be a cleavable linker. The identity of such a cleavable linker (L) is not particularly limited. Exemplary linkers may for example comprise any kind and combinations of (natural) amino acids, as long as they are cleavable by, for example, enzymatic, chemical, or other suitable means and methods. A particularly preferred linker (L) in the context of the present invention may comprise a cleavable amino acid sequence. Preferably, wherein said cleavable amino acid sequence is selected from the group consisting of the following: Tobacco Etch Virus (TEV) protease, thrombin, factor Xa, human rhinovirus type 143C protease (HRV 3C). Alternatively, l (in, for example, formula (I), formula (II), formula (III), or formula (IV)) may be 0, so that L (in, for example, formula (I), formula (II), formula (III), or formula (IV)) may be absent (and the N- terminal or C-terminal light-responsive affinity tag (X) is directly coupled to the N-terminus or the C- terminus of the polypeptide of interest (P), respectively. As detailed herein above and illustratively shown in the enclosed Figure 2, the present inventors have surprisingly found that the (N-terminal or C-terminal) light-responsive affinity tag (as provided herein, as comprised in the polypeptide provided, or as employed in the herein provided method) has particularly high affinity to α-cyclodextrin (or a solid phase comprising α-cyclodextrin or α-cyclodextrin groups). Accordingly, in the context of the herein provided method, said solid phase may comprise α-cyclodextrin groups. The solid phase (as employed in the herein provided method) may also be the solid phase as detailed in any other aspect of the present invention. The skilled person is aware that solid (or stationary) phases may comprise a structural matrix (such as for example agarose) that may not or may essentially not contribute to the specificity of a solid phase (such as a solid phase comprising α-cyclodextrin) to a ligand (such as a polypeptide comprising an N-terminal or C- terminal affinity tag as provided herein). It is understood that such a structural matrix primarily provides a structure and / or stability to said solid phase and as such facilitates its incorporation in, inter alia, chromatography columns or the like. Accordingly, in the context of the herein provided method, said solid phase may comprise α-cyclodextrin groups and may (further) comprise a structural matrix. The identity of such a structural matrix is not particularly limited, as long as the skilled person can link said structural matrix to α-cyclodextrin (or α-cyclodextrin groups). Exemplary and non-limiting examples of such structural matrices are provided in Table 2. Means and methods of (chemical) coupling of α-cyclodextrin to a structural matrix are illustratively detailed in the enclosed Example 1M and Figure 9. Accordingly, in the context of the herein provided method, said solid phase may (further) comprise a structural matrix, preferably wherein said structural matrix is selected from the group consisting of agarose, a cross-linked form of agarose, cellulose, starch, dextran, polymethacrylate, polystyrene, polyacrylamide and silica gel, more preferably agarose or a cross-linked form of agarose (such as, for example, Sepharose). Accordingly, in the context of the herein provided method, α-cyclodextrin (or α-cyclodextrin groups) may be covalently linked to said structural matrix. It may be preferred that α-cyclodextrin is covalently linked to said structural matrix via a linker. The identity of such a linker is not particularly limited in the context of the present invention. It may, however, be preferred that said linker is derived from 1,4-bis(2,3-epoxypropoxy)butane, 1-chloro-acetylchloride, or cyanogen bromide, preferably from 1,4-bis(2,3-epoxypropoxy)butane. As mentioned herein above, in the context of the herein provided method for the isolation and / or purification of a polypeptide comprising an N-terminal or a C-terminal light-responsive affinity tag from a liquid phase, step (b) comprises irradiating the light-responsive affinity tag with a wavelength of light that changes said non-natural light-responsive amino acid to a second configuration such that it has a decreased affinity to said solid phase as compared to the affinity thereof in step (a). In this context, the skilled person is aware that in order to allow for the light-controlled affinity purification of, e.g., a polypeptide comprising an N-terminal or a C-terminal light-responsive affinity tag, said solid phase may preferably be translucent. Accordingly, in the context of the herein provided method said structural matrix may be transparent or translucent. Accordingly, said structural matrix may be light-transmissive at least for UV light in the wavelength range from about 310 nm to about 370 nm. In the context of the present invention, it is further advantageous that said solid phase (such as, for example, a solid phase comprising α-cyclodextrin linked to Sepharose via a 1,4-bis(2,3-epoxypropoxy)butane- derived linker) is light-resistant. Accordingly, in the context of the present invention said solid phase may be light-resistant, at least in the wavelength range from about 300 nm to about 500 nm. The present inventors have surprisingly found that the herein provided solid phase can be reused at least 10 times, at least 15 times, at least 20 times, at least 30 times, at least 40 times, at least 50 times for affinity chromatography (see also Fig.21). Also, the presence of various widely applied biochemical reagents (such as 10 mM DTT or TCEP, 6 M GdnHCl, 8 M urea or 1 M NaOH) did not affect performance of the herein provided solid phase. In the context of the present invention said solid phase may be a matrix, a hydrogel, a bead, a chip, a glass surface, a plastic surface, a gold surface, a silver surface, or a plate such as a microtiter well plate. In the context of the present invention, said solid phase may be the affinity matrix of an affinity chromatography column. Accordingly, said matrix, said hydrogel, or said bead may be the affinity matrix of an affinity chromatography column. The present invention further relates to a polypeptide comprising the N-terminal or the C-terminal light- responsive affinity tag as obtained by and / or obtainable by the herein above detailed method for the isolation and / or purification of a polypeptide comprising an N-terminal or a C-terminal light-responsive affinity tag from a liquid phase. As detailed herein above, in the context of the present invention it is envisaged that the herein detailed light- responsive affinity tag may also be coupled to other (non-proteinaceous) molecules of interest. Accordingly, the present invention further relates to a molecule of interest comprising the above detailed light-responsive affinity tag as obtained by and / or obtainable by the herein above detailed method. The present invention further relates to a composition comprising the herein above detailed polypeptide comprising the N-terminal or the C-terminal light-responsive affinity tag. Such a composition is not particularly limited (and may also refer, for example, to a cell suspension or crude extract thereof, or the like). It may, however, be preferred herein, that such a composition refers to a composition as obtained and / or obtainable be the herein above detailed method for the isolation and / or purification of a polypeptide comprising an N-terminal or a C-terminal light-responsive affinity tag from a liquid phase. Accordingly, it may be preferred herein that the herein provided composition comprising the herein above detailed polypeptide comprising the N-terminal or the C-terminal light-responsive affinity tag is obtained by eluting said polypeptide (from the herein above detailed solid phase comprising α-cyclodextrin) with the (elution) buffer. As is, inter alia, illustratively demonstrated in the non-limiting Examples 5 and / or 6, the chromatographic purification of a composition comprising a polypeptide comprising the herein provided light-responsive affinity tag allows for depleting and / or removing contaminants (such as other undesired polypeptides) from said composition. Accordingly, in the context of the herein provided (purified) composition, said polypeptide comprising the N-terminal or the C-terminal light-responsive affinity tag constitutes at least about 10 mol%, at least about 20 mol%, at least about 30 mol%, at least about 40 mol%, at least about 50 mol%, at least about 60 mol%, at least about 70 mol%, at least about 80 mol%, at least about 85 mol%, at least about 86 mol%, at least about 87 mol%, at least about 88 mol%, at least about 89 mol%, at least about 90 mol%, at least about 91 mol%, at least about 92 mol%, at least about 93 mol%, at least about 94 mol%, at least about 95 mol%, at least about 96 mol%, at least about 97 mol%, at least about 98 mol%, at least about 99 mol%, about 100 mol% of the total polypeptide content of said composition, preferably constitutes at least about 90 mol% of the total polypeptide content of said composition. It is envisaged that the herein above provided method for cleaving the light-responsive affinity tag from the polypeptide of interest may preferably also be applied to a polypeptide comprising the N-terminal or the C- terminal light-responsive affinity tag as obtained by and / or obtainable by the herein above detailed method for the isolation and / or purification of a polypeptide comprising an N-terminal or a C-terminal light- responsive affinity tag from a liquid phase (given that said polypeptide comprises a cleavable linker, for example, as detailed herein above). The method for cleaving the light-responsive affinity tag from the polypeptide of interest may be as detailed herein above. In a further aspect, the present invention relates to a solid phase comprising α-cyclodextrin. As detailed herein above and illustratively shown in the enclosed Figure 2, the present inventors have surprisingly found that the (N-terminal or C-terminal) light-responsive affinity tag (as provided herein, as comprised in the polypeptide provided, or as employed in the herein provided method) has particularly high affinity to α-cyclodextrin (or a solid phase comprising α-cyclodextrin or α-cyclodextrin groups). Accordingly, the present invention relates to a solid or stationary phase comprising α-cyclodextrin groups. The solid phase (as provided herein) may also be the solid phase as detailed in any other aspect of the present invention. The skilled person is aware that solid phases may comprise a structural matrix (such as for example agarose) that may not or may essentially not contribute to the specificity of a solid phase (such as a solid phase comprising α-cyclodextrin) to a ligand (such as a polypeptide comprising an N-terminal or C-terminal affinity tag as provided herein). It is understood that such a structural matrix primarily provides a structure to said solid phase and as such facilitates its incorporation in, inter alia, chromatography columns or the like. Accordingly, the herein provided solid phase comprising α-cyclodextrin groups and may further comprise a structural matrix. The identity of such a structural matrix is not particularly limited, as long as the skilled person can link said structural matrix to α-cyclodextrin (or α-cyclodextrin groups). In the context of the present invention, any kind of coupling (including non-covalent coupling) may be envisaged, however, covalent coupling is preferred. Exemplary and non-limiting examples of such structural matrices are provided in Table 2. Means and methods of (chemical) coupling of α-cyclodextrin to a structural matrix are illustratively detailed in the enclosed Example 1M and Figure 9. Table 2: Overview of some exemplary activated chromatography materials (i.e., exemplary structural matrices) suitable for coupling of α-cyclodextrin. Accordingly, the herein provided solid phase comprising α-cyclodextrin groups may (further) comprise a structural matrix, preferably wherein said structural matrix is selected from the group consisting of agarose, a cross-linked form of agarose, cellulose, starch, dextran, polymethacrylate, polystyrene, polyacrylamide and silica gel, more preferably agarose or a cross-linked form of agarose (such as, for example, Sepharose). Accordingly, in the context of the herein provided solid phase comprising α-cyclodextrin groups, said α- cyclodextrin (or said α-cyclodextrin groups) may be covalently linked to said structural matrix. It may be preferred that α-cyclodextrin is covalently linked to said structural matrix via a linker or via an amino group. The identity of such a linker is not particularly limited in the context of the present invention. It may, however, be preferred that said linker is derived from 1,4-bis(2,3-epoxypropoxy)butane, 1-chloro- acetylchloride, or cyanogen bromide, preferably from 1,4-bis(2,3-epoxypropoxy)butane. Accordingly, in a preferred embodiment the herein provided solid phase comprising α-cyclodextrin further comprises a structural matrix covalently linked to said α-cyclodextrin (groups) via a linker, preferably wherein said structural matrix is agarose or a cross-linked form of agarose (such as, for example, Sepharose) and, preferably wherein said linker is derived from 1,4-bis(2,3-epoxypropoxy)butane. As mentioned herein above, in the context of (herein provided) methods employing the herein provided solid phase for the isolation and / or purification of a polypeptide comprising an N-terminal or a C-terminal light-responsive affinity tag from a liquid phase, it may be advantageous if said solid phase is translucent. Accordingly, the herein provided solid phase (comprising α-cyclodextrin groups) may preferably be translucent. Accordingly, in the context of the herein provided solid phase said structural matrix may be transparent or translucent. Accordingly, said structural matrix may be light-transmissive at least for UV light in the wavelength range from about 310 nm to about 370 nm. In the context of the present invention, it is further advantageous that said solid phase (such as, for example, a solid phase comprising α-cyclodextrin linked to Sepharose via a 1,4-bis(2,3-epoxypropoxy)butane- derived linker) is light-resistant. Accordingly, in the context of the present invention said solid phase may be light-resistant, at least in the wavelength range from about 300 nm to about 500 nm. The present inventors have surprisingly found that the herein provided solid phase can be reused at least 10 times, at least 15 times, at least 20 times, at least 30 times, at least 40 times, at least 50 times for affinity chromatography (see also Fig.21). Also, the presence of various widely applied biochemical reagents (such as 10 mM DTT or TCEP, 6 M GdnHCl, 8 M urea or 1 M NaOH) did not affect performance of the herein provided solid phase. In the context of the present invention said solid phase may be a matrix, a hydrogel, a bead, a chip, a glass surface, a plastic surface, a gold surface, a silver surface or a plate such as a microtiter well plate. In the context of the present invention, said solid phase may be the affinity matrix of an affinity chromatography column. Accordingly, said matrix, said hydrogel or said bead may be the affinity matrix of an affinity chromatography column. In a further aspect, the present invention relates to an aminoacyl tRNA synthetase (aaRS) with substrate specificity for benzazo-phenylalanine or a derivative thereof, wherein said aaRS is characterized in that: it comprises enzymatic activity for charging a cognate suppressor tRNA with benzazo- phenylalanine (Baf) or a derivate thereof, preferably wherein said derivate is a non-natural light- responsive amino acid selected from the group consisting of p-amino-benzazo-phenylalanine and p- carboxy-benzazo-phenylalanine, and it comprises an amino acid sequence with at least 70%, at least 80%, at least 85%, at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, preferably at least 95%, more preferably at least 96%, even more preferably at least 97%, even more preferably at least 98%, even more preferably at least 99%, even more preferably 100% amino acid sequence identity to SEQ ID NO: 14, wherein: (a) the amino acid at position 295 in the amino acid sequence of SEQ ID NO: 14 or a position corresponding to this position is substituted with an amino acid selected from the group consisting of L; and / or (b) the amino acid at position 304 in the amino acid sequence of SEQ ID NO: 14 or a position corresponding to this position is substituted with an amino acid selected from the group consisting of S; and / or (c) the amino acid at position 346 in the amino acid sequence of SEQ ID NO: 14 or a position corresponding to this position is substituted with an amino acid selected from the group consisting of A. As detailed herein above, aminoacyl tRNA synthetases with specificities to various substrates are known in the art. In the context of aminoacyl tRNA synthetases, substrate specificity refers to the specificity of said aaRS to incorporate the desired amino acid (such as Baf) into the cognate suppressor RNA. Importantly, such an (engineered) aaRS must not incorporate any undesired amino acid into the cognate suppressor tRNA. Accordingly, an aaRS “with substrate specificity for benzazo-phenylalanine or a derivative thereof” may be able to incorporate benzazo-phenylalanine or a derivative thereof into the cognate suppressor tRNA, however, in the context of the present invention, should not be able to incorporate any other amino acids into said tRNA. In the context of the present invention, the derivate of Baf is not particularly limited. In the context of the aminoacyl tRNA synthetase (aaRS) with substrate specificity for benzazo-phenylalanine or a derivative thereof, said derivative is preferably selected from benzazo- phenylalanine, p-amino-benzazo-phenylalanine and p-carboxy-benzazo-phenylalanine, more preferably from benzazo-phenylalanine or p-amino-benzazo-phenylalanine. Accordingly, “substrate specificity” may herein refer to the specificity of an aaRS to charge the cognate suppressor tRNA with benzazo- phenylalanine (Baf), p-amino-benzazo-phenylalanine or p-carboxy-benzazo-phenylalanine. In the context of the present invention, an aaRS that can charge a suppressor tRNA with Baf (or a derivate thereof) may also be termed “BafRS”. As is detailed in the illustrative and non-limiting Example 7, the present inventors have surprisingly identified amino acid residues in an aaRS that, when substituted, improve the enzymatic activity of said aaRS towards benzazo-phenylalanine or a derivative thereof. Said amino acid residues (and the respective advantageous amino acid substitutions) are illustratively shown in the non-limiting Figure 10 E. Figure 10 B to D illustratively demonstrate the surprising and advantageous effects of said amino acid substitutions (or combinations thereof). Here, it is shown that even a single amino acid substitution may already have advantageous effects on the enzymatic activity of the respective BafRS. The combination of various amino acid substitutions was further advantageous with regard to the enzymatic activity of the aaRS. Accordingly, the present invention relates to an aminoacyl tRNA synthetase (aaRS) with substrate specificity for benzazo-phenylalanine or a derivative thereof, wherein said aaRS is characterized in that: it comprises enzymatic activity for charging a cognate suppressor tRNA with benzazo- phenylalanine (Baf) or a derivate thereof, preferably wherein said derivate is a non-natural light- responsive amino acid selected from the group consisting of p-amino-benzazo-phenylalanine and p- carboxy-benzazo-phenylalanine, and it comprises an amino acid sequence with at least 70%, at least 80%, at least 85%, at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, preferably at least 95%, more preferably at least 96%, even more preferably at least 97%, even more preferably at least 98%, even more preferably at least 99%, even more preferably 100% amino acid sequence identity to SEQ ID NO: 14, wherein: (a) the amino acid at position 295 in the amino acid sequence of SEQ ID NO: 14 or a position corresponding to this position is substituted with an amino acid selected from the group consisting of L and R; and / or (b) the amino acid at position 304 in the amino acid sequence of SEQ ID NO: 14 or a position corresponding to this position is substituted with an amino acid selected from the group consisting of S; and / or (c) the amino acid at position 346 in the amino acid sequence of SEQ ID NO: 14 or a position corresponding to this position is substituted with an amino acid selected from the group consisting of A; and / or (d) the amino acid at position 221 in the amino acid sequence of SEQ ID NO: 14 or a position corresponding to this position is substituted with an amino acid selected from the group consisting of R. Preferably, the aminoacyl tRNA synthetase (aaRS) with substrate specificity for benzazo-phenylalanine or a derivative thereof of the present invention is characterized in that: it comprises enzymatic activity for charging a cognate suppressor tRNA with benzazo- phenylalanine (Baf) or a derivate thereof, preferably wherein said derivate is a non-natural light- responsive amino acid selected from the group consisting of p-amino-benzazo-phenylalanine and p- carboxy-benzazo-phenylalanine, and it comprises an amino acid sequence with at least 70%, at least 80%, at least 85%, at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, preferably at least 95%, more preferably at least 96%, even more preferably at least 97%, even more preferably at least 98%, even more preferably at least 99%, even more preferably 100% amino acid sequence identity to SEQ ID NO: 14, wherein: (a) the amino acid at position 295 in the amino acid sequence of SEQ ID NO: 14 or a position corresponding to this position is substituted with an amino acid selected from the group consisting of L and R; and (b) the amino acid at position 304 in the amino acid sequence of SEQ ID NO: 14 or a position corresponding to this position is substituted with an amino acid selected from the group consisting of S; and (c) the amino acid at position 346 in the amino acid sequence of SEQ ID NO: 14 or a position corresponding to this position is substituted with an amino acid selected from the group consisting of A. The herein provided aaRS may further comprise one or more deletion(s), substitution(s), insertion(s), and / or addition(s) of one or more amino acid(s), and wherein: (a) the amino acid at position 295 in the amino acid sequence of SEQ ID NO: 14 or a position corresponding to this position is substituted with an amino acid selected from the group consisting of L and R; and / or (b) the amino acid at position 304 in the amino acid sequence of SEQ ID NO: 14 or a position corresponding to this position is substituted with an amino acid selected from the group consisting of S; and / or (c) the amino acid at position 346 in the amino acid sequence of SEQ ID NO: 14 or a position corresponding to this position is substituted with an amino acid selected from the group consisting of A; and / or (d) the amino acid at position 221 in the amino acid sequence of SEQ ID NO: 14 or a position corresponding to this position is substituted with an amino acid selected from the group consisting of R. The herein provided aaRS may further comprise one or more deletion(s), substitution(s), insertion(s), and / or addition(s) of one or more amino acid(s), and wherein: (a) the amino acid at position 295 in the amino acid sequence of SEQ ID NO: 14 or a position corresponding to this position is substituted with an amino acid selected from the group consisting of L and R; and / or (b) the amino acid at position 304 in the amino acid sequence of SEQ ID NO: 14 or a position corresponding to this position is substituted with an amino acid selected from the group consisting of S; and / or (c) the amino acid at position 346 in the amino acid sequence of SEQ ID NO: 14 or a position corresponding to this position is substituted with an amino acid selected from the group consisting of A. As detailed herein above, the herein provided aaRS may be orthogonal to a (cognate) suppressor tRNA. In the context of the present invention, said cognate suppressor tRNA may comprise an anticodon, and wherein said anticodon is complementary to a stop codon. Said stop codon may be selected from the group consisting of UAG, UGA, and UAA, preferably UAG. In the context of the present invention, the suppressor tRNA is not particularly limited, as long as it forms a (suitable) orthogonal tRNA / aaRS pair with the herein provided aaRS, and wherein it comprises an anticodon which is complementary to a stop codon selected from the group consisting of UAG, UGA, and UAA, preferably UAG. In the context of the present invention, said cognate suppressor tRNA may preferably be selected from the group consisting of: (a) a nucleic acid molecule comprising a nucleic acid sequence of SEQ ID NO: 70; and (b) a nucleic acid molecule that hybridizes with a nucleic acid molecule comprising a nucleic acid sequence complementary to the nucleotide sequence of SEQ ID NO: 70 and that encodes a suppressor tRNA, wherein said suppressor tRNA forms or is capable of forming a cloverleaf structure and comprises an anticodon, and wherein said anticodon is complementary to said stop codon (e.g., UAG, UGA, and UAA). As illustratively shown in the non-limiting Figure 10, the herein provided aaRS has particularly high substrate specificity to benzazo-phenylalanine (Baf), accordingly, the non-natural light-responsive amino acid to be incorporated using the herein provided aaRS may preferably be benzazo-phenylalanine, p-amino- benzazo-phenylalanine, or p-carboxy-benzazo-phenylalanine, more preferably benzazo-phenylalanine or p-amino-benzazo-phenylalanine, most preferably benzazo-phenylalanine. Examples 1J and 1L provide illustrative means and methods for the synthesis of said non-natural light-responsive amino acids. The herein provided aaRS preferably incorporates non-natural light-responsive amino acids (such as Baf) when they are in the trans-configuration. Accordingly, the herein provided aaRS may have substrate specificity for trans-benzazo-phenylalanine, trans-p-amino-benzazo-phenylalanine, and / or trans-p- carboxy-benzazo-phenylalanine. Accordingly, the non-natural light-responsive amino acid to be incorporated using the herein provided aaRS may preferably be trans-benzazo-phenylalanine, trans-p- amino-benzazo-phenylalanine and / or trans-p-carboxy-benzazo-phenylalanine. Benzazo-phenylalanine or derivates thereof may be particularly hydrophobic, which may limit the efficiency of their incorporation into a suppressor tRNA due to limited solubility of such non-natural light- responsive amino acids. As detailed in the enclosed Example 3, the present inventors have surprisingly found means and methods to increase the solubility of such non-natural light-responsive amino acids (such as, in particular, Baf). Namely, it was found that such non-natural light-responsive amino acids (such as, in particular, Baf) may be complexed and / or solubilized using β-cyclodextrin. Accordingly, the present invention further relates to a method of solubilizing a non-natural (light- responsive) amino acid using β-cyclodextrin or (2-hydroxypropyl)-β-cyclodextrin or by complexing said non-natural (light-responsive) amino acid using / with β-cyclodextrin or (2-hydroxypropyl)-β-cyclodextrin. In a particular preferred embodiment, the herein provided aaRS comprises an amino acid sequence selected from the group consisting of SEQ ID NO: 15 to SEQ ID NO: 22, preferably SEQ ID NO: 21. As mentioned above and as detailed in the illustrative Example 7 and Figure 10, the herein provided aaRS comprises improved enzymatic activity. Accordingly, in the context of the present invention, the herein provided aaRS may have increased enzymatic activity for charging said cognate suppressor tRNA with a non-natural light-responsive amino acid selected from the group consisting of Baf, p-amino-benzazo- phenylalanine, and p-carboxy-benzazo-phenylalanine as compared to the reference aaRS with an amino acid sequence of SEQ ID NO: 14. Accordingly, in the context of the present invention, the herein provided aaRS may have at least about 1.5- fold, at least about 2-fold, at least about 3-fold, at least about 4-fold, at least about 5-fold, at least about 6- fold, at least about 7-fold, at least about 8-fold, at least about 9-fold, preferably at least about 10-fold increased enzymatic activity for charging said cognate suppressor tRNA with an amino acid selected from the group consisting of Baf, p-amino-benzazo-phenylalanine, and p-carboxy-benzazo-phenylalanine as compared to the reference aaRS with an amino acid sequence of SEQ ID NO: 14. The present invention further relates to a nucleic acid molecule encoding the herein provided aaRS, wherein said aaRS may be as detailed herein above. Accordingly, the present invention relates to a nucleic acid molecule encoding an aaRS with substrate specificity for benzazo-phenylalanine or a derivative thereof, wherein said aaRS is characterized in that: it comprises enzymatic activity for charging a cognate suppressor tRNA with benzazo- phenylalanine (Baf) or a derivate thereof, preferably wherein said derivate is a non-natural light- responsive amino acid selected from the group consisting of p-amino-benzazo-phenylalanine and p- carboxy-benzazo-phenylalanine, and it comprises an amino acid sequence with at least 70%, at least 80%, at least 85%, at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, preferably at least 95%, more preferably at least 96%, even more preferably at least 97%, even more preferably at least 98%, even more preferably at least 99%, even more preferably 100% amino acid sequence identity to SEQ ID NO: 14, wherein: (a) the amino acid at position 295 in the amino acid sequence of SEQ ID NO: 14 or a position corresponding to this position is substituted with an amino acid selected from the group consisting of L and R; and / or (b) the amino acid at position 304 in the amino acid sequence of SEQ ID NO: 14 or a position corresponding to this position is substituted with an amino acid selected from the group consisting of S; and / or (c) the amino acid at position 346 in the amino acid sequence of SEQ ID NO: 14 or a position corresponding to this position is substituted with an amino acid selected from the group consisting of A; and / or (d) the amino acid at position 221 in the amino acid sequence of SEQ ID NO: 14 or a position corresponding to this position is substituted with an amino acid selected from the group consisting of R. The herein provided nucleic acid molecule encoding said aaRS with substrate specificity for benzazo- phenylalanine or a derivative thereof may be selected from the group consisting of the following: (a) a nucleic acid molecule comprising a nucleic acid sequence of SEQ ID NO: 60 to SEQ ID NO: 67; and (b) a nucleic acid molecule that hybridizes with a nucleic acid molecule comprising a nucleic acid sequence complementary to the nucleotide sequence of SEQ ID NO: 60 to SEQ ID NO: 67 and that encodes a polypeptide with aaRS activity. In the context of the present invention, aaRS activity may refer to the enzymatic activity of an aaRS, in particular it may refer to the ability of an aaRS to charge its cognate tRNA with a non-natural light- responsive amino acid (such as, for example, Baf). The present invention further provided for a nucleic acid vector comprising the herein above detailed nucleic acid molecule encoding the herein provided aaRS. Accordingly, the present invention relates to a nucleic acid vector comprising a nucleic acid molecule encoding an aaRS with substrate specificity for benzazo-phenylalanine or a derivative thereof, wherein said aaRS is characterized in that: it comprises enzymatic activity for charging a cognate suppressor tRNA with benzazo- phenylalanine (Baf) or a derivate thereof, preferably wherein said derivate is a non-natural light- responsive amino acid selected from the group consisting of p-amino-benzazo-phenylalanine and p- carboxy-benzazo-phenylalanine, and it comprises an amino acid sequence with at least 70%, at least 80%, at least 85%, at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, preferably at least 95%, more preferably at least 96%, even more preferably at least 97%, even more preferably at least 98%, even more preferably at least 99%, even more preferably 100% amino acid sequence identity to SEQ ID NO: 14, wherein: (a) the amino acid at position 295 in the amino acid sequence of SEQ ID NO: 14 or a position corresponding to this position is substituted with an amino acid selected from the group consisting of L and R; and / or (b) the amino acid at position 304 in the amino acid sequence of SEQ ID NO: 14 or a position corresponding to this position is substituted with an amino acid selected from the group consisting of S; and / or (c) the amino acid at position 346 in the amino acid sequence of SEQ ID NO: 14 or a position corresponding to this position is substituted with an amino acid selected from the group consisting of A; and / or (d) the amino acid at position 221 in the amino acid sequence of SEQ ID NO: 14 or a position corresponding to this position is substituted with an amino acid selected from the group consisting of R. The herein provided nucleic acid vector comprising a nucleic acid molecule encoding the herein provided aaRS may further comprise a suppressor tRNA, wherein said suppressor tRNA forms a suitable orthogonal tRNA / aaRS pair with said aaRS. In the context of the present invention, the expression of said aaRS may be inducible. The skilled person is aware of means and methods suitable for rendering the expression of, for example, a herein provided aaRS inducible. Such means and methods may, for example, be the expression of said aaRS under the control of an inducible promoter. Such inducible promoters are well known in the art and include for example arabinose-inducible promoters, as is further detailed in the enclosed, non-limiting Example 3. The present invention further relates to a host cell comprising the herein above detailed aaRS, the herein above detailed nucleic acid molecule (encoding said aaRS), and / or the herein above detailed nucleic acid vector (comprising said nucleic acid molecule). In a further aspect, the present invention relates to a method for the recombinant expression and / or the recombinant production of a polypeptide comprising a non-natural light-responsive amino acid, wherein said method comprises the recombinant expression of a polypeptide comprising a non-natural light- responsive amino acid in the presence of an aaRS as defined herein above, a cognate suppressor tRNA, and a non-natural light-responsive amino acid. Accordingly, the present invention relates to a method for the recombinant expression and / or the recombinant production of a polypeptide comprising a non-natural light-responsive amino acid, wherein said method comprises the recombinant expression of a polypeptide comprising a non-natural light- responsive amino acid in the presence of an aaRS, a cognate suppressor tRNA, and a non-natural light- responsive amino acid, wherein said aaRS is characterized in that: it comprises enzymatic activity for charging a cognate suppressor tRNA with benzazo- phenylalanine (Baf) or a derivate thereof, preferably wherein said derivate is a non-natural light- responsive amino acid selected from the group consisting of p-amino-benzazo-phenylalanine and p- carboxy-benzazo-phenylalanine, and it comprises an amino acid sequence with at least 70%, at least 80%, at least 85%, at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, preferably at least 95%, more preferably at least 96%, even more preferably at least 97%, even more preferably at least 98%, even more preferably at least 99%, even more preferably 100% amino acid sequence identity to SEQ ID NO: 14, wherein: (a) the amino acid at position 295 in the amino acid sequence of SEQ ID NO: 14 or a position corresponding to this position is substituted with an amino acid selected from the group consisting of L and R; and / or (b) the amino acid at position 304 in the amino acid sequence of SEQ ID NO: 14 or a position corresponding to this position is substituted with an amino acid selected from the group consisting of S; and / or (c) the amino acid at position 346 in the amino acid sequence of SEQ ID NO: 14 or a position corresponding to this position is substituted with an amino acid selected from the group consisting of A; and / or (d) the amino acid at position 221 in the amino acid sequence of SEQ ID NO: 14 or a position corresponding to this position is substituted with an amino acid selected from the group consisting of R. In the context of the present invention said cognate suppressor tRNA may be as defined herein above. Accordingly, in the context of the herein provided method for the recombinant expression and / or the recombinant production of a polypeptide comprising an N-terminal or a C-terminal light-responsive affinity tag, said cognate suppressor tRNA may comprise an anticodon, wherein said anticodon is complementary to a stop codon, preferably wherein said stop codon is selected from the group consisting of UAG, UGA, and UAA, more preferably UAG. Accordingly, in the context of the herein provided method for the recombinant expression and / or the recombinant production of a polypeptide comprising an N-terminal or a C-terminal light-responsive affinity tag, said cognate suppressor tRNA may preferably be selected from the group consisting of: (a) a nucleic acid molecule comprising a nucleic acid sequence of SEQ ID NO: 70; and (b) a nucleic acid molecule that hybridizes with a nucleic acid molecule comprising a nucleic acid sequence complementary to the nucleotide sequence of SEQ ID NO: 70 and that encodes a suppressor tRNA, wherein said suppressor tRNA forms or is capable of forming a cloverleaf structure and comprises an anticodon, and wherein said anticodon is complementary to said stop codon (e.g., UAG, UGA, and UAA). Accordingly, the present invention relates to a method for the recombinant expression and / or the recombinant production of a polypeptide comprising a non-natural light-responsive amino acid, wherein said method comprises the recombinant expression of a polypeptide comprising a non-natural light- responsive amino acid in the presence of an aaRS, a cognate suppressor tRNA, and a non-natural light- responsive amino acid, wherein said aaRS is characterized in that: it comprises enzymatic activity for charging a cognate suppressor tRNA with benzazo- phenylalanine (Baf) or a derivate thereof, preferably wherein said derivate is a non-natural light- responsive amino acid selected from the group consisting of p-amino-benzazo-phenylalanine and p- carboxy-benzazo-phenylalanine, and it comprises an amino acid sequence with at least 70%, at least 80%, at least 85%, at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, preferably at least 95%, more preferably at least 96%, even more preferably at least 97%, even more preferably at least 98%, even more preferably at least 99%, even more preferably 100% amino acid sequence identity to SEQ ID NO: 14, wherein: (a) the amino acid at position 295 in the amino acid sequence of SEQ ID NO: 14 or a position corresponding to this position is substituted with an amino acid selected from the group consisting of L and R; and / or (b) the amino acid at position 304 in the amino acid sequence of SEQ ID NO: 14 or a position corresponding to this position is substituted with an amino acid selected from the group consisting of S; and / or (c) the amino acid at position 346 in the amino acid sequence of SEQ ID NO: 14 or a position corresponding to this position is substituted with an amino acid selected from the group consisting of A; and / or (d) the amino acid at position 221 in the amino acid sequence of SEQ ID NO: 14 or a position corresponding to this position is substituted with an amino acid selected from the group consisting of R; and preferably wherein said non-natural light-responsive amino acid is selected from benzazo-phenylalanine (Baf), p-amino-benzazo-phenylalanine and p-carboxy-benzazo-phenylalanine, more preferably from benzazo-phenylalanine, and wherein said cognate suppressor tRNA may preferably be selected from the group consisting of: (a) a nucleic acid molecule comprising a nucleic acid sequence of SEQ ID NO: 70; and (b) a nucleic acid molecule that hybridizes with a nucleic acid molecule comprising a nucleic acid sequence complementary to the nucleotide sequence of SEQ ID NO: 70 and that encodes a suppressor tRNA, wherein said suppressor tRNA forms a cloverleaf structure and comprises an anticodon, and wherein said anticodon is complementary to said stop codon (e.g., UAG, UGA, and UAA). In the context of the herein provided method for the recombinant expression and / or the recombinant production of a polypeptide comprising a non-natural light-responsive amino acid, the non-natural light- responsive amino acid may be Baf or a derivate thereof, wherein said derivate may be a non-natural light- responsive amino acid selected from the group consisting of p-amino-benzazo-phenylalanine and p- carboxy-benzazo-phenylalanine. Preferably, wherein said non-natural light-responsive amino acid is Baf. Examples 1J and 1L provide illustrative means and methods for the synthesis of said non-natural light- responsive amino acids. As detailed herein above, in the context of the present invention an aaRS may preferably incorporate non- natural light-responsive amino acids (such as Baf) when they are in the trans-configuration. Accordingly, in the context of the present invention, an aaRS may have substrate specificity for trans-benzazo- phenylalanine, trans-p-amino-benzazo-phenylalanine and / or trans-p-carboxy-benzazo-phenylalanine. Accordingly, the non-natural light-responsive amino acid to be incorporated in the context of the herein provided method may preferably be trans-benzazo-phenylalanine, trans-p-amino-benzazo-phenylalanine and / or trans-p-carboxy-benzazo-phenylalanine. Benzazo-phenylalanine or derivates thereof may be particularly hydrophobic, which may limit the efficiency of their incorporation into a suppressor tRNA due to limited solubility of such non-natural light- responsive amino acids. As detailed in the enclosed Example 3, the present inventors have surprisingly found means and methods to increase the solubility of such non-natural light-responsive amino acids (such as, in particular, Baf). Namely, it was found that such non-natural light-responsive amino acids (such as, in particular, Baf) may be complexed and / or solubilized using β-cyclodextrin. In a preferred embodiment of the herein provided method, said aaRS comprises an amino acid sequence selected from the group consisting of SEQ ID NO: 15 to SEQ ID NO: 22, preferably SEQ ID NO: 21. As mentioned above and as detailed in the illustrative Example 7 and Figure 10, an aaRS in accordance with the present invention (such as, for example, an aaRS comprising an amino acid sequence selected from the group consisting of SEQ ID NO: 15 to SEQ ID NO: 22) may have improved enzymatic activity. Accordingly, in the context of the herein provided method, such an aaRS may have increased enzymatic activity for charging said cognate suppressor tRNA with a non-natural light-responsive amino acid selected from the group consisting of Baf, p-amino-benzazo-phenylalanine and p-carboxy-benzazo-phenylalanine as compared to the reference aaRS with an amino acid sequence of SEQ ID NO: 14. Accordingly, in the context of the herein provided method, an aaRS in accordance with the present invention (such as, for example, an aaRS comprising an amino acid sequence selected from the group consisting of SEQ ID NO: 15 to SEQ ID NO: 22) may have at least about 1.5-fold, at least about 2-fold, at least about 3-fold, at least about 4-fold, at least about 5-fold, at least about 6-fold, at least about 7-fold, at least about 8-fold, at least about 9-fold, preferably at least about 10-fold increased enzymatic activity for charging said cognate suppressor tRNA with an amino acid selected from the group consisting of Baf, p- amino-benzazo-phenylalanine and p-carboxy-benzazo-phenylalanine as compared to the reference aaRS with an amino acid sequence of SEQ ID NO: 14. In the context of the herein provided method for the recombinant expression and / or the recombinant production of a polypeptide of comprising a non-natural light-responsive amino acid, the identity of said polypeptide is not particularly limited, and accordingly, any polypeptide comprising a non-natural light- responsive amino acid may be recombinantly expressed and / or produced by this method (and / or by the herein above provided aminoacyl tRNA synthetase (aaRS). However, as detailed herein above the herein provided method for the recombinant expression and / or the recombinant production of a polypeptide of comprising a non-natural light-responsive amino acid and / or the herein provided aminoacyl tRNA synthetase (aaRS) may be particularly useful in the recombinant expression and / or the recombinant production of a polypeptide of any one of formulas (I) to (IV), as detailed herein above. In a further aspect, the present invention relates to a kit comprising one or more selected from the group consisting of the following (a) to (f); wherein (a) is selected from one or more of the group consisting of the following (a1) to (a6): (a1) the polypeptide comprising the N-terminal or C-terminal light-responsive affinity tag as provided herein above, (a2) the nucleic acid molecule (encoding the herein above provided polypeptide comprising the N-terminal or C-terminal light-responsive affinity tag of (a1)), (a3) the nucleic acid vector (comprising the herein above provided nucleic acid molecule of (a2)), (a4) the light-responsive affinity tag as provided herein above, (a5) the nucleic acid molecule (encoding the herein above provided light-responsive affinity tag of (a4)), (a6) the nucleic acid vector (comprising the herein above provided nucleic acid molecule of (a5)); (b) is selected from one or more of the group consisting of the following (b1) to (b3): (b1) the aaRS as provided herein above, (b2) the nucleic acid molecule (encoding the herein above provided aaRS of (b1)), (b3) the nucleic acid vector (comprising the herein above provided nucleic acid molecule of (b2)); (c) is selected from one or more of the group consisting of the following (c1) to (c3): (c1) the cognate suppressor tRNA as provided herein above, (c2) the nucleic acid molecule (encoding the herein above provided suppressor tRNA of (c1)), (c3) the nucleic acid vector (comprising the herein above provided nucleic acid molecule of (c2)); (d) is a host cell selected from one or more of the group consisting of (d1) to (d2): (d1) a host cell for the recombinant expression of the herein above provided polypeptide comprising the N-terminal or C-terminal light-responsive affinity tag, wherein said host cell comprises or harbors the herein above provided nucleic acid molecule of (a2), (b2), and / or (c2) and / or the herein above provided nucleic acid vector of (a3), (b3), and / or (c3), (d2) a host cell for the recombinant expression of the herein above provided light-responsive affinity tag, wherein said host cell comprises or harbors the herein above provided nucleic acid molecule of (a5), (b2), and / or (c2) and / or the herein above provided nucleic acid vector of (a6), (b3), and / or (c3); (e) is selected from one or more of the group consisting of the following (e1) to (e3): (e1) benzazo-phenylalanine (Baf), (e2) p-amino-benzazo-phenylalanine, and (e3) p-carboxy-benzazo-phenylalanine;and (f) is the solid phase as provided herein above. In the context of the present invention, said kit may comprise one or more selected from the group defined as (a1) to (a3), preferably wherein said kit further comprises one or more selected from the group defined as (b) to (f), even more preferably wherein said kit comprises (b), (c), (d1), (e), and (f). In the context of the present invention, said kit may comprise one or more selected from the group defined as (a4) to (a6), preferably wherein said kit further comprises one or more selected from the group defined as (b) to (f), even more preferably wherein said kit comprises (b), (c), (d2), (e), and (f). In the context of the present invention, the herein provided kit may comprise any combination of features (a), (b), (c), (d), and / or (e). The herein provided kit may further comprise a UV light source, preferably one or more LED light sources emitting one or more wavelength(s) of light selected from one or more wavelength(s) of light from about 310 nm to about 370 nm, more preferably from about 345 nm to about 365 nm, more preferably from about 350 nm to about 355 nm and, optionally, a second light source, preferably wherein said second light source is selected from one or more LED light sources emitting one or more wavelength(s) of light from about 405 nm to about 470 nm, preferably from about 420 nm to about 430 nm. The wavelength that is emitted from said one or more LED light source may be switched, thereby allowing illumination with the above- mentioned wavelength or avoiding illumination of the non-natural light-responsive amino acid (in particular, when no other light sources are present and the non-natural light-responsive amino acid is left in the dark). As also demonstrated in Figure 20 A and B, in the context of the present invention it was surprisingly found that contacting a solid phase (e.g., comprising α-cyclodextrin) with a POI coupled to the herein provided light-responsive affinity tag (as well as the optional subsequent washing step) can be performed in the presence of light having a wavelength that induces the switch from the cis- to the trans- configuration of said non-natural light-responsive amino acid (e.g., in the present of light having a wavelength of about 430 nm). Alternatively, said contacting step (as well as the optional subsequent washing step) can be performed in the dark. As illustrated in Figure 20 and discussed herein above, a wavelength of e.g., 430 nm results in a higher quantity / yield as compared to darkness. See also Figure 23 providing a schematic and non-limiting illustration of the herein provided means and method. Accordingly, in the context of the present invention, it is preferred that the UV light source can be readily switched. Exemplary and non-limiting UV light sources are illustrated in Figure 7. The present invention further relates to the use of the herein provided kit, the herein above provided polypeptide comprising the N-terminal or the C-terminal light-responsive affinity tag, the polypeptide of interest as obtained by or as obtainable by the herein above provided method for cleaving the light- responsive affinity tag from the polypeptide of interest and / or the herein above provided light-responsive affinity tag in an in vitro or an in vivo assay. In the context of the present invention such an in vitro or an in vivo assay is not particularly limited. Preferably, said in vitro or said in vivo assay is a binding assay, an immunochemical assay, an enzyme assay, and / or a cell culture assay. However, also other assays are envisaged herein. Furthermore, other uses of the herein provided kit, the herein above provided polypeptide comprising the N-terminal or the C-terminal light-responsive affinity tag, the polypeptide of interest as obtained by or as obtainable by the herein above provided method for cleaving the light-responsive affinity tag from the polypeptide of interest, and / or the herein above provided light-responsive affinity tag are also envisaged herein. The same applies for methods employing the same. The present invention also relates to a host or host cell that does not encode a functional ribosomal release factor 1 (RF1 alias PrfA) or is a RF1 knockdown strain that expresses a functional RF1. Said host cell may be as defined anywhere herein above or below. As detailed in Example 1S, the present inventors have surprisingly generated a RF-1 knockdown strain and could even more surprisingly demonstrate that RF-1 knockdown (as opposed to an RF-1 knockout strain / knockout mutant of the state of the art) resulted in improved Baf incorporation while maintaining rapid growth and high recombinant protein expression capacity of the genetically modified E. coli strain. The herein provided knockdown strains (such as the RF1 knockdown strain) preferably have about or at least 10%, about or at least 20%, about or at least 30%, about or at least 40%, about or at least 50% reduced expression of the respective gene or activity of the encoded gene product (i.e., protein / polypeptide such as RF1) as compared to a reference strain, optionally wherein the reduced expression or activity is assessed by quantifying amber . Accordingly, the present invention also relates to a host or host cell that is a RF1 knockdown strain that expresses a functional RF1, wherein the expression or activity of said functional RF1 is reduced by about or at least 10%, about or at least 20%, about or at least 30%, about or at least 40%, about or at least 50% as compared to a reference strain and optionally as quantified via amber stop codon suppression efficiency. In the context of the present invention, “a knockdown strain" (also termed “knockdown mutant” herein; such as, e.g., an RF1 knockdown strain) is a bacterial strain that expressed a given gene product (such as RF1) at a lower level or with lower activity as compared to a reference strain. Accordingly, the herein provided knockdown strains have reduced / lowered expression of the respective gene or activity of the encoded gene product (e.g., RF1) as compared to a reference strain, optionally wherein the reduced expression or activity is assessed by quantifying amber stop codon suppression efficiency. Such a knockdown strain may be naturally occurring or may have been generated by genetic engineering. When generated by genetic engineering (such as in the case of the herein provided NEBExpress(lowRF1) strain; see Example 1S), a reference strain may be the respective wildtype strain (e.g., a strain that shares all or essentially all genetic material with the given knockdown strain with the exception of the desired mutation; such as RF1; for example, E. coli NEBExpress). Means and methods for the generation of knockdown strains include, inter alia, those detailed in Example 1S. Alternatively, the activity of the encoded gene product (e.g., RF1) may be lowered as a result of one or more point mutations / amino acid exchanges. Further, the skilled person is readily in the position to determine whether the expression of a given gene product is altered (i.e., increased or decreased) as compared to the expression of the gene product in a reference strain. Such means and methods include, for example, quantitative real-time polymerase chain reaction (qRT-PCR), RNA sequencing, or the like. For example, the skilled person can design primers capable of specifically binding the coding region of e.g., RF1 (as well as primers binding to a suitable reference gene), amplify RF1 (as well as the suitable reference gene) from cDNA (that has been generated by reverse transcription from: (i) the presumable knockdown strain (e.g., NEBExpress(lowRF1)) and (ii) a suitable reference strain (e.g., NEBExpress wildtype)), in qPCR reactions and subsequently compute whether and to what extend the expression of RF1 is altered in the knockdown strain as compared to the reference strain. The skilled person is further aware that amber stop codon suppression can be used in the context of the present invention in order to assess if and to what extend an RF1 knockdown strain is characterized by reduced RF1 expression or reduced RF1 activity. Efficiency of amber stop codon suppression may be assessed via the assessment of, e.g., Baf incorporation efficiency into a polypeptide as detailed in the enclosed examples. Brief Description of Drawings The present invention is further described by reference to the following non-limiting figures. The figures show: Fig. 1. Structure and photochemistry of Baf. (A) Photo-induced cis / trans-isomerization of Baf. (B, C) While the structure of the azo-benzene side chain in trans-Baf is mostly planar and elongated (B), the one of cis-BAF is twisted and more bulky due to the steric repulsion between the two aromatic rings (C). (D) UV-Vis spectra of the trans- and cis-states of Baf. A 50 µM solution of Baf in 100 mM Tris / HCl pH 8.0 either equilibrated under daylight (solid line) or after irradiation with 355 nm UV light for 30 min (dashed line), respectively. Wavelengths of absorption maxima are indicated. (E) Time-dependent increase in absorption at 326 nm during irradiation of a 50 µM trans-Baf solution at 355 nm with a UV LED from the top. (F) Thermal re-isomerization of cis-Baf (50 µM) at 25±1°C in the dark as spectrophotometrically monitored at long measurement intervals (12 h). The data in (E) and (F) were subjected to exponential curve fit. Fig.2. Complex formation between the cis- and trans-states of Baf and α-CD or β-CD. (A, B) Structural model of the complex between trans-Baf and ^-CD (A, front view; B, side view) generated using ChemDraw3D (structure energy-minimized with the MM2 method). (C) Titration of 50 µM trans-Baf in 2 mL 100 mM Tris / HCl pH 8.0 with a 50 µM solution of ^-CD in the same buffer. (D) Titration of cis-Baf (100 µM) with ^-CD (solid circles) in comparison with buffer alone (hollow circles). (E) Titration of trans- BAF (50 µM) with ^-CD. (F) Titration of cis-Baf (100 µM) with ^-CD. For all titrations – except for (D), where a straight line fit was applied – the small (negative or positive, respectively) change in absorbance at the diagnostic wavelengths of 426 nm for cis-Baf and 326 nm for trans-BAF during complex formation with the CD was monitored and the curves were fitted using Eq.1. Fig.3. Genetic system for the efficient cotranslational incorporation of Baf into recombinant proteins produced in E. coli. (A) Expression vector pSB19 encoding all three components needed for the biosynthesis of a POI carrying Baf, which is encoded by an amber stop codon: (i) the coding region for the POI (here: sfGFPa39) under control of the lacUV5p / o, (ii) the gene for tRNAPylcarrying an anticodon complementary to the amber stop codon, expressed from the lpp promoter, (iii) the coding region for an engineered version of PylRS, BafRS#34, under control of the araBADp / o. Apart from the relevant regulatory regions (repressor genes araC and lacI as well as origin of replication), the vector additionally harbors a transcriptional fusion of the genes for ^-lactamase and chloramphenicol-acetyltransferase, which confer ampicillin (Amp) and chloramphenicol (Cam) resistance, respectively. The latter was equipped with an amber stop codon at a permissible position (residue 112), thus allowing selection for E. coli growth in the presence of Cam in the course of directed evolution of PylRS to accept a nnAa substrate. (B) Deletion of RF-1 in the genome of the E. coli B strain NEBExpress, i.e. the prfA cistron within the operon flanked by the hemA and prmC genes, and its replacement by the coding region for the kanamycin resistance protein. (C) Subsequent deletion of the malE cistron, as part of the mal operon, in the genome of NEBExpress(^RF1) and its replacement by the coding region for the streptomycin resistance protein, resulting in NEBExpress(^RF1 / ^MBP). (D, E) Directed evolution of PylRS to efficiently charge tRNAPylwith Baf. (D) Exemplary FACS measurements (GFP signals, 105events each) comparing the initial PylRS mutant encoded on pSB15-BafRS#0 (dashed line) with the pSB19-BafRS#34 plasmid (solid line), both harboring the sfGFPa39 reporter protein gene, in the NEBExpress(^RF1) strain background. (E) MFI of sfGFPa39 determined by FACS (for duplicate cultures, error bars representing 50 % of the difference between the two measurements) in the presence of different Baf concentrations in the culture medium, using the same experimental setup. Fig. 4. α-CD affinity chromatography of purified colored POIs. (A) Scheme of the recombinant (mature) protein constructs for Azurin and mScarlet, both carrying a C-terminal Azo-tag with the Baf residue. (B) Retention of (pre-purified) Azurin-GG-Baf (top) and mScarlet-GG-Baf (bottom) to an ^-CD affinity column (1 mL bed volume) after washing with 1 mL buffer. The minor fraction of protein that had not incorporated the C-terminal Baf residue via amber suppression is already partially washed out of the column with the buffer flow. (C) The elution of mScarlet-Strep-GG-Baf under different illumination conditions monitored via its specific fluorescence in the chromatography fractions. The column was either loaded with the protein and (i) washed directly under 355 nm UV light (dashed line) or (ii) washed under daylight (grey solid line) and followed by elution upon exposure to 355 nm (black solid line). (D) Separation of a mixture of Azurin-Strep-GG-Baf and mScarlet-Strep, here without the Azo-tag, on the ^-CD affinity column. While mScarlet (dashed box) does not bind to the column and is quickly washed out, Azurin-Strep- GG-Baf (solid box) is retained in the upper zone of the column and afterwards specifically eluted via exposure to UV light. Fig. 5. One-step purification of different Azo-tagged POIs from complex protein mixtures via light- controlled α-CD affinity chromatography. Protein solutions were applied to a column with 1 mL bed volume under daylight and, after washing with buffer, the bound protein was eluted via illumination at 355 nm (in the dark lab). (A) Isolation of cystatin C carrying the C-terminal GG-Baf sequence from the periplasmic cell extract of NEBExpress(^RF1). (B) Isolation of Azurin carrying the C-terminal GG-Baf sequence from the total cell extract of NEBExpress(^RF1), with 5 mM MBP added in the lysis buffer. (C) Isolation of mScarlet carrying the C-terminal GG-Baf sequence from the total cell extract under similar conditions. (D) Isolation of mScarlet3 carrying the N-terminal Ala-Baf-Gly sequence from the total cell extract, again under similar conditions. Note that the two additional lower bands in the elution fractions are obviously due to a specific backbone cleavage within mScarlet3 (cf. Fig. 12A). This prominent post- maturation hydrolysis, which has also been described by others (Lazzari-Dean et al., 2022), was observed in all mScarlet(3) preparations, even when using other purification methods and in the absence of the Azo- tag, but not for sfGFP (cf. Fig. 13E). (E) Parallelled isolation of the ^-lactamase AmpC carrying the C- terminal GG-Baf sequence from the total cell extract of NEBExpress(^RF1) using 10 wells of a 96-well receiver plate filled with 200 µl ^-CD resin each. AmpC was purified as essentially homogenous protein without significant well-to-well difference. AmpC without an Azo-tag or untransformed NEBExpress(^RF1) cells served as negative controls. (F) Colorimetric assay to measure the AmpC enzyme activity in aliquots of the eluate from (E) after mixing with CENTA substrate in a 96-well microtest plate. (G) Parallelled affinity purification of the anti-CEA scFv antibody fragment T84.66 carrying the C-terminal GG-Baf sequence from the periplasmic extract of NEBExpress(^RF1), followed by ELISA to assess antigen-binding activity in 10 separately eluted aliquots. scFv bound to a CEA-coated microtiter plate was detected via an antibody-HRP conjugate directed against the Strep-tag II using ABTS substrate. Untransformed NEBExpress(^RF1) cells served as negative controls (3 wells each). Fig. 6. Chemical synthesis schemes for Baf and NH2-Baf. (A) Synthesis scheme for L- benzazophenylalanine (Baf); further details can be found in Example 1J. (B) Synthesis scheme for 4-(4- aminophenyl)diazenyl-L-phenylalanine dihydrochloride (NH2-Baf); further details can be found in Example 1L. Fig. 7. Home-made devices for the photo-induced trans / cis-isomerization of Baf. (A, B) LED device for the irradiation at two wavelengths, 355 nm or 430 nm, of samples in a 4 mL (1x1 cm2) quartz cuvette from the top for UV / Vis measurements in a photometer. (C, D) Setup for the illumination of the ^-CD chromatography matrix (1 mL bed volume in a Pierce disposable 2 mL column) at 355 nm using in total up to 16 LEDs (4 vertical rows with each 4 LEDs; 2 rows with each 4 LEDs in an earlier version). Due to restrictions in commercial availability, LEDs with 355 nm wavelength were chosen, despite the presumably optimal wavelength of 350 nm for efficiently switching trans→cis (cf. Fig. 8). It was confirmed that the light pathlength within the ^-CD affinity column is not limiting in this setup (in particular in the absence of a strongly absorbing protein) using a handheld spectrometer (OHSP-350UV; Hangzhou Hopoo Light&Color Technology, Zhejiang, China). (E) Setup for the illumination of two rows of a 96-well receiver plate (one LED per well). (F, G, H) Extended setup that allows illumination of the column either at 355 nm (G; 4x4 LEDs, each 1.2-2.4 mW, front and back rows of LEDs) or at 430 nm (H; 2x4 LEDs, each 27 mW, middle rows of LEDs). Fig. 8. Spectral changes upon transition between trans- and cis-configurations of Baf and their complex formation with CDs. (A) Ratio of ^trans / ^cis of a 50 ^M solution of Baf in 100 mM Tris / HCl pH 8.0 (cf. Fig. 1D) plotted versus the wavelength. A prominent maximum at 350 nm indicates the optimal wavelength for photo-induced trans-to-cis isomerization with a theoretical PSS ratio of 8.5. (B) Choice of the available LED wavelength governs the experimentally achievable PSS ratio. For example, when irradiating trans-Baf at 280 nm UV light, only a low degree of cis-isomerization takes place at stationary state, whereas upon subsequent irradiation at 355 nm the cis-configuration is almost quantitatively adopted in a short time. Conversely, subsequent irradiation at 280 nm again results in a mixed trans- / cis-equilibrium, which shifts almost completely to the trans-state if exposed to visible light at 430 nm. (C) Smoothed absorption spectra from a typical titration experiment of 50 μM trans-BAF in 2 mL 100 mM Tris / HCl pH 8.0 (cf. Fig.1D) with 50 mM ^-CD in the same buffer revealing shifts in ^max and amplitude for both bands. Fig. 9. Light-controlled adsorption and desorption of Baf on / from a synthesized α-CD affinity column. (A) Chemical synthesis of the ^-CD-conjugated Sepharose matrix. (B) A light-controlled chromatography experiment with Baf. (1) 100 ^L of 5 mM trans-Baf in 10 mM NaOH was loaded on the ^-CD affinity column (1 mL bed volume). (2) The column was washed with 10 bed volumes of 100 mM Tris / HCl 8.0, 0.5 M NaCl; the yellow band corresponding to the adsorbed Baf (dashed box) is essentially retained at the top. (3) The column was illuminated at 355 nm for 10 min. (4, 5, 6) The column was washed with 0.5 mL buffer aliquots, leading to the complete elution of Baf. Fig. 10. Directed evolution of PylRS to efficiently charge tRNAPylwith Baf and / or NH2-Baf. (A) Selection of a library generated by error-prone PCR of BafRS#0 for improved incorporation of the nnAa after bacterial growth in the presence of 1 mM NH2-Baf. The histogram depicts the sfGFPa39 fluorescence (105events) measured by FACS. The fluorescence of the clones obtained after the final selection round of this first directed evolution campaign (black solid line) clearly increased compared to the initial variant BafRS#0 (grey dashed line) and to the pooled transformants directly obtained after the random mutagenesis (grey solid line). (B) MFI of sfGFPa39 in the presence of 0.5 mM Baf (grey), 0.5 mM NH2-Baf (black) or in the absence of a nnAa (white) as measured by FACS (105events) for several mutants resulting from the directed evolution of BafRS#0 (N=4). (C) MFI of sfGFPa39 measured by FACS as in (B) for several mutants obtained either from the directed evolution of BafRS#0 or by specific combination of beneficial mutations (N=4). (D) MFI of sfGFPa39 in the presence of 0.5 mM Baf (grey), 0.5 mM NH2-Baf (black) or in the absence of a nnAa (white) as determined by FACS (105events) for the PylRS mutants BafRS#0 and BafRS#34 expressed from either the pSB15 or the pSB19 vector (N=3). (E) Amino acid sequence alignment of relevant PylRS mutants. Mutations discussed in the Examples are highlighted bold. Fig.11. Purification of Azurin-Strep-GG-Baf from the bacterial periplasmic extract via α-CD affinity chromatography. (A) The periplasmic cell fraction of NEBExpress(^RF1) containing the secreted POI was directly applied to the ^-CD affinity column (1 mL bed volume), followed by washing with 3 bed volumes of buffer (under daylight) until all host cell proteins had eluted. While a large portion of the blue protein remained bound at the top of the column during this step, some unbound Azurin also appeared in the flow-through. However, upon 355 nm UV light exposure, the remaining bound Azurin-Strep-GG-Baf specifically eluted from the column without contaminating host cell proteins. (B) Absorption spectrum of the flow-through (dotted line) and the light-induced eluate fractions (solid line) following exposure to daylight (in order to revert Baf to the trans-configuration). (trans)-Baf absorption was largely absent in the unbound Azurin fraction compared to the eluate, indicating a partial lack of the C-terminal Baf residue in the biosynthetic protein. Fig. 12. ESI-MS analyses of posttranslational modifications observed for POIs in this study. (A) Specific polypeptide bond cleavage in Gly-Baf-GG-mScarlet3. Apart from the intact mature fluorescent protein (calc.27233.59 Da), this mass spectrum reveals a peak for an N-terminal fragment up to the residue preceding Met as part of the fluorophore (calc.7653.56) as well as for two distinct C-terminal fragments, one including the cyclized and oxidized fluorophore (calc. 19598.05 Da) and another one without cyclisation and missing the Met residue (calc.19486.90 Da). (B, C) Reductive cleavage of NH2-Baf after incorporation into sfGFPa39. Deconvoluted ESI mass spectrum of sfGFPa39 expressed in the presence of (B) Baf (calc.27965.3 Da) or (C) NH2-Baf (calc.27980.5 Da). The shift of the major peak in the latter case indicates a possible reductive cleavage of the azo-bond, thus forming para-amino-L-phenylalanine (NH2- Phe), which is not seen for Baf. Fig. 13. Identification of the bacterial MBP as a specific contaminant that reversibly adsorbs to the α-CD affinity matrix in a light-independent manner. (A) Purification of Ala-Baf-GG-Azurin-Strep from the total cell extract of NEBExpress(^RF1) via ^-CD affinity chromatography. Note the contaminating band (arrow), which slowly elutes irrespective of illumination and was later identified as MBP. (B) A total cell lysate of NEBExpress(^RF1) was applied to the ^-CD affinity column and all host cell proteins were washed out via buffer flow (25 mM Tris pH 8.0, 150 mM NaCl) within 2 bed volumes, except for one protein that showed retarded elution and was still detectable after 10 bed volumes. (C) MBP from the bacterial lysate was specifically eluted when a washing buffer containing 50 mM maltose was applied as competing ligand. (D) Late wash fractions were pooled and concentrated and the contaminating protein was identified as MBP (MalE) by ESI-MS analysis (calc.40707.32 Da for the mature secreted protein). In addition, this protein was subjected to a trypsin digest and 16 peptide fragments were identified in the tandem MS / MS mode after RP-UHPLC, covering 58 % of the known amino acid sequence (UniProt ID: P0AEX9, excluding the signal peptide). (E) Purification of the intact sfGFP with an N-terminal Gly-Baf- Gly-Pro sequence via ^-CD chromatography from the total cell extract of NEBExpress(^RF1 / ^MBP). No contamination by bacterial proteins was evident in the eluate, even though no maltose was added as competing ligand. (F) Photographs of the ^-CD column during purification of sfGFP as described in (E). sfGFP was retained at the top of the column (white box) after washing under daylight (left) but was efficiently eluted with one column volume washing buffer when exposed to 355 nm UV light (right). Fig. 14. SPOT assay for optimizing the flanking amino acids on both sides of the Baf residue within the Azo-tag. (A) 15% SDS-PAGE of the ^-CD-conjugated PhoA indicating an average labelling of 1 to 5 ^-CD groups (~1100 Da) per enzyme subunit (47.2 kDa). The faint band at higher molecular weight presumably corresponds to the chemically cross-linked enzyme dimer. (B) Heat map representing the signal intensities after incubation of the SPOT membrane supporting C-terminally immobilized Xaa-Baf-Yaa peptides with the PhoA conjugate from (A), followed by chromogenic reaction. The identity of Xaa and Yaa residues in the synthetic peptide sequences is indicated on both axes, respectively. Fig. 15. Comparison of different sequences surrounding the Baf residue in a recombinant protein carrying the N-terminal Azo-tag. (A) A total cell extract (1 mL) of NEBExpress(^RF1) after expression of mScarlet3 equipped with an N-terminal Azo-tag comprising either Gly-Baf-Gly. Gly-Gly-Baf-Gly, Ser- Baf-Pro or Ala-Baf-Gly was loaded on an ^-CD affinity column (1 mL bed volume). This column is depicted after washing with 1 mL and (in total) 3 mL chromatography buffer, respectively (without UV light exposure). The Gly-Baf-Gly version showed stronger retardation on the affinity matrix than Ala-Baf- Gly. Moreover, the sequence Ser-Baf-Pro revealed inferior binding to the column, despite its promising behavior in the SPOT assay. (B) The ^-CD affinity column was washed with a larger buffer volume than normally used (9 mL) prior to the UV light exposure, and mScarlet fluorescence was determined in 250 µl fractions. Again, the Gly-Baf-Gly sequence (solid line) led to lower protein loss during the washing steps, if compared with the Ala-Baf-Gly version (dashed line), and higher yield of mScarlet3 eluted from the ^- CD affinity column upon 355 nm UV light exposure. Fig. 16. Light-controlled α-CD affinity chromatography of Azo-tagged GST and a nanobody in the microtiter plate format. (A) Isolation of GST carrying the N-terminal Gly-Baf-Gly sequence from the total cell extract of NEBExpress(^RF1), applied (in 0.5 mL aliquots) to 11 wells of a 96-well receiver plate (filled with 200 µl ^-CD resin per well). Untransformed NEBExpress(^RF1) served as a negative control (four wells). Chromatography and UV light-induced elution were directly performed in the GST assay buffer. The SDS-PAGE shows the eluates of wells 1–5, demonstrating high protein purity and low well-to- well difference. (B) GST enzyme activity was measured in the presence of glutathione and CDNB. (C) The anti-Her2 nanobody 2Rs15d was expressed with the N-terminal Gly-Baf-Gly sequence in the cytoplasm of NEBExpress(^RF1), and the total cell extract (0.5 mL aliquots) was applied to 12 wells of the receiver plate as in (A). Antigen-binding activity in the eluted protein fractions was quantified on a HER2-coated microtiter plate via detection with an antibody-HRP conjugate directed against the Strep-tag II using ABTS substrate. Fig.17. Influence of the buffer composition on the α-CD affinity chromatography. (A) Replacing NaCl by K2SO4 in the chromatography buffer (25 mM Tris / Cl pH 8.0, 150 mM NaCl versus 50 mM Tris / Cl pH 8.0, 100 mM K2SO4) resulted in a slightly better retention of Azurin-Strep-GG-Baf on the ^-CD column. (B) ^-CD affinity chromatography was performed with mScarlet-Strep-GG-Baf using different buffer salts, followed by quantification of the mScarlet fluorescence in 0.5 mL fractions. The use of K2SO4 (with its higher ionic strength; solid line) throughout the chromatography resulted in some lower loss of protein during the extensive washing steps (6 mL in total) and higher yield upon the UV light-induced elution if compared to NaCl (dashed line). Fig. 18: Light-controll...

Claims

New PCT-patent application Technische Universität München Vossius Ref.: AG2706 PCT S3 CLAIMS 1. A method for the isolation and / or purification of a polypeptide comprising an N-terminal or a C- terminal light-responsive affinity tag from a liquid phase, wherein the method comprises the steps of: (a) contacting said liquid phase with a solid phase, wherein said light-responsive affinity tag comprises a non-natural light-responsive α-amino acid, and wherein said non-natural light-responsive α-amino acid is in a first configuration so that it has high affinity to said solid phase; and (b) irradiating the light-responsive affinity tag with a wavelength of light that changes said non- natural light-responsive α-amino acid to a second configuration such that it has a decreased affinity to said solid phase as compared to the affinity thereof in step (a) and eluting said polypeptide comprising the N-terminal or the C-terminal light-responsive affinity tag.

2. The method of claim 1, wherein said polypeptide comprises a structure of formula (I) or of formula (II): X-[L-]lP (I) P[-L]l-X (II) wherein X is a light-responsive affinity tag, L is a linker, l is 1 or 0, so that L can be present or absent, P is a polypeptide of interest, wherein in formula (I) X-[L-]l is linked to the amino-terminus of P, and wherein in formula (II) [-L]l-X is linked to the carboxy-terminus of P.

3. The method of claim 2, wherein [X-] of formula (I) comprises a structure of [A-]aB-[C-]c so that the polypeptide of formula (I) is a polypeptide with a structure according to formula (III) [A-]aB-[C-]c[L-]lP (III), wherein [-X] of formula (II) comprises a structure of [-A]a-B[-C]c, so that said polypeptide of formula (II) is a polypeptide with a structure according to formula (IV) P[-L]l[-C]c-B[-A]a(IV), wherein A comprises one or more amino acid(s), a is 1 or 0, so that A can be present or absent, B is a non-natural light-responsive α-amino acid, C comprises one or more amino acid(s), c is 1 or 0, so that C can be present or absent, wherein in formula (III) [A-]aB-[C-]c[L-]lis linked to the amino-terminus of P, and wherein in formula (IV) [-L]l[-C]c-B[-A]ais linked to the carboxy-terminus of P.

4. A polypeptide comprising an N-terminal or a C-terminal light-responsive affinity tag, wherein said polypeptide comprises a structure of formula (III) or of formula (IV): [A-]aB-[C-]c[L-]lP (III), P[-L]l[-C]c-B[-A]a (IV), wherein A comprises one or more amino acid(s), a is 1 or 0, so that A can be present or absent, B is a non-natural light-responsive α-amino acid, C comprises one or more amino acid(s), c is 1 or 0, so that C can be present or absent, L is a linker, l is 1 or 0, so that L can be present or absent, P is a polypeptide of interest, wherein [A-]aB-[C-]c in formula (III) and [-C]c-B[-A]a in formula (IV) is a light-responsive affinity tag,wherein in formula (III) [A-]aB-[C-]c[L-]l is linked to the amino-terminus of P, and wherein in formula (IV) [-L]l[-C]c-B[-A]a is linked to the carboxy-terminus of P.

5. A light-responsive affinity tag, wherein said light-responsive affinity tag comprises a structure of formula (V) or formula (VI): [A-]aB-[C]c(V) [C]c-B[-A]a,(VI) wherein A comprises one or more amino acid(s), a is 1 or 0, so that A can be present or absent, B is a non-natural light-responsive α-amino acid, C comprises one or more amino acid(s), c is 1 or 0, so that C can be present or absent.

6. The polypeptide of claim 4, or the light-responsive affinity tag of claim 5, wherein said non-natural light-responsive α-amino acid is in a first configuration or in a second configuration.

7. The polypeptide of claim 6, the method of claim 3, or the light-responsive affinity tag of claim 6, wherein said first configuration is the trans-configuration of an azo-group comprised in said non- natural light-responsive α-amino acid and wherein said second configuration is the cis-configuration of said azo-group.

8. The polypeptide of any one of claim 4, 6 and 7, the method of claim 3 and 7, or the light-responsive affinity tag of any one of claim 5 to 7, wherein said non-natural light-responsive α-amino acid is selected from the group consisting of benzazo-phenylalanine (Baf), p-amino-benzazo-phenylalanine, and p-carboxy-benzazo-phenylalanine, preferably wherein said non-natural light-responsive α- amino acid is Baf.

9. The polypeptide of any one of claims 4 and 6 to 8, the method of any one of claims 3, 7 and 8, or the light-responsive affinity tag of any one of claims 5 to 8, wherein a is 1.

10. The polypeptide of claim 9, the method of claim 9, or the light-responsive affinity tag of claim 9, wherein A comprises one or more natural amino acid(s), preferably wherein A comprises less than about 10 amino acid(s).

11. The polypeptide of claim 9 or 10, the method of claim 9 or 10, or the light-responsive affinity tag of claim 9 or 10, wherein A comprises one or more amino acid(s) selected from the group consisting of Gly, Pro, Ala, and Ser, preferably one or more Gly residue(s).

12. The polypeptide of any one of claims 9 to 11, the method of any one of claims 9 to 11, or the light- responsive affinity tag of any one of claims 9 to 11, wherein A comprises one or two amino acid(s) selected from the group consisting of Gly, Pro, Ala, and Ser, preferably one amino acid.

13. The polypeptide of any one of claims 9 to 12, the method of any one of claims 9 to 12, or the light- responsive affinity tag of any one of claims 9 to 12, wherein A comprises one or two Gly residue(s), preferably one Gly residue.

14. The polypeptide of any one of claims 4 and 6 to 8, the method of any one of claims 3, 7 and 8, or the light-responsive affinity tag of any one of claims 5 to 8, wherein a is 0.

15. The polypeptide of any one of claims 4 and 6 to 14, the method of any one of claims 3 and 7 to 14, or the light-responsive affinity tag of any one of claims 5 to 14, wherein c is 1.

16. The polypeptide of claim 15, the method of claim 15, or the light-responsive affinity tag of claim 15, wherein C comprises one or more natural amino acid(s), preferably C comprises less than about 10 amino acids.

17. The polypeptide of claim 15 or 16, the method of claim 15 or 16, or the light-responsive affinity tag of claim 15 or 16, wherein C comprises one or more amino acid(s) selected from the group consisting of Gly, Pro, Ala, and Ser, preferably one or more Gly residue(s).

18. The polypeptide of any one of claims 15 to 17, the method of any one of claims 15 to 17, or the light- responsive affinity tag of any one of claims 15 to 17, wherein C comprises one or two amino acid(s) selected from the group consisting of Gly, Pro, Ala, and Ser, preferably Gly and Pro.

19. The polypeptide of any one of claims 15 to 18, the method of any one of claims 15 to 18, or the light- responsive affinity tag of any one of claims 15 to 18, wherein C comprises one or two Gly residue(s), preferably one Gly residue.

20. The polypeptide of any one of claims 4 and 6 to 14, the method of any one of claims 3 and 7 to 14, or the light-responsive affinity tag of any one of claims 5 to 14, wherein c is 0.

21. The polypeptide of any one of claims 4 and 6 to 8, the method of any one of claims 3, 7 and 8, or the light-responsive affinity tag of any one of claims 5 to 8, wherein said light-responsive affinity tag consists of 1 to 5 amino acids.

22. The polypeptide of claim 21, the method of claim 21, or the light-responsive affinity tag of claim 21, wherein said light-responsive affinity tag consists of about 4 amino acids.

23. The polypeptide of claim 21, the method of claim 21, or the light-responsive affinity tag of claim 21, wherein said light-responsive affinity tag consists of about 3 amino acids.

24. The polypeptide of claim 21, the method of claim 21, or the light-responsive affinity tag of claim 21, wherein said light-responsive affinity tag consists of about 2 amino acids, preferably wherein said light-responsive affinity tag consists of B-Gly or Gly-B, more preferably wherein said light- responsive affinity tag consists of Baf-Gly or Gly-Baf.

25. The polypeptide of claim 21, the method of claim 21, or the light-responsive affinity tag of claim 21, wherein said light-responsive affinity tag comprises an amino acid sequence selected from the group consisting of B-Gly-Gly, Gly-B-Gly-Gly (SEQ ID NO: 23 to 25), Ala-B-Gly-Gly (SEQ ID NO: 26 to 28), Gly-B-Gly-Pro (SEQ ID NO: 29 to 31), Ala-B-Gly-Pro (SEQ ID NO: 32 to 34), Gly-B-Gly, Ala-B-Gly, Gly-B-Ala, Gly-Gly-B, Gly-Gly-B-Gly (SEQ ID NO: 35 to 37), and Pro-Gly-B-Gly (SEQ ID NO: 38 to 40).

26. The polypeptide of claim 21 or 23, the method of claim 21 or 23, or the light-responsive affinity tag of claim 21 or 23, wherein said light-responsive affinity tag comprises an amino acid sequence consisting of Gly-B-Gly.

27. The polypeptide of claim 21 or 23, the method of claim 21 or 23, or the light-responsive affinity tag of claim 21 or 23, wherein said light-responsive affinity tag comprises an amino acid sequence consisting of Gly-B-Gly, and wherein B is Baf.

28. The polypeptide of any one of claims 7 to 27, the method of any one of claims 7 to 27, or the light- responsive affinity tag of any one of claims 7 to 27, wherein the configuration of B can be switched from the trans-configuration to the cis-configuration by irradiation with a specific wavelength of light, preferably wherein said wavelength of light is selected from one or more wavelength(s) of light from about 310 nm to about 370 nm, more preferably from about 345 nm to about 365 nm, more preferably from about 350 nm to about 355 nm.

29. The polypeptide of any one of claims 7 to 28, the method of any one of claims 7 to 28, or the light- responsive affinity tag of any one of claims 7 to 28, wherein the configuration of B can be switched from the cis-configuration to the trans-configuration by irradiation with a specific wavelength of light, preferably wherein said wavelength of light is selected from one or more wavelength(s) of light from about 405 nm to about 470 nm and / or daylight, preferably from about 420 nm to about 430 nm and / or daylight.

30. The polypeptide of claim 28 or 29, the method of claim 28 or 29, or the light-responsive affinity tag of claim 28 or 29, wherein the switch of said configuration alters its affinity towards α-cyclodextrin.

31. The polypeptide of any one of claims 7 to 30, the method of any one of claims 7 to 30, or the light- responsive affinity tag of any one of claims 7 to 30, wherein when in the trans-configuration, B forms or is capable of forming a complex with α-cyclodextrin, preferably as determined by spectroscopic analysis during titration of B in the trans-configuration with α-cyclodextrin.

32. The polypeptide of any one of claims 7 to 31, the method of any one of claims 7 to 31, or the light- responsive affinity tag of any one of claims 7 to 31, wherein when in the cis-configuration, B does not form a stable complex with α-cyclodextrin, preferably as determined by spectroscopic analysis during titration of B in the cis-configuration with α-cyclodextrin.

33. The polypeptide of any one of claims 7 to 32, the method of any one of claims 7 to 32, or the light- responsive affinity tag of any one of claims 7 to 32, wherein when in the trans-configuration, B comprises an equilibrium dissociation constant (KD) of about or less than about 91 µM ± 5 µM when contacted with α-cyclodextrin, preferably wherein KD is determined by spectroscopic analysis during titration of B in the trans-configuration with α-cyclodextrin.

34. The polypeptide of any one of claims 7 to 33, the method of any one of claims 7 to 33, or the light- responsive affinity tag of any one of claims 7 to 33, wherein when irradiated with visible light having about 405 nm to about 470 nm and / or daylight, at least about 80% of the polypeptide of formula (I) or (II) comprise B in the trans-configuration.

35. The polypeptide of any one of claims 7 to 34, the method of any one of claims 7 to 34, or the light- responsive affinity tag of any one of claims 7 to 34, wherein when irradiated with visible light having about 405 nm to about 470 nm and / or daylight for about or less than about 30 min, at least about 80% of said light-responsive affinity tag comprise B in the trans-configuration which is maintained for at least about 60 min under daylight or in the dark.

36. The polypeptide of any one of claims 7 to 35, the method of any one of claims 7 to 35, or the light- responsive affinity tag of any one of claims 7 to 35, wherein when irradiated with UV light having about 310 nm to about 370 nm, at least about 90% of said light-responsive affinity tag comprise B inthe cis-configuration.

37. The polypeptide of any one of claims 7 to 36, the method of any one of claims 7 to 36, or the light- responsive affinity tag of any one of claims 7 to 36, wherein when irradiated with UV light having about 310 nm to about 370 nm for about or less than about 30 min and subsequently not irradiated with visible light, at least about 90% of said light-responsive affinity tag comprise B in the cis- configuration which is maintained for at least about 60 min in the dark.

38. The polypeptide o of any one of claims 7 to 37, or the method of any one of claims 7 to 37, wherein P is selected from the group consisting of an oligopeptide, a polypeptide, a protein, an immunoglobulin or an antigen-binding fragment thereof, a binding protein, a growth factor, a signaling protein, an enzyme, and / or a complex thereof, optionally, wherein said polypeptide further comprises a signal peptide, preferably wherein said signal peptide is selected from the group consisting of OmpA, OmpF, PhoA, MalE, PelB, stII, DsbC.

39. The polypeptide of any one of claims 4 and 6 to 38, or the method of any one of claims 2, 3 and 7 to 38, wherein l is 1.

40. The polypeptide of claim 39, or the method of claim 39, wherein L comprises an amino acid sequence selected from the group consisting of the following: Glu-Asn-Leu-Tyr-Phe-Gln-Ser-Gly (SEQ ID NO: 41), Glu-Asn-Leu-Tyr-Phe-Gln-Ser-Ala (SEQ ID NO: 42), Leu-Val-Pro-Arg-Gly-Ser (SEQ ID NO: 43), Ile-Glu-Gly-Arg (SEQ ID NO: 44), Leu-Glu-Val-Leu-Phe-Gln-Gly-Pro (SEQ ID NO: 45).

41. The polypeptide of claim 39, or the method of claim 39, wherein L is a cleavable linker, preferably wherein L comprises a cleavable amino acid sequence selected from the group consisting of the following: Tobacco Etch Virus (TEV) protease, thrombin, factor Xa, human rhinovirus type 143C protease (HRV 3C).

42. The polypeptide of any one of claims 4 and 6 to 38, or the method of any one of claims 2, 3 and 7 to 38, wherein l is 0.

43. The method of any one of claims 2, 3 and 7 to 42, wherein during step (a) said N-terminal or C- terminal light-responsive affinity tag is irradiated with a wavelength of light that is capable of switching the configuration of said non-natural light-responsive α-amino acid from the cis- configuration to the trans-configuration, preferably wherein said wavelength of light is selected fromone or more wavelength(s) of light from about 405 nm to about 470 nm and / or daylight, preferably from about 410 nm to about 440 nm, more preferably from about 420 nm to about 430 nm and / or daylight.

44. The method of any one of claims 2, 3 and 7 to 43, wherein during step (a) said N-terminal or C- terminal light-responsive affinity tag is not irradiated with light, and / or wherein during step (b) said N-terminal or C-terminal light-responsive affinity tag is irradiated with a wavelength of light that changes said non-natural light-responsive α-amino acid to a second configuration for about or less than about 30 min and subsequently is not irradiated with light.

45. The method of any one of claims 2, 3 and 7 to 44, wherein said solid phase comprises α-cyclodextrin groups, and wherein said solid phase further comprises a structural matrix, preferably wherein said structural matrix is selected from the group consisting of agarose, a cross-linked form of agarose, cellulose, starch, dextran, polymethacrylate, polystyrene, polyacrylamide, and silica gel, more preferably agarose or a cross-linked form of agarose, preferably wherein said structural matrix is transparent or translucent.

46. The method of claim 45, wherein said α-cyclodextrin is covalently linked to said structural matrix, optionally wherein said α-cyclodextrin is covalently linked to said structural matrix via a linker, preferably wherein said linker is derived from 1,4-bis(2,3-epoxypropoxy)butane, 1-chloro- acetylchloride, or cyanogen bromide, preferably from 1,4-bis(2,3-epoxypropoxy)butane.

47. A solid phase comprising α-cyclodextrin groups, wherein said solid phase further comprises agarose or a cross-linked form of agarose as a structural matrix covalently linked to said α-cyclodextrin via a linker derived from 1,4-bis(2,3-epoxypropoxy)butane, preferably wherein said structural matrix is transparent or translucent.

48. The method of claim 45 or 46, or the solid phase of claim 47, wherein said solid phase is a matrix, a hydrogel, a bead, a chip, a glass surface, a plastic surface, a gold surface, a silver surface, or a plate such as a microtiter well plate, preferably wherein said matrix, said hydrogel, or said bead is the affinity matrix of an affinity chromatography column.

49. A method for cleaving the light-responsive affinity tag from the polypeptide of interest of claim 41, wherein the method comprises the steps of: (a) cleaving said cleavable linker; and (b) purifying the polypeptide of interest,optionally wherein the step of cleaving said cleavable linker comprises contacting said cleavable linker with a cleaving reagent, preferably wherein said cleaving reagent is selected from the group consisting of one or more enzyme(s), preferably Tobacco Etch Virus (TEV) protease, thrombin, factor Xa, human rhinovirus type 143C protease (HRV 3C) preferably TEV protease.

50. A nucleic acid molecule encoding the polypeptide comprising the N-terminal or the C-terminal light- responsive affinity tag of any one of claims 4 and 6 to 42, or encoding the light-responsive affinity tag of any one of claims 7 to 37.

51. The nucleic acid molecule of claim 50, wherein B is encoded by a stop codon, preferably wherein said stop codon is selected from the group consisting of UAG, UGA, and UAA, more preferably UAG.

52. The nucleic acid molecule of claim 50 or 51 encoding said polypeptide comprising the N-terminal, wherein the nucleic acid sequence encoding for P is replaced with a multiple cloning site.

53. A nucleic acid vector comprising the nucleic acid molecule of any one of claims 50 to 52, preferably wherein said nucleic acid vector further comprises one or more nucleic acid sequence(s) encoding one or more selected from the group consisting of the following: (a) an aminoacyl tRNA synthetase (aaRS); (b) a suppressor tRNA; and (c) an antibiotic selection marker, optionally wherein said nucleic acid molecule encoding the aaRS is selected from the group consisting of the following: (i) a nucleic acid molecule comprising a nucleic acid sequence of SEQ ID NO: 60 to SEQ ID NO: 67; (ii) a nucleic acid molecule that hybridizes with a nucleic acid molecule comprising a nucleic acid sequence complementary to the nucleotide sequence of SEQ ID NO: 60 to SEQ ID NO: 67 and that encodes a polypeptide with aaRS activity; (iii) a nucleic acid molecule encoding a polypeptide comprising an amino acid sequence of SEQ ID NO: 15 to SEQ ID NO: 22; (iv) a nucleic acid molecule encoding a polypeptide comprising an amino acid sequence of SEQ ID NO: 15 to SEQ ID NO: 22 with a deletion, substitution, insertion, and / or addition of one or more amino acid(s), and wherein said polypeptide comprises aaRS activity; and (v) a nucleic acid molecule encoding a polypeptide comprising an amino acid sequence with at least about 80% amino acid sequence identity to the amino acid sequence of SEQ ID NO: 15 to SEQ ID NO: 22, and wherein said polypeptide comprises aaRS activity, andoptionally wherein said nucleic acid molecule encoding the suppressor tRNA is selected from the group consisting of the following: (A) a nucleic acid molecule comprising a nucleic acid sequence of SEQ ID NO: 70; and (B) a nucleic acid molecule that hybridizes with a nucleic acid molecule comprising a nucleic acid sequence complementary to the nucleotide sequence of SEQ ID NO: 70 and that encodes a suppressor tRNA, wherein said suppressor tRNA forms or is capable of forming a cloverleaf structure and comprises an anticodon, and wherein said anticodon is complementary to a stop codon selected from the group consisting of UAG, UGA, and UAA, preferably UAG, and optionally wherein said nucleic acid vector comprises a nucleic acid sequence of SEQ ID NO: 68,SEQ ID NO: 69, SEQ ID NO: 72 or SEQ ID NO:

73.

54. A host cell or a host comprising the nucleic acid molecule of any one of claims 50 to 52, and / or the nucleic acid vector of claim 53, optionally wherein said host cell or said host is prokaryotic, preferably wherein said host cell or said host is selected from the group consisting of Escherichia coli (E. coli), Bacillus subtilis, Corynebacterium glutamicum and Pseudomonas fluorescens, preferably E. coli, optionally wherein said host cell or said host is an E. coli B strain or an E. coli K12 strain, preferably an E. coli B strain, optionally wherein said E. coli B strain is NEBExpress.

55. The host cell or the host of claim 54, wherein said host cell or said host does not encode a functional ribosomal release factor 1 (RF1 alias PrfA) or is a RF1 knockdown strain that expresses a functional RF1, and preferably wherein said host cell or said host does not encode a functional maltose binding protein (MBP) or is a MBP knockdown strain.

56. An aminoacyl tRNA synthetase (aaRS) with substrate specificity for benzazo-phenylalanine or a derivative thereof, wherein said aaRS is characterized in that: it comprises enzymatic activity for charging a cognate suppressor tRNA with benzazo- phenylalanine (Baf) or a derivate thereof, preferably wherein said derivate is a non-natural light- responsive α-amino acid selected from the group consisting of p-amino-benzazo-phenylalanine and p-carboxy-benzazo-phenylalanine, and it comprises an amino acid sequence with at least 95% amino acid sequence identity to SEQ ID NO: 14, wherein: (a) the amino acid at position 295 in the amino acid sequence of SEQ ID NO: 14 or a position corresponding to this position is substituted with an amino acid selected from the group consisting of L and R; (b) the amino acid at position 304 in the amino acid sequence of SEQ ID NO: 14 or a position corresponding to this position is substituted with an amino acid selected from the group consisting of S; and / or(c) the amino acid at position 346 in the amino acid sequence of SEQ ID NO: 14 or a position corresponding to this position is substituted with an amino acid selected from the group consisting of A, preferably wherein said aaRS further comprises one or more deletion(s), substitution(s), insertion(s), and / or addition(s) of one or more amino acid(s), and wherein: (i) the amino acid at position 295 in the amino acid sequence of SEQ ID NO: 14 or a position corresponding to this position is substituted with an amino acid selected from the group consisting of L and R; (ii) the amino acid at position 304 in the amino acid sequence of SEQ ID NO: 14 or a position corresponding to this position is substituted with an amino acid selected from the group consisting of S; and / or (iii) the amino acid at position 346 in the amino acid sequence of SEQ ID NO: 14 or a position corresponding to this position is substituted with an amino acid selected from the group consisting of A.

57. A nucleic acid molecule encoding the aaRS of claim 56, optionally (a) a nucleic acid molecule comprising a nucleic acid sequence of SEQ ID NO: 60 to SEQ ID NO: 67; and (b) a nucleic acid molecule that hybridizes with a nucleic acid molecule comprising a nucleic acid sequence complementary to the nucleotide sequence of SEQ ID NO: 60 to SEQ ID NO: 67 and that encodes a polypeptide with aaRS activity..

58. A nucleic acid vector comprising the nucleic acid molecule of claim 57, preferably wherein said nucleic acid vector further comprises a suppressor tRNA, and wherein said suppressor tRNA forms a suitable orthogonal tRNA / aaRS pair with said aaRS, optionally wherein expression of said aaRS is inducible.

59. A host cell or a host comprising the aaRS of claim 56, the nucleic acid molecule of claim 57, and / or the nucleic acid vector claim 58.

60. A method for the recombinant expression and / or the recombinant production of a polypeptide of comprising a non-natural light-responsive α-amino acid, wherein said method comprises the recombinant expression of a polypeptide comprising a non-natural light-responsive α-amino acid in the presence of the aaRS of claim 56, a cognate suppressor tRNA, and a non-natural light-responsive α-amino acid.

61. A kit comprising one or more selected from the group consisting of the following (a) to (e); wherein(a) is selected from one or more of the group consisting of the following (a1) to (a6): (a1) the polypeptide comprising the N-terminal or C-terminal light-responsive affinity tag of any one of claims 4 and 6 to 42, (a2) the nucleic acid molecule of any one of claims 50 to 52 encoding the polypeptide of claims 4 and 6 to 42, (a3) the nucleic acid vector of claim 53 encoding the polypeptide of claims 4 and 6 to 42, (a4) the light-responsive affinity tag of any one of claims 5 to 37, (a5) the nucleic acid molecule of claim 50 to 51 encoding the light-responsive affinity tag of any one of claims 5 to 37, (a6) the nucleic acid of claim 53 encoding the light-responsive affinity tag of any one of claims 5 to 37; (b) is selected from one or more of the group consisting of the following (b1) to (b3): (b1) the aaRS of claim 56, (b2) the nucleic acid molecule of claim 57, (b3) the nucleic acid vector of any one of claim 58; (c) is selected from one or more of the group consisting of the following (c1) to (c3): (c1) a cognate suppressor tRNA, preferably wherein said suppressor tRNA is selected from the group consisting of: (i) a nucleic acid molecule comprising a nucleic acid sequence of SEQ ID NO: 70; and (ii) a nucleic acid molecule that hybridizes with a nucleic acid molecule comprising a nucleic acid sequence complementary to the nucleotide sequence of SEQ ID NO: 70 and that encodes a suppressor tRNA, wherein said suppressor tRNA forms a cloverleaf structure and comprises an anticodon, (c2) a nucleic acid molecule encoding the suppressor tRNA of (c1), (c3) a nucleic acid vector comprising the nucleic acid molecule of (c2); (d) is a host cell selected from one or more of the group consisting of (d1) to (d2): (d1) a host cell for the recombinant expression of the herein above provided polypeptide comprising the N-terminal or C-terminal light-responsive affinity tag, wherein said host cell comprises or harbors the herein above provided nucleic acid molecule of (a2), (b2), and / or (c2) and / or the herein above provided nucleic acid vector of (a3), (b3), and / or (c3), (d2) a host cell for the recombinant expression of the herein above provided light-responsive affinity tag, wherein said host cell comprises or harbors the herein above provided nucleic acid molecule of (a5), (b2), and / or (c2) and / or the herein above provided nucleic acid vector of (a6), (b3), and / or (c3); (e) is selected from one or more of the group consisting of the following (e1) to (e3): (e1) benzazo-phenylalanine (Baf),(e2) p-amino-benzazo-phenylalanine, and (e3) p-carboxy-benzazo-phenylalanine; and (f) is the solid phase of claim 47 or 48.

62. The kit of claim 61, wherein said kit comprises one or more selected from the group defined as (a1) to (a3) in claim 61, preferably wherein said kit further comprises one or more selected from the group defined as (b) to (f) in claim 61, even more preferably wherein said kit comprises (b), (c), (d1), (e), and (f) in claim 61.

63. The kit of claim 61, wherein said kit comprises one or more selected from the group defined as (a4) to (a6), preferably wherein said kit further comprises one or more selected from the group defined as (b) to (f) in claim 61, even more preferably wherein said kit comprises (b), (c), (d2), (e), and (f) in claim 61.

64. The kit of claim 61 to 63, wherein said kit further comprises a UV light source, preferably one or more LED light sources emitting one or more wavelength(s) of light selected from one or more wavelength(s) of light from about 310 nm to about 370 nm, more preferably from about 345 nm to about 365 nm, more preferably from about 350 nm to about 355 nm and, optionally, a second light source, preferably wherein said second light source is selected from one or more LED light sources emitting one or more wavelength(s) of light from about 405 nm to about 470 nm, preferably from about 420 nm to about 430 nm.

65. Use of the kit of any one of claims 61 to 64, the polypeptide comprising the N-terminal or the C- terminal light-responsive affinity tag of any one of claim 4 or 6 to 42, and / or the light-responsive affinity tag of any one of claims 5 to 37 in an in vitro or an in vivo assay, preferably wherein said in vitro or said in vivo assay is a binding assay, an enzyme assay, and / or a cell culture assay.