Beta-1,3-n-acetylglucosaminyltransferase mutants

Abstract

The present invention is in the technical field of synthetic biology, metabolic engineering and cell cultivation. The invention describes advantageous mutants of a reference beta beta-1,3-N- acetylglucosaminyltransferase represented by SEQ ID NO 01, as well as a cell comprising said mutant beta- 1,3-N-acetylglucosaminyltransferase. The invention further describes methods for the production of a lacto-N-triose II (LN3)-containing oligosaccharide or a mixture comprising at least two different LN3- containing oligosaccharides, wherein a beta-1,3-N-acetylglucosaminyltransferase mutant is used (optionally present in a cell).

Description

[0001]Beta-1,3-N-acetylglucosaminyltransferase mutantsField of the invention The present invention is in the technical field of synthetic biology, metabolic engineering and cell cultivation. The invention describes advantageous mutants of a reference beta beta-1,3-N- acetylglucosaminyltransferase represented by SEQ ID NO 01, as well as a cell comprising said mutant beta- 1,3-N-acetylglucosaminyltransferase. The invention further describes methods for the production of a lacto-N-triose II (LN3)-containing oligosaccharide or a mixture comprising at least two different LN3- containing oligosaccharides, wherein a beta-1,3-N-acetylglucosaminyltransferase mutant is used (optionally present in a cell). Background of the invention To date oligosaccharides are gaining more and more attention as these diverse molecules exert a range of important biological activities and are widely distributed in all living organisms. An example of such oligosaccharides are the milk oligosaccharides (MOs) (Usashima T. et al., 2011, Nova Biomedical Books, New York ISBN 978-1-61122-831-1). These oligosaccharides play important roles in a variety of normal physiological and pathological processes, such as cell metastasis, signal transduction, intercellular adhesion, inflammation and immune response. An example of such saccharides are milk saccharides (Urashima T. et al., 2011, Milk Oligosaccharides, Nova Biomedical Books, New York ISBN 978-1-61122- 831-1; Coppa et al, 2013, Ital. J. Pediatr. 2013, 39(2)), in particular milk oligosaccharides (MOs), i.e. (oligo)saccharides which are found in milk of animals such as mammals and humans (Urashima et al, 2011; Coppa et al, 2013). A replete amount of milk saccharide structures have been elucidated so far. The majority of milk oligosaccharides found in animals such as mammals and humans comprise lactose at the reducing end (Urashima et al, 2011). Other milk oligosaccharides comprise N-acetyllactosamine (Gal-β1,4-GlcNAc) or lacto-N-biose (Gal-β1,3-GlcNAc) at the reducing end (Urashima et al, 2011; Wrigglesworth etal, 2020, PLoS ONE 15(12); Urashima et al, 2013, Biosci. Biotechnol. Biochem 77(3): p.455-466; Wei et al, 2018, Sci. Rep. 8:4688). Examples hereof are 3-FLN (Gal-β1,4-(Fuc-α1,3-)GlcNAc; also known as Lewis xantigen), 3’-SLN (Neu5Ac-α2,3-Gal-β1,4-GlcNAc), 6’-SLN (Neu5Ac-α2,6-Gal-β1,4-GlcNAc) (Urashima et al,2011; Wrigglesworth et al, 2020; Wei et al, 2018). Such milk, more specifically, human milk is to date considered as the best food for newborns and infants. It is composed of several fractions of which milk oligosaccharides are the fourth largest fraction. Besides lactose, human milk, as well as milk of other mammals, contains various structurally diverse oligosaccharides which are also known as human milk oligosaccharides (HMOs) or mammalian milk oligosaccharides (MMOs), respectively (Urashima T. et al., 2011). The importance of MOs for mammalian and human infant nutrition is directly linked to their biological activities including protection of the neonate from pathogens, supporting development of the infant’s immune system and cognitive abilities. HMOs and MMOs are further known to act as decoys to reduce the risk of infections by bacterial and viral pathogens which adhere to human cells by binding to these cells’ surface glycoproteins. Additionally, various HMOs and MMOs possess an anti-inflammatory effect and act as immunomodulators (e.g. reducing the risk of developing food allergies). Altogether, these beneficial effects make milk oligosaccharides, especially mammalian (MMOs) and human milk oligosaccharides (HMOs), attractive components in the nutritional industry for the production of infant formulas or as dietary supplements for children and adults. In efforts to improve the nutritional value of infant formula and expand the use of mammalian and human milk oligosaccharides, there has been an increased interest in the synthetic production of thesecompounds. The enzyme beta-1,3-N-acetylglucosaminyltransferase (e.g. LgtA) is involved in thebiosynthetic pathway of a wide variety of (human / mammalian) milk oligosaccharides. It transfers a N- acetylglucosamine to a galactose of a suitable acceptor saccharide as well known to the skilled person. Unfortunately, the beta-1,3-N-acetylglucosaminyltransferase typically generates unwanted byproducts, including conversion of a desired (human / mammalian) milk oligosaccharide into a longer-chain oligosaccharide, which both decreases product purity and reduces overall yield. It is hence an object of the present invention to provide a beta-1,3-N-acetylglucosaminyltransferase mutant that reduces theproduction of unwanted byproducts (i.e. increased substrate specificity). Alternative beta-1,3-N-acetylglucosaminyltransferase mutants have been described in WO2022 / 133093. While these mutants produce less unwanted byproducts, they generally suffer from a significant reduction in their enzymatic activity, resulting in a much lower amount of the desired (human / mammalian) milk oligosaccharide compared to the unmutated, i.e. reference beta-1,3-N-acetylglucosaminyltransferase. It is hence anotherobject of the present invention to enhance the enzymatic activity of reference beta-1,3-N-acetylglucosaminyltranserases or beta-1,3-N-acetylglucosaminyltranserase mutants having an increasedsubstrate specificity to yield higher amounts of the desired (human / mammalian) milk oligosaccharide.Summary of the inventionIn a first aspect, the invention provides a beta-1,3-N-acetylglucosaminyltransferase mutant comprising anamino acid sequence that differs from the full-length amino acid sequence of a reference beta-1,3-N- acetylglucosaminyltransferase represented by SEQ ID NO 01 in at least one or more non-conservativeamino acid substitutions at 1-363 of SEQ ID NO 01. Said mutant surprisingly has an improved activityand / or specificity compared to the reference beta-1,3-N-acetylglucosaminyltransferase.In a second aspect, the invention provides a nucleic acid encoding the beta-1,3-N-acetylglucosaminyltransferase mutant according to the first aspect of the invention.In a third aspect, the invention provides a cell that comprises a beta-1,3-N-acetylglucosaminyltransferasemutant according to the first aspect of the invention and / or that comprises a nucleic acid according to the second aspect of the invention.In a fourth aspect, the invention provides a method for the production of a lacto-N-triose II (LN3)-containing oligosaccharide or a mixture comprising at least two different LN3-containing oligosaccharides, wherein a beta-1,3-N-acetylglucosaminyltransferase mutant according to the first aspect is provided or wherein a cell according to the third aspect of the invention is provided. Detailed description of the invention Beta-1,3-N-acetylglucosaminyltransferase mutantIn a first aspect, the invention provides a beta-1,3-N-acetylglucosaminyltransferase mutant comprising anamino acid sequence that differs from the full-length amino acid sequence of a reference beta-1,3-N- acetylglucosaminyltransferase represented by SEQ ID NO 01 in at least one or more non-conservativeamino acid substitutions at 1-363 (preferably at 17-363, more preferably at 17-349, even more preferablyat 89-349, even more preferably at 171-349, most preferably at 180-349) of SEQ ID NO 01; preferablydiffers from the full-length amino acid sequence of a reference beta-1,3-N-acetylglucosaminyltransferase represented by SEQ ID NO 01 in one or more non-conservative amino acid substitutions at 1-301 (preferably at 17-301, more preferably at 89-301, even more preferably at 171-301, even more preferably at 180-301, most preferably at 180-298) of SEQ ID NO 01 and / or one or more non-conservative amino acid substitutions at 302-363 (preferably at 302-349 or at 321-363, more preferably at 321-349) of SEQ ID NO 01. Optionally said amino acid sequence of the beta-1,3-N-acetylglucosaminyltransferase mutant further differs in one or more conservative amino acid substitutions at 1-363 (preferably at 17-363, morepreferably at 17-349) of SEQ ID NO 01. Alternatively or additionally, said amino acid sequence of the beta-1,3-N-acetylglucosaminyltransferase mutant optionally further differs in one or more amino acids missingat 1-363, preferably at 340-349, of SEQ ID NO 01.Throughout the application and claims, the expression “one or more” is interchangeably used with “at least one”. Throughout the application and claims, the expression “one or more non-conservative amino acid substitutions” is preferably replaced with “1-12 non-conservative amino acid substitutions”, more preferably replaced with “1-10 non-conservative amino acid substitutions”, even more preferably replaced with “1-8 non-conservative amino acid substitutions”, most preferably replaced with “1-6 non- conservative amino acid substitutions”. Throughout the application and claims, the expression “one or more conservative amino acid substitutions” is preferably replaced with “1-40 conservative amino acid substitutions”, more preferably replaced with “1-30 conservative amino acid substitutions”, even more preferably replaced with “1-20 conservative amino acid substitutions”, most preferably replaced with “1-10 conservative amino acid substitutions”. For the sake of clarity, throughout the application and claims,the expression “x-y” refers to a range from and including x to and including y. For example, 1-10 non- conservative amino acid substitutions means that 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10 non-conservative amino acid substitutions are present.In a preferred embodiment, the beta-1,3-N-acetylglucosaminyltransferase mutant comprises an aminoacid sequence that differs from the full-length amino acid sequence of a reference beta-1,3-N- acetylglucosaminyltransferase represented by SEQ ID NO 01 in at least: (i) one or more non-conservative amino acid substitutions at 302-363 (preferably at 302-349 orat 321-363, more preferably at 321-349) of SEQ ID NO 01; and (ii) optionally:- one or more non-conservative amino acid substitutions at 1-301 (preferably at 17-301,more preferably at 89-301, even more preferably at 171-301, even more preferably at 180-301, most preferably at 180-298) of SEQ ID NO 01. In an alternative preferred embodiment, the beta-1,3-N-acetylglucosaminyltransferase mutant comprises an amino acid sequence that differs from the full-length amino acid sequence of a reference beta-1,3-N- acetylglucosaminyltransferase represented by SEQ ID NO 01 in at least: (i) one or more non-conservative amino acid substitutions at 1-301 (preferably at 17-301, morepreferably at 89-301, even more preferably at 171-301, even more preferably at 180-301, most preferably at 180-298) of SEQ ID NO 01; and (ii) optionally:- one or more non-conservative amino acid substitutions at 302-363 (preferably at 302-349or at 321-363, more preferably at 321-349) of SEQ ID NO 01. In a more preferred embodiment, the beta-1,3-N-acetylglucosaminyltransferase mutant comprises an amino acid sequence that differs from the full-length amino acid sequence of a reference beta-1,3-N- acetylglucosaminyltransferase represented by SEQ ID NO 01 in at least: (i) one or more non-conservative amino acid substitutions at 302-363 (preferably at 302-349 orat 321-363, more preferably at 321-349) of SEQ ID NO 01; and (ii) optionally:- one or more non-conservative amino acid substitutions at 1-301 (preferably at 17-301,more preferably at 89-301, even more preferably at 171-301, even more preferably at 180-301, most preferably at 180-298) of SEQ ID NO 01; and / or -one or more conservative amino acid substitutions at 1-363 (preferably at 17-363, morepreferably at 17-349) of SEQ ID NO 01. In an alternative more preferred embodiment, the beta-1,3-N-acetylglucosaminyltransferase mutant comprises an amino acid sequence that differs from the full-length amino acid sequence of a reference beta-1,3-N-acetylglucosaminyltransferase represented by SEQ ID NO 01 in at least: (i) one or more non-conservative amino acid substitutions at 1-301 (preferably at 17-301, morepreferably at 89-301, even more preferably at 171-301, even more preferably at 180-301, most preferably at 180-298) of SEQ ID NO 01; and (ii) optionally:- one or more non-conservative amino acid substitutions at 302-363 (preferably at 302-349or at 321-363, more preferably at 321-349) of SEQ ID NO 01; and / or -one or more conservative amino acid substitutions at 1-363 (preferably at 17-363, morepreferably at 17-349) of SEQ ID NO 01.In an even more preferred embodiment, the beta-1,3-N-acetylglucosaminyltransferase mutant comprises an amino acid sequence that differs from the full-length amino acid sequence of a reference beta-1,3-N- acetylglucosaminyltransferase represented by SEQ ID NO 01 in at least: (i) one or more non-conservative amino acid substitutions at 302-363 (preferably at 302-349 orat 321-363, more preferably at 321-349) of SEQ ID NO 01; and (ii) optionally:- one or more non-conservative amino acid substitutions at 1-301 (preferably at 17-301,more preferably at 89-301, even more preferably at 171-301, even more preferably at 180-301, most preferably at 180-298) of SEQ ID NO 01; and / or -one or more conservative amino acid substitutions at 1-363 (preferably at 17-363, morepreferably at 17-349) of SEQ ID NO 01; and / or -one or more amino acids missing at 1-363, preferably at 340-349, of SEQ ID NO 01,preferably missing amino acids 340-349 of SEQ ID NO 01. In an alternative even more preferred embodiment, the beta-1,3-N-acetylglucosaminyltransferase mutant comprises an amino acid sequence that differs from the full-length amino acid sequence of areference beta-1,3-N-acetylglucosaminyltransferase represented by SEQ ID NO 01 in at least:(i) one or more non-conservative amino acid substitutions at 1-301 (preferably at 17-301, morepreferably at 89-301, even more preferably at 171-301, even more preferably at 180-301, most preferably at 180-298) of SEQ ID NO 01; and (ii) optionally:- one or more non-conservative amino acid substitutions at 302-363 (preferably at 302-349or at 321-363, more preferably at 321-349) of SEQ ID NO 01; and / or -one or more conservative amino acid substitutions at 1-363 (preferably at 17-363, morepreferably at 17-349) of SEQ ID NO 01; and / or- one or more amino acids missing at 1-363, preferably at 340-349, of SEQ ID NO 01,preferably missing amino acids 340-349 of SEQ ID NO 01. In an even more preferred embodiment, the beta-1,3-N-acetylglucosaminyltransferase mutant comprises an amino acid sequence that differs from the full-length amino acid sequence of a reference beta-1,3-N-acetylglucosaminyltransferase represented by SEQ ID NO 01 in at least:(i) one or more non-conservative amino acid substitutions at 302-363 (preferably at 302-349 orat 321-363, more preferably at 321-349) of SEQ ID NO 01; and (ii) one or more non-conservative amino acid substitutions at 1-301 (preferably at 17-301, morepreferably at 89-301, even more preferably at 171-301, even more preferably at 180-301, most preferably at 180-298) of SEQ ID NO 01.In an even more preferred embodiment, the beta-1,3-N-acetylglucosaminyltransferase mutant comprisesan amino acid sequence that differs from the full-length amino acid sequence of a reference beta-1,3-N- acetylglucosaminyltransferase represented by SEQ ID NO 01 in at least: (i) one or more non-conservative amino acid substitutions at 302-363 (preferably at 302-349 orat 321-363, more preferably at 321-349) of SEQ ID NO 01; and (ii) one or more non-conservative amino acid substitutions at 1-301 (preferably at 17-301, morepreferably at 89-301, even more preferably at 171-301, even more preferably at 180-301, most preferably at 180-298) of SEQ ID NO 01; and (iii) optionally:- one or more conservative amino acid substitutions at 1-363 (preferably at 17-363, morepreferably at 17-349) of SEQ ID NO 01; and / or -one or more amino acids missing at 1-363, preferably at 340-349, of SEQ ID NO 01,preferably missing amino acids 340-349 of SEQ ID NO 01. In a most preferred embodiment, the beta-1,3-N-acetylglucosaminyltransferase mutant comprises an amino acid sequence that differs from the full-length amino acid sequence of a reference beta-1,3-N- acetylglucosaminyltransferase represented by SEQ ID NO 01 in at least: (i) one or more non-conservative amino acid substitutions at 302-363 (preferably at 302-349 orat 321-363, more preferably at 321-349) of SEQ ID NO 01; and (ii) one or more non-conservative amino acid substitutions at 1-301 (preferably at 17-301, morepreferably at 89-301, even more preferably at 171-301, even more preferably at 180-301, most preferably at 180-298) of SEQ ID NO 01; and (iii) optionally:- one or more conservative amino acid substitutions at 1-363 (preferably at 17-363, more preferably at 17-349) of SEQ ID NO 01.Throughout the application and claims, it is particularly preferred to replace the expression “differs in atleast” by the expression “only differs in”. In other words, each embodiment disclosed throughout theapplication and claims reciting the wording “differs in at least”, i.e. indicating that additional differencesmay be present in addition to those explicitly recited in the embodiment, is preferably replaced with thesame embodiment but wherein the differences are restricted to those explicitly recited in the original embodiment (i.e. by changing the wording “differs in at least” into “only differs in”). For example, an explicitly recited embodiment discloses that the beta-1,3-N-acetylglucosaminyltransferase mutant comprises an amino acid sequence that differs from the full-length amino acid sequence of a reference beta-1,3-N-acetylglucosaminyltransferase represented by SEQ ID NO 01 in at least: (i) one or more non-conservative amino acid substitutions at 302-363 (preferably at 302-349 orat 321-363, more preferably at 321-349) of SEQ ID NO 01; and (ii) optionally:- one or more non-conservative amino acid substitutions at 1-301 (preferably at 17-301,more preferably at 89-301, even more preferably at 171-301, even more preferably at 180-301, most preferably at 180-298) of SEQ ID NO 01; and / or -one or more conservative amino acid substitutions at 1-363 (preferably at 17-363, morepreferably at 17-349) of SEQ ID NO 01; and / or -one or more amino acids missing at 1-363, preferably at 340-349, of SEQ ID NO 01,preferably missing amino acids 340-349 of SEQ ID NO 01. In this embodiment, the amino acid sequence of the mutant comprises one or more non-conservative amino acid substitutions at 302-363 of SEQ ID NO 01. Optionally, said amino acid sequence further differs from SEQ ID NO 01. This can be due to one or more of the optional features and / or due to one or more other features not explicitly recited in the embodiment. As it is preferred throughout the application and claims, to replace “differs in at least” into “only differs in”, this embodiment is preferably replaced with an embodiment disclosing that the beta-1,3-N-acetylglucosaminyltransferase mutant comprises an amino acid sequence that only differs from the full-length amino acid sequence of a reference beta-1,3-N- acetylglucosaminyltransferase represented by SEQ ID NO 01 in: (i) one or more non-conservative amino acid substitutions at 302-363 (preferably at 302-349 orat 321-363, more preferably at 321-349) of SEQ ID NO 01; and (ii) optionally:- one or more non-conservative amino acid substitutions at 1-301 (preferably at 17-301,more preferably at 89-301, even more preferably at 171-301, even more preferably at 180-301, most preferably at 180-298) of SEQ ID NO 01; and / or -one or more conservative amino acid substitutions at 1-363 (preferably at 17-363, more preferably at 17-349) of SEQ ID NO 01; and / or -one or more amino acids missing at 1-363, preferably at 340-349, of SEQ ID NO 01,preferably missing amino acids 340-349 of SEQ ID NO 01. Hence, this new embodiment is also explicitly and unambiguously disclosed in the application as filed as well as each “only differs in” variant of embodiments with the wording “differs in at least”. The amino acid sequence of the mutant in the exemplary new embodiment differs from the reference in one or more non-conservative amino acid substitutions at 302-363 of SEQ ID NO 01 and optionally one or more of the three features enlisted under (ii). Further differences are excluded due to the wording “only differs in”. The feature “beta-1,3-N-acetylglucosaminyltransferase mutant“ is preferably as described in the Section “Mutant beta-1,3-N-acetylglucosaminyltransferase“. The feature “reference beta-1,3-N-acetylglucosaminyltransferase“ is preferably as described in the Section “Reference beta-1,3-N-acetylglucosaminyltransferase“. The feature “non-conservative amino acid substitutions at 302-363 of SEQ ID NO 01“ is preferably asdescribed in the Section “Non-conservative amino acid substitution(s) at 302-363“.The feature “non-conservative amino acid substitutions at 1-301 of SEQ ID NO 01“ is preferably asdescribed in the Section “Non-conservative amino acid substitution(s) at 1-301“.The feature “conservative amino acid substitutions at 1-363 of SEQ ID NO 01 “ is preferably as describedin the Section “Conservative amino acid substitution(s) at 1-363“.The feature “amino acids missing at 1-363 of SEQ ID NO 01” is preferably as described in the Section“Amino acid(s) missing at 1-363“. Reference beta-1,3-N-acetylglucosaminyltransferaseIn an embodiment of the first aspect of the invention, the full-length amino acid sequence of the referencebeta-1,3-N-acetylglucosaminyltransferase is represented by SEQ ID NO 01. In a preferred embodiment, said reference beta-1,3-N-acetylglucosaminyltransferase is capable to transfer a N-acetylglucosamine (GlcNAc) from a suitable donor (preferably UDP-GlcNAc) to a suitableacceptor saccharide (preferably lactose) in a beta-1,3-linkage. In other words, it is preferred that saidreference beta-1,3-N-acetylglucosaminyltransferase is active. Said acceptor saccharide preferablycontains (i) a galactose at its non-reducing end and / or (ii) a GlcNAc-beta-1,6-galactose at its non-reducingend; more preferably said acceptor saccharide comprises lactose or GlcnAc-beta-1,6-lactose, optionallysaid acceptor saccharide further comprises one or more monosaccharides (preferably selected from the list consisting of fucose, N-acetylglucosamine and galactose); even more preferably said acceptor saccharide is lactose, GlcnAc-beta-1,6-lactose, LNT or LNnT, even more preferably said acceptorsaccharide is lactose or GlcnAc-beta-1,6-lactose, most preferably said acceptor saccharide is lactose. Thereference beta-1,3-N-acetylglucosaminyltransferase is preferable capable to transfer a GlcNAc from asuitable donor (preferably UDP-GlcNAc) to a galactose of said acceptor saccharide (preferably whereinsaid galactose is present at the non-reducing end of the acceptor saccharide or wherein said galactose is part of a GlcNAc-beta-1,6-galactose at the non-reducing end of the acceptor saccharide). The skilled person can readily assess whether a beta-1,3-N-acetylglucosaminyltransferase is active or not (it is fore example referred to Blixt et al, 1999, Glycobiology 9(10): p.1061-1071; which is incorporated by reference), by bringing it into contact with said suitable donor and said suitable acceptor saccharide underconditions suitable for the transfer of GlcNAc from said donor to said acceptor saccharide. A cellularmethod or a cell-free method (e.g. enzymatic method) are suitable. Suitable conditions include a pH of 5-10 (optimal pH is 7.0-8.0) and a temperature of 20-50°C (optimal temperature is 20-30°C). Further, thepresence of a divalent cation is required, wherein Mn2+is the most effective activator.In the context of the invention, a beta-1,3-N-acetylglucosaminyltransferase is active when at least 10.0 %,preferably at least 20.0%, more preferably at least 25.0%, even more preferably at least 50.0% of theacceptor saccharide is modified by the enzyme (i.e. is modified by the addition of a GlcNAc in a beta-1,3-linkage). In another preferred embodiment, the full-length amino acid sequence of the reference beta-1,3-N- acetylglucosaminyltransferase is represented by SEQ ID NO 03, 04 or 05, preferably by SEQ ID NO 03 or 04, most preferably by SEQ ID NO 03.Throughout the application and claims “SEQ ID NO 05” is preferably replaced with the expression “SEQ ID06 or 07”, more preferably replaced with “SEQ ID NO 06”. For the sake of clarity, SEQ ID NO 05 is theconsensus sequence of SEQ ID NO 06 and SEQ ID NO 07.SEQ ID NO 03 is the amino acid sequence of Neisseria polysaccharea beta-1,3-N-acetylglucosaminyltransferase (origin sequence is unknown).SEQ ID NO 04 is the amino acid sequence of Neisseria gonorrhoeae beta-1,3-N-acetylglucosaminyltransferase (origin sequence is Germany).SEQ ID NO 06 is the amino acid sequence of Neisseria meningitidis beta-1,3-N-acetylglucosaminyltransferase (origin sequence is United Kingdom).SEQ ID NO 07 is the amino acid sequence of Neisseria meningitidis beta-1,3-N-acetylglucosaminyltransferase (Uniprot Q8KI61, sequence version 1). Throughout the application and claims, conservative and non-conservative amino acid substitutionstypically are relative to SEQ ID NO 01 (i.e. the full-length amino acid sequence of the reference beta-1,3-N-acetylglucosaminyltransferase), unless specifically stated otherwise. For example, F339 of SEQ ID NO01 refers to the phenylalanine (F) at position 339 of SEQ ID NO 01. The skilled person will understand thatwhen the reference beta-1,3-N-acetylglucosaminyltransferase is specified to be represented by any one of SEQ ID NO 03, 04, 05, 06 or 07, that one has to align (in such way that there is an optimal overlapbetween the sequences) said SEQ ID NO 03, 04, 05, 06 and 07 with SEQ ID NO 01 so as to localize theamino acid of SEQ ID NO 01 correctly in SEQ ID NO 03, 04, 05, 06 or 07, respectively. For the sake of clarity,it is referred to Table 1 wherein the amino acid positions of the different sequences are indicated in function of the amino acid sequence of SEQ ID NO 01. For example, the amino acid (i.e. phenylalanine, F)at position 339 of SEQ ID NO 01 corresponds with position 339 of SEQ ID NO 03, position 322 of SEQ IDNO 04, position 339 of SEQ ID NO 05, position 339 of SEQ ID NO 07 and position 338 of SEQ ID NO 07. Table 1. SEQ ID NO 01 and the position of each amino acid of SEQ ID NO 01 in SEQ ID NO 01, 03-07.“I” means that this amino acid of SEQ ID NO 01 is absent in the particular sequence.P iti i P iti i P iti i P iti i P iti i P iti in C26 26 10 26 26 26A 27 27 11 27 27 27 X67 67 51 67 67 67X 68 68 52 68 68 68 I108 108 91 108 108 107A 109 109 92 109 109 108 K149 149 132 149 149 148D 150 150 133 150 150 149 M190 190 173 190 190 189R 191 191 174 191 191 190 V231 231 214 231 231 230K 232 232 215 232 232 231 R272 272 255 272 272 271F 273 273 256 273 273 272 D313 313 296 313 313 312T 314 314 297 314 314 313 X354 / 337 / / / X 355 / 338 / / / Conservative amino acid substitution(s) at 1-363In an optional embodiment of the first aspect of the invention, the beta-1,3-N-acetylglucosaminyltransferase mutant according to the invention comprises an amino acid sequence that further differs from the full-length amino acid sequence of a reference beta-1,3-N- acetylglucosaminyltransferase represented by SEQ ID NO 01 (it is referred to the Section “Reference beta- 1,3-N-acetylglucosaminyltransferase”) in one or more conservative amino acid substitutions. In the context of the present invention, a “conservative amino acid substitution” is the substitution of anamino acid by another structurally-related amino acid, i.e. an amino acid having a side-chain with similarphysicochemical properties. In the context of the present invention, throughout the application andclaims, the amino acid classification system according to IMGT (ImMunoGeneTics) is used (Pommié et al,2004, J. Mol. Recognit. 17(1): p. 17-32). The classification of the 20 common amino acids according toIMGT consists of several standardized classes that have been defined by the properties of their side chains(hydropathy, volume, chemical, charge, hydrogen donor or acceptor atoms, and polarity). Accordingly, a conservative amino acid substitution is preferably the substitution of an amino acid fromone IMGT class to another amino acid from the same IMGT class. Preferably, said IMGT class ishydrophobic class, neutral hydropathy class, hydrophilic class, positively charged class, uncharged class, negatively charged class, polar class, non-polar class or aromatic class. Accordingly, in the context of the present invention, a conservative amino acid substitution is more preferably the substitution of: -an aromatic amino acid (i.e. W, Y, F) by another aromatic amino acid (i.e. W, Y, F);- a polar amino acid (i.e. R, N, D, Q, E, H, K, S, T, Y) by another polar amino acid (i.e. R, N, D, Q, E, H,K, S, T, Y); -a non-polar amino acid (i.e. A, C, G, I, L, M, F, P, W, V) by another non-polar amino acid (i.e. A, C,G, I, L, M, F, P, W, V); -a hydrophobic amino acid (i.e. I, V, L, F, C, M, A, W) by another hydrophobic amino acid (i.e. I, V,L, F, C, M, A, W);- a hydrophilic amino acid (i.e. N, D, Q, E, K, R) by another hydrophilic amino acid (i.e. N, D, Q, E, K,R); -an amino acid with neither a hydrophobic nor hydrophilic side chain (i.e. G, T, S, Y, P, H) by anotheramino acid with neither a hydrophobic nor hydrophilic side chain (i.e. G, T, S, Y, P, H);- an amino acid with a positively charged side chain at physiological pH (i.e. R, H, K) by anotheramino acid with a positively charged side chain at physiological pH (i.e. R, H, K);- an amino acid with a negatively charged side chain at physiological pH (i.e. D, E) by another aminoacid with a negatively charged side chain at physiological pH (i.e. D, E), or -an amino acid with a neutral side chain at physiological pH (i.e. A, N, C, Q, G, I, L, M, F, P, S, T, WY, V) by another amino acid with an uncharged side chain at physiological pH (A, N, C, Q, G, I, L,M, F, P, S, T, W, Y, V). As understood by the skilled person, “a hydrophobic amino acid” refers to an amino acid having a hydrophobic side chain. Said hydrophobic amino acid is I, V, L, F, C, M, A or W (ranked from most hydrophobic, i.e. I, to least hydrophobic, i.e. W). As understood by the skilled person, “a hydrophilic amino acid” refers to an amino acid having a hydrophilic side chain. Said hydrophilic amino acid is R, K, E, Q, D or N (ranked from most hydrophilic, i.e. R, to least hydrophilic, i.e. N). In the context of the present invention, the terms “amino acid with a negatively charged side chain at physiological pH” and “negatively charged amino acid” are used interchangeably herein. Likewise, the terms “amino acid with a positively charged side chain at physiological pH” are used interchangeably herein. Likewise, the terms “amino acid with a neutral side chain at physiological pH” and “uncharged amino acid” are used interchangeably herein. The term “neutral amino acid” can refer to an amino acid having neither a hydrophobic nor a hydrophilic side chain in the context of the property “hydropathy”; or can refer to an amino acid having a neutral side chain at physiological pH in the context of the property “charge” as disclosed herein. For clarity reasons, in the context of the present invention, unless specifically stated otherwise, “neutral amino acid” refers to an amino acid having neither a hydrophobic nor a hydrophilic side chain, whereas “uncharged amino acid” refers to an amino acid having a neutral side chain at physiological pH. Throughout the application and claims, the expression “one or more conservative amino acid substitutions” is preferably replaced with “1-40 conservative amino acid substitutions”, more preferably replaced with “1-30 conservative amino acid substitutions”, even more preferably replaced with “1-20 conservative amino acid substitutions”, most preferably replaced with “1-10 conservative amino acid substitutions”.The introduction of one or more conservative amino acid substitutions preferably does not significantlyimprove the activity or specificity of the reference beta-1,3-N-acetylglucosaminyltransferase (it is referredto the Section “Mutant beta-1,3-N-acetylglucosaminyltransferase” wherein said activity and specificityare further disclosed in detail). The feature “does not significantly improve the activity or specificity” means that the conservative amino acid substitutions do not alter the activity or specificity to an extent that it is considered an improvement as defined in the Section “Mutant beta-1,3-N- acetylglucosaminyltransferase”. Non-conservative amino acid substitution(s) at 302-363 In a preferred embodiment of the first aspect of the invention, the beta-1,3-N- acetylglucosaminyltransferase mutant according to the invention comprises an amino acid sequence that differs from the full-length amino acid sequence of a reference beta-1,3-N-acetylglucosaminyltransferase represented by SEQ ID NO 01 (it is referred to the Section “Reference beta-1,3-N- acetylglucosaminyltransferase”) in at least one or more non-conservative amino acid substitutions at 302- 363 of SEQ ID NO 01. Throughout the application and claims, the expression “302-363 of SEQ ID NO 01” is preferably replaced with “302-349 of SEQ ID NO 01” or alternatively with “321-363 of SEQ ID NO 01”, more preferably replaced with “321-349 of SEQ ID NO 01”. In the context of the invention, a “non-conservative amino acid substitution” is an amino acid substitutionwhich is not a conservative amino acid substitution as defined herein (it is referred to the Section“Conservative amino acid substitution(s) at 1-363”). Accordingly, a non-conservative amino acid substitution is preferably the substitution of (i) an amino acid from one IMGT class to another amino acid from a different IMGT class, preferably a different IMGT classwithin the same property (i.e. hydropathy, volume, chemical, charge, hydrogen donor or acceptor atoms,or polarity; more preferably hydropathy, chemical, charge or polarity; most preferably hydropathy, charge or polarity), or (ii) an aromatic amino acid (W, Y, F) into a non-aromatic amino acid, preferably an amino acid with a side chain that is less hydrophobic than the side chain of the aromatic amino acid that is substituted (it is referred to the property hydropathy according to the IMGT system as disclosed herein). Amino acids are classified (according to IMGT classification system) as follows based on the property “hydropathy”: -Hydrophobic: I, V, L, F, C, M, A, W (ranked from most hydrophobic, i.e. I, to least hydrophobic, i.e.W); -Neutral (neither a hydrophobic nor hydrophilic side chain): G, T, S, Y, P, H (ranked from mosthydrophobic, i.e. G, to most hydrophilic, i.e. H); -Hydrophilic: R, K, E, Q, D, N (ranked from most hydrophilic, i.e. R, to least hydrophilic, i.e. N).Preferably, a non-conservative amino acid substitution based on the property “hydropathy” is thesubstitution of a hydrophobic amino acid by a hydrophilic amino acid or vice versa. A neutral (neither ahydrophobic nor hydrophilic side chain) is preferably substituted by an amino acid with a side chain thatis either hydrophobic or hydrophilic. However, in the present context of the invention (Section “Non-conservative amino acid substitution(s) at 302-366”), within the context of “hydropathy” it is particularlypreferred that a non-conservative amino acid substitution is the substitution of a hydrophobic amino acidby a hydrophilic amino acid or vice versa, and not the substitution of a neutral (neither a hydrophobic norhydrophilic side chain) amino acid, but such an amino acid can be a non-conservative amino acidsubstitution based on another property as discussed herein. For example, a non-conservative amino acidsubstitution of T can be the substitution into a non-polar amino acid as T is a polar amino acid. Amino acids are classified (according to IMGT classification system) as follows based on the property “volume”: -Very small: G, A, S (ranked from largest, i.e., to smallest, i.e. );- Small: C, D, P, N, T (ranked from largest, i.e., to smallest, i.e. );- Medium: E, V, Q, H (ranked from largest, i.e., to smallest, i.e. );- Large: M, I, L, K, R (ranked from largest, i.e., to smallest, i.e. );- Very large: F, Y, W (ranked from largest, i.e., to smallest, i.e. ).Amino acids are classified (according to IMGT classification system) as follows based on the property “chemical”: -Aliphatic: A, G, I, L, P, V;- Aromatic: F, W, Y;- Sulfur: C, M;- Hydroxyl: S, T;- Basic: R, H, K;- Acidic: D, E;- Amide: N, Q.Amino acids are classified (according to IMGT classification system) as follows based on the property “charge”: -Positively charged: R, H, K;- Negatively charged: D, E;- Uncharged: A, N, C, Q, G, I, L, M, F, P, S, T, W, Y, V.Preferably, a non-conservative amino acid substitution based on the property “charge” is the substitutionof a positively charged amino acid by a negatively charged amino acid or uncharged amino acid; or anegatively charged amino acid by a positively charged amino acid or uncharged amino acid. Amino acids are classified (according to IMGT classification system) as follows based on the property “hydrogen donor or acceptor atoms”: -Donor: R, K, W;- Acceptor: D, E;- Donor and acceptor: N, Q, H, S, T, Y;- None: A, C, G, I, L, M, F, P, V.Amino acids are classified (according to IMGT classification system) as follows based on the property “polarity”: -Polar: R, N, D, Q, E, H, K, S, T, Y ;- Non-polar: A, C, G, I, L, M, F, P, W, V.Accordingly, a non-conservative amino acid substitution is more preferably the substitution of (i) anaromatic amino acid by a non-aromatic amino acid or vice versa; (ii) a non-polar amino acid by a polar amino acid or vice versa; (iii) a hydrophobic amino acid by a hydrophilic amino acid or vice versa; (iv) a positively charged amino acid by a negatively charged amino acid or uncharged amino acid; or (v) a negatively charged amino acid by a positively charged amino acid or uncharged amino acid. Said “aromatic amino acid”, non-aromatic amino acid”, “non-polar amino acid”, “polar amino acid”, “hydrophobic amino acid”, “hydrophilic amino acid”, “positively charged amino acid”, “negatively charged amino acid” and “uncharged amino acid” are as disclosed earlier herein. Accordingly, a non-conservative amino acid substitution in the present context of the invention (Section“Non-conservative amino acid substitution(s) at 302-363”) is even more preferably the substitution of (i)an aromatic amino acid by a non-aromatic amino acid or vice versa; (ii) a non-polar amino acid by a polar amino acid or vice versa; (iii) a hydrophobic amino acid by a hydrophilic amino acid or vice versa or (iv) a positively charged amino acid by a negatively charged amino acid or uncharged amino acid. Said “aromatic amino acid”, non-aromatic amino acid”, “non-polar amino acid”, “polar amino acid”, “hydrophobic amino acid”, “hydrophilic amino acid”, “positively charged amino acid”, “negatively charged amino acid” and “uncharged amino acid” are as disclosed earlier herein. Accordingly, a non-conservative amino acid substitution in the present context of the invention (Section “Non-conservative amino acid substitution(s) at 302-363”) is most preferably the substitution of (i) an aromatic amino acid by a non-aromatic amino acid or vice versa; (ii) a non-polar amino acid by a polar amino acid or vice versa; or (iii) a positively charged amino acid by a negatively charged amino acid or uncharged amino acid. Said “aromatic amino acid”, non-aromatic amino acid”, “non-polar amino acid”, “polar amino acid”, “positively charged amino acid”, “negatively charged amino acid” and “uncharged amino acid” are as disclosed earlier herein. In a more preferred embodiment, one or more non-conservative amino acid substitutions at 302-363 of SEQ ID NO 01 is the substitution of one or more aromatic amino acids into a non-aromatic amino acid. Preferably, said aromatic amino acid is selected from the list consisting of phenylalanine (F), tyrosine (Y) and tryptophan (W), more preferably selected from the list consisting of phenylalanine (F) and tyrosine (Y), most preferably phenylalanine (F). For the sake of clarity, the substitution of one or more aromatic amino acids into a non-aromatic amino acid, wherein said aromatic amino acid is selected from the list consisting of F, Y and W, also encompasses the situation wherein one F, one Y or one W is substituted. It also encompasses the situation wherein one or more F are substituted, one or more Y are substituted, or one or more W are substituted. It also encompasses the situation wherein one or more F are substituted and optionally one or more Y are substituted and optionally one or more W are substituted etc. Throughout the application and claims, unless specifically stated otherwise, a non-aromatic amino acid is selected form the list consisting of R, K, E, Q, D, N, H, P, S, T, G, A, M, C, L, V and I, preferably selected from the list consisting of A, G, I, L, V, N, Q, M, C, D, E, R and K, more preferably selected from the list consisting of A, G, N, Q, M, C, D, E, R and K, even more preferably selected from the list consisting of A, G, N, Q, M, D, E, R and K, even more preferably selected from the list consisting of A, G, N, Q, M, D and E, even morepreferably selected from the list consisting of A, G, N, Q and M, even more preferably selected from thelist consisting of A, G, N and M, even more preferably selected from the list consisting of A, N and M, most preferably N or A. In the context of the present invention, it is particularly preferred that said non-aromatic amino acid is an amino acid with a side chain that is less hydrophobic than the side chain of said aromatic amino acid. Hence, the aromatic amino acid W is preferably substituted into G, T, S, P, H, N, D, Q, E, K or R, more preferably into G, N, Q, D, E, R or K, even more preferably into G, N, Q, D or E, even more preferably into G, N or Q, even more preferably into G or N, most preferably into N. Hence, the aromatic amino acid Y is preferably substituted into P, H, N, D, Q, E, K or R, more preferably into N, Q, D, E, R or K, even more preferably into N, Q, D or E, even more preferably into N or Q, most preferably into N.Hence, the aromatic amino acid F is preferably substituted into C, M, A, G, T, S, P, H, N, D, Q, E, K or R,more preferably into A, G, N, Q, M, C, D, E, R or K, even more preferably into A, G, N, Q, M, C, D, E, R or K,even more preferably into A, G, N, Q, M, D, E, R or K, even more preferably into A, G, N, Q, M, D or E, evenmore preferably into A, G, N, Q or M, even more preferably into A, G, N or M, even more preferably intoA, N or M, even more preferably into N or A, most preferably into A.In an even more preferred embodiment, said one or more aromatic amino acid substitutions at 302-363of SEQ ID NO 01 is the substitution of one or more amino acids selected from the list consisting of F339, F333, F323, F309, F304, Y338, Y306 and W320, preferably selected from the list consisting of F339, F333, F323 and F304, into an non-aromatic amino acid. In an additional and / or alternative even more preferred embodiment, and particularly preferred in thecontext of the present invention, said one or more aromatic amino acid substitutions at 302-363 of SEQID NO 01 is the substitution of at least F339, F333, F323, F309, F304, Y338, Y306 or W320, preferably atleast F339, F333, F323 or F304, most preferably at least F339, into a non-aromatic amino acid.In a most preferred embodiment, said one or more aromatic amino acid substitutions at 302-363 of SEQ ID NO 01 is the substitution of only F339, F333, F323, F309, F304, Y338, Y306 or W320, preferably onlyF339, F333, F323 or F304, most preferably only F339, into a non-aromatic amino acid as disclosed herein.In an additional and / or alternative more preferred embodiment, one or more non-conservative aminoacid substitutions at 302-363 of SEQ ID NO 01 is the substitution of one or more non-polar amino acidsinto a polar amino acid. Preferably, said non-polar amino acid is selected from the list consisting of A, C, G, I, L, M, F, P, W and V, more preferably selected from the list consisting of A, C, G, I, L, M, P and V, even more preferably selected from the list consisting of A, C, G, I, L, M and P, even more preferably selected from the list consisting of A, G, L, M and P, even more preferably selected from the list consisting of A, G, L and P, most preferablyA. For the sake of clarity, the substitution of one or more non-polar amino acids into a polar amino acid,wherein said non-polar amino acid is selected from for example the list consisting of A, L, I and G, alsoencompasses the situation wherein one A, one L, one I or one G is substituted. It also encompasses thesituation wherein one or more A are substituted, one or more L are substituted, one or more I aresubstituted or one or more G are substituted. It also encompasses the situation wherein one or more Aare substituted and optionally one or more L are substituted and optionally one or more I are substitutedand one or more G are substituted etc.Throughout the application and claims, unless specifically stated otherwise, a polar amino acid is selectedform the list consisting of R, N, D, Q, E, H, K, S, T and Y, preferably selected from the list consisting of D, E, S, N, Q and T, more preferably selected from the list consisting of D, E, S and T, most preferably selected from the list consisting of D, E and S. In the context of the present invention, it is particularly preferred that A is substituted into R, N, D, Q, E, H, K, S, T or Y, more preferably into D, E, N, Q, S, T or Y, even more preferably into D, E, N, Q, S or T, even more preferably into S, D, E or T, even more preferably into S, D or E, most preferably into D or S. In the context of the present invention, it is particularly preferred that P is substituted into R, N, D, Q, E,H, K, S, T or Y, more preferably into D, E, S, N, Q or T, even more preferably into D, E, S or T, most preferablyinto D, E or S. In the context of the present invention, it is particularly preferred that L is substituted into R, N, D, Q, E, H, K, S, T or Y, more preferably into D, E, S, N, Q or T, even more preferably into D, E, S or T, even more preferably into D, E or S, even more preferably into D or E, most preferably into D.In the context of the present invention, it is particularly preferred that G is substituted into R, N, D, Q, E,H, K, S, T or Y, more preferably into D, E, S, N, Q or T, even more preferably into D, E, S or T, even more preferably into D, E or S, most preferably into S.In the context of the present invention, it is particularly more preferred that said polar amino acid is anamino acid with a side chain that is negatively charged at physiological pH or that is uncharged atphysiological pH. Hence, a non-polar amino acid as disclosed herein is preferably substituted into D, E, N, Q, S, T or Y, more preferably substituted into D, E, N, Q, S or T, even more preferably into D, E, S or T, most preferably into D, E or S.In an even more preferred embodiment, said one or more non-polar amino acid substitutions at 302-363of SEQ ID NO 01 is the substitution of one or more amino acids selected from the list consisting of F304,L305, C308, F309, L315, P315, P316, A317 (unless S is present at position 317), G318, A319, W320, L321,F323, A324, A325, G327, M329, L332, F333, L335, F339, G340, I341, L342, L345 and L346 (or I346),preferably selected from the list consisting of L305, C308, L315, P315, P316, A317 (unless S is present atposition 317), G318, A319, L321, A324, A325, G327, M329, L332, L335, G340, I341, L342, L345 and L346,more preferably selected from the list consisting of L305, L315, P315, P316, A317 (unless S is present atposition 317), G318, A319, l321, A324, A325, L332, L335, G340, I341, L342, L345, L346 (or I346), evenmore preferably selected from the list consisting of L315, P315, P316, A317 (unless S is present at position317), G318, A319, L321, A324, A325, G327, L332, L335, G340, I341, L342, L345 and L346 (or I346), even more preferably selected from the list consisting of P315 (or L315), P316, A317 (unless S is present at position 317), G318, A319, A324, A325, L332 and G340, even more preferably selected from the list consisting of P315 (or L315), P316, A317 (unless S is present at position 317), G318, A319, A324, A325 and G340, even more preferably selected from the list consisting of P315 (or L315), P316, A317 (unless S is present at position 317), G318, A319, A324 and A325, most preferably selected from the list consisting ofP315 (or L315), P316, A317 (unless S is present at position 317), G318 and A319, into a polar amino acid.In an alternative even more preferred embodiment, said one or more non-polar amino acid substitutionsat 302-363 of SEQ ID NO 01 is the substitution of one or more amino acids selected from the list consisting of L321, F323, A324, A325, G327, M329, L332, F333, L335, F339, G340, I341, L342, L345 and L346 (or I346), preferably selected from the list consisting of L321, A324, A325, G327, M329, L332, L335, G340,I341, L342, L345 and L346 (or I346), even more preferably selected from the list consisting of L321, A324,A325, G327, L332, L335, G340, I341, L342, L345 and L346 (or I346), even more preferably selected from the list consisting of A324, A325, L332 and G340, even more preferably selected from the list consisting of A324, A325 and G340, most preferably selected from the list consisting of A324 and A325, into a polar amino acid. In an even more preferred embodiment, said one or more non-polar amino acid substitutions at 302-363of SEQ ID NO 01 is the substitution of at least A317 (unless S is present at position 317) and A319,preferably at least P316, A317 (unless S is present at position 317) and A319, more preferably at leastL315 (or P315), P316, A317 (unless S is present at position 317), G318 and A319, into a polar amino acid.In an alternative even more preferred embodiment, said one or more non-polar amino acid substitutionsat 302-363 of SEQ ID NO 01 is the substitution of at least A324 and A325. In an even more preferred embodiment, said one or more non-polar amino acid substitutions at 302-363 of SEQ ID NO 01 is the substitution of only A324 and A325.In a most preferred embodiment, said one or more non-polar amino acid substitutions at 302-363 of SEQID NO 01 is the substitution of only A317 (unless S is present at position 317) and A319, preferably onlyP316, A317 (unless S is present at position 317) and A319, more preferably only L315 (or P315), P316, A317 (unless S is present at position 317), G318 and A319, into a polar amino acid; optionally wherein A324 and / or A325 are substituted into a polar amino acid as disclosed herein. As the skilled person is familiar with, a particular amino acid can belong to different IMGT classes depending on the property as disclosed earlier herein. For example, phenylalanine (F) is an aromatic amino acid and hence a non-conservative amino acid substitution would be the substitution into a non- aromatic amino acid. At the same time, phenylalanine (F) is also a non-polar amino acid and hence a non- conservative amino acid substitution would be the substitution into a polar amino acid. For the sake of clarity, throughout the present Section (“Non-conservative amino acid substitution(s) at 302-366“), when an amino acid is an aromatic amino acid, then a non-conservative amino acid substitution is particularlypreferred to be the substitution into a non-aromatic amino acid as described herein.In an additional and / or alternative more preferred embodiment, one or more non-conservative amino acid substitutions at 302-363 of SEQ ID NO 01 is the substitution of one or more amino acids having a sidechain that is positively charged at physiological pH into an amino acid having a side chain that is unchargedor negatively charged at physiological pH, preferably into an amino acid having a side chain that is negatively charged at physiological pH. Preferably, said amino acid having a side chain that is positively charged at physiological pH is R or K, morepreferably R. For the sake of clarity, the substitution of one or more amino acids having a side chain thatis positively charged at physiological pH into an amino acid having a side chain that is uncharged or negatively charged at physiological pH, wherein said amino acid having a side chain that is positivelycharged at physiological pH is R or K, also encompasses the situation wherein one R or one K is substituted.It also encompasses the situation wherein one or more R are substituted or one or more K are substituted.It also encompasses the situation wherein one or more R are substituted and optionally one or more Kare substituted. It also encompasses the situation wherein one or more K are substituted and optionallyone or more R are substituted. Preferably, said amino acid having a side chain that is positively charged at physiological pH is substituted into an amino acid selected from the list consisting of aspartate (D), glutamate (E), serine (S), asparagine (N), glutamine (Q) and threonine (T), more preferably selected from the list consisting of aspartate (D), glutamate (E), asparagine (N) and glutamine (Q), most preferably D or E. In an even more preferred embodiment, said one or more amino acids having a side chain that is positivelycharged at physiological pH substitutions at 302-363 of SEQ ID NO 01 is the substitution of one or moreamino acids selected from the list consisting of R302, R303, K310, R311, R328, R330, R331, R336, R344, K347, R349, R350, R353 and K359, preferably selected from the list consisting of R302, R303, K310, R311,R328, R330, R331, R336, R344, K347 and R349, more preferably selected form the list consisting of R328,R330, R331, R336, R344, K347 and R349, even more preferably selected from the list consisting of R328, R330, R331 and R336, most preferably R336. In an even more preferred embodiment, said one or more amino acid having a side chain that is positively charged at physiological pH substitutions at 302-363 of SEQ ID NO 01 is the substitution of at least R302, R303, K310, R311, R328, R330, R331, R336, R344, K347, R349, R350, R353 or K359, preferably at least R302, R303, K310, R311, R328, R330, R331, R336, R344, K347 or R349, more preferably at least R328, R330, R331, R336, R344, K347 or R349, even more preferably at least R328, R330, R331 or R336, most preferably at least R336, into an amino acid having a side chain that is uncharged or negatively charged at physiological pH (preferably into an amino acid having a side chain that is negatively charged at physiological pH). In a most preferred embodiment, said one or more amino acid having a side chain that is positively charged at physiological pH substitutions at 302-363 of SEQ ID NO 01 is the substitution of only R302, R303, K310, R311, R328, R330, R331, R336, R344, K347, R349, R350, R353 or K359, preferably only R302, R303, K310, R311, R328, R330, R331, R336, R344, K347 or R349, more preferably only R328, R330, R331, R336, R344, K347 or R349, even more preferably only R328, R330, R331 or R336, most preferably only R336, into an amino acid having a side chain that is uncharged or negatively charged at physiological pH (preferably into an amino acid having a side chain that is negatively charged at physiological pH) as disclosed herein. In an additional and / or alternative more preferred embodiment, one or more non-conservative amino acid substitutions at 302-363 of SEQ ID NO 01 is the substitution of one or more T and / or one or more Q, preferably one or more T, into a non-polar amino acid. Preferably, said non-polar amino acid is selected from the list consisting of A, C, G, I, L, M, F, P, W and V,more preferably selected from the list consisting of M, C, A, G and P , even more preferably selected fromthe list consisting of M, C, A and G, most preferably selected from the list consisting of M, A and G.It is particularly preferred in the context of the present invention that said non-polar amino acid is not an aromatic amino acid and that said non-polar amino acid is less hydrophobic than F. In an even more preferred embodiment, one or more non-conservative amino acid substitutions at 302-363 of SEQ ID NO 01 is the substitution of one or more T selected from the list consisting of T312, T314and T334, preferably T314. In an additional and / or alternative even more preferred embodiment, one or more non-conservative amino acid substitutions at 302-363 of SEQ ID NO 01 is the substitution of one or more Q selected from the list consisting of Q307 and Q337. In an even more preferred embodiment, said one or more T and / or one or more Q (preferably one or more T) substitutions at 302-363 of SEQ ID NO 01 is the substitution of at least T312, T314 or T334, preferably at least T314, into a non-polar amino acid as disclosed herein. In a most preferred embodiment, said one or more T and / or one or more Q (preferably one or more T)substitutions at 302-363 of SEQ ID NO 01 is the substitution of only T312, T314 or T334, preferably only T314, into a non-polar amino acid as disclosed herein. In an even more preferred embodiment, said one or more non-conservative amino acid substitutions at 302-363 of SEQ ID NO 01 is the substitution of at least one or more aromatic amino acids into a non-aromatic amino acid as disclosed in the present Section “Non-conservative amino acid substitution(s) at302-363”. Preferably, the expression “at least” is replaced with “only”, i.e. no additional non-conservative aminoacid substitutions at 302-363 of SEQ ID NO 01 are present than what is explicitly recited.It is particularly preferred that said “one or more aromatic amino acid substitutions into a non-aromatic amino acid” is the substitution of at least F339, F333, F323, F309, F304, Y338, Y306 or W320, preferablyat least F339, F333, F323 or F304, most preferably at least F339, into a non-aromatic amino acid asdisclosed in the present Section “Non-conservative amino acid substitution(s) at 302-363”.It is particularly more preferred that said “one or more aromatic amino acid substitutions into a non-aromatic amino acid” is the substitution of only F339, F333, F323, F309, F304, Y338, Y306 or W320, preferably only F339, F333, F323 or F304, most preferably at least F339, into a non-aromatic amino acid as disclosed in the present Section “Non-conservative amino acid substitution(s) at 302-363”. In an even more preferred embodiment, said one or more non-conservative amino acid substitutions at 302-363 of SEQ ID NO 01 is the substitution of at least: (i) one or more aromatic amino acids into a non-aromatic amino acid as disclosed in the presentSection “Non-conservative amino acid substitution(s) at 302-363”; and (ii) preferably one or more non-polar amino acids into a polar amino acid as disclosed in thepresent Section “Non-conservative amino acid substitution(s) at 302-363”. Preferably, the expression “at least” is replaced with “only”, i.e. no additional non-conservative amino acid substitutions at 302-363 of SEQ ID NO 01 are present than what is explicitly recited. It is particularly preferred that said “one or more aromatic amino acid substitutions into a non-aromatic amino acid” is the substitution of at least F339, F333, F323, F309, F304, Y338, Y306 or W320, preferablyat least F339, F333, F323 or F304, most preferably at least F339, into a non-aromatic amino acid asdisclosed in the present Section “Non-conservative amino acid substitution(s) at 302-363”.It is particularly more preferred that said “one or more aromatic amino acid substitutions into a non-aromatic amino acid” is the substitution of only F339, F333, F323, F309, F304, Y338, Y306 or W320, preferably only F339, F333, F323 or F304, most preferably at least F339, into a non-aromatic amino acid as disclosed in the present Section “Non-conservative amino acid substitution(s) at 302-363”. It is particularly preferred that said “one or more non-polar amino acid substitutions into a polar amino acid” is the substitution of (a) at least A317 (unless S is present at position 317) and A319, preferably atleast P316, A317 (unless S is present at position 317) and A319, more preferably at least P316, A317 (unless S is present at position 317), G318 and A319, even more preferably at least L315 (or P315), P316, A317 (unless S is present at position 317), G318 and A319, into a polar amino acid as disclosed in thepresent Section “Non-conservative amino acid substitution(s) at 302-363”; or (b) at least A324 and A325,into a polar amino acid as disclosed in the present Section “Non-conservative amino acid substitution(s) at 302-363”. It is particularly more preferred that said “one or more non-polar amino acid substitutions into a polar amino acid” is the substitution of (a) only A317 (unless S is present at position 317) and A319, preferablyonly P316, A317 (unless S is present at position 317) and A319, more preferably only P316, A317 (unlessS is present at position 317), G318 and A319, even more preferably only L315 (or P315), P316, A317 (unless S is present at position 317), G318 and A319, into a polar amino acid as disclosed in the present Section “Non-conservative amino acid substitution(s) at 302-363”; or (b) only A324 and A325, into a polar amino acid as disclosed in the present Section “Non-conservative amino acid substitution(s) at 302-363”. In an even more preferred embodiment, said one or more non-conservative amino acid substitutions at 302-363 of SEQ ID NO 01 is the substitution of at least: (i) one or more aromatic amino acids into a non-aromatic amino acid as disclosed in the presentSection “Non-conservative amino acid substitution(s) at 302-363”; and (ii) preferably one or more non-polar amino acids into a polar amino acid as disclosed in thepresent Section “Non-conservative amino acid substitution(s) at 302-363”; and (iii) optionally:- one or more amino acids having a side chain that is positively charged at physiologicalpH into an amino acid having a side chain that is uncharged or negatively charged at physiological pH, preferably into an amino acid having a side chain that is negatively charged at physiological pH, as disclosed in the present Section “Non-conservative amino acid substitution(s) at 302-363”. Preferably, the expression “at least” is replaced with “only”, i.e. no additional non-conservative amino acid substitutions at 302-363 of SEQ ID NO 01 are present than what is explicitly recited. It is particularly preferred that said “one or more aromatic amino acid substitutions into a non-aromatic amino acid” is the substitution of at least F339, F333, F323, F309, F304, Y338, Y306 or W320, preferablyat least F339, F333, F323 or F304, most preferably at least F339, into a non-aromatic amino acid asdisclosed in the present Section “Non-conservative amino acid substitution(s) at 302-363”.It is particularly more preferred that said “one or more aromatic amino acid substitutions into a non-aromatic amino acid” is the substitution of only F339, F333, F323, F309, F304, Y338, Y306 or W320, preferably only F339, F333, F323 or F304, most preferably at least F339, into a non-aromatic amino acid as disclosed in the present Section “Non-conservative amino acid substitution(s) at 302-363”. It is particularly preferred that said “one or more non-polar amino acid substitutions into a polar aminoacid” is the substitution of (a) at least A317 (unless S is present at position 317) and A319, preferably atleast P316, A317 (unless S is present at position 317) and A319, more preferably at least P316, A317 (unless S is present at position 317), G318 and A319, even more preferably at least L315 (or P315), P316, A317 (unless S is present at position 317), G318 and A319, into a polar amino acid as disclosed in the present Section “Non-conservative amino acid substitution(s) at 302-363”; or (b) at least A324 and A325, into a polar amino acid as disclosed in the present Section “Non-conservative amino acid substitution(s) at 302-363”. It is particularly more preferred that said “one or more non-polar amino acid substitutions into a polaramino acid” is the substitution of (a) only A317 (unless S is present at position 317) and A319, preferablyonly P316, A317 (unless S is present at position 317) and A319, more preferably only P316, A317 (unlessS is present at position 317), G318 and A319, even more preferably only L315 (or P315), P316, A317 (unless S is present at position 317), G318 and A319, into a polar amino acid as disclosed in the present Section “Non-conservative amino acid substitution(s) at 302-363”; or (b) only A324 and A325, into a polar amino acid as disclosed in the present Section “Non-conservative amino acid substitution(s) at 302-363”. It is particularly preferred that said “one or more amino acid having a side chain that is positively charged at physiological pH substitutions into an amino acid having a side chain that is uncharged or negatively charged at physiological pH (preferably into an amino acid having a side chain that is negatively charged at physiological pH)” is the substitution of at least R302, R303, K310, R311, R328, R330, R331, R336, R344, K347, R349, R350, R353 or K359, preferably at least R302, R303, K310, R311, R328, R330, R331, R336,R344, K347 or R349, more preferably at least R328, R330, R331, R336, R344, K347 or R349, even morepreferably at least R328, R330, R331 or R336, most preferably at least R336. It is particularly more preferred that said “one or more amino acid having a side chain that is positively charged at physiological pH substitutions into an amino acid having a side chain that is uncharged or negatively charged at physiological pH (preferably into an amino acid having a side chain that is negatively charged at physiological pH)” is the substitution of only R302, R303, K310, R311, R328, R330, R331, R336, R344, K347, R349, R350, R353 or K359, preferably only R302, R303, K310, R311, R328, R330, R331, R336, R344, K347 or R349, more preferably only R328, R330, R331, R336, R344, K347 or R349, even more preferably only R328, R330, R331 or R336, most preferably only R336. In an alternative even more preferred embodiment, said one or more non-conservative amino acid substitutions at 302-363 of SEQ ID NO 01 is the substitution of at least: (i) one or more aromatic amino acids into a non-aromatic amino acid as disclosed in the presentSection “Non-conservative amino acid substitution(s) at 302-363”; and (ii) preferably one or more non-polar amino acids into a polar amino acid as disclosed in thepresent Section “Non-conservative amino acid substitution(s) at 302-363”; and (iii) optionally:- one or more T and / or one or more Q, preferably one or more T, into a non-polar aminoacid as disclosed in the present Section “Non-conservative amino acid substitution(s) at 302-363”. Preferably, the expression “at least” is replaced with “only”, i.e. no additional non-conservative amino acid substitutions at 302-363 of SEQ ID NO 01 are present than what is explicitly recited. It is particularly preferred that said “one or more aromatic amino acid substitutions into a non-aromatic amino acid” is the substitution of at least F339, F333, F323, F309, F304, Y338, Y306 or W320, preferablyat least F339, F333, F323 or F304, most preferably at least F339, into a non-aromatic amino acid asdisclosed in the present Section “Non-conservative amino acid substitution(s) at 302-363”.It is particularly more preferred that said “one or more aromatic amino acid substitutions into a non-aromatic amino acid” is the substitution of only F339, F333, F323, F309, F304, Y338, Y306 or W320, preferably only F339, F333, F323 or F304, most preferably at least F339, into a non-aromatic amino acid as disclosed in the present Section “Non-conservative amino acid substitution(s) at 302-363”. It is particularly preferred that said “one or more non-polar amino acid substitutions into a polar amino acid” is the substitution of (a) at least A317 (unless S is present at position 317) and A319, preferably at least P316, A317 (unless S is present at position 317) and A319, more preferably at least P316, A317 (unless S is present at position 317), G318 and A319, even more preferably at least L315 (or P315), P316, A317 (unless S is present at position 317), G318 and A319, into a polar amino acid as disclosed in the present Section “Non-conservative amino acid substitution(s) at 302-363”; or (b) at least A324 and A325, into a polar amino acid as disclosed in the present Section “Non-conservative amino acid substitution(s) at 302-363”. It is particularly more preferred that said “one or more non-polar amino acid substitutions into a polaramino acid” is the substitution of (a) only A317 (unless S is present at position 317) and A319, preferablyonly P316, A317 (unless S is present at position 317) and A319, more preferably only P316, A317 (unless S is present at position 317), G318 and A319, even more preferably only L315 (or P315), P316, A317 (unless S is present at position 317), G318 and A319, into a polar amino acid as disclosed in the present Section “Non-conservative amino acid substitution(s) at 302-363”; or (b) only A324 and A325, into a polar amino acid as disclosed in the present Section “Non-conservative amino acid substitution(s) at 302-363”. It is particularly preferred that said “one or more T and / or one or more Q substitutions into a non-polar amino acid” is the substitution of at least T312, T314 or T334, preferably at least T314, into a non-polaramino acid as disclosed in the present Section “Non-conservative amino acid substitution(s) at 302-363”.It is particularly more preferred that said “one or more T and / or one or more Q substitutions into a non-polar amino acid” is the substitution of only T312, T314 or T334, preferably only T314, into a non-polaramino acid as disclosed in the present Section “Non-conservative amino acid substitution(s) at 302-363”.In an even more preferred embodiment, said one or more non-conservative amino acid substitutions at 302-363 of SEQ ID NO 01 is the substitution of at least: (i) one or more aromatic amino acids into a non-aromatic amino acid as disclosed in the presentSection “Non-conservative amino acid substitution(s) at 302-363”; and (ii) preferably one or more non-polar amino acids into a polar amino acid as disclosed in thepresent Section “Non-conservative amino acid substitution(s) at 302-363”; and (iii) optionally:- one or more amino acids having a side chain that is positively charged at physiologicalpH into an amino acid having a side chain that is uncharged or negatively charged at physiological pH, preferably into an amino acid having a side chain that is negatively charged at physiological pH, as disclosed in the present Section “Non-conservative amino acid substitution(s) at 302-363”; and / or -one or more T and / or one or more Q, preferably one or more T, into a non-polar aminoacid as disclosed in the present Section “Non-conservative amino acid substitution(s) at 302-363”. Preferably, the expression “at least” is replaced with “only”, i.e. no additional non-conservative amino acid substitutions at 302-363 of SEQ ID NO 01 are present than what is explicitly recited. It is particularly preferred that said “one or more aromatic amino acid substitutions into a non-aromatic amino acid” is the substitution of at least F339, F333, F323, F309, F304, Y338, Y306 or W320, preferablyat least F339, F333, F323 or F304, most preferably at least F339, into a non-aromatic amino acid asdisclosed in the present Section “Non-conservative amino acid substitution(s) at 302-363”.It is particularly more preferred that said “one or more aromatic amino acid substitutions into a non-aromatic amino acid” is the substitution of only F339, F333, F323, F309, F304, Y338, Y306 or W320, preferably only F339, F333, F323 or F304, most preferably at least F339, into a non-aromatic amino acid as disclosed in the present Section “Non-conservative amino acid substitution(s) at 302-363”. It is particularly preferred that said “one or more non-polar amino acid substitutions into a polar amino acid” is the substitution of (a) at least A317 (unless S is present at position 317) and A319, preferably at least P316, A317 (unless S is present at position 317) and A319, more preferably at least P316, A317 (unless S is present at position 317), G318 and A319, even more preferably at least L315 (or P315), P316, A317 (unless S is present at position 317), G318 and A319, into a polar amino acid as disclosed in the present Section “Non-conservative amino acid substitution(s) at 302-363”; or (b) at least A324 and A325, into a polar amino acid as disclosed in the present Section “Non-conservative amino acid substitution(s) at 302-363”. It is particularly more preferred that said “one or more non-polar amino acid substitutions into a polar amino acid” is the substitution of (a) only A317 (unless S is present at position 317) and A319, preferably only P316, A317 (unless S is present at position 317) and A319, more preferably only P316, A317 (unless S is present at position 317), G318 and A319, even more preferably only L315 (or P315), P316, A317 (unless S is present at position 317), G318 and A319, into a polar amino acid as disclosed in the present Section “Non-conservative amino acid substitution(s) at 302-363”; or (b) only A324 and A325, into a polar amino acid as disclosed in the present Section “Non-conservative amino acid substitution(s) at 302-363”. It is particularly preferred that said “one or more amino acid having a side chain that is positively charged at physiological pH substitutions into an amino acid having a side chain that is uncharged or negatively charged at physiological pH (preferably into an amino acid having a side chain that is negatively charged at physiological pH)” is the substitution of at least R302, R303, K310, R311, R328, R330, R331, R336, R344, K347, R349, R350, R353 or K359, preferably at least R302, R303, K310, R311, R328, R330, R331, R336, R344, K347 or R349, more preferably at least R328, R330, R331, R336, R344, K347 or R349, even more preferably at least R328, R330, R331 or R336, most preferably at least R336. It is particularly more preferred that said “one or more amino acid having a side chain that is positively charged at physiological pH substitutions into an amino acid having a side chain that is uncharged or negatively charged at physiological pH (preferably into an amino acid having a side chain that is negatively charged at physiological pH)” is the substitution of only R302, R303, K310, R311, R328, R330, R331, R336, R344, K347, R349, R350, R353 or K359, preferably only R302, R303, K310, R311, R328, R330, R331, R336, R344, K347 or R349, more preferably only R328, R330, R331, R336, R344, K347 or R349, even more preferably only R328, R330, R331 or R336, most preferably only R336. It is particularly preferred that said “one or more T and / or one or more Q substitutions into a non-polar amino acid” is the substitution of at least T312, T314 or T334, preferably at least T314, into a non-polaramino acid as disclosed in the present Section “Non-conservative amino acid substitution(s) at 302-363”.It is particularly more preferred that said “one or more T and / or one or more Q substitutions into a non-polar amino acid” is the substitution of only T312, T314 or T334, preferably only T314, into a non-polaramino acid as disclosed in the present Section “Non-conservative amino acid substitution(s) at 302-363”.In an even more preferred embodiment, said one or more non-conservative amino acid substitutions at302-363 of SEQ ID NO 01 is the substitution of at least: (i) one or more aromatic amino acids into a non-aromatic amino acid as disclosed in the presentSection “Non-conservative amino acid substitution(s) at 302-363”; and (ii) one or more non-polar amino acids into a polar amino acid as disclosed in the present Section“Non-conservative amino acid substitution(s) at 302-363”; and (iii) optionally:- one or more amino acids having a side chain that is positively charged at physiologicalpH into an amino acid having a side chain that is uncharged or negatively charged at physiological pH, preferably into an amino acid having a side chain that is negatively charged at physiological pH, as disclosed in the present Section “Non-conservative amino acid substitution(s) at 302-363”; and / or- one or more T and / or one or more Q, preferably one or more T, into a non-polar aminoacid as disclosed in the present Section “Non-conservative amino acid substitution(s) at 302-363”. Preferably, the expression “at least” is replaced with “only”, i.e. no additional non-conservative amino acid substitutions at 302-363 of SEQ ID NO 01 are present than what is explicitly recited. It is particularly preferred that said “one or more aromatic amino acid substitutions into a non-aromatic amino acid” is the substitution of at least F339, F333, F323, F309, F304, Y338, Y306 or W320, preferablyat least F339, F333, F323 or F304, most preferably at least F339, into a non-aromatic amino acid asdisclosed in the present Section “Non-conservative amino acid substitution(s) at 302-363”.It is particularly more preferred that said “one or more aromatic amino acid substitutions into a non-aromatic amino acid” is the substitution of only F339, F333, F323, F309, F304, Y338, Y306 or W320, preferably only F339, F333, F323 or F304, most preferably at least F339, into a non-aromatic amino acid as disclosed in the present Section “Non-conservative amino acid substitution(s) at 302-363”. It is particularly preferred that said “one or more non-polar amino acid substitutions into a polar amino acid” is the substitution of (a) at least A317 (unless S is present at position 317) and A319, preferably at least P316, A317 (unless S is present at position 317) and A319, more preferably at least P316, A317 (unless S is present at position 317), G318 and A319, even more preferably at least L315 (or P315), P316, A317 (unless S is present at position 317), G318 and A319, into a polar amino acid as disclosed in the present Section “Non-conservative amino acid substitution(s) at 302-363”; or (b) at least A324 and A325, into a polar amino acid as disclosed in the present Section “Non-conservative amino acid substitution(s) at 302-363”. It is particularly more preferred that said “one or more non-polar amino acid substitutions into a polar amino acid” is the substitution of (a) only A317 (unless S is present at position 317) and A319, preferably only P316, A317 (unless S is present at position 317) and A319, more preferably only P316, A317 (unless S is present at position 317), G318 and A319, even more preferably only L315 (or P315), P316, A317 (unless S is present at position 317), G318 and A319, into a polar amino acid as disclosed in the present Section “Non-conservative amino acid substitution(s) at 302-363”; or (b) only A324 and A325, into a polar amino acid as disclosed in the present Section “Non-conservative amino acid substitution(s) at 302-363”. It is particularly preferred that said “one or more amino acid having a side chain that is positively charged at physiological pH substitutions into an amino acid having a side chain that is uncharged or negatively charged at physiological pH (preferably into an amino acid having a side chain that is negatively charged at physiological pH)” is the substitution of at least R302, R303, K310, R311, R328, R330, R331, R336, R344, K347, R349, R350, R353 or K359, preferably at least R302, R303, K310, R311, R328, R330, R331, R336, R344, K347 or R349, more preferably at least R328, R330, R331, R336, R344, K347 or R349, even more preferably at least R328, R330, R331 or R336, most preferably at least R336. It is particularly more preferred that said “one or more amino acid having a side chain that is positively charged at physiological pH substitutions into an amino acid having a side chain that is uncharged or negatively charged at physiological pH (preferably into an amino acid having a side chain that is negatively charged at physiological pH)” is the substitution of only R302, R303, K310, R311, R328, R330, R331, R336, R344, K347, R349, R350, R353 or K359, preferably only R302, R303, K310, R311, R328, R330, R331, R336, R344, K347 or R349, more preferably only R328, R330, R331, R336, R344, K347 or R349, even more preferably only R328, R330, R331 or R336, most preferably only R336. It is particularly preferred that said “one or more T and / or one or more Q substitutions into a non-polar amino acid” is the substitution of at least T312, T314 or T334, preferably at least T314, into a non-polaramino acid as disclosed in the present Section “Non-conservative amino acid substitution(s) at 302-363”.It is particularly more preferred that said “one or more T and / or one or more Q substitutions into a non-polar amino acid” is the substitution of only T312, T314 or T334, preferably only T314, into a non-polaramino acid as disclosed in the present Section “Non-conservative amino acid substitution(s) at 302-363”.In a most preferred embodiment, said one or more non-conservative amino acid substitutions at 302-363of SEQ ID NO 01 is the substitution of at least: (i) one or more aromatic amino acids into a non-aromatic amino acid as disclosed in the presentSection “Non-conservative amino acid substitution(s) at 302-363”; and (ii) one or more non-polar amino acids into a polar amino acid as disclosed in the present Section“Non-conservative amino acid substitution(s) at 302-363”. Preferably, the expression “at least” is replaced with “only”, i.e. no additional non-conservative amino acid substitutions at 302-363 of SEQ ID NO 01 are present than what is explicitly recited. It is particularly preferred that said “one or more aromatic amino acid substitutions into a non-aromatic amino acid” is the substitution of at least F339, F333, F323, F309, F304, Y338, Y306 or W320, preferablyat least F339, F333, F323 or F304, most preferably at least F339, into a non-aromatic amino acid asdisclosed in the present Section “Non-conservative amino acid substitution(s) at 302-363”.It is particularly more preferred that said “one or more aromatic amino acid substitutions into a non-aromatic amino acid” is the substitution of only F339, F333, F323, F309, F304, Y338, Y306 or W320, preferably only F339, F333, F323 or F304, most preferably at least F339, into a non-aromatic amino acid as disclosed in the present Section “Non-conservative amino acid substitution(s) at 302-363”. It is particularly preferred that said “one or more non-polar amino acid substitutions into a polar amino acid” is the substitution of (a) at least A317 (unless S is present at position 317) and A319, preferably at least P316, A317 (unless S is present at position 317) and A319, more preferably at least P316, A317 (unless S is present at position 317), G318 and A319, even more preferably at least L315 (or P315), P316, A317 (unless S is present at position 317), G318 and A319, into a polar amino acid as disclosed in the present Section “Non-conservative amino acid substitution(s) at 302-363”; or (b) at least A324 and A325, into a polar amino acid as disclosed in the present Section “Non-conservative amino acid substitution(s) at 302-363”. It is particularly more preferred that said “one or more non-polar amino acid substitutions into a polar amino acid” is the substitution of (a) only A317 (unless S is present at position 317) and A319, preferably only P316, A317 (unless S is present at position 317) and A319, more preferably only P316, A317 (unless S is present at position 317), G318 and A319, even more preferably only L315 (or P315), P316, A317 (unless S is present at position 317), G318 and A319, into a polar amino acid as disclosed in the present Section “Non-conservative amino acid substitution(s) at 302-363”; or (b) only A324 and A325, into a polar amino acid as disclosed in the present Section “Non-conservative amino acid substitution(s) at 302-363”.amino acid as disclosed in the present Section “Non-conservative amino acid substitution(s) at 302-363”.Non-conservative amino acid substitution(s) at 1-301 In a preferred embodiment of the first aspect of the invention, the beta-1,3-N- acetylglucosaminyltransferase mutant according to the invention comprises an amino acid sequence that differs from the full-length amino acid sequence of a reference beta-1,3-N-acetylglucosaminyltransferase represented by SEQ ID NO 01 (it is referred to the Section “Reference beta-1,3-N- acetylglucosaminyltransferase”) in at least one or more non-conservative amino acid substitutions at 1- 301 of SEQ ID NO 01. Throughout the application and claims, the expression “1-301 of SEQ ID NO 01” is preferably replacedwith “17-301 of SEQ ID NO 01”, more preferably replaced with “89-301 of SEQ ID NO 01”, even morepreferably replaced with “158-301 of SEQ ID NO 01”, even more preferably replaced with “171-301 of SEQ ID NO 01”, even more preferably replaced with “180-301 of SEQ ID NO 01”, most preferably replaced with “180-298 of SEQ ID NO 01”. In the context of the invention, a “non-conservative amino acid substitution” is an amino acid substitution which is not a conservative amino acid substitution as defined herein (it is referred to the Section “Conservative amino acid substitution(s) at 1-363”). Accordingly, a non-conservative amino acid substitution is preferably the substitution of (i) an amino acid from one IMGT class to another amino acid from a different IMGT class, preferably a different IMGT class within the same property (i.e. hydropathy, volume, chemical, charge, hydrogen donor or acceptor atoms, or polarity; more preferably hydropathy, chemical, charge or polarity; most preferably hydropathy, charge or polarity), or (ii) an aromatic amino acid (W, Y, F) into a non-aromatic amino acid, preferably an amino acid with a side chain that is less hydrophobic than the side chain of the aromatic amino acid that is substituted (it is referred to the property hydropathy according to the IMGT system as disclosed herein). Amino acids are classified (according to IMGT classification system) as follows based on the property “hydropathy”: -Hydrophobic: I, V, L, F, C, M, A, W (ranked from most hydrophobic, i.e. I, to least hydrophobic, i.e.W);- Neutral (neither a hydrophobic nor hydrophilic side chain): G, T, S, Y, P, H (ranked from mosthydrophobic, i.e. G, to most hydrophilic, i.e. H); -Hydrophilic: R, K, E, Q, D, N (ranked from most hydrophilic, i.e. R, to least hydrophilic, i.e. N).Preferably, a non-conservative amino acid substitution based on the property “hydropathy” is the substitution of (a) a hydrophobic amino acid by a hydrophilic amino acid or neutral (neither a hydrophobicnor hydrophilic side chain) amino acid, preferably by a hydrophilic amino acid, or (b) a hydrophilic aminoacid by a hydrophobic amino acid or neutral (neither a hydrophobic nor hydrophilic side chai) amino acid, preferably by a hydrophobic amino acid. A neutral (neither a hydrophobic nor hydrophilic side chain) is preferably substituted by an amino acid with a side chain that is either hydrophobic or hydrophilic. In thecontext of the present invention (Section “Non-conservative amino acid substitution(s) at 1-301”), withinthe context of “hydropathy” it is particularly preferred that a non-conservative amino acid substitution isthe substitution of a hydrophobic amino acid by a hydrophilic amino acid or vice versa, whereas a non- conservative amino acid substitution of a neutral (neither a hydrophobic nor hydrophilic side chain) is preferably based on another property as discussed herein (i.e. not “hydropathy”, but for example “polarity” wherein for example T is substituted into a non-polar amino acid as T is a polar amino acid)unless it concerns proline (P). The latter is preferably substituted into a hydrophobic amino acid (P is inthe context of hydropathy a neutral amino acid, i.e. neither a hydrophobic nor hydrophilic side chain) or into a polar amino acid (as P is also a non-polar amino acid). Amino acids are classified (according to IMGT classification system) as follows based on the property “volume”: -Very small: G, A, S (ranked from largest, i.e., to smallest, i.e. );- Small: C, D, P, N, T (ranked from largest, i.e., to smallest, i.e. );- Medium: E, V, Q, H (ranked from largest, i.e., to smallest, i.e. );- Large: M, I, L, K, R (ranked from largest, i.e., to smallest, i.e. );- Very large: F, Y, W (ranked from largest, i.e., to smallest, i.e. ).Amino acids are classified (according to IMGT classification system) as follows based on the property “chemical”: -Aliphatic: A, G, I, L, P, V;- Aromatic: F, W, Y;- Sulfur: C, M;- Hydroxyl: S, T;- Basic: R, H, K;- Acidic: D, E;- Amide: N, Q.Amino acids are classified (according to IMGT classification system) as follows based on the property “charge”:- Positively charged: R, H, K;- Negatively charged: D, E;- Uncharged: A, N, C, Q, G, I, L, M, F, P, S, T, W, Y, V.Preferably, a non-conservative amino acid substitution based on the property “charge” in the presentcontext of the invention (Section “Non-conservative amino acid substitution(s) at 1-301”) is thesubstitution of (i) a positively charged amino acid by a negatively charged amino acid or uncharged aminoacid; (ii) an uncharged amino acid by a positively charged amino acid or negatively charged amino acid; or(iii) a negatively charged amino acid by a positively charged amino acid or uncharged amino acid. Morepreferably, a non-conservative amino acid substitution based on the property “charge” is the substitution of a positively charged amino acid by a negatively charged amino acid or uncharged amino acid; or a negatively charged amino acid by a positively charged amino acid or uncharged amino acid. Amino acids are classified (according to IMGT classification system) as follows based on the property “hydrogen donor or acceptor atoms”: -Donor: R, K, W;- Acceptor: D, E;- Donor and acceptor: N, Q, H, S, T, Y;- None: A, C, G, I, L, M, F, P, V.Amino acids are classified (according to IMGT classification system) as follows based on the property “polarity”: -Polar: R, N, D, Q, E, H, K, S, T, Y ;- Non-polar: A, C, G, I, L, M, F, P, W, V.Accordingly, a non-conservative amino acid substitution in the present context of the invention (Section“Non-conservative amino acid substitution(s) at 1-301”) is most preferably the substitution of (i) anaromatic amino acid by a non-aromatic amino acid; (ii) a non-polar amino acid by a polar amino acid; (iii)a proline by a polar amino acid or a hydrophobic amino acid; (iv) a hydrophobic amino acid by a hydrophilicamino acid or neutral amino acid (i.e. neither a hydrophobic nor hydrophilic side chain), preferably by ahydrophilic amino acid; (v) a polar amino acid by a non-polar amino acid; (vi) a positively charged aminoacid by a negatively charged amino acid or uncharged amino acid; or (vii) a negatively charged amino acid by a positively charged amino acid or uncharged amino acid. Said “aromatic amino acid”, non-aromatic amino acid”, “non-polar amino acid”, “polar amino acid”, “hydrophobic amino acid”, “hydrophilic amino acid”, “positively charged amino acid”, “negatively charged amino acid” and “uncharged amino acid” are as disclosed earlier herein. In a more preferred embodiment, one or more non-conservative amino acid substitutions at 1-301 of SEQ ID NO 01 is the substitution of one or more aromatic amino acids into a non-aromatic acid. Preferably, said aromatic amino acid is selected from the list consisting of phenylalanine (F), tyrosine (Y)and tryptophan (W), more preferably selected from the list consisting of tryptophan (W) and tyrosine (Y),most preferably tyrosine (Y). For the sake of clarity, the substitution of one or more aromatic amino acidsinto a non-aromatic amino acid, wherein said aromatic amino acid is selected from the list consisting of F, Y and W, also encompasses the situation wherein one F, one Y or one W is substituted. It also encompasses the situation wherein one or more F are substituted, one or more Y are substituted, or one or more W are substituted. It also encompasses the situation wherein one or more F are substituted and optionally one or more Y are substituted and optionally one or more W are substituted etc. Throughout the application and claims, unless specifically stated otherwise, a non-aromatic amino acid is selected form the list consisting of R, K, E, Q, D, N, H, P, S, T, G, A, M, C, L, V and I, preferably selected from the list consisting of A, G, I, L, V, N, Q, M, C, D, E, R and K, more preferably selected from the list consisting of A, G, N, Q, M, C, D, E, R and K, even more preferably selected from the list consisting of A, G, N, Q, M, D, E, R and K, even more preferably selected from the list consisting of A, G, N, Q, M, D and E, even more preferably selected from the list consisting of A, G, N, Q and M, even more preferably selected from the list consisting of A, G, N and M, even more preferably selected from the list consisting of A, N and M, mostpreferably N or A. In the context of the present invention, it is particularly preferred that a F or a W issubstituted into A, G, N, Q, M, D, or E, more preferably into A, G, N, Q or M, even more preferably into A,G, N or M, even more preferably into A, N or M, most preferably into A or N. In the context of the presentinvention, it is particularly preferred that a Y is substituted into A, G, N, Q, M, D, or E, more preferably into A, G, N, Q or M, even more preferably into A, G, N or M, even more preferably into A, N or M, most preferably into N or M.In an even more preferred embodiment, said one or more aromatic amino acid substitutions at 1-301 ofSEQ ID NO 01 is the substitution of one or more amino acids selected from the list consisting of W141, W164, F176, F177, F179, Y201, Y211, F213, Y215, Y225, Y226, Y233, F263, F269, F273, Y278 and F298; preferably selected from the list consisting of W164, F176, F177, F179, Y201, Y211, F213, Y215, Y225, Y226, Y233 and F298; more preferably selected from the list consisting of W164, F176, F177, F179, Y201, Y211, F213, Y215, Y225, Y226 and Y233; even more preferably selected form the list consisting of Y201, Y211, Y215, Y225 and Y226; even more preferably Y211 or Y226; most preferably Y211, into a non- aromatic amino acid. In an alternative even more preferred embodiment, said one or more aromatic amino acid substitutions at 1-301 of SEQ ID NO 01 is the substitution of one or more amino acids selected from the list consistingof W207, W214 and Y244, preferably W214, into a non-aromatic amino acid. The increased substratespecificity for lactose over a longer-chain oligosaccharide compared to the reference beta-1,3-N- acetylglucosaminyltransferase (it is referred to the Section “Mutant beta-1,3-N- acetylglucosaminyltransferase”) has been described in WO2022 / 133093 (said substitutions are herein disclosed as W206, W214 and Y243, respectively; the corresponding parts of the description and examples are incorporated by reference herein). In an alternative even more preferred embodiment, said one or more aromatic amino acid substitutions at 1-301 of SEQ ID NO 01 is the substitution of one or more amino acids selected from the list consisting of W141, W164, F176, F177, F179, Y201, W207, Y211, F213, W214, Y215, Y225, Y226, Y233, Y244, F263, F269, F273, Y278 and F298; preferably selected from the list consisting of W164, F176, F177, F179, Y201, Y211, F213, W214, Y215, Y225, Y226, Y233 and F298; more preferably selected from the list consisting of F176, F177, F179, Y201, Y211, F213, W214, Y215, Y225, Y226 and Y233; even more preferably selected form the list consisting of Y201, Y211, W214, Y215, Y225 and Y226; even more preferably Y211, Y226 orW214; even more preferably Y211 or W214, most preferably Y211.In an even more preferred embodiment, and particularly preferred in the context of the present invention,said one or more aromatic amino acid substitutions at 1-301 of SEQ ID NO 01 is the substitution of at least W141, W164, F176, F177, F179, Y201, W207, Y211, F213, W214, Y215, Y225, Y226, Y233, Y244, F263,F269, F273, Y278 or F298; preferably at least W164, F176, F177, F179, Y201, Y211, F213, W214, Y215,Y225, Y226, Y233 or F298; more preferably at least F176, F177, F179, Y201, Y211, F213, W214, Y215, Y225,Y226 or Y233; even more preferably at least Y201, Y211, W214, Y215, Y225 or Y226; even more preferablyat least Y211, Y226 or W214; even more preferably at least Y211 or W214, most preferably at least Y211. In an even more preferred embodiment, said one or more aromatic amino acid substitutions at 1-301 ofSEQ ID NO 01 is the substitution of only W141, W164, F176, F177, F179, Y201, W207, Y211, F213, W214,Y215, Y225, Y226, Y233, Y244, F263, F269, F273, Y278 or F298; preferably only W164, F176, F177, F179,Y201, Y211, F213, W214, Y215, Y225, Y226, Y233 or F298; more preferably only F176, F177, F179, Y201,Y211, F213, W214, Y215, Y225, Y226 or Y233; even more preferably only Y201, Y211, W214, Y215, Y225or Y226; even more preferably only Y211, Y226 or W214; even more preferably only Y211 or W214, most preferably only Y211.As the skilled person is familiar with, a particular amino acid can belong to different IMGT classesdepending on the property as disclosed earlier herein. For example, phenylalanine (F) is an aromatic amino acid and hence a non-conservative amino acid substitution would be the substitution into a non- aromatic amino acid. At the same time, phenylalanine (F) is also a hydrophobic amino acid and hence a non-conservative amino acid substitution would be the substitution into a hydrophilic amino acid or a neutral amino acid (neither a hydrophobic nor a hydrophilic side chain), preferably into a hydrophilic amino acid. For the sake of clarity, throughout the present Section (“Non-conservative amino acid substitution(s) at 1-301“), when an amino acid is an aromatic amino acid, then a non-conservative amino acid substitution is particularly preferred to be the substitution into a non-aromatic amino acid. In an additional and / or alternative more preferred embodiment, one or more non-conservative aminoacid substitutions at 1-301 of SEQ ID NO 01 is the substitution of one or more non-polar amino acids intoa polar amino acid. Preferably, said non-polar amino acid is selected from the list consisting of A, C, G, I, L, M, F, P, W and V, more preferably selected from the list consisting of A, C, G, I, L, M, P and V, even more preferably selected from the list consisting of P, G, A, L, M, V and I, even more preferably selected from the list consisting ofP, G and A, most preferably P or G. For the sake of clarity, the substitution of one or more non-polar aminoacids into a polar amino acid, wherein said non-polar amino acid is selected from for example the listconsisting of P, G and A, also encompasses the situation wherein one P, one G, or one A is substituted. Italso encompasses the situation wherein one or more P are substituted, one or more G are substituted, orone or more A are substituted. It also encompasses the situation wherein one or more P are substitutedand optionally one or more G are substituted and optionally one or more A are substituted etc.In the present context of the invention (Section “Non-conservative amino acid substitution(s) at 1-301”,unless specifically stated otherwise, a polar amino acid is selected form the list consisting of R, N, D, Q, E,H, K, S, T and Y, preferably selected from the list consisting of D, E, S, N, Q, T, R and K, more preferablyselected from the list consisting of D, E, S, T, R and K, even more preferably selected from the list consistingof D, E, S and R, most preferably S or R.In the context of the present invention, it is particularly preferred that G is substituted into D, E, S, N, Q,T, R, K, H or Y, more preferably into D, E, S, N, Q, T, R or K, even more preferably into D, E, S, T, R or K,even more preferably into S, T, R or K, even more preferably into R or K, most preferably into R. In the context of the present invention, it is particularly preferred that P is substituted into D, E, S, N, Q, T, R, K, H or Y, more preferably into D, E, S, N, Q, T, R or K, more preferably into D, E, S, T, R or K, even morepreferably into S, T, D or E, even more preferably into S, T or D, even more preferably into S or T, mostpreferably into S. In the context of the present invention, it is particularly preferred that A is substituted into D, E, S, N, Q, T, R, K, H or Y, more preferably into D, E, S, N, Q, T, R, K or Y, even more preferably intoD, E, S, T, R, K or Y, even more preferably into D, E, S, R or Y, most preferably into S, D or E. In the contextof the present invention, it is particularly preferred that I is substituted into D, E, S, N, Q, T, R, K, H or Y, more preferably into D, E, S, T, R, K or Y, even more preferably into D, E, S, R or Y, most preferably into Y.In an even more preferred embodiment, said one or more non-polar amino acid substitutions at 1-301 ofSEQ ID NO 01 is the substitution of one or more amino acids selected from the list consisting of G151, L154, A155, P178, P182, M190, P227, A229, A252 and P294; preferably selected from the list consistingof G151, L154, A155, P178, P182, A252 and P294; more preferably selected from the list consisting ofP178, P182 and P294; even more preferably P178 or P182, most preferably P182.In an alternative even more preferred embodiment, said one or more non-polar amino acid substitutions at 1-301 of SEQ ID NO 01 is the substitution of one or more amino acids selected from the list consistingof G180, A259, L230, M188, I183, V217, V231, A285, A27, P89, A301, A208, V231, I251, I255 and A259;preferably selected from the list consisting of G180, A259, L230, M188, I183, V217, V231, A285, A27, P89 and A301, more preferably selected from the list consisting of G180, A259, L230, M188, I183, V217, V231, A285, A27 and P89; even more preferably selected from the list consisting of G180, A259, L230, M188, I183, V217, V231, A285 and A27; even more preferably selected from the list consisting of G180, A259,L230, M188, I183 and V217; even more preferably selected from the list consisting of G180, A259, L230and M188; most preferably G180. The increased substrate specificity for lactose over a longer-chainoligosaccharide compared to the reference beta-1,3-N-acetylglucosaminyltransferase (it is referred to the Section “Mutant beta-1,3-N-acetylglucosaminyltransferase”) has been described in WO2022 / 133093 (said substitutions are herein disclosed as G179, A258, L229, M187, I182, V216, V230, A284, A27, P89, A300, A207, V230, I250, I254 and A258, respectively; the corresponding parts of the description and examples are incorporated by reference herein). In an alternative even more preferred embodiment, said one or more non-polar amino acid substitutions at 1-301 of SEQ ID NO 01 is the substitution of one or more amino acids selected from the list consisting of A27, P89, G151, L154, A155, P178, G180, P182, I183, M188, M190, A208, V217, P227, A229, L230, V231, I251, A252, I255, A259, P294 and A301; preferably selected from the list consisting of A27, P89, G151, L154, A155, P178, G180, P182, I183, M188, A208, V217, L230, V231, I251, A252, I255, A259, P294 and A301; more preferably selected from the list consisting of A27, P89, P178, G180, P182, I183, M188, V217,L230, V231, A252, A259, A285, P294 and A301, even more preferably selected from the list consisting ofA27, P89, P178, G180, P182, I183, M188, V217, L230, V231, A259, A285 and P294; even more preferablyselected from the list consisting of A27, P178, G180, P182, I183, M188, V217, L230, V231, A259 and A285;even more preferably selected from the list consisting of G180, P182, I183, M188, V217, L230 and A259;even more preferably selected from the list consisting of G180, P182, M188, L230 and A259; even more preferably selected from the list consisting of G180 and P182, most preferably G180. In an even more preferred embodiment, and particularly preferred in the context of the present invention, said one or more non-polar amino acid substitutions at 1-301 of SEQ ID NO 01 is the substitution of at least A27, P89, G151, L154, A155, P178, G180, P182, I183, M188, M190, A208, V217, P227,A229, L230, V231, I251, A252, I255, A259, P294 or A301; preferably at least A27, P89, G151, L154, A155, P178, G180, P182, I183, M188, A208, V217, L230, V231, I251, A252, I255, A259, P294 or A301; more preferably at least A27, P89, P178, G180, P182, I183, M188, V217, L230, V231, A252, A259, A285, P294 or A301, even more preferably at least A27, P89, P178, G180, P182, I183, M188, V217, L230, V231, A259, A285 or P294; even more preferably at least A27, P178, G180, P182, I183, M188, V217, L230, V231, A259 or A285; even more preferably at least G180, P182, I183, M188, V217, L230 or A259; even more preferably at least G180, P182, M188, L230 or A259; even more preferably at least G180 or P182, most preferably at least G180. In an even more preferred embodiment, said one or more non-polar amino acid substitutions at 1-301 of SEQ ID NO 01 is the substitution of only A27, P89, G151, L154, A155, P178, G180, P182, I183, M188, M190, A208, V217, P227,A229, L230, V231, I251, A252, I255, A259, P294 or A301; preferably only A27, P89, G151, L154, A155, P178, G180, P182, I183, M188, A208, V217, L230, V231, I251, A252, I255, A259, P294 or A301; more preferably only A27, P89, P178, G180, P182, I183, M188, V217, L230, V231, A252, A259, A285, P294 or A301, even more preferably only A27, P89, P178, G180, P182, I183, M188, V217, L230, V231, A259, A285 or P294; even more preferably only A27, P178, G180, P182, I183, M188, V217, L230, V231, A259 or A285; even more preferably only G180, P182, I183, M188, V217, L230 or A259; even more preferably only G180, P182, M188, L230 or A259; even more preferably only G180 or P182, most preferably only G180. As the skilled person is familiar with, a particular amino acid can belong to different IMGT classesdepending on the property as disclosed earlier herein. For example, alanine (A) is a non-polar amino acidand hence a non-conservative amino acid substitution would be the substitution into a polar amino acid.At the same time, alanine (A) is also a hydrophobic amino acid and hence a non-conservative amino acidsubstitution would be the substitution into a hydrophilic amino acid or a neutral amino acid (i.e. neither a hydrophobic nor a hydrophilic side chain), preferably into a hydrophilic amino acid. In this regard it isnoted that each hydrophobic amino acid is a non-polar amino acid. With the exception of G and P, eachnon-polar amino acid is a hydrophobic amino acid. Further, the list of amino acids either belonging to the group of hydrophilic amino acids or neutral amino acids (i.e. neither a hydrophobic nor a hydrophilic side chain) is identical to the group of polar amino acids, except that P and G are also present (and not in the list of polar amino acids). Hence, the skilled person will understand that a non-conservative amino acid substitution of a non-polar amino acid and that of a hydrophobic amino acid is similar. For the sake of clarity, throughout the present Section (“Non-conservative amino acid substitution(s) at1-301“), when an amino acid is a hydrophobic amino acid, then a non-conservative amino acidsubstitution is particularly preferred to be the substitution into a hydrophilic amino acid or a neutral amino acid (i.e. neither a hydrophobic nor a hydrophilic side chain), preferably into a hydrophilic amino acid. For the sake of clarity, throughout the present Section (“Non-conservative amino acid substitution(s) at 1-301“), when an amino acid is a proline (P), then a non-conservative amino acid substitution is particularly preferred to be the substitution into a polar amino acid or a hydrophobic amino acid, preferably into a polar amino acid as disclosed further herein. In an additional and / or alternative more preferred embodiment, one or more non-conservative aminoacid substitutions at 1-301 of SEQ ID NO 01 is the substitution of one or more proline into a polar aminoacid or a hydrophobic amino acid, preferably into a polar amino acid.Preferably, said polar amino acid is selected form the list consisting of R, N, D, Q, E, H, K, S, T and Y, morepreferably selected from the list consisting of D, E, S, N, Q, T, R and K, even more preferably selected from the list consisting of D, E, S, T, R and K, even more preferably selected from the list consisting of S, T, Dand E, even more preferably selected from the list consisting of S, T and D, even more preferably S or T,most preferably into S. Preferably, said hydrophobic amino acid is selected from the list consisting of I, V, L, C, M and A, more preferably selected from the list consisting of I, L, C, M and A, even more preferably selected from the list consisting of L, M and A, most preferably L or M.In the context of the present invention, it is particularly preferred that P89 is substituted into L, M, A, D,E, S, N, Q, T, R or K, preferably into L, M, A, D, E, S, T, R and K, more preferably into L, M, A, S, T, D or E, even more preferably into L, M, A, S, T or D, even more preferably into L, M, A, S or T, even more preferably into L, M, S or T, most preferably into T. In the context of the present invention, it is particularly preferred that P182 is substituted into L, M, A, D, E, S, N, Q, T, R or K, preferably into L, M, A, D, E, S, T, R and K, more preferably into L, M, A, S, T, D or E, even more preferably into L, M, A, S, T or D, even more preferably into L, M, A, S or T, even more preferably into L, M, S or T, most preferably into S.In an even more preferred embodiment, said one or more proline substitutions at 1-301 of SEQ ID NO 01is the substitution of one or more amino acids selected from the list consisting of P178, P182, P227 andP294; preferably selected from the list consisting of P178, P182 and P294; most preferably P182.In an alternative even more preferred embodiment, said one or more proline substitutions at 1-301 ofSEQ ID NO 01 is the substitution of P89. The increased substrate specificity for lactose over a longer-chainoligosaccharide compared to the reference beta-1,3-N-acetylglucosaminyltransferase (it is referred to the Section “Mutant beta-1,3-N-acetylglucosaminyltransferase”) has been described in WO2022 / 133093 (said substitution is herein disclosed as P89; the corresponding parts of the description and examples are incorporated by reference herein). In an alternative even more preferred embodiment, said one or more proline substitutions at 1-301 of SEQ ID NO 01 is the substitution of one or more amino acids selected from the list consisting of P89, P178, P182, P227 and P294; more preferably selected from the list consisting of P89, P178, P182 and P294, even more preferably selected from the list consisting of P89 and P182, most preferably P182. In an even more preferred embodiment, and particularly preferred in the context of the present invention,said one or more proline substitutions at 1-301 of SEQ ID NO 01 is the substitution of at least P89, P178,P182, P227 or P294; preferably at least P89, P178, P182 or P294, more preferably at least P89 or P182, most preferably at least P182.In an even more preferred embodiment, said one or more proline substitutions at 1-301 of SEQ ID NO 01is the substitution of only P89, P178, P182, P227 or P294, preferably only P89, P178, P182 or P294, more preferably only P89 or P182, most preferably only P182. For the sake of clarity, throughout the present Section (“Non-conservative amino acid substitution(s) at 1-301“), when an amino acid is a proline (P), then a non-conservative amino acid substitution is particularly preferred to be the substitution into a polar amino acid or a hydrophobic amino acid, preferably into a polar amino acid as disclosed further herein. In an additional and / or alternative more preferred embodiment, one or more non-conservative aminoacid substitutions at 1-301 of SEQ ID NO 01 is the substitution of one or more hydrophobic amino acidsinto a hydrophilic amino acid or a neutral amino acid (i.e. neither a hydrophobic nor hydrophilic sidechain), preferably into a hydrophilic amino acid. For the sake of clarity, the substitution of one or more hydrophobic amino acids into e.g. a hydrophilic amino acid, wherein said hydrophobic amino acid is selected from for example the list consisting of L, A and M, also encompasses the situation wherein one L, one A, or one M is substituted. It also encompasses the situation wherein one or more L are substituted, one or more A are substituted, or one or more M are substituted. It also encompasses the situation wherein one or more L are substituted and optionally one or more A are substituted and optionally one or more M are substituted etc.Preferably, said hydrophobic amino acid is selected from the list consisting of I, V, L, C, M and A, morepreferably selected from the list consisting of I, V, L, M and A, even more preferably selected from the list consisting of L, A and M. Preferably, said hydrophilic amino acid is selected from the list consisting of D, E, N, Q, R, and K, more preferably selected from the list consisting of D, E, R and K, even more preferably selected from the list consisting of D, E and R, even more preferably selected from the list consisting of D and E, most preferably D. Preferably, said neutral amino acid (i.e. neither a hydrophobic nor hydrophilic side chain) is selected from the list consisting of G, T, S, Y, P and H, more preferably selected from the list consisting of G, T, S, Y and P, even more preferably selected from the list consisting of G, S, T and P, even more preferably selected from the list consisting of G, S and P, most preferably G or P. In the context of the present invention, it is particularly preferred that A is substituted into D, E, S, N, Q, T, R, K, H, Y, G or P, more preferably into D, E, S, N, Q, T, R, K, Y, G or P, even more preferably into D, E, S,N, Q, T, R, K, Y or G, even more preferably into D, E, S, T, R, K, Y or G, even more preferably into D, E, S, R,Y or G, even more preferably into S, D, E or G, most preferably into S, D or E. In the context of the presentinvention, it is particularly preferred that M is substituted into D, E, S, N, Q, T, R, K, H, Y, G or P, morepreferably into D, E, S, N, Q, T, R, K, Y, G or P, even more preferably into D, E, S, N, Q, T, R, K, Y or P, even more preferably into D, E, S, T, R, K, Y or P, even more preferably into S, T, Y or P, even more preferably into S, Y or P, most preferably into P. In the context of the present invention, it is particularly preferred that I is substituted into D, E, S, N, Q, T, R, K, H, Y, G or P, more preferably into D, E, S, N, Q, T, R, K, H, Y or G, even more preferably into D, E, S, N, Q, T, R, K, H or Y, even more preferably into D, E, S, T, R, K or Y, even more preferably into D, E, S, R or Y, most preferably into Y. In the context of the present invention,it is particularly preferred that L is substituted into D, E, S, N, Q, T, R, K, H, Y, G or P, more preferably intoD, E, S, N, Q, T, R, K, Y, G or P, even more preferably into D, E, S, N, Q, T, R, K, Y or P, even more preferably into D, E, S, T, R, K, Y or P, even more preferably into S, T, Y or P, even more preferably into S, Y or P, most preferably into P. In the context of the present invention, it is particularly preferred that V is substitutedinto D, E, S, N, Q, T, R, K, H, Y, G or P, more preferably into D, E, S, N, Q, T, R, K, Y, G or P, even morepreferably into D, E, S, N, Q, T, R, K, Y or G, even more preferably into D, E, S, T, R, K, Y or G, even more preferably into D, E, S, R, Y or G, even more preferably into S, D, E or G, most preferably into S, D or E.In an even more preferred embodiment, said one or more hydrophobic amino acid substitutions at 1-301of SEQ ID NO 01 is the substitution of one or more amino acids selected from the list consisting of L154,A155, M190, A229 and A252; preferably selected from the list consisting of L154, A155 and A252.In an alternative even more preferred embodiment, said one or more hydrophobic amino acidsubstitutions at 1-301 of SEQ ID NO 01 is the substitution of one or more amino acids selected from thelist consisting of A259, L230, M188, I183, V217, V231, A285, A27, A301, A208, V231, I251 and I255;preferably selected from the list consisting of A259, L230, M188, I183, V217, V231, A285, A27 and A301,more preferably selected from the list consisting of A259, L230, M188, I183, V217, V231, A285 and A27;even more preferably selected from the list consisting of A259, L230, M188, I183 and V217; even morepreferably selected from the list consisting of A259, L230 and M188; most preferably M188. The increasedsubstrate specificity for lactose over a longer-chain oligosaccharide compared to the reference beta-1,3- N-acetylglucosaminyltransferase (it is referred to the Section “Mutant beta-1,3-N- acetylglucosaminyltransferase”) has been described in WO2022 / 133093 (said substitutions are herein disclosed as A258, L229, M187, I182, V216, V230, A284, A27, A300, A207, V230, I250 and I254, respectively; the corresponding parts of the description and examples are incorporated by reference herein). In an alternative even more preferred embodiment, said one or more hydrophobic amino acid substitutions at 1-301 of SEQ ID NO 01 is the substitution of one or more amino acids selected from the list consisting of A27, L154, A155, I183, M188, M190, A208, V217, P227, L230, V231, I251, A252, I255, A259 and A301; preferably selected from the list consisting of A27, L154, A155, I183, M188, A208, V217,L230, V231, I251, A252, I255, A259 and A301; more preferably selected from the list consisting of A27,I183, M188, V217, L230, V231, A252, A259, A285 and A301, even more preferably selected from the listconsisting of A27, I183, M188, V217, L230, V231, A259 and A285; even more preferably selected from thelist consisting of I183, M188, V217, L230 and A259; even more preferably selected from the list consisting of M188, L230 and A259; most preferably M188. In an even more preferred embodiment, and particularly preferred in the context of the present invention, said one or more hydrophobic amino acid substitutions at 1-301 of SEQ ID NO 01 is the substitution of at least A27, L154, A155, I183, M188, M190, A208, V217, P227, A229, L230, V231, I251, A252, I255, A259 or A301; preferably at least A27, L154, A155, I183, M188, A208, V217, L230, V231, I251, A252, I255, A259 or A301; more preferably at least A27, I183, M188, V217, L230, V231, A252, A259, A285 or A301, even more preferably at least A27, I183, M188, V217, L230, V231, A259 or A285; even more preferably at least I183, M188, V217, L230 or A259; even more preferably at least M188, L230 or A259; most preferably at least M188. In an even more preferred embodiment, said one or more hydrophobic amino acid substitutions at 1-301of SEQ ID NO 01 is the substitution of only A27, L154, A155, I183, M188, M190, A208, V217, P227, A229,L230, V231, I251, A252, I255, A259 or A301; preferably only A27, L154, A155, I183, M188, A208, V217, L230, V231, I251, A252, I255, A259 or A301; more preferably only A27, I183, M188, V217, L230, V231, A252, A259, A285 or A301, even more preferably only A27, I183, M188, V217, L230, V231, A259 or A285; even more preferably only I183, M188, V217, L230 or A259; even more preferably only M188, L230 or A259; most preferably only M188. In an additional and / or alternative more preferred embodiment, one or more non-conservative amino acid substitutions at 1-301 of SEQ ID NO 01 is the substitution of one or more polar amino acids into a non-polar amino acid. Preferably, a polar amino acid is selected form the list consisting of R, N, D, Q, E, H, K, S, T and Y, preferablyselected from the list consisting of D, E, S, N, Q, T, R, H and K, more preferably selected from the listconsisting of S, T, N, Q and H, even more preferably selected from the list consisting of S, T, N and Q. Preferably, said non-polar amino acid is selected from the list consisting of A, C, G, I, L, M, F, P, W and V, more preferably selected from the list consisting of A, C, G, I, L, M, P and V, even more preferably selected from the list consisting of P, G, A, L, M, V and I, even more preferably selected from the list consisting ofP, G, A, L, V and I, even more preferably selected from the list consisting of P, G and A, most preferably Gor A. For the sake of clarity, the substitution of one or more polar amino acids into a non-polar aminoacid, wherein said polar amino acid is selected from for example the list consisting of S, N and Q, alsoencompasses the situation wherein one S, one N, or one Q is substituted. It also encompasses the situationwherein one or more S are substituted, one or more N are substituted, or one or more Q are substituted.It also encompasses the situation wherein one or more N are substituted and optionally one or more Sare substituted and optionally one or more Q are substituted etc.In the context of the present invention, it is particularly preferred that S is substituted into A, C, G, I, L, M,F, P, W or V , more preferably into A, C, G, I, L, M, P or V, even more preferably into P, G, A, L, M, V or I,even more preferably into P, G, A, L, V or I, even more preferably into P, G or A, most preferably into G orA. In the context of the present invention, it is particularly preferred that T is substituted into A, C, G, I, L, M,F, P, W or V, more preferably into A, C, G, I, L, M, P or V, even more preferably into P, G, A, L, M, V or I,even more preferably into P, G, A, L, V or I, even more preferably into P, G or A, most preferably into G or A.In the context of the present invention, it is particularly preferred that N is substituted into A, C, G, I, L,M, F, P, W or V, more preferably into A, C, G, I, L, M, P or V, even more preferably into P, G, A, L, M, V orI, even more preferably into P, G, A, L, V or I, even more preferably into P, G or A, even more preferably into G or A, most preferably into G.In the context of the present invention, it is particularly preferred that Q is substituted into A, C, G, I, L,M, F, P, W or V, more preferably into A, C, G, I, L, M, P or V, even more preferably into P, G, A, L, M, V orI, even more preferably into P, G, A, L, V or I, even more preferably into V, L, I, G or A, even more preferably into V, L, I or G, even more preferably into V, L or I, most preferably into V. In an even more preferred embodiment, said one or more polar amino acid substitutions at 1-301 of SEQ ID NO 01 is the substitution of one or more amino acids selected from the list consisting of K149, D150,N152, R153, R156, H157, H158, K232, S242, K257, K270, R272 and R279; preferably S242.In an alternative even more preferred embodiment, said one or more polar amino acid substitutions at 1- 301 of SEQ ID NO 01 is the substitution of one or more amino acids selected from the list consisting of N186, Q212, E171, K291, S245, E295, E299, R300, N181, H184, T187, R234, H236, S241, K243, H244, S245,Q248, Q256 and S266; preferably selected from the list consisting of N186, Q212, E171, K291, S245, E295,E299, R300 and K243; more preferably selected from the list consisting of N186, Q212, E171, K291, S245,E295, E299 and R300, even more preferably selected from the list consisting of N186, Q212, E171, K291and S245; even more preferably selected from the list consisting of N186, Q212, E171 and K291; evenmore preferably selected from the list consisting of Q212, E171 and K291; most preferably E171 or K291. The increased substrate specificity for lactose over a longer-chain oligosaccharide compared to the reference beta-1,3-N-acetylglucosaminyltransferase (it is referred to the Section “Mutant beta-1,3-N- acetylglucosaminyltransferase”) has been described in WO2022 / 133093 (said substitutions are herein disclosed as N185, Q211, E170, K290, S244, E294, E298, R299, N180, H183, T186, R233, H235, S240, K242,S244, Q247, Q255 and S265, respectively; the corresponding parts of the description and examples areincorporated by reference herein). In an alternative even more preferred embodiment, said one or more polar amino acid substitutions at 1- 301 of SEQ ID NO 01 is the substitution of one or more amino acids selected from the list consisting of K149, D150, N152, R153, R156, H157, H158, E171, N181, H184, N186, T187, Q212, K232, R234, H236,S241, S242, K243, H244, S245, Q248, H249, Q256, K257, S266, K270, R272, R279, K291, E295, E299 andR300; preferably selected from the list consisting of H158, E171, N186, Q212, S242, S245, H249, Q256, K291, E295, E299, R300 and A301, more preferably selected from the list consisting of H158, E171, N186,Q212, S242, S245, H249, Q256 and K291; even more preferably selected from the list consisting of H158,E171, N186, Q212, S245, H249, Q256 and K291; even more preferably selected from the list consisting ofH158, E171, N186, Q212, H249, Q256 and K291; even more preferably H158, N186, H249, Q212 and Q256,even more preferably selected from the list consisting of H158, H249, Q212 and Q256; most preferablyQ212. In an even more preferred embodiment, and particularly preferred in the context of the present invention, said one or more polar amino acid substitutions at 1-301 of SEQ ID NO 01 is the substitution of at least K149, D150, N152, R153, R156, H157, H158, E171, N181, H184, N186, T187, Q212, K232, R234, H236, S241, S242, K243, H244, S245, Q248, H249, Q256, S266, K270, R272, R279, K291, E295, E299 or R300; more preferably at least H158, E171, N186, Q212, S242, S245, H249, Q256, K291, E295, E299, R300 orA301, even more preferably at least H158, E171, N186, Q212, S242, S245, H249, Q256 or K291; even morepreferably at least H158, E171, N186, Q212, S245, H249, Q256 or K291; even more preferably at leastH158, E171, N186, Q212, H249, Q256 or K291; even more preferably at least H158, N186, H249, Q212 orQ256, even more preferably at least H158, H249, Q212 or Q256; most preferably at least Q212.In an alternative even more preferred embodiment, said one or more polar amino acid substitutions at 1-301 of SEQ ID NO 01 is the substitution of only K149, D150, N152, R153, R156, H157, H158, E171, N181,H184, N186, T187, Q212, K232, R234, H236, S241, S242, K243, H244, S245, Q248, H249, Q256, S266, K270,R272, R279, K291, E295, E299 or R300; more preferably only H158, E171, N186, Q212, S242, S245, H249, Q256, K291, E295, E299, R300 or A301, even more preferably only H158, E171, N186, Q212, S242, S245,H249, Q256 or K291; even more preferably only H158, E171, N186, Q212, S245, H249, Q256 or K291; evenmore preferably only H158, E171, N186, Q212, H249, Q256 or K291; even more preferably only H158,N186, H249, Q212 or Q256, even more preferably only H158, H249, Q212 or Q256; most preferably onlyQ212. In a most preferred embodiment, said one or more polar amino acid substitutions at 1-301 of SEQ ID NO 01 is the substitution of only: -E295, E299 and R300; or- Q212; or- N186; or- K291; or- E171.In an alternative most preferred embodiment, said one or more polar amino acid substitutions at 1-301of SEQ ID NO 01 is the substitution of at least H158, H249 or Q256, more preferably the substitution of atleast H249 and Q256, even more preferably the substitution of at least H158, H249 and Q256, most preferably the substitution of only H158, H249 and Q256. As the skilled person is familiar with, a particular amino acid can belong to different IMGT classes depending on the property as disclosed earlier herein. For the sake of clarity, throughout the present Section (“Non-conservative amino acid substitution(s) at 1-301“), when an amino acid is a D or E (i.e. an amino acid with a negatively charged side chain at physiological pH), then a non-conservative amino acid substitution is particularly preferred to be the substitution into a positively charged amino acid (i.e. amino acid with a positively charged side chain at physiological pH) or uncharged amino acid (i.e. an amino acid with a neutral side chain at physiological pH), preferably into a positively charged amino acid, as disclosedfurther herein. For the sake of clarity, throughout the present Section (“Non-conservative amino acidsubstitution(s) at 1-301“), when an amino acid is a R, K or H (i.e. an amino acid with a positively charged side chain at physiological pH), then a non-conservative amino acid substitution is particularly preferred to be the substitution into a negatively charged amino acid (i.e. amino acid with a negatively charged side chain at physiological pH) or uncharged amino acid (i.e. an amino acid with a neutral side chain at physiological pH), preferably into a negatively charged amino acid, as disclosed further herein. In an additional and / or alternative more preferred embodiment, one or more non-conservative amino acid substitutions at 1-301 of SEQ ID NO 01 is the substitution of one or more amino acids having a positively charged side chain at physiological pH (i.e. positively charged amino acid) into an amino acid having a negatively charged side chain at physiological pH (i.e. negatively charged amino acid) or an aminoacid having a neutral side chain at physiological pH (i.e. uncharged amino acid), preferably into anuncharged amino acid.Preferably, a positively charged amino acid is selected form the list consisting of R, H and K, morepreferably K or R, most preferably K. Preferably, a negatively charged amino acid is D or E, more preferably D. Preferably, an uncharged amino acid is selected from the list consisting of A, N, C, Q, G, I, L, M, F, P, S, T, W, Y and V, more preferably selected from the list consisting of A, N, C, Q, G, I, L, M, P, S, T and V, even more preferably selected from the list consisting of N, Q, S and T, even more preferably N or Q, most preferably Q. For the sake of clarity, the substitution of one or more amino acids having a side chain that is positively charged at physiological pH into an amino acid having a side chain that is uncharged or negatively charged at physiological pH, wherein said amino acid having a side chain that is positively charged at physiological pH is R or K, also encompasses the situation wherein one R or one K is substituted. It also encompasses the situation wherein one or more R are substituted or one or more K are substituted. It also encompasses the situation wherein one or more R are substituted and optionally one or more K are substituted. It also encompasses the situation wherein one or more K are substituted and optionally one or more R are substituted. In the context of the present invention, it is particularly preferred that an amino acid having a positivelycharged side chain at physiological pH (i.e. R, H or K, preferably K or R, most preferably K) is substitutedinto A, N, C, Q, G, I, L, M, P, S, T, V, D or E, preferably into N, Q, S, T, D or E, more preferably into N, Q, S, T or D, even more preferably into N, Q, S or T, even more preferably into N or Q, most preferably into Q.In an even more preferred embodiment, said one or more positively charged amino acid substitutions at1-301 of SEQ ID NO 01 is the substitution of one or more amino acids selected from the list consisting of K149, R153, R156, H157, H158, R169, H170, K232, K257, K270, R272 and R279; preferably selected from the list consisting of R169, H170, K232, K257, K270, R272 and R279; most preferably R169 or H170. In an alternative even more preferred embodiment, said one or more positively charged amino acid substitutions at 1-301 of SEQ ID NO 01 is the substitution of one or more amino acids selected from thelist consisting of K291, R300, H184, R234, H236, K243 and H244; preferably selected from the listconsisting of K243, K291 and R300; most preferably K291 or R300. The increased substrate specificity forlactose over a longer-chain oligosaccharide compared to the reference beta-1,3-N- acetylglucosaminyltransferase (it is referred to the Section “Mutant beta-1,3-N- acetylglucosaminyltransferase”) has been described in WO2022 / 133093 (said substitutions are herein disclosed as K290, R299, H183, R233, H235 and K242, respectively; the corresponding parts of the description and examples are incorporated by reference herein). In an alternative even more preferred embodiment, said one or more positively charged amino acid substitutions at 1-301 of SEQ ID NO 01 is the substitution of one or more amino acids selected from the list consisting of K149, R153, R156, H157, H158, R169, H170, H184, K232, R234, H236, K243, H244, K257, K270, R272, R279, K291 and R300; preferably selected from the list consisting of R169, H170, H184, K232,K243, K257, K270, R272, R279, K291 and R300; more preferably selected from the list consisting of H184,K232, K243, K257, K270, R272, R279, K291 and R300; even more preferably selected from the list consisting of K232, K243, K291 and R300; even more preferably selected from the list consisting of K243, K291 and R300; most preferably K291 or R300. In an even more preferred embodiment, and particularly preferred in the context of the present invention,said one or more positively charged amino acid substitutions at 1-301 of SEQ ID NO 01 is the substitutionof at least K149, R153, R156, H157, H158, R169, H170, H184, K232, R234, H236, K243, H244, K257, K270, R272, R279, K291 or R300; preferably at least R169, H170, H184, K232, K243, K257, K270, R272, R279, K291 or R300; more preferably at least H184, K232, K243, K257, K270, R272, R279, K291 or R300; even more preferably at least K232, K243, K291 or R300; even more preferably at least K243, K291 or R300; most preferably at least K291 or R300.In an even more preferred embodiment, said one or more positively charged amino acid substitutions at1-301 of SEQ ID NO 01 is the substitution of only K149, R153, R156, H157, H158, R169, H170, H184, K232, R234, H236, K243, H244, K257, K270, R272, R279, K291 or R300; preferably only R169, H170, H184, K232, K243, K257, K270, R272, R279, K291 or R300; more preferably only H184, K232, K243, K257, K270, R272, R279, K291 or R300; even more preferably only K232, K243, K291 or R300; even more preferably only K243, K291 or R300; most preferably only K291 or R300. In an additional and / or alternative more preferred embodiment, one or more non-conservative amino acid substitutions at 1-301 of SEQ ID NO 01 is the substitution of one or more amino acids having anegatively charged side chain at physiological pH (i.e. negatively charged amino acid) into an amino acidhaving a positively charged side chain at physiological pH (i.e. positively charged amino acid) or an aminoacid having a neutral side chain at physiological pH (i.e. uncharged amino acid), preferably into an uncharged amino acid. Preferably, a negatively charged amino acid is D or E, more preferably E. Preferably, a positively charged amino acid is selected form the list consisting of R, H and K, morepreferably H or R, most preferably R.Preferably, an uncharged amino acid is selected from the list consisting of A, N, C, Q, G, I, L, M, F, P, S, T, W, Y and V, more preferably selected from the list consisting of A, N, C, Q, G, I, L, M, P, S, T and V, even more preferably selected from the list consisting of G, L, M, N, Q, S and T, even more preferably G, L, N or Q, most preferably N or L. For the sake of clarity, the substitution of one or more amino acids having a side chain that is negativelycharged at physiological pH into an amino acid having a side chain that is uncharged or positively chargedat physiological pH, wherein said amino acid having a side chain that is negatively charged at physiologicalpH is D or E, also encompasses the situation wherein one D or one E is substituted. It also encompassesthe situation wherein one or more D are substituted or one or more E are substituted. It also encompassesthe situation wherein one or more D are substituted and optionally one or more E are substituted. It alsoencompasses the situation wherein one or more E are substituted and optionally one or more D aresubstituted. In the context of the present invention, it is particularly preferred that an amino acid having a negatively charged side chain at physiological pH (i.e. D or E, preferably E) is substituted into A, N, C, Q, G, I, L, M, P, S, T, V, R, H or K, even more preferably selected from the list consisting of G, L, M, N, Q, S, T, or R, even more preferably G, L, N, R or Q, most preferably N, L or R.In an even more preferred embodiment, said one or more negatively charged amino acid substitutions at1-301 of SEQ ID NO 01 is the substitution of one or more amino acids selected from the list consisting ofD150, E209, E228, E287and E290, preferably E228 or E290.In an alternative even more preferred embodiment, said one or more negatively charged amino acid substitutions at 1-301 of SEQ ID NO 01 is the substitution of one or more amino acids selected from thelist consisting of E171, E295 and E299, preferably E171. The increased substrate specificity for lactose overa longer-chain oligosaccharide compared to the reference beta-1,3-N-acetylglucosaminyltransferase (it is referred to the Section “Mutant beta-1,3-N-acetylglucosaminyltransferase”) has been described in WO2022 / 133093 (said substitutions are herein disclosed as E170, E294 and E298, respectively; the corresponding parts of the description and examples are incorporated by reference herein). In an alternative even more preferred embodiment, said one or more negatively charged amino acid substitutions at 1-301 of SEQ ID NO 01 is the substitution of one or more amino acids selected from thelist consisting of D150, E171, E209, E228, E287, E290, E295 and E299, preferably selected from the listconsisting of E171, E228, E290, E295 and E299, more preferably selected form the list consisting of E171, E295 and E299, most preferably E171. In an even more preferred embodiment, and particularly preferred in the context of the present invention, said one or more negatively charged amino acid substitutions at 1-301 of SEQ ID NO 01 is the substitution of at least D150, E171, E209, E228, E287, E290, E295 or E299, more preferably at least E171, E228, E290, E295 or E299, even more preferably at least E171, E295 or E299, most preferably at least E171. In an alternative even more preferred embodiment, said one or more negatively charged amino acid substitutions at 1-301 of SEQ ID NO 01 is the substitution of only D150, E171, E209, E228, E287, E290, E295 or E299, more preferably only E171, E228, E290, E295 or E299, even more preferably only E171, E295 or E299, most preferably only E171. In a most preferred embodiment, said one or more negatively charged amino acid substitutions at 1-301 of SEQ ID NO 01 is the substitution of only: -E295 and E299 and optionally E171, preferably E295 and E299; or- E171.Aforementioned more preferred embodiments reflect the most preferred categories of non-conservativeamino acid substitution(s) at 1-301 of SEQ ID NO 01 within the context of the present invention, i.e.:- an aromatic amino acid into a non-aromatic amino acid (as described earlier herein);- a non-polar amino acid by a polar amino acid (as described earlier herein);- a proline into a polar amino acid or a hydrophobic amino acid (as described earlier herein);- a hydrophobic amino acid into a hydrophilic amino acid or a neutral amino acid (as describedearlier herein); -a polar amino acid into a non-polar amino acid (as described earlier herein);- a positively charged amino acid into a negatively charged amino acid or uncharged amino acid (asdescribed earlier herein); and -a negatively charged amino acid into a positively charged amino acid or uncharged amino acid (asdescribed earlier herein). Said categories have a different level of preference within the scope of the invention, i.e. ranked frommost preferred to least preferred: a non-polar amino acid into a polar amino acid (as described earlierherein; a proline into a polar amino acid or a hydrophobic amino acid (as described earlier herein); anaromatic amino acid into a non-aromatic amino acid (as described earlier herein); a hydrophobic amino acid into a hydrophilic amino acid or a neutral amino acid (as described earlier herein); a polar amino acid into a non-polar amino acid (as described earlier herein); a positively charged amino acid into a negatively charged amino acid or uncharged amino acid (as described earlier herein); a negatively charged amino acid into a positively charged amino acid or uncharged amino acid (as described earlier herein). In the context of the present Section “Non-conservative amino acid substitution(s) at 1-301”, the mutant beta-1,3-N-acetylglucosaminyltransferase according to the invention comprises one or more non- conservative amino acid substitutions within a category (see above) and optionally one or more non- conservative amino acid substitutions within a different category (see above). It is more preferred that the mutant beta-1,3-N-acetylglucosaminyltransferase according to the invention comprises one or morenon-conservative amino acid substitutions within a single category (see above) and no further non-conservative amino acid substitutions at 1-301 within other of said categories. For the sake of clarity, an amino acid can belong to more than one of said categories. For example, tryptophan (W) is a non-polar amino acid, but also a hydrophobic amino acid and an aromatic amino acid. As indicated earlier in the present Section “Non-conservative amino acid substitution(s) at 1-301”, and summarized in Table 2 below, it is particularly preferred that the non-conservative amino acid substitution of W is the substitution into a non-aromatic amino acid. Table 2 Most preferred category of non-conservative amino acid A LNon-aromatic Hydrophobic amino acid into a hydrophilic amino acid or a Hydrophobic neutral amino acid, preferably into a hydrophilic amino acid o Positively charged Non-aromatic P itiv l h r d min id int n tiv l h r d mino o o o In an even more preferred embodiment, said one or more non-conservative amino acid substitutions at 1-301 of SEQ ID NO 01 is the substitution of at least one or more aromatic amino acids into a non-aromatic amino acid as disclosed in the present Section “Non-conservative amino acid substitution(s) at 1-301”;optionally and preferably wherein further:- one or more hydrophobic amino acids are substituted into a hydrophilic amino acid or neutralamino acid, preferably into a hydrophilic amino acid, as disclosed in the present Section “Non- conservative amino acid substitution(s) at 1-301”; it is particularly preferred that said hydrophobic amino acid(s) is / are selected from the list consisting of A27, L154, A155, I183, M188, M190, A208,V217, P227, L230, V231, I251, A252, I255, A259 and A301; preferably selected from the list consisting of A27, L154, A155, I183, M188, A208, V217, L230, V231, I251, A252, I255, A259 and A301; more preferably selected from the list consisting of A27, I183, M188, V217, L230, V231, A252, A259, A285 and A301, even more preferably selected from the list consisting of A27, I183, M188, V217, L230, V231, A259 and A285; even more preferably selected from the list consisting of I183, M188, V217, L230 and A259; even more preferably selected from the list consisting of M188, L230 and A259; most preferably M188; and / or- one or more polar amino acids are substituted into a non-polar amino acid as disclosed in thepresent Section “Non-conservative amino acid substitution(s) at 1-301”; it is particularly preferredthat said polar amino acid(s) is / are selected from the list consisting of K149, D150, N152, R153, R156, H157, H158, E171, N181, H184, N186, T187, Q212, K232, R234, H236, S241, S242, K243, H244, S245, Q248, H249, Q256, K257, S266, K270, R272, R279, K291, E295, E299 and R300; preferably selected from the list consisting of H158, E171, N186, Q212, S242, S245, K291, E295, E299, R300 and A301, more preferably selected from the list consisting of H158, E171, N186, Q212, S242, S245, H249, Q256 and K291; even more preferably selected from the list consistingof H158, E171, N186, Q212, S245, H249, Q256 and K291; even more preferably selected from thelist consisting of H158, E171, N186, Q212, H249, Q256 and K291; even more preferably selectedfrom the list consisting of H158, N186, H249, Q212 and Q256, even more preferably selected from the list consisting of H158, N186, H249, Q212 and Q256; most preferably Q212; wherein it isfurther preferred (as disclosed earlier) herein that: owhen said polar amino acid is also a positively charged amino acid, that it is substitutedinto a negatively charged amino acid or an uncharged amino acid, preferably into an uncharged amino acid, and owhen said polar amino acid is also a positively charged amino acid, that it is substitutedinto a negatively charged amino acid or an uncharged amino acid, preferably into an uncharged amino acid; -and / or P89 into a polar amino acid or a hydrophobic amino acid, preferably into a polar aminoacid, as disclosed in the present Section “Non-conservative amino acid substitution(s) at 1-301. Preferably, the expression “at least” is replaced with “only”, i.e. no additional non-conservative amino acid substitutions at 1-301 of SEQ ID NO 01 are present than what is explicitly recited. It is particularly preferred that said “one or more aromatic amino acid substitutions into a non-aromatic amino acid” is the substitution of at least W141, W164, F176, F177, F179, Y201, W207, Y211, F213, W214, Y215, Y225, Y226, Y233, Y244, F263, F269, F273, Y278 or F298; preferably at least W164, F176, F177, F179, Y201, Y211, F213, W214, Y215, Y225, Y226, Y233 or F298; more preferably at least F176, F177, F179, Y201, Y211, F213, W214, Y215, Y225, Y226 or Y233; even more preferably at least Y201, Y211, W214, Y215, Y225 or Y226; even more preferably at least Y211, Y226 or W214; even more preferably at least Y211 or W214, most preferably at least Y211, into a non-aromatic amino acid as disclosed in the present Section “Non- conservative amino acid substitution(s) at 1-301”.It is particularly more preferred that said “one or more aromatic amino acid substitutions into a non-aromatic amino acid” is the substitution of only W141, W164, F176, F177, F179, Y201, W207, Y211, F213,W214, Y215, Y225, Y226, Y233, Y244, F263, F269, F273, Y278 or F298; preferably only W164, F176, F177,F179, Y201, Y211, F213, W214, Y215, Y225, Y226, Y233 or F298; more preferably only F176, F177, F179,Y201, Y211, F213, W214, Y215, Y225, Y226 or Y233; even more preferably only Y201, Y211, W214, Y215,Y225 or Y226; even more preferably only Y211, Y226 or W214; even more preferably only Y211 or W214, most preferably only Y211, into a non-aromatic amino acid as disclosed in the present Section “Non- conservative amino acid substitution(s) at 1-301”. In an alternative even more preferred embodiment, said one or more non-conservative amino acidsubstitutions at 1-301 of SEQ ID NO 01 is the substitution of at least one or more proline into a polaramino acid or a hydrophobic amino acid, preferably into a polar amino acid, as disclosed in the present Section “Non-conservative amino acid substitution(s) at 1-301”; optionally and preferably wherein further: -one or more hydrophobic amino acids are substituted into a hydrophilic amino acid or neutralamino acid, preferably into a hydrophilic amino acid, as disclosed in the present Section “Non- conservative amino acid substitution(s) at 1-301”; it is particularly preferred that said hydrophobic amino acid(s) is / are selected from the list consisting of A27, L154, A155, I183, M188, M190, A208, V217, P227, L230, V231, I251, A252, I255, A259 and A301; preferably selected from the list consisting of A27, L154, A155, I183, M188, A208, V217, L230, V231, I251, A252, I255, A259 and A301; more preferably selected from the list consisting of A27, I183, M188, V217, L230, V231, A252, A259, A285 and A301, even more preferably selected from the list consisting of A27, I183, M188, V217, L230, V231, A259 and A285; even more preferably selected from the list consisting of I183, M188, V217, L230 and A259; even more preferably selected from the list consisting of M188, L230 and A259; most preferably M188; and / or -one or more polar amino acids are substituted into a non-polar amino acid as disclosed in thepresent Section “Non-conservative amino acid substitution(s) at 1-301”; it is particularly preferred that said polar amino acid(s) is / are selected from the list consisting of K149, D150, N152, R153, R156, H157, H158, E171, N181, H184, N186, T187, Q212, K232, R234, H236, S241, S242, K243, H244, S245, Q248, H249, Q256, K257, S266, K270, R272, R279, K291, E295, E299 and R300; preferably selected from the list consisting of H158, E171, N186, Q212, S242, S245, H249, Q256, K291, E295, E299, R300 and A301, more preferably selected from the list consisting of H158, E171, N186, Q212, S242, S245, H249, Q256 and K291; even more preferably selected from the listconsisting of H158, E171, N186, Q212, S245, H249, Q256 and K291; even more preferably selectedfrom the list consisting of H158, E171, N186, Q212, H249, Q256 and K291; even more preferablyselected from the list consisting of H158, N186, H249, Q212 and Q256, even more preferably selected from the list consisting of H158, H249, Q212 and Q256; most preferably Q212; whereinit is further preferred (as disclosed earlier) herein that: owhen said polar amino acid is also a positively charged amino acid, that it is substitutedinto a negatively charged amino acid or an uncharged amino acid, preferably into an uncharged amino acid, and owhen said polar amino acid is also a positively charged amino acid, that it is substitutedinto a negatively charged amino acid or an uncharged amino acid, preferably into an uncharged amino acid; -and / or P89 into a polar amino acid or a hydrophobic amino acid, preferably into a polar amino acid, as disclosed in the present Section “Non-conservative amino acid substitution(s) at 1-301. Preferably, the expression “at least” is replaced with “only”, i.e. no additional non-conservative amino acid substitutions at 1-301 of SEQ ID NO 01 are present than what is explicitly recited.It is particularly preferred that said “one or more proline substitutions into a polar amino acid or ahydrophobic amino acid, preferably into a polar amino acid” is the substitution of at least P89, P178, P182, P227 or P294; preferably at least P89, P178, P182 or P294, more preferably at least P89 or P182, most preferably at least P182, into a polar amino acid or a hydrophobic amino acid, preferably into a polaramino acid, as disclosed in the present Section “Non-conservative amino acid substitution(s) at 1-301”.It is particularly more preferred that said “one or more proline substitutions into a polar amino acid or ahydrophobic amino acid, preferably into a polar amino acid” is the substitution of only P89, P178, P182, P227 or P294, preferably only P89, P178, P182 or P294, more preferably only P89 or P182, most preferablyonly P182, into a polar amino acid or a hydrophobic amino acid, preferably into a polar amino acid, asdisclosed in the present Section “Non-conservative amino acid substitution(s) at 1-301”. In an alternative even more preferred embodiment, said one or more non-conservative amino acid substitutions at 1-301 of SEQ ID NO 01 is the substitution of at least one or more non-polar amino acids into a polar amino acid as disclosed in the present Section “Non-conservative amino acid substitution(s) at 1-301”; optionally and preferably wherein further: -one or more hydrophobic amino acids are substituted into a hydrophilic amino acid or neutralamino acid, preferably into a hydrophilic amino acid, as disclosed in the present Section “Non- conservative amino acid substitution(s) at 1-301”; it is particularly preferred that said hydrophobicamino acid(s) is / are selected from the list consisting of A27, L154, A155, I183, M188, M190, A208, V217, P227, L230, V231, I251, A252, I255, A259 and A301; preferably selected from the list consisting of A27, L154, A155, I183, M188, A208, V217, L230, V231, I251, A252, I255, A259 and A301; more preferably selected from the list consisting of A27, I183, M188, V217, L230, V231, A252, A259, A285 and A301, even more preferably selected from the list consisting of A27, I183, M188, V217, L230, V231, A259 and A285; even more preferably selected from the list consisting of I183, M188, V217, L230 and A259; even more preferably selected from the list consisting of M188, L230 and A259; most preferably M188; and / or -one or more polar amino acids are substituted into a non-polar amino acid as disclosed in thepresent Section “Non-conservative amino acid substitution(s) at 1-301”; it is particularly preferred that said polar amino acid(s) is / are selected from the list consisting of K149, D150, N152, R153, R156, H157, H158, E171, N181, H184, N186, T187, Q212, K232, R234, H236, S241, S242, K243, H244, S245, Q248, H249, Q256, K257, S266, K270, R272, R279, K291, E295, E299 and R300; preferably selected from the list consisting of H158, E171, N186, Q212, S242, S245, H249, Q256, K291, E295, E299, R300 and A301, more preferably selected from the list consisting of H158, E171,N186, Q212, S242, S245, H249, Q256 and K291; even more preferably selected from the listconsisting of H158, E171, N186, Q212, S245, H249, Q256 and K291; even more preferably selectedfrom the list consisting of H158, E171, N186, Q212, H249, Q256 and K291; even more preferablyselected from the list consisting of H158, N186, H249, Q212 and Q256, even more preferably selected from the list consisting of H158, H249, Q212 and Q256; most preferably Q212; whereinit is further preferred (as disclosed earlier) herein that: owhen said polar amino acid is also a positively charged amino acid, that it is substitutedinto a negatively charged amino acid or an uncharged amino acid, preferably into an uncharged amino acid, and owhen said polar amino acid is also a positively charged amino acid, that it is substitutedinto a negatively charged amino acid or an uncharged amino acid, preferably into an uncharged amino acid; -and / or P89 into a polar amino acid or a hydrophobic amino acid, preferably into a polar aminoacid, as disclosed in the present Section “Non-conservative amino acid substitution(s) at 1-301. Preferably, the expression “at least” is replaced with “only”, i.e. no additional non-conservative amino acid substitutions at 1-301 of SEQ ID NO 01 are present than what is explicitly recited.It is particularly preferred that said “one or more non-polar amino acid substitutions into a polar aminoacid” is the substitution of at least A27, P89, G151, L154, A155, P178, G180, P182, I183, M188, M190, A208, V217, P227,A229, L230, V231, I251, A252, I255, A259, P294 or A301; preferably at least A27, P89,G151, L154, A155, P178, G180, P182, I183, M188, A208, V217, L230, V231, I251, A252, I255, A259, P294or A301; more preferably at least A27, P89, P178, G180, P182, I183, M188, V217, L230, V231, A252, A259, A285, P294 or A301, even more preferably at least A27, P89, P178, G180, P182, I183, M188, V217, L230, V231, A259, A285 or P294; even more preferably at least A27, P178, G180, P182, I183, M188, V217, L230, V231, A259 or A285; even more preferably at least G180, P182, I183, M188, V217, L230 or A259; even more preferably at least G180, P182, M188, L230 or A259; even more preferably at least G180 or P182, most preferably at least G180, into a polar amino acid as disclosed in the present Section “Non- conservative amino acid substitution(s) at 1-301”.It is particularly more preferred that said “one or more non-polar amino acid substitutions into a polaramino acid” is the substitution of only A27, P89, G151, L154, A155, P178, G180, P182, I183, M188, M190, A208, V217, P227,A229, L230, V231, I251, A252, I255, A259, P294 or A301; preferably only A27, P89, G151, L154, A155, P178, G180, P182, I183, M188, A208, V217, L230, V231, I251, A252, I255, A259, P294 or A301; more preferably only A27, P89, P178, G180, P182, I183, M188, V217, L230, V231, A252, A259,A285, P294 or A301, even more preferably only A27, P89, P178, G180, P182, I183, M188, V217, L230,V231, A259, A285 or P294; even more preferably only A27, P178, G180, P182, I183, M188, V217, L230, V231, A259 or A285; even more preferably only G180, P182, I183, M188, V217, L230 or A259; even more preferably only G180, P182, M188, L230 or A259; even more preferably only G180 or P182, most preferably only G180, into a polar amino acid as disclosed in the present Section “Non-conservative amino acid substitution(s) at 1-301”. In an even more preferred embodiment, said one or more non-conservative amino acid substitutions at 1-301 of SEQ ID NO 01 is the substitution of at least one or more aromatic amino acids into a non-aromaticamino acid as disclosed in the present Section “Non-conservative amino acid substitution(s) at 1-301”;optionally and preferably wherein further:- one or more hydrophobic amino acids are substituted into a hydrophilic amino acid or neutralamino acid, preferably into a hydrophilic amino acid, as disclosed in the present Section “Non- conservative amino acid substitution(s) at 1-301”; it is particularly preferred that said hydrophobic amino acid(s) is / are selected from the list consisting of A27, L154, A155, I183, M188, M190, A208, V217, P227, L230, V231, I251, A252, I255, A259 and A301; preferably selected from the list consisting of A27, L154, A155, I183, M188, A208, V217, L230, V231, I251, A252, I255, A259 and A301; more preferably selected from the list consisting of A27, I183, M188, V217, L230, V231, A252, A259, A285 and A301, even more preferably selected from the list consisting of A27, I183, M188, V217, L230, V231, A259 and A285; even more preferably selected from the list consisting of I183, M188, V217, L230 and A259; even more preferably selected from the list consisting of M188, L230 and A259; most preferably M188; and / or -one or more polar amino acids are substituted into a non-polar amino acid as disclosed in thepresent Section “Non-conservative amino acid substitution(s) at 1-301”; it is particularly preferred that said polar amino acid(s) is / are selected from the list consisting of K149, D150, N152, R153, R156, H157, H158, E171, N181, H184, N186, T187, Q212, K232, R234, H236, S241, S242, K243, H244, S245, Q248, H249, Q256, K257, S266, K270, R272, R279, K291, E295, E299 and R300; preferably selected from the list consisting of H158, E171, N186, Q212, S242, S245, H249, Q256, K291, E295, E299, R300 and A301, more preferably selected from the list consisting of H158, E171, N186, Q212, S242, S245, H249, Q256 and K291; even more preferably selected from the listconsisting of H158, E171, N186, Q212, S245, H249, Q256 and K291; even more preferably selectedfrom the list consisting of H158, E171, N186, Q212, H249, Q256 and K291; even more preferablyselected from the list consisting of H158, N186, Q212, H249 and Q256, even more preferably selected from the list consisting of H158, H249, Q212 and Q256; most preferably Q212; whereinit is further preferred (as disclosed earlier) herein that: owhen said polar amino acid is also a positively charged amino acid, that it is substitutedinto a negatively charged amino acid or an uncharged amino acid, preferably into an uncharged amino acid, and owhen said polar amino acid is also a positively charged amino acid, that it is substitutedinto a negatively charged amino acid or an uncharged amino acid, preferably into an uncharged amino acid; -and / or P89 into a polar amino acid or a hydrophobic amino acid, preferably into a polar aminoacid, as disclosed in the present Section “Non-conservative amino acid substitution(s) at 1-301. Preferably, the expression “at least” is replaced with “only”, i.e. no additional non-conservative amino acid substitutions at 1-301 of SEQ ID NO 01 are present than what is explicitly recited. It is particularly preferred that said “one or more aromatic amino acid substitutions into a non-aromatic amino acid” is the substitution of at least W141, W164, F176, F177, F179, Y201, W207, Y211, F213, W214, Y215, Y225, Y226, Y233, Y244, F263, F269, F273, Y278 or F298; preferably at least W164, F176, F177, F179, Y201, Y211, F213, W214, Y215, Y225, Y226, Y233 or F298; more preferably at least F176, F177, F179, Y201,Y211, F213, W214, Y215, Y225, Y226 or Y233; even more preferably at least Y201, Y211, W214, Y215, Y225or Y226; even more preferably at least Y211, Y226 or W214; even more preferably at least Y211 or W214, most preferably at least Y211, into a non-aromatic amino acid as disclosed in the present Section “Non- conservative amino acid substitution(s) at 1-301”.It is particularly more preferred that said “one or more aromatic amino acid substitutions into a non-aromatic amino acid” is the substitution of only W141, W164, F176, F177, F179, Y201, W207, Y211, F213, W214, Y215, Y225, Y226, Y233, Y244, F263, F269, F273, Y278 or F298; preferably only W164, F176, F177, F179, Y201, Y211, F213, W214, Y215, Y225, Y226, Y233 or F298; more preferably only F176, F177, F179, Y201, Y211, F213, W214, Y215, Y225, Y226 or Y233; even more preferably only Y201, Y211, W214, Y215, Y225 or Y226; even more preferably only Y211, Y226 or W214; even more preferably only Y211 or W214, most preferably only Y211, into a non-aromatic amino acid as disclosed in the present Section “Non- conservative amino acid substitution(s) at 1-301”. In an even more preferred embodiment, said one or more non-conservative amino acid substitutions at1-301 of SEQ ID NO 01 is the substitution of at least one or more proline into a polar amino acid or ahydrophobic amino acid, preferably into a polar amino acid, as disclosed in the present Section “Non- conservative amino acid substitution(s) at 1-301”; optionally and preferably wherein further: -one or more hydrophobic amino acids are substituted into a hydrophilic amino acid or neutralamino acid, preferably into a hydrophilic amino acid, as disclosed in the present Section “Non- conservative amino acid substitution(s) at 1-301”; it is particularly preferred that said hydrophobic amino acid(s) is / are selected from the list consisting of A27, L154, A155, I183, M188, M190, A208, V217, P227, L230, V231, I251, A252, I255, A259 and A301; preferably selected from the list consisting of A27, L154, A155, I183, M188, A208, V217, L230, V231, I251, A252, I255, A259 and A301; more preferably selected from the list consisting of A27, I183, M188, V217, L230, V231, A252, A259, A285 and A301, even more preferably selected from the list consisting of A27, I183, M188, V217, L230, V231, A259 and A285; even more preferably selected from the list consisting of I183, M188, V217, L230 and A259; even more preferably selected from the list consisting of M188, L230 and A259; most preferably M188; and / or -one or more polar amino acids are substituted into a non-polar amino acid as disclosed in thepresent Section “Non-conservative amino acid substitution(s) at 1-301”; it is particularly preferred that said polar amino acid(s) is / are selected from the list consisting of K149, D150, N152, R153, R156, H157, H158, E171, N181, H184, N186, T187, Q212, K232, R234, H236, S241, S242, K243, H244, S245, Q248, H249, Q256, K257, S266, K270, R272, R279, K291, E295, E299 and R300; preferably selected from the list consisting of H158, E171, N186, Q212, S242, S245, H249, Q256, K291, E295, E299, R300 and A301, more preferably selected from the list consisting of H158, E171, N186, Q212, S242, S245, H249, Q256 and K291; even more preferably selected from the listconsisting of H158, E171, N186, Q212, S245, H249, Q256 and K291; even more preferably selectedfrom the list consisting of H158, E171, N186, Q212, H249, Q256 and K291; even more preferablyselected from the list consisting of H158, N186, H249, Q212 and Q256, even more preferably selected from the list consisting of H158, H249, Q212 and Q256; most preferably Q212; whereinit is further preferred (as disclosed earlier) herein that: owhen said polar amino acid is also a positively charged amino acid, that it is substitutedinto a negatively charged amino acid or an uncharged amino acid, preferably into an uncharged amino acid, and owhen said polar amino acid is also a positively charged amino acid, that it is substitutedinto a negatively charged amino acid or an uncharged amino acid, preferably into an uncharged amino acid; -and / or P89 into a polar amino acid or a hydrophobic amino acid, preferably into a polar aminoacid, as disclosed in the present Section “Non-conservative amino acid substitution(s) at 1-301. Preferably, the expression “at least” is replaced with “only”, i.e. no additional non-conservative amino acid substitutions at 1-301 of SEQ ID NO 01 are present than what is explicitly recited. It is particularly preferred that said “one or more proline substitutions into a polar amino acid or a hydrophobic amino acid, preferably into a polar amino acid” is the substitution of at least P89, P178, P182, P227 or P294; preferably at least P89, P178, P182 or P294, more preferably at least P89 or P182, most preferably at least P182, into a polar amino acid or a hydrophobic amino acid, preferably into a polaramino acid, as disclosed in the present Section “Non-conservative amino acid substitution(s) at 1-301”.It is particularly more preferred that said “one or more proline substitutions into a polar amino acid or ahydrophobic amino acid, preferably into a polar amino acid” is the substitution of only P89, P178, P182, P227 or P294, preferably only P89, P178, P182 or P294, more preferably only P89 or P182, most preferablyonly P182, into a polar amino acid or a hydrophobic amino acid, preferably into a polar amino acid, asdisclosed in the present Section “Non-conservative amino acid substitution(s) at 1-301”. In a most preferred embodiment, said one or more non-conservative amino acid substitutions at 1-301 ofSEQ ID NO 01 is the substitution of at least one or more non-polar amino acids into a polar amino acid asdisclosed in the present Section “Non-conservative amino acid substitution(s) at 1-301”; optionally and preferably wherein further: -one or more hydrophobic amino acids are substituted into a hydrophilic amino acid or neutralamino acid, preferably into a hydrophilic amino acid, as disclosed in the present Section “Non- conservative amino acid substitution(s) at 1-301”; it is particularly preferred that said hydrophobicamino acid(s) is / are selected from the list consisting of A27, L154, A155, I183, M188, M190, A208, V217, P227, L230, V231, I251, A252, I255, A259 and A301; preferably selected from the list consisting of A27, L154, A155, I183, M188, A208, V217, L230, V231, I251, A252, I255, A259 and A301; more preferably selected from the list consisting of A27, I183, M188, V217, L230, V231, A252, A259, A285 and A301, even more preferably selected from the list consisting of A27, I183, M188, V217, L230, V231, A259 and A285; even more preferably selected from the list consisting of I183, M188, V217, L230 and A259; even more preferably selected from the list consisting of M188, L230 and A259; most preferably M188; and / or -one or more polar amino acids are substituted into a non-polar amino acid as disclosed in thepresent Section “Non-conservative amino acid substitution(s) at 1-301”; it is particularly preferred that said polar amino acid(s) is / are selected from the list consisting of K149, D150, N152, R153, R156, H157, H158, E171, N181, H184, N186, T187, Q212, K232, R234, H236, S241, S242, K243, H244, S245, Q248, H249, Q256, K257, S266, K270, R272, R279, K291, E295, E299 and R300; preferably selected from the list consisting of H158, E171, N186, Q212, S242, S245, H249, Q256, K291, E295, E299, R300 and A301, more preferably selected from the list consisting of H158, E171, N186, Q212, S242, S245, H249, Q256 and K291; even more preferably selected from the listconsisting of H158, E171, N186, Q212, S245, H249, Q256 and K291; even more preferably selectedfrom the list consisting of H158, E171, N186, Q212, H249, Q256 and K291; even more preferablyselected from the list consisting of H158, N186, H249, Q212 and Q256, even more preferably selected from the list consisting of H158, H249, Q212 and Q256; most preferably Q212; whereinit is further preferred (as disclosed earlier) herein that: owhen said polar amino acid is also a positively charged amino acid, that it is substitutedinto a negatively charged amino acid or an uncharged amino acid, preferably into an uncharged amino acid, and owhen said polar amino acid is also a positively charged amino acid, that it is substitutedinto a negatively charged amino acid or an uncharged amino acid, preferably into an uncharged amino acid; -and / or P89 into a polar amino acid or a hydrophobic amino acid, preferably into a polar aminoacid, as disclosed in the present Section “Non-conservative amino acid substitution(s) at 1-301. Preferably, the expression “at least” is replaced with “only”, i.e. no additional non-conservative amino acid substitutions at 1-301 of SEQ ID NO 01 are present than what is explicitly recited. It is particularly preferred that said “one or more non-polar amino acid substitutions into a polar amino acid” is the substitution of at least A27, P89, G151, L154, A155, P178, G180, P182, I183, M188, M190, A208, V217, P227,A229, L230, V231, I251, A252, I255, A259, P294 or A301; preferably at least A27, P89,G151, L154, A155, P178, G180, P182, I183, M188, A208, V217, L230, V231, I251, A252, I255, A259, P294or A301; more preferably at least A27, P89, P178, G180, P182, I183, M188, V217, L230, V231, A252, A259, A285, P294 or A301, even more preferably at least A27, P89, P178, G180, P182, I183, M188, V217, L230, V231, A259, A285 or P294; even more preferably at least A27, P178, G180, P182, I183, M188, V217, L230, V231, A259 or A285; even more preferably at least G180, P182, I183, M188, V217, L230 or A259; even more preferably at least G180, P182, M188, L230 or A259; even more preferably at least G180 or P182, most preferably at least G180, into a polar amino acid as disclosed in the present Section “Non- conservative amino acid substitution(s) at 1-301”.It is particularly more preferred that said “one or more non-polar amino acid substitutions into a polaramino acid” is the substitution of only A27, P89, G151, L154, A155, P178, G180, P182, I183, M188, M190, A208, V217, P227,A229, L230, V231, I251, A252, I255, A259, P294 or A301; preferably only A27, P89, G151, L154, A155, P178, G180, P182, I183, M188, A208, V217, L230, V231, I251, A252, I255, A259, P294 or A301; more preferably only A27, P89, P178, G180, P182, I183, M188, V217, L230, V231, A252, A259,A285, P294 or A301, even more preferably only A27, P89, P178, G180, P182, I183, M188, V217, L230,V231, A259, A285 or P294; even more preferably only A27, P178, G180, P182, I183, M188, V217, L230, V231, A259 or A285; even more preferably only G180, P182, I183, M188, V217, L230 or A259; even more preferably only G180, P182, M188, L230 or A259; even more preferably only G180 or P182, most preferably only G180, into a polar amino acid as disclosed in the present Section “Non-conservative amino acid substitution(s) at 1-301”. It is another preferred embodiment that one or more of said non-conservative amino acid substitutions at 1-301 of SEQ ID NO 01 is the substitution of one or more amino acids selected from the list consisting of G180, A259, L230, M188, N186, Q212, E171, I183, V217, K291, V231, S245, A285, A27, P89, E295, E299, R300, A301, N181, H184, T187, W207, A208, W214, V231, R234, H236, S241, K243, H244, Y244, S245,Q248, I251, I255, Q256, A259 and S266; preferably selected from the list consisting of G180, A259, L230,M188, N186, Q212, E171, I183, V217, K291, V231, S245, A285, A27, P89, E295, E299, R300 and A301, more preferably selected from the list consisting of G180, A259, L230, M188, N186, Q212, E171, I183, V217, K291, V231, S245, A285, A27 and P89; even more preferably selected from the list consisting of G180, A259, L230, M188, N186, Q212, E171, I183, V217, K291, V231, S245, A285 and A27; even more preferably selected from the list consisting of G180, A259, L230, M188, N186, Q212, E171, I183, V217 and K291; even more preferably selected from the list consisting of G180, A259, L230, M188, N186, Q212;most preferably G180. The increased substrate specificity for lactose over a longer-chain oligosaccharide compared to the reference beta-1,3-N-acetylglucosaminyltransferase (it is referred to the Section “Mutant beta-1,3-N-acetylglucosaminyltransferase”) has been described in WO2022 / 133093 (said substitutions are herein disclosed as G179, A258, L229, M187, N185, Q211, E170, I182, V216, K290, V230, S244, A284, A27, P89, E294, E298, R299, A300, N180, H183, T186, W206, A207, W213, V230, R233, H235, S240, K242, H243, Y243, S244, Q247, I250, I254, Q255, A258 and S265, respectively; the corresponding parts of the description and examples are incorporated by reference herein). More preferably, wherein one or more of said non-conservative amino acid substitutions at 1-301 of SEQ ID NO 01 is the substitution of one or more amino acids selected from the list consisting of G180, A259, L230, M188, N186 and Q212, preferably G180. Even more preferably, wherein one or more of said non-conservative amino acid substitutions at 1-301 of SEQ ID NO 01 is the substitution of: -one or more amino acids selected from the list consisting of G180, A259, L230, M188, N186and Q212, preferably G180; and -preferably one or more selected form the list consisting of P89, E171, I183, V217, K291, V231,S245, A285, A27, E295, E299, R300 and A301, more preferably selected from the list consisting of P89, E171, I183, V217, K291, V231, S245, A285 and A27, even more preferably selected from the list consisting of P89, E171, I183, V217 and K291. It is an additional and / or alternative preferred embodiment that one or more of said non-conservativeamino acid substitutions at 1-301 of SEQ ID NO 01 is the substitution of one or more amino acids selectedfrom the list consisting of W141, K149, D150, G151, N152, R153, L154, A155, R156, H157, H158, W164, R169, H170, F176, F177, P178, F179, P182, M190, Y201, E209, Y211, F213, Y215, Y225, Y226, P227, E228, A229, K232, Y233, S242, H249, A252, Q256, K257, F263, F269, K270, R272, F273, Y278, R279, E287, E290, P294 and F298; preferably selected from the list consisting of H158, W164, F176, F177, P178, F179, P182, Y201, Y211, F213, Y215, Y225, Y226, Y233, S242, H249, A252, Q256, F263, F269, F273, Y278, P294 and F298; more preferably selected from the list consisting of H158, W164, F176, F177, P178, F179, P182, Y201, Y211, F213, Y215, Y225, Y226, Y233, S242, H249, Q256, P294 and F 298; even more preferably selected from the list consisting of H158, W164, F176, F177, P178, F179, P182, Y201, Y211, F213, Y215,Y225, Y226, Y233, H249 and Q256; even more preferably selected form the list consisting of H158, P182,Y201, Y211, Y215, Y225, Y226, H249 and Q256; even more preferably selected from the list consisting ofH158, P182, Y211, Y226, H249 and Q256, even more preferably selected from the list consisting of P182,Y211 and Y226; even more preferably P182 or Y211; most preferably P182.More preferably, wherein one or more of said non-conservative amino acid substitutions at 1-301 of SEQ ID NO 01 is the substitution of one or more amino acids selected from the list consisting of P182, Y201, Y211, Y215, Y225 and Y226, preferably selected from the list consisting of P182, Y211 and Y226, morepreferably P182 or Y211; most preferably P182. Even more preferably, wherein one or more of said non-conservative amino acid substitutions at 1-301 of SEQ ID NO 01 is the substitution of: -one or more amino acids selected from the list consisting of P182, Y201, Y211, Y215, Y225 andY226; preferably selected from the list consisting of P182, Y211 and Y226; most preferablyP182; and -one or more selected form the list consisting of P89, E171, I183, V217, K291, V231, S245, A285,A27, E295, E299, R300 and A301, preferably selected from the list consisting of P89, E171, I183, V217, K291, V231, S245, A285 and A27, more preferably selected from the list consisting of P89, E171, I183, V217 and K291.It is a more preferred embodiment that one or more of said non-conservative amino acid substitutions at1-301 of SEQ ID NO 01 is the substitution of one or more amino acids selected from the list consisting of A27, P89, W141, K149, D150, G151, N152, R153, L154, A155, R156, H157, H158, W164, E171, F176, F177, P178, F179, G180, N181, P182, I183, H184, N186, T187, M188, Y201, W207, A208, Y211, Q212, F213, W214, Y215, V217, Y225, Y226, L230, V231, Y233, R234, H236, S241, S242, K243, H244, Y244, S245, Q248, H249, I251, A252, I255, Q256, A259, F263, S266, F269, F273, Y278, N181, K291, P294, E295, F298, E299, R300 and A301; preferably selected from the list consisting of A27, P89, W164, E171, F176, F177, P178, F179, G180, P182, I183, N186, M188, Y201, Y211, Q212, F213, Y215, V217, Y225, Y226, L230, V231, Y233, S242, S245, A252, A259, F263, F269, F273, Y278, A285, K291, P294, E295, F298, E299, R300 and A301, more preferably selected from the list consisting of A27, P89, W164, E171, F176, F177, P178, F179, G180, P182, I183, N186, M188, Y201, Y211, Q212, F213, Y215, V217, Y225, Y226, L230, V231, Y233, S242, S245, A259, A285, K291, P294 and F298; even more preferably selected from the list consisting of A27, W164, E171, F176, F177, P178, F179, G180, P182, I183, N186, M188, Y201, Y211, Q212, F213, Y215, V217, Y225, Y226, L230, V231, Y233, S245, A259, A285 and K291; even more preferably selected from the list consisting of E171, G180, P182, I183, N186, M188, Y201, Y211, Q212, Y215, V217, Y225, Y226, L230, A259and K291; even more preferably selected from the list consisting of G180, P182, N186, M188, Y211 , Q212,L230 and A259; even more preferably selected from the list consisting of G180 and P182, most preferably G180. More preferably, wherein one or more of said non-conservative amino acid substitutions at 1-301 of SEQ ID NO 01 is the substitution of one or more amino acids selected from the list consisting of W141, G180, P182, N186, M188, Y201, Y211, Q212, Y215, Y225, Y226, L230 and A259; preferably selected from the listconsisting of G180, P182 and Y211; more preferably selected from G180 and P182.Even more preferably, wherein one or more of said non-conservative amino acid substitutions at 1-301 of SEQ ID NO 01 is the substitution of: -one or more amino acids selected from the list consisting of W141, G180, P182, N186, M188,Y201, Y211, Q212, Y215, Y225, Y226, L230, and A259; preferably selected from the list consisting of G180, P182 and Y211; more preferably G180 and / or P182; even more preferably G180 or P182; most preferably G180; and -preferably one or more selected form the list consisting of A27, P89, E171, I183, V217, V231,S245, A285, K291, E295, E299, R300 and A301, more preferably selected from the list consisting of A27, P89, E171, I183, V217, V231, S245, A285 and K291, even more preferably selected from the list consisting of P89, E171, I183, V217 and K291.It is an alternative more preferred embodiment that one or more of said non-conservative amino acidsubstitutions at 1-301 of SEQ ID NO 01 is the substitution of one or more amino acids selected from thelist consisting of H158, H249 and Q256, preferably is the substitution of H249, Q256 and optionallyH158, more preferably is the substitution of H249, Q256 and H158. More preferably, wherein one or more of said non-conservative amino acid substitutions at 1-301 of SEQ ID NO 01 is the substitution of: -one or more amino acids selected from the list consisting of H158, H249 and Q256,preferably H249, Q256 and optionally H158, more preferably H158, H249 and Q256; and -preferably G180 and / or P182, more preferably G180 or P182, most preferably G180.It is an even more preferred embodiment that one or more of said non-conservative amino acidsubstitutions at 1-301 of SEQ ID NO 01 is the substitution of one or more amino acids selected from thelist consisting of A27, P89, W141, K149, D150, G151, N152, R153, L154, A155, R156, H157, H158, W164,E171, F176, F177, P178, F179, G180, N181, P182, I183, H184, N186, T187, M188, Y201, W207, A208, Y211, Q212, F213, W214, Y215, V217, Y225, Y226, L230, V231, Y233, R234, H236, S241, S242, K243, H244, Y244,S245, Q248, H249, I251, A252, I255, Q256, A259, F263, S266, F269, F273, Y278, N181, K291, P294, E295,F298, E299, R300 and A301; preferably selected from the list consisting of A27, P89, W164, E171, F176, F177, P178, F179, G180, P182, I183, N186, M188, Y201, Y211, Q212, F213, Y215, V217, Y225, Y226, L230, V231, Y233, S242, S245, A252, A259, F263, F269, F273, Y278, A285, K291, P294, E295, F298, E299, R300 and A301, more preferably selected from the list consisting of A27, P89, W164, E171, F176, F177, P178, F179, G180, P182, I183, N186, M188, Y201, Y211, Q212, F213, Y215, V217, Y225, Y226, L230, V231, Y233, S242, S245, A259, A285, K291, P294 and F298; even more preferably selected from the list consisting of A27, W164, E171, F176, F177, P178, F179, G180, P182, I183, N186, M188, Y201, Y211, Q212, F213, Y215, V217, Y225, Y226, L230, V231, Y233, S245, A259, A285 and K291; even more preferably selected from the list consisting of E171, G180, P182, I183, N186, M188, Y201, Y211, Q212, Y215, V217, Y225, Y226, L230,A259 and K291; even more preferably selected from the list consisting of G180, P182, N186, M188, Y211 ,Q212, L230 and A259; even more preferably selected from the list consisting of G180 and P182, most preferably G180. More preferably, wherein one or more of said non-conservative amino acid substitutions at 1-301 of SEQ ID NO 01 is the substitution of one or more amino acids selected from the list consisting of W141, G180, P182, N186, M188, Y201, Y211, Q212, Y215, Y225, Y226, L230 and A259; preferably selected from the listconsisting of G180, P182 and Y211; more preferably selected from G180 and P182.Even more preferably, wherein one or more of said non-conservative amino acid substitutions at 1-301 of SEQ ID NO 01 is the substitution of: -one or more amino acids selected from the list consisting of W141, G180, P182, N186, M188,Y201, Y211, Q212, Y215, Y225, Y226, L230, and A259; preferably selected from the list consisting of G180, P182 and Y211; more preferably G180 and / or P182; even more preferably G180 or P182; most preferably G180; and -preferably one or more selected form the list consisting of A27, P89, E171, I183, V217, V231,S245, A285, K291, E295, E299, R300 and A301, more preferably selected from the list consisting of A27, P89, E171, I183, V217, V231, S245, A285 and K291, even more preferably selected from the list consisting of P89, E171, I183, V217 and K291. Amino acid(s) missing at 1-363In an optional embodiment of the first aspect of the invention, the beta-1,3-N-acetylglucosaminyltransferase mutant according to the invention comprises an amino acid sequence that further differs from the full-length amino acid sequence of a reference beta-1,3-N- acetylglucosaminyltransferase represented by SEQ ID NO 01 (it is referred to the Section “Reference beta-1,3-N-acetylglucosaminyltransferase”) in one or more amino acids missing at 1-363 of SEQ ID NO 01,preferably at 340-349 of SEQ ID NO 01, more preferably at 340-363 of SEQ ID NO 01. In this context, it is preferred that one or more consecutive amino acids are missing at 1-363 of SEQ ID NO 01, more preferably that one or more consecutive amino acids are missing at 340-349 of SEQ ID NO 01, even more preferably that all amino acids are missing at 340-349 of SEQ ID NO 01, most preferably that all amino acids are missing at 340-363 of SEQ ID NO 01. Throughout the application and claims, the expression “one or more” is interchangeably used with “at least one”. Throughout the application and claims, the expression “one or more amino acids missing” ispreferably replaced with “1-40 amino acids missing”, more preferably replaced with “1-30 amino acidsmissing”, even more preferably replaced with “1-25 amino acids missing”, even more preferably replacedwith “1-20 amino acids missing”, even more preferably replaced with “1-10 amino acids missing”, mostpreferably replaced with “1-5 amino acids missing”.In another optional embodiment of the first aspect of the invention, the beta-1,3-N-acetylglucosaminyltransferase mutant according to the invention comprises an amino acid sequence that misses one or more amino acids, preferably one or more consecutive amino acids, at 1-16 of SEQ ID NO 01. In another optional embodiment of the first aspect of the invention, the beta-1,3-N- acetylglucosaminyltransferase mutant according to the invention comprises an amino acid sequence that misses one or more amino acids, preferably one or more consecutive amino acids, at 350-363 of SEQ ID NO 01. Mutant beta-1,3-N-acetylglucosaminyltransferase In a preferred embodiment of the first aspect of the invention, the beta-1,3-N-acetylglucosaminyltransferase mutant according to the invention comprises an amino acid sequence thathas at least 80.0% sequence similarity with the full-length amino acid sequence represented by SEQ ID NO 02. Throughout the application and claims, “at least 80.0% sequence similarity” is preferably replaced with “at least 85.0% sequence similarity”, more preferably with “at least 87.5% sequence similarity”, even more preferably with “at least 90.0% sequence similarity, even more preferably with “at least 92.5% sequence similarity”, even more preferably with “at least 95.0% sequence similarity”, even more preferably with “at least 97.5% sequence similarity”, even more preferably with “at least 98.0% sequence similarity”, even more preferably with “at least 99.0% sequence similarity”, most preferably with “at least 100.0% sequence similarity”. For the sake of clarity, SEQ ID NO 02 is identical with SEQ ID NO 01, except that it misses amino acids 1- 16 and 350-363 of SEQ ID NO 01.In the context of the present invention, “ % sequence similarity” refers to the percentage of amino acidsof an amino acid sequence that either match exactly or that resemble the amino acids of the reference amino acid sequence (e.g. SEQ ID NO 01) over the full-length of the reference sequence. An amino acid that resembles another amino acid preferably corresponds with a so-called conservative amino acid substitution (it is referred to the Section “Conservative amino acid substitution(s) at 1-363“). For the sake of clarity, in the expression (or similar expression) “amino acid sequence 1 having at least 80.0% sequencesimilarity with the full-length amino acid sequence represented by SEQ ID NO 02”, the reference sequenceis SEQ ID NO 02. In other words, said expression means that amino acid sequence 1 has to have at least 80.0% sequence similarity with SEQ ID NO 02 over the full-length of said SEQ ID NO 02. For the purpose of this invention, the overall sequence similarity of a protein is preferably determined by the program EMBOSS Needle 5.0 (https: / / galaxy-iuc.github.io / emboss-5.0-docs / needle.html) with thedefault parameters, i.e. the substitution matrix EBLOSUM62, the gap opening penalty is 10 and the gapextension penalty is 0.5. In the context of the present invention, it is a particularly preferred embodiment that the beta-1,3-N- acetylglucosaminyltransferase mutant according to the invention comprises an amino acid sequence that has at least 80.0% sequence similarity with the full-length amino acid sequence of the reference beta-1,3- N-acetylglucosaminyltransferase (it is referred to the Section “Reference beta-1,3-N-acetylglucosaminyltransferase”). Said reference beta-1,3-N-acetylglucosaminyltransferase is preferablyrepresented by SEQ ID NO 01, more preferably represented by SEQ ID NO 03, 04 or 05, even more preferably represented by SEQ ID NO 03 or 04, most preferably represented by SEQ ID NO 03.In an additional and / or alternative preferred embodiment, the beta-1,3-N-acetylglucosaminyltransferasemutant according to the invention comprises an amino acid sequence that has at least 80.0% sequence identity with the full-length amino acid sequence represented by SEQ ID NO 02. Throughout the application and claims, “at least 80.0% sequence identity” is preferably replaced with “at least 85.0% sequence identity”, more preferably with “at least 87.5% sequence identity”, even more preferably with “at least 90.0% sequence identity, even more preferably with “at least 92.5% sequenceidentity”, even more preferably with “at least 95.0% sequence identity”, even more preferably with “atleast 97.5% sequence identity”, even more preferably with “at least 98.0% sequence identity”, even more preferably with “at least 99.0% sequence identity”, most preferably with “at least 100.0% sequence identity”. In the context of the present invention, “ % sequence identity” refers to the percentage of amino acids of an amino acid sequence that match exactly the amino acids of the reference amino acid sequence (e.g. SEQ ID NO 01) over the full-length of the reference sequence. For the sake of clarity, in the expression (or similar expression) “amino acid sequence 1 having at least 80.0% sequence identity with the full-length amino acid sequence represented by SEQ ID NO 02”, the reference sequence is SEQ ID NO 02. In other words, said expression means that amino acid sequence 1 has to have at least 80.0% sequence identity with SEQ ID NO 02 over the full-length of said SEQ ID NO 02. For the purpose of this invention, the overall sequence identity of a protein is preferably determined bythe program EMBOSS Needle 5.0 (https: / / galaxy-iuc.github.io / emboss-5.0-docs / needle.html) withdefault parameters (the substitution matrix EBLOSUM62, the gap opening penalty 10, and the gapextension penalty 0.5).In another preferred embodiment, the beta-1,3-N-acetylglucosaminyltransferase mutant according to theinvention comprises at least 320, preferably at least 325, more preferably at least 330, even morepreferably at least 333, even more preferably at least 340, most preferably at least 345, amino acid residues. In an additional and / or alternative preferred embodiment, the beta-1,3-N-acetylglucosaminyltransferasemutant according to the invention consists of ≤ 400, preferably ≤ 380, more preferably ≤ 370, even morepreferably ≤ 363, even more preferably ≤ 355, most preferably ≤ 350, amino acid residues. In a more preferred embodiment, the amino acid sequence of the beta-1,3-N-acetylglucosaminyl- transferase mutant according to the invention has the same length as the amino acid sequence of the reference beta-1,3-N-acetylglucosaminyltransferase (it is referred to the Section “Reference beta-1,3-N- acetylglucosaminyltransferase”). In another preferred embodiment, the beta-1,3-N-acetylglucosaminyltransferase mutant according to the invention does not lack all amino acids at 321-349 of SEQ ID NO 01, preferably wherein said mutant does not lack one or more amino acids at 321-339 of SEQ ID NO 01, more preferably wherein said mutant does not lack one or more amino acids at 321-349 of SEQ ID NO 01. The present invention essentially relates to the introduction of one or more non-conservative amino acid substitutions into a reference beta-1,3-N-acetylglucosaminyltransferase (it is referred to the Section“Reference beta-1,3-N-acetylglucosaminyltransferase”) in order to improve the activity and / or specificityof the reference beta-1,3-N-acetylglucosaminyltransferase. In a preferred embodiment, the beta-1,3-N-acetylglucosaminyltransferase mutant according to the invention comprises an amino acid sequence that differs from the full-length amino acid sequence of areference beta-1,3-N-acetylglucosaminyltransferase represented by SEQ ID NO 01 (it is referred to theSection “Reference beta-1,3-N-acetylglucosaminyltransferase”) and that has an increased activity compared to the reference beta-1,3-N-acetylglucosaminyltransferase. The activity of the mutant beta- 1,3-N-acetylglucosaminyltransferase is preferably at least 5.0%, more preferably at least 10.0%, even more preferably at least 20.0%, even more preferably at least 30.0%, even more preferably at least 40.0%, even more preferably at least 50.0%, even more preferably at least 60.0%, even more preferably at least 70.0%, even more preferably at least 80.0%, even more preferably at least 90.0%, most preferably at least100.0%, higher compared to the reference beta-1,3-N-acetylglucosaminyltransferase. Throughout thedescription and claims, the terms “has an increased (or higher) activity” and “exhibits an increased (orhigher) activity” are mutually exchangeable. Throughout the description and claims, the terms “higher” and “increased” are mutually exchangeable. The activity of the mutant and reference enzymes are preferably assessed using the same assay and under the same conditions. The skilled person can readily assess the activity as described in the Section “Reference beta-1,3-N-acetylglucosaminyltransferase”. Preferably, said activity is the conversion of lactose into a lacto-N-triose II (LN3)-containingoligosaccharide (it is referred to the fourth aspect of the invention wherein said LN3-containingoligosaccharide is disclosed in further detail), preferably LNnT. In a method for the production of a LN3-containing oligosaccharide (preferably LN3-containing mammalian milk oligosaccharide (MMO)) or amixture comprising at least two different LN3-containing oligosaccharides (preferably LN3-containingMMOs) (it is referred to the fourth aspect of the invention), said mutant beta-1,3-N-acetylglucosaminyltransferase preferably increases the yield of said oligosaccharide or mixture of saidoligosaccharides relative to a corresponding method in which the reference beta-1,3-N-acetylglucosaminyltransferase is used. Preferably said LN3-containing oligosaccharide (it is referred to thefourth aspect of the invention wherein said LN3-containing oligosaccharide is disclosed in further detail),is LN3, a LNnT-containing oligosaccharide or a LNT-containing oligosaccharide, more preferably LN3 or aLNnT-containing oligosaccharide, even more preferably a LNnT-containing oligosaccharide, mostpreferably LNnT. Preferably, said at least two different LN3-containing oligosaccharides (it is referred tothe fourth aspect of the invention wherein said MMOs are disclosed in further detail), are selected fromthe list consisting of LN3, LNT-containing oligosaccharide and LNnT-containing oligosaccharide, morepreferably are selected from the list consisting of LN3 and LNnT-containing oligosaccharide, mostpreferably said at least two different LN3-containing oligosaccharides are LNnT and pLNnH and optionallyLN3. Preferably, said yield is at least 10.0%, more preferably at least 20.0%, even more preferably at least30.0%, even more preferably at least 40.0%, even more preferably at least 50.0%, even more preferably at least 60.0%, even more preferably at least 70.0%, even more preferably at least 80.0%, even morepreferably at least 90.0%, even more preferably at least 100.0%, even more preferably at least 125.0%,even more preferably at least 150.0%, most preferably at least 200.0%, higher compared to the referencebeta-1,3-N-acetylglucosaminyltransferase. The term “yield” refers to the amount of oligosaccharide,preferably expressed in mass (e.g. mg or g), more preferably expressed in mass / volume (e.g. mg / L or g / L).In this context of the invention (i.e. activity, yield), it is particularly preferred that the beta-1,3-N-acetylglucosaminyltransferase mutant according to the invention differs from the full-length amino acid sequence of the reference beta-1,3-N-acetylglucosaminyltransferase represented by SEQ ID NO 01 in at least one or more non-conservative amino acid substitutions at 302-363 of SEQ ID NO 01 (it is referred to the Section “Non-conservative amino acid substitution(s) at 302-363”). In an additional and / or alternative preferred embodiment, the beta-1,3-N-acetylglucosaminyltransferase mutant according to the invention comprises an amino acid sequence that differs from the full-length amino acid sequence of a reference beta-1,3-N-acetylglucosaminyltransferase represented by SEQ ID NO01 (it is referred to the Section “Reference beta-1,3-N-acetylglucosaminyltransferase”) and that has anincreased substrate specificity for lactose over a longer-chain oligosaccharide (preferably a longer-chainMMO) compared to the reference beta-1,3-N-acetylglucosaminyltransferase. Preferably, said longer-chain oligosaccharide (preferably longer-chain MMO) is selected from the list consisting of LNnT, pLNnH,GlcNAc-beta-1,6-LNnT, LNT, LNH, pLNH, pLNH II, pLNnH II and GlcNAc-beta-1,6-LNT, optionally whereinsaid longer-chain oligosaccharide further consists of one or more fucose residues (preferably alpha-1-3-linked fucose residues). More preferably, said longer-chain oligosaccharide (preferably longer-chainMMO) is selected from the list consisting of LNnT, pLNnH, GlcNAc-beta-1,6-LNnT, LNT, LNH, pLNH, pLNHII, pLNnH II, GlcNAc-beta-1,6-LNT, LNFP-I, LNFP-II, LNFP-III, LNFP-V, LNnFP-V (i.e. LNFP-VI), DFLNH andDFLNH (a). Even more preferably, said longer-chain oligosaccharide (preferably longer-chain MMO) is selected from the list consisting of LNnT, pLNnH, GlcNAc-beta-1,6-LNnT, LNFP-III and LNnFP-V. Even morepreferably, said longer-chain oligosaccharide (preferably longer-chain MMO) is selected from the listconsisting of LNnT, pLNnH and GlcNAc-beta-1,6-LNnT. Even more preferably, said longer-chainoligosaccharide (preferably longer-chain MMO) is LNnT or pLNnH. Most preferably, said longer-chainoligosaccharide (preferably longer-chain MMO) is LNnT. One preferred way to assess said substratespecificity is to provide an equimolar amount of lactose and said longer-chain MMO and bring these acceptor saccharides into contact with UDP-GlcNAc and the beta-1,3-N-acetylglucosaminyltransferase(mutant vs reference as control) under conditions suitable for the transfer of GlcNAc from said UDP-GlcNAc to said acceptor saccharides (it is referred to the Section “Reference beta-1,3-N-acetylglucosaminyltransferase” in this regard). This can be done in an enzymatic assay or in a cellular assay(it is also referred to the fourth aspect in this regard), preferably in an enzymatic assay. The ratio (mol %)between LN3 (i.e. GlcNAc-beta-1,3-lactose) and the GlcNAc-beta-1,3-modified longer-chainoligosaccharide (e.g. GlcNAc-beta-1,3-LNnT) represents the substrate specificity of the enzyme for lactoseover the longer-chain oligosaccharide. Another more preferred way to assess said substrate specificity isto use a recombinant cell (e.g. recombinant Escherichia coli cell) that is genetically engineered for theproduction of the longer-chain oligosaccharide (it is also referred to the fourth aspect of the invention),i.e. comprises a pathway for the production of said longer-chain oligosaccharide (preferably longer-chainMMO), and that either is capable to produce lactose or that is able to take up lactose. In this particularcontext of the present invention, a recombinant cell that is genetically engineered for the production of LNnT is most preferred. Such a cell comprises a beta-1,3-N-acetylglucosaminyltransferase and a beta-1,4- galactosyltransferase. When lactose is fed to such a cell, the cell will produce LNnT but a fraction of theLNnT may be further modified by the beta-1,3-N-acetylglucosaminyltransferase and optionally furthergalactosylated by the beta-1,4-galactosyltranferase, this process may repeats itself. In other words, depending on the substrate specificity of the beta-1,3-N-acetylglucosaminyltransferase, LNnT andoptionally longer oligosaccharide (preferably MMO) structures may be formed. As the skilled personunderstands, such a cell can be used to assess the substrate specificity of the mutant beta-1,3-N- acetylglucosaminyltransferase and the reference beta-1,3-N-acetylglucosaminyltransferase. Indeed, a recombinant cell for the production of LNnT can be provided wherein the beta-1,3-N-acetylglucosaminyltransferase is the mutant beta-1,3-N-acetylglucosaminyltransferase which is thencultivated to produce said LNnT. Under identical cultivation conditions, a genetically identical recombinant cell (except that it contains the reference beta-1,3-N-acetylglucosaminyltransferase and not the mutant beta-1,3-N-acetylglucosaminyltransferase) can be cultivated in parallel for the same amount of time. At the end, the amount of each saccharide present in each cultivation can be assessed (it is alsoreferred to the Examples wherein this is further disclosed). The ratio between (i) LNnT (and LN3 if present),and (ii) LNnT (and LN3 if present) and each further elongated oligosaccharide resembles the enzyme’ssubstrate specificity for lactose over LNnT. The higher the ratio, the more specific the enzyme is for lactose over LNnT. Alternatively, the enzyme’s substrate specificity is assessed by the ratio between (i) pLNnH (and any further elongated oligosaccharide if present) and (ii) total amount of oligosaccharides (i.e. LN3,LNnT, pLNnH and any further elongated oligosaccharide if present). The lower the ratio, the more specificthe enzyme is for lactose. The amount of each oligosaccharide can be expressed in mass or mass / volume. Preferably, the mass is corrected for the molecular mass of the oligosaccharide (in other words, not the mass but the amount of molecules is taken into account). The substrate specificity for lactose over said longer-chain oligosaccharide (preferably longer-chain MMO) of the mutant beta-1,3-N-acetylglucosaminyltransferase is preferably at least 5.0%, more preferably at least 10.0%, even more preferably at least 20.0%, even more preferably at least 30.0%, even more preferably at least 40.0%, even more preferably at least 50.0%, even more preferably at least 60.0%, even more preferably at least 70.0%, even more preferably at least 80.0%, even more preferably at least 90.0%, even more preferably at least 100.0%, even more preferably at least 125.0%, even more preferably atleast 150.0%, even more preferably at least 200.0%, even more preferably at least 300.0%, even morepreferably at least 400.0%, even more preferably at least 500.0%, even more preferably at least 600.0%,even more preferably at least 700.0%, even more preferably at least 800.0%, even more preferably at least 800.0%, even more preferably at least 900.0%, most preferably at least 1000.0%, higher compared to the reference beta-1,3-N-acetylglucosaminyltransferase. In this context of the invention (i.e. substrate specificity), it is particularly preferred that the beta-1,3-N- acetylglucosaminyltransferase mutant according to the invention differs from the full-length amino acid sequence of the reference beta-1,3-N-acetylglucosaminyltransferase represented by SEQ ID NO 01 in atleast one or more non-conservative amino acid substitutions at 1-301 of SEQ ID NO 01 (it is referred tothe Section “Non-conservative amino acid substitution(s) at 1-301”). Depending on whether one aims for the production of mainly a single oligosaccharide, preferably a singleMMO, (and hence want to avoid further modification of this oligosaccharide) or a mixture of saidoligosaccharide (preferably MMO) with further elongated oligosaccharides, one can choose a mutantbeta-1,3-N-acetylglucosaminyltransferase with a certain substrate specificity for lactose over a longer-chain oligosaccharide (preferably a longer-chain MMO).In a more preferred embodiment, the beta-1,3-N-acetylglucosaminyltransferase mutant according to theinvention comprises an amino acid sequence that has at least 80.0% sequence similarity, preferably atleast 80.0% sequence identity, with:- SEQ ID NO 08, preferably SEQ ID NO 09, 10 or 11, more preferably SEQ ID NO 09, 10, 12 or 13,even more preferably SEQ ID NO 09 or 10, most preferably SEQ ID NO 09; and wherein the aminoacid at position 339 of said amino acid sequence of the mutant (position 322 in case of SEQ IDNO 10, position 338 in case of SEQ ID NO 13) is selected from the list consisting of C, M, A, G, T,S, P, H, N, D, Q, E, K and R, preferably selected from the list consisting of A, G, N, Q, M, C, D, E, R and K, more preferably selected from the list consisting of A, G, N, Q, M, C, D, E, R and K, even more preferably selected from the list consisting of A, G, N, Q, M, D, E, R and K, even more preferably selected from the list consisting of A, G, N, Q, M, D and E, even more preferablyselected from the list consisting of A, G, N, Q and M, even more preferably selected from the listconsisting of A, G, N and M, even more preferably selected from the list consisting of A, N andM, even more preferably N or A, most preferably A; or- SEQ ID NO 14, preferably SEQ ID NO 15, 16 or 17, more preferably SEQ ID NO 15, 16, 18 or 19,even more preferably SEQ ID NO 15 or 16, most preferably SEQ ID NO 15; and wherein the aminoacid at position 333 of said amino acid sequence of the mutant (position 316 in case of SEQ IDNO 16, position 332 in case of SEQ ID NO 19) is selected from the list consisting of C, M, A, G, T,S, P, H, N, D, Q, E, K and R, preferably selected from the list consisting of A, G, N, Q, M, C, D, E, R and K, more preferably selected from the list consisting of A, G, N, Q, M, C, D, E, R and K, even more preferably selected from the list consisting of A, G, N, Q, M, D, E, R and K, even more preferably selected from the list consisting of A, G, N, Q, M, D and E, even more preferably selected from the list consisting of A, G, N, Q and M, even more preferably selected from the list consisting of A, G, N and M, even more preferably selected from the list consisting of A, N and M, even more preferably N or A, most preferably A; or- SEQ ID NO: 20, preferably SEQ ID NO 21, 22 or 23, more preferably SEQ ID NO 21, 22, 24 or 25,even more preferably SEQ ID NO 21 or 22, most preferably SEQ ID NO 21; and wherein the amino acid at position 323 of said amino acid sequence of the mutant (position 306 in case of SEQ IDNO 22, position 322 in case of SEQ ID NO 25) is selected from the list consisting of C, M, A, G, T,S, P, H, N, D, Q, E, K and R, preferably selected from the list consisting of A, G, N, Q, M, C, D, E, R and K, more preferably selected from the list consisting of A, G, N, Q, M, C, D, E, R and K, even more preferably selected from the list consisting of A, G, N, Q, M, D, E, R and K, even more preferably selected from the list consisting of A, G, N, Q, M, D and E, even more preferably selected from the list consisting of A, G, N, Q and M, even more preferably selected from the list consisting of A, G, N and M, even more preferably selected from the list consisting of A, N and M, even more preferably N or A, most preferably A; or- SEQ ID NO: 26, preferably SEQ ID NO 27, 28 or 29, more preferably SEQ ID NO 27, 28, 30 or 31,even more preferably SEQ ID NO 27 or 28, most preferably SEQ ID NO 27; and wherein the amino acid at position 304 of said amino acid sequence of the mutant (position 287 in case of SEQ IDNO 28, position 303 in case of SEQ ID NO 31) is selected from the list consisting of C, M, A, G, T,S, P, H, N, D, Q, E, K and R, preferably selected from the list consisting of A, G, N, Q, M, C, D, E, R and K, more preferably selected from the list consisting of A, G, N, Q, M, C, D, E, R and K, even more preferably selected from the list consisting of A, G, N, Q, M, D, E, R and K, even more preferably selected from the list consisting of A, G, N, Q, M, D and E, even more preferably selected from the list consisting of A, G, N, Q and M, even more preferably selected from the list consisting of A, G, N and M, even more preferably selected from the list consisting of A, N and M, even more preferably N or A, most preferably A;preferably with: -SEQ ID NO 08, preferably SEQ ID NO 09, 10 or 11, more preferably SEQ ID NO 09, 10, 12 or 13,even more preferably SEQ ID NO 09 or 10, most preferably SEQ ID NO 09; and wherein the amino acid at position 339 of said amino acid sequence of the mutant (position 322 in case of SEQ IDNO 10, position 338 in case of SEQ ID NO 13) is selected from the list consisting of C, M, A, G, T,S, P, H, N, D, Q, E, K and R, preferably selected from the list consisting of A, G, N, Q, M, C, D, E, R and K, more preferably selected from the list consisting of A, G, N, Q, M, C, D, E, R and K, even more preferably selected from the list consisting of A, G, N, Q, M, D, E, R and K, even more preferably selected from the list consisting of A, G, N, Q, M, D and E, even more preferably selected from the list consisting of A, G, N, Q and M, even more preferably selected from the list consisting of A, G, N and M, even more preferably selected from the list consisting of A, N and M, even more preferably N or A, most preferably A; or- SEQ ID NO 14, preferably SEQ ID NO 15, 16 or 17, more preferably SEQ ID NO 15, 16, 18 or 19,even more preferably SEQ ID NO 15 or 16, most preferably SEQ ID NO 15; and wherein the amino acid at position 333 of said amino acid sequence of the mutant (position 316 in case of SEQ IDNO 16, position 332 in case of SEQ ID NO 19) is selected from the list consisting of C, M, A, G, T,S, P, H, N, D, Q, E, K and R, preferably selected from the list consisting of A, G, N, Q, M, C, D, E, R and K, more preferably selected from the list consisting of A, G, N, Q, M, C, D, E, R and K, even more preferably selected from the list consisting of A, G, N, Q, M, D, E, R and K, even more preferably selected from the list consisting of A, G, N, Q, M, D and E, even more preferably selected from the list consisting of A, G, N, Q and M, even more preferably selected from the list consisting of A, G, N and M, even more preferably selected from the list consisting of A, N and M, even more preferably N or A, most preferably A; or- SEQ ID NO: 20, preferably SEQ ID NO 21, 22 or 23, more preferably SEQ ID NO 21, 22, 24 or 25,even more preferably SEQ ID NO 21 or 22, most preferably SEQ ID NO 21; and wherein the amino acid at position 323 of said amino acid sequence of the mutant (position 306 in case of SEQ IDNO 22, position 322 in case of SEQ ID NO 25) is selected from the list consisting of C, M, A, G, T,S, P, H, N, D, Q, E, K and R, preferably selected from the list consisting of A, G, N, Q, M, C, D, E, R and K, more preferably selected from the list consisting of A, G, N, Q, M, C, D, E, R and K, even more preferably selected from the list consisting of A, G, N, Q, M, D, E, R and K, even more preferably selected from the list consisting of A, G, N, Q, M, D and E, even more preferably selected from the list consisting of A, G, N, Q and M, even more preferably selected from the list consisting of A, G, N and M, even more preferably selected from the list consisting of A, N andM, even more preferably N or A, most preferably A;more preferably with: -SEQ ID NO 08, preferably SEQ ID NO 09, 10 or 11, more preferably SEQ ID NO 09, 10, 12 or 13,even more preferably SEQ ID NO 09 or 10, most preferably SEQ ID NO 09; and wherein the amino acid at position 339 of said amino acid sequence of the mutant (position 322 in case of SEQ IDNO 10, position 338 in case of SEQ ID NO 13) is selected from the list consisting of C, M, A, G, T,S, P, H, N, D, Q, E, K and R, preferably selected from the list consisting of A, G, N, Q, M, C, D, E, R and K, more preferably selected from the list consisting of A, G, N, Q, M, C, D, E, R and K, even more preferably selected from the list consisting of A, G, N, Q, M, D, E, R and K, even more preferably selected from the list consisting of A, G, N, Q, M, D and E, even more preferably selected from the list consisting of A, G, N, Q and M, even more preferably selected from the list consisting of A, G, N and M, even more preferably selected from the list consisting of A, N and M, even more preferably N or A, most preferably A; or- SEQ ID NO 14, preferably SEQ ID NO 15, 16 or 17, more preferably SEQ ID NO 15, 16, 18 or 19,even more preferably SEQ ID NO 15 or 16, most preferably SEQ ID NO 15; and wherein the amino acid at position 333 of said amino acid sequence of the mutant (position 316 in case of SEQ IDNO 16, position 332 in case of SEQ ID NO 19) is selected from the list consisting of C, M, A, G, T,S, P, H, N, D, Q, E, K and R, preferably selected from the list consisting of A, G, N, Q, M, C, D, E, R and K, more preferably selected from the list consisting of A, G, N, Q, M, C, D, E, R and K, even more preferably selected from the list consisting of A, G, N, Q, M, D, E, R and K, even more preferably selected from the list consisting of A, G, N, Q, M, D and E, even more preferably selected from the list consisting of A, G, N, Q and M, even more preferably selected from the list consisting of A, G, N and M, even more preferably selected from the list consisting of A, N and M, even more preferably N or A, most preferably A;most preferably with: -SEQ ID NO 08, preferably SEQ ID NO 09, 10 or 11, more preferably SEQ ID NO 09, 10, 12 or 13,even more preferably SEQ ID NO 09 or 10, most preferably SEQ ID NO 09; and wherein the amino acid at position 339 of said amino acid sequence of the mutant (position 322 in case of SEQ IDNO 10, position 338 in case of SEQ ID NO 13) is selected from the list consisting of C, M, A, G, T,S, P, H, N, D, Q, E, K and R, preferably selected from the list consisting of A, G, N, Q, M, C, D, E, R and K, more preferably selected from the list consisting of A, G, N, Q, M, C, D, E, R and K, even more preferably selected from the list consisting of A, G, N, Q, M, D, E, R and K, even more preferably selected from the list consisting of A, G, N, Q, M, D and E, even more preferably selected from the list consisting of A, G, N, Q and M, even more preferably selected from the list consisting of A, G, N and M, even more preferably selected from the list consisting of A, N and M, even more preferably N or A, most preferably A. For the sake of clarity, said “sequence similarity” and “sequence identity” are as defined earlier in the present Section “Mutant beta-1,3-N-acetylglucosaminyltransferase”.For the sake of clarity, SEQ ID NO 08 represents a F339 mutant of the reference beta-1,3-N-acetylglucosaminyltransferase represented with SEQ ID NO 01. The corresponding mutant amino sequence when the reference beta-1,3-N-acetylglucosaminyltransferase is represented with SEQ ID NO 03, 04, 05, 06 or 07 (it is referred to the Section “Reference beta-1,3-N-acetylglucosaminyltransferase”and also in particular Table 1), is SEQ ID NO 09, 10, 11, 12 or 13, respectively. In this regard, for the sakeof clarity and as an example for similar type of embodiments throughout the application and claims, theexpression “mutant comprises an amino acid sequence that has at least 80.0% sequence similarity (preferably at least 80.0% sequence identity) with SEQ ID NO ‘X’ and wherein the amino acid at position ‘Y’ of said amino acid sequence of the mutant is selected from the list consisting of ‘a, b and c’ “ is to be understood as a beta-1,3-N-acetylglucosaminyltransferase mutant that comprises an amino acid sequence (i) having at least 80.0% sequence similarity (preferably at least 80.0% sequence identity) with the full-length amino acid sequence represented by SEQ ID ‘X’, and (ii) wherein the amino at position ‘Y’ has to be a, b or c. The position ‘Y’ is expressed in function of SEQ ID ‘X’ and should be approached in the same way as elaborated earlier herein (it is particularly referred to the Section “Reference beta-1,3-N- acetylglucosaminyltransferase” and in particular to Table 1).For the sake of clarity, SEQ ID NO 14 represents a F333 mutant of the reference beta-1,3-N-acetylglucosaminyltransferase represented with SEQ ID NO 01. The corresponding mutant amino sequence when the reference beta-1,3-N-acetylglucosaminyltransferase is represented with SEQ ID NO 03, 04, 05, 06 or 07 (it is referred to the Section “Reference beta-1,3-N-acetylglucosaminyltransferase”and also in particular Table 1), is SEQ ID NO 15, 16, 17, 18 or 19, respectively.For the sake of clarity, SEQ ID NO 20 represents a F323 mutant of the reference beta-1,3-N-acetylglucosaminyltransferase represented with SEQ ID NO 01. The corresponding mutant amino sequence when the reference beta-1,3-N-acetylglucosaminyltransferase is represented with SEQ ID NO 03, 04, 05, 06 or 07 (it is referred to the Section “Reference beta-1,3-N-acetylglucosaminyltransferase”and also in particular Table 1), is SEQ ID NO 21, 22, 23, 24 or 25, respectively.For the sake of clarity, SEQ ID NO 26 represents a F304 mutant of the reference beta-1,3-N-acetylglucosaminyltransferase represented with SEQ ID NO 01. The corresponding mutant amino sequence when the reference beta-1,3-N-acetylglucosaminyltransferase is represented with SEQ ID NO 03, 04, 05, 06 or 07 (it is referred to the Section “Reference beta-1,3-N-acetylglucosaminyltransferase” and also in particular Table 1), is SEQ ID NO 27, 28, 29, 30 or 31, respectively. In an even more preferred embodiment, the beta-1,3-N-acetylglucosaminyltransferase mutant according to the invention comprises an amino acid sequence that has at least 80.0% sequence similarity, preferably at least 80.0% sequence identity, with:- SEQ ID NO 32, preferably SEQ ID NO 33, 34 or 35, more preferably SEQ ID NO 33, 34, 36 or 37,even more preferably SEQ ID NO 33 or 34, most preferably SEQ ID NO 33; and wherein:o the amino acid at position 339 of said amino acid sequence of the mutant (position322 in case of SEQ ID NO 34, position 338 in case of SEQ ID NO 37) is selected from thelist consisting of C, M, A, G, T, S, P, H, N, D, Q, E, K and R, preferably selected from the list consisting of A, G, N, Q, M, C, D, E, R and K, more preferably selected from the list consisting of A, G, N, Q, M, C, D, E, R and K, even more preferably selected from the list consisting of A, G, N, Q, M, D, E, R and K, even more preferably selected from the list consisting of A, G, N, Q, M, D and E, even more preferably selected from the list consisting of A, G, N, Q and M, even more preferably selected from the list consisting of A, G, N and M, even more preferably selected from the list consisting of A, N and M, even more preferably N or A, most preferably A; ando the amino acid at position 182 of said amino acid sequence of the mutant (position165 in case of SEQ ID NO 34, position 181 in case of SEQ ID NO 37) is selected from thelist consisting of L, M, A, D, E, S, N, Q, T, R and K, preferably selected from the listconsisting of L, M, A, D, E, S, T, R and K, more preferably selected from the list consistingof L, M, A, S, T, D and E, even more preferably selected form the list consisting of L, M,A, S, T and D, even more preferably selected from the list consisting of L, M, A, S andT, even more preferably selected from the list consisting of L, M, S and T, mostpreferably S;- SEQ ID NO 38, preferably SEQ ID NO 39, 40 or 41, more preferably SEQ ID NO 39, 40, 42 or 43,even more preferably SEQ ID NO 39 or 40, most preferably SEQ ID NO 39; and wherein:o the amino acid at position 339 of said amino acid sequence of the mutant (position322 in case of SEQ ID NO 40, position 338 in case of SEQ ID NO 43) is selected from thelist consisting of C, M, A, G, T, S, P, H, N, D, Q, E, K and R, preferably selected from the list consisting of A, G, N, Q, M, C, D, E, R and K, more preferably selected from the list consisting of A, G, N, Q, M, C, D, E, R and K, even more preferably selected from the list consisting of A, G, N, Q, M, D, E, R and K, even more preferably selected from the list consisting of A, G, N, Q, M, D and E, even more preferably selected from the list consisting of A, G, N, Q and M, even more preferably selected from the list consisting of A, G, N and M, even more preferably selected from the list consisting of A, N and M, even more preferably N or A, most preferably A; ando the amino acid at position 180 of said amino acid sequence of the mutant (position163 in case of SEQ ID NO 40, position 179 in case of SEQ ID NO 43) is selected from thelist consisting of D, E, S, N, Q, T, R, K, H and Y, more preferably selected from the listconsisting of D, E, S, N, Q, T, R and K, even more preferably selected from the listconsisting of D, E, S, T, R and K, even more preferably selected from the list consistingof S, T, R and K, even more preferably R or K, most preferably R; or- SEQ ID NO: 44, preferably SEQ ID NO 45, 46 or 47, more preferably SEQ ID NO 45, 46, 48 or 49,even more preferably SEQ ID NO 45 or 46, most preferably SEQ ID NO 45; and wherein:o the amino acid at position 339 of said amino acid sequence of the mutant (position322 in case of SEQ ID NO 46, position 338 in case of SEQ ID NO 49) is selected from thelist consisting of C, M, A, G, T, S, P, H, N, D, Q, E, K and R, preferably selected from the list consisting of A, G, N, Q, M, C, D, E, R and K, more preferably selected from the list consisting of A, G, N, Q, M, C, D, E, R and K, even more preferably selected from the list consisting of A, G, N, Q, M, D, E, R and K, even more preferably selected from the list consisting of A, G, N, Q, M, D and E, even more preferably selected from the list consisting of A, G, N, Q and M, even more preferably selected from the list consisting of A, G, N and M, even more preferably selected from the list consisting of A, N and M, even more preferably N or A, most preferably A; ando the amino acid at position 211 of said amino acid sequence of the mutant (position194 in case of SEQ ID NO 46, position 210 in case of SEQ ID NO 49) is selected from thelist consisting of A, G, N, Q, M, D, and E, more preferably selected from the list consisting of A, G, N, Q and M, even more preferably selected from the list consisting of A, G, N and M, even more preferably selected from the list consisting of A, N and M, most preferably M or N; or- SEQ ID NO 100, preferably SEQ ID NO 101, 102 or 103, more preferably SEQ ID NO 101, 102, 104or 105, even more preferably SEQ ID NO 101 or 102, most preferably SEQ ID NO 101; andwherein: othe amino acid at position 339 of said amino acid sequence of the mutant (position322 in case of SEQ ID NO 102, position 338 in case of SEQ ID NO 105) is selected from the list consisting of C, M, A, G, T, S, P, H, N, D, Q, E, K and R, preferably selected from the list consisting of A, G, N, Q, M, C, D, E, R and K, more preferably selected from the list consisting of A, G, N, Q, M, C, D, E, R and K, even more preferably selected from the list consisting of A, G, N, Q, M, D, E, R and K, even more preferably selected from the list consisting of A, G, N, Q, M, D and E, even more preferably selected from the list consisting of A, G, N, Q and M, even more preferably selected from the list consisting of A, G, N and M, even more preferably selected from the list consisting of A, N and M, even more preferably N or A, most preferably A; and othe amino acid at position 249 of said amino acid sequence of the mutant (position232 in case of SEQ ID NO 102, position 248 in case of SEQ ID NO 105) is selected fromthe list consisting of A, C, G, I, L, M, F, P, W and V, preferably selected from the list consisting of W, F, G and A, more preferably W or F, most preferably F; and othe amino acid at position 256 of said amino acid sequence of the mutant (position239 in case of SEQ ID NO 102, position 255 in case of SEQ ID NO 105) is selected from the list consisting of A, C, G, I, L, M, F, P, W and V, preferably selected from the listconsisting of W, F, G and A, more preferably W or F, most preferably W; or- SEQ ID NO 106, preferably SEQ ID NO 107, 108 or 109, more preferably SEQ ID NO 107, 108, 110or 111, even more preferably SEQ ID NO 107 or 108, most preferably SEQ ID NO 107; andwherein: othe amino acid at position 339 of said amino acid sequence of the mutant (position322 in case of SEQ ID NO 108, position 338 in case of SEQ ID NO 111) is selected from the list consisting of C, M, A, G, T, S, P, H, N, D, Q, E, K and R, preferably selected from the list consisting of A, G, N, Q, M, C, D, E, R and K, more preferably selected from the list consisting of A, G, N, Q, M, C, D, E, R and K, even more preferably selected from the list consisting of A, G, N, Q, M, D, E, R and K, even more preferably selected from the list consisting of A, G, N, Q, M, D and E, even more preferably selected from the list consisting of A, G, N, Q and M, even more preferably selected from the list consisting of A, G, N and M, even more preferably selected from the list consisting of A, N and M, even more preferably N or A, most preferably A; and othe amino acid at position 158 of said amino acid sequence of the mutant (position241 in case of SEQ ID NO 108, position 157 in case of SEQ ID NO 111) is selected fromthe list consisting of A, C, G, I, L, M, F, P, W and V, preferably selected from the list consisting of W, F, G and A, more preferably W or F, most preferably W; and othe amino acid at position 249 of said amino acid sequence of the mutant (position232 in case of SEQ ID NO 108, position 248 in case of SEQ ID NO 111) is selected from the list consisting of A, C, G, I, L, M, F, P, W and V, preferably selected from the list consisting of W, F, G and A, more preferably W or F, most preferably F; and othe amino acid at position 256 of said amino acid sequence of the mutant (position239 in case of SEQ ID NO 108, position 255 in case of SEQ ID NO 111) is selected from the list consisting of A, C, G, I, L, M, F, P, W and V, preferably selected from the list consisting of W, F, G and A, more preferably W or F, most preferably W; preferably with: -SEQ ID NO 32, preferably SEQ ID NO 33, 34 or 35, more preferably SEQ ID NO 33, 34, 36 or 37,even more preferably SEQ ID NO 33 or 34, most preferably SEQ ID NO 33; and wherein: othe amino acid at position 339 of said amino acid sequence of the mutant (position322 in case of SEQ ID NO 34, position 338 in case of SEQ ID NO 37) is selected from thelist consisting of C, M, A, G, T, S, P, H, N, D, Q, E, K and R, preferably selected from the list consisting of A, G, N, Q, M, C, D, E, R and K, more preferably selected from the list consisting of A, G, N, Q, M, C, D, E, R and K, even more preferably selected from the list consisting of A, G, N, Q, M, D, E, R and K, even more preferably selected from the list consisting of A, G, N, Q, M, D and E, even more preferably selected from the list consisting of A, G, N, Q and M, even more preferably selected from the list consisting of A, G, N and M, even more preferably selected from the list consisting of A, N and M, even more preferably N or A, most preferably A; ando the amino acid at position 182 of said amino acid sequence of the mutant (position165 in case of SEQ ID NO 34, position 181 in case of SEQ ID NO 37) is selected from thelist consisting of L, M, A, D, E, S, N, Q, T, R and K, preferably selected from the listconsisting of L, M, A, D, E, S, T, R and K, more preferably selected from the list consisting of L, M, A, S, T, D and E, even more preferably selected form the list consisting of L, M, A, S, T and D, even more preferably selected from the list consisting of L, M, A, S and T, even more preferably selected from the list consisting of L, M, S and T, most preferably S;- SEQ ID NO 38, preferably SEQ ID NO 39, 40 or 41, more preferably SEQ ID NO 39, 40, 42 or 43,even more preferably SEQ ID NO 39 or 40, most preferably SEQ ID NO 39; and wherein: othe amino acid at position 339 of said amino acid sequence of the mutant (position322 in case of SEQ ID NO 40, position 338 in case of SEQ ID NO 43) is selected from thelist consisting of C, M, A, G, T, S, P, H, N, D, Q, E, K and R, preferably selected from the list consisting of A, G, N, Q, M, C, D, E, R and K, more preferably selected from the list consisting of A, G, N, Q, M, C, D, E, R and K, even more preferably selected from the list consisting of A, G, N, Q, M, D, E, R and K, even more preferably selected from the list consisting of A, G, N, Q, M, D and E, even more preferably selected from the list consisting of A, G, N, Q and M, even more preferably selected from the list consisting of A, G, N and M, even more preferably selected from the list consisting of A, N and M, even more preferably N or A, most preferably A; ando the amino acid at position 180 of said amino acid sequence of the mutant (position163 in case of SEQ ID NO 40, position 179 in case of SEQ ID NO 43) is selected from thelist consisting of D, E, S, N, Q, T, R, K, H and Y, more preferably selected from the listconsisting of D, E, S, N, Q, T, R and K, even more preferably selected from the listconsisting of D, E, S, T, R and K, even more preferably selected from the list consistingof S, T, R and K, even more preferably R or K, most preferably R; or- SEQ ID NO 100, preferably SEQ ID NO 101, 102 or 103, more preferably SEQ ID NO 101, 102, 104or 105, even more preferably SEQ ID NO 101 or 102, most preferably SEQ ID NO 101; and wherein:o the amino acid at position 339 of said amino acid sequence of the mutant (position322 in case of SEQ ID NO 102, position 338 in case of SEQ ID NO 105) is selected from the list consisting of C, M, A, G, T, S, P, H, N, D, Q, E, K and R, preferably selected from the list consisting of A, G, N, Q, M, C, D, E, R and K, more preferably selected from the list consisting of A, G, N, Q, M, C, D, E, R and K, even more preferably selected from the list consisting of A, G, N, Q, M, D, E, R and K, even more preferably selected from the list consisting of A, G, N, Q, M, D and E, even more preferably selected from the list consisting of A, G, N, Q and M, even more preferably selected from the list consisting of A, G, N and M, even more preferably selected from the list consisting of A, N and M, even more preferably N or A, most preferably A; and othe amino acid at position 249 of said amino acid sequence of the mutant (position232 in case of SEQ ID NO 102, position 248 in case of SEQ ID NO 105) is selected from the list consisting of A, C, G, I, L, M, F, P, W and V, preferably selected from the list consisting of W, F, G and A, more preferably W or F, most preferably F; and othe amino acid at position 256 of said amino acid sequence of the mutant (position239 in case of SEQ ID NO 102, position 255 in case of SEQ ID NO 105) is selected from the list consisting of A, C, G, I, L, M, F, P, W and V, preferably selected from the list consisting of W, F, G and A, more preferably W or F, most preferably W; or- SEQ ID NO 106, preferably SEQ ID NO 107, 108 or 109, more preferably SEQ ID NO 107, 108, 110or 111, even more preferably SEQ ID NO 107 or 108, most preferably SEQ ID NO 107; andwherein: othe amino acid at position 339 of said amino acid sequence of the mutant (position322 in case of SEQ ID NO 108, position 338 in case of SEQ ID NO 111) is selected from the list consisting of C, M, A, G, T, S, P, H, N, D, Q, E, K and R, preferably selected from the list consisting of A, G, N, Q, M, C, D, E, R and K, more preferably selected from the list consisting of A, G, N, Q, M, C, D, E, R and K, even more preferably selected from the list consisting of A, G, N, Q, M, D, E, R and K, even more preferably selected from the list consisting of A, G, N, Q, M, D and E, even more preferably selected from the list consisting of A, G, N, Q and M, even more preferably selected from the list consisting of A, G, N and M, even more preferably selected from the list consisting of A, N and M, even more preferably N or A, most preferably A; and othe amino acid at position 158 of said amino acid sequence of the mutant (position241 in case of SEQ ID NO 108, position 157 in case of SEQ ID NO 111) is selected from the list consisting of A, C, G, I, L, M, F, P, W and V, preferably selected from the list consisting of W, F, G and A, more preferably W or F, most preferably W; and othe amino acid at position 249 of said amino acid sequence of the mutant (position 232 in case of SEQ ID NO 108, position 248 in case of SEQ ID NO 111) is selected from the list consisting of A, C, G, I, L, M, F, P, W and V, preferably selected from the list consisting of W, F, G and A, more preferably W or F, most preferably F; and othe amino acid at position 256 of said amino acid sequence of the mutant (position239 in case of SEQ ID NO 108, position 255 in case of SEQ ID NO 111) is selected from the list consisting of A, C, G, I, L, M, F, P, W and V, preferably selected from the list consisting of W, F, G and A, more preferably W or F, most preferably W; more preferably with: -SEQ ID NO 32, preferably SEQ ID NO 33, 34 or 35, more preferably SEQ ID NO 33, 34, 36 or 37,even more preferably SEQ ID NO 33 or 34, most preferably SEQ ID NO 33; and wherein: othe amino acid at position 339 of said amino acid sequence of the mutant (position322 in case of SEQ ID NO 34, position 338 in case of SEQ ID NO 37) is selected from thelist consisting of C, M, A, G, T, S, P, H, N, D, Q, E, K and R, preferably selected from the list consisting of A, G, N, Q, M, C, D, E, R and K, more preferably selected from the list consisting of A, G, N, Q, M, C, D, E, R and K, even more preferably selected from the list consisting of A, G, N, Q, M, D, E, R and K, even more preferably selected from the list consisting of A, G, N, Q, M, D and E, even more preferably selected from the list consisting of A, G, N, Q and M, even more preferably selected from the list consisting of A, G, N and M, even more preferably selected from the list consisting of A, N and M, even more preferably N or A, most preferably A; ando the amino acid at position 182 of said amino acid sequence of the mutant (position165 in case of SEQ ID NO 34, position 181 in case of SEQ ID NO 37) is selected from thelist consisting of L, M, A, D, E, S, N, Q, T, R and K, preferably selected from the list consisting of L, M, A, D, E, S, T, R and K, more preferably selected from the list consisting of L, M, A, S, T, D and E, even more preferably selected form the list consisting of L, M, A, S, T and D, even more preferably selected from the list consisting of L, M, A, S and T, even more preferably selected from the list consisting of L, M, S and T, most preferably S; or- SEQ ID NO 38, preferably SEQ ID NO 39, 40 or 41, more preferably SEQ ID NO 39, 40, 42 or 43,even more preferably SEQ ID NO 39 or 40, most preferably SEQ ID NO 39; and wherein: othe amino acid at position 339 of said amino acid sequence of the mutant (position322 in case of SEQ ID NO 40, position 338 in case of SEQ ID NO 43) is selected from thelist consisting of C, M, A, G, T, S, P, H, N, D, Q, E, K and R, preferably selected from the list consisting of A, G, N, Q, M, C, D, E, R and K, more preferably selected from the list consisting of A, G, N, Q, M, C, D, E, R and K, even more preferably selected from the list consisting of A, G, N, Q, M, D, E, R and K, even more preferably selected from the list consisting of A, G, N, Q, M, D and E, even more preferably selected from the list consisting of A, G, N, Q and M, even more preferably selected from the list consisting of A, G, N and M, even more preferably selected from the list consisting of A, N and M, even more preferably N or A, most preferably A; ando the amino acid at position 180 of said amino acid sequence of the mutant (position163 in case of SEQ ID NO 40, position 179 in case of SEQ ID NO 43) is selected from thelist consisting of D, E, S, N, Q, T, R, K, H and Y, more preferably selected from the list consisting of D, E, S, N, Q, T, R and K, even more preferably selected from the list consisting of D, E, S, T, R and K, even more preferably selected from the list consisting of S, T, R and K, even more preferably R or K, most preferably R;most preferably with:- SEQ ID NO 38, preferably SEQ ID NO 39, 40 or 41, more preferably SEQ ID NO 39, 40, 42 or 43,even more preferably SEQ ID NO 39 or 40, most preferably SEQ ID NO 39; and wherein: othe amino acid at position 339 of said amino acid sequence of the mutant (position322 in case of SEQ ID NO 40, position 338 in case of SEQ ID NO 43) is selected from thelist consisting of C, M, A, G, T, S, P, H, N, D, Q, E, K and R, preferably selected from the list consisting of A, G, N, Q, M, C, D, E, R and K, more preferably selected from the list consisting of A, G, N, Q, M, C, D, E, R and K, even more preferably selected from the list consisting of A, G, N, Q, M, D, E, R and K, even more preferably selected from the list consisting of A, G, N, Q, M, D and E, even more preferably selected from the list consisting of A, G, N, Q and M, even more preferably selected from the list consisting of A, G, N and M, even more preferably selected from the list consisting of A, N and M, even more preferably N or A, most preferably A; ando the amino acid at position 180 of said amino acid sequence of the mutant (position163 in case of SEQ ID NO 40, position 179 in case of SEQ ID NO 43) is selected from thelist consisting of D, E, S, N, Q, T, R, K, H and Y, more preferably selected from the list consisting of D, E, S, N, Q, T, R and K, even more preferably selected from the list consisting of D, E, S, T, R and K, even more preferably selected from the list consisting of S, T, R and K, even more preferably R or K, most preferably R. For the sake of clarity, said “sequence similarity” and “sequence identity” are as defined earlier in the present Section “Mutant beta-1,3-N-acetylglucosaminyltransferase”.For the sake of clarity, SEQ ID NO 32 represents a F339+P182 mutant of the reference beta-1,3-N-acetylglucosaminyltransferase represented with SEQ ID NO 01. The corresponding mutant amino sequence when the reference beta-1,3-N-acetylglucosaminyltransferase is represented with SEQ ID NO03, 04, 05, 06 or 07 (it is referred to the Section “Reference beta-1,3-N-acetylglucosaminyltransferase”and also in particular Table 1), is SEQ ID NO 33, 34, 35, 36 or 37, respectively.For the sake of clarity, SEQ ID NO 38 represents a F339+G180 mutant of the reference beta-1,3-N-acetylglucosaminyltransferase represented with SEQ ID NO 01. The corresponding mutant amino sequence when the reference beta-1,3-N-acetylglucosaminyltransferase is represented with SEQ ID NO 03, 04, 05, 06 or 07 (it is referred to the Section “Reference beta-1,3-N-acetylglucosaminyltransferase”and also in particular Table 1), is SEQ ID NO 39, 40, 41, 42 or 43, respectively.For the sake of clarity, SEQ ID NO 44 represents a F339+Y211 mutant of the reference beta-1,3-N-acetylglucosaminyltransferase represented with SEQ ID NO 01. The corresponding mutant amino sequence when the reference beta-1,3-N-acetylglucosaminyltransferase is represented with SEQ ID NO 03, 04, 05, 06 or 07 (it is referred to the Section “Reference beta-1,3-N-acetylglucosaminyltransferase”and also in particular Table 1), is SEQ ID NO 45, 46, 47, 48 or 49, respectively.In an even more preferred embodiment, the beta-1,3-N-acetylglucosaminyltransferase mutant according to the invention comprises an amino acid sequence that has at least 80.0% sequence similarity, preferably at least 80.0% sequence identity, with: -SEQ ID NO 50, preferably SEQ ID NO 51, 52 or 53, more preferably SEQ ID NO 51, 52, 54 or 55,even more preferably SEQ ID NO 51 or 52, most preferably SEQ ID NO 51; and wherein:o the amino acid at position 339 of said amino acid sequence of the mutant (position322 in case of SEQ ID NO 52, position 338 in case of SEQ ID NO 55) is selected from thelist consisting of C, M, A, G, T, S, P, H, N, D, Q, E, K and R, preferably selected from the list consisting of A, G, N, Q, M, C, D, E, R and K, more preferably selected from the list consisting of A, G, N, Q, M, C, D, E, R and K, even more preferably selected from the list consisting of A, G, N, Q, M, D, E, R and K, even more preferably selected from the list consisting of A, G, N, Q, M, D and E, even more preferably selected from the list consisting of A, G, N, Q and M, even more preferably selected from the list consisting of A, G, N and M, even more preferably selected from the list consisting of A, N and M, even more preferably N or A, most preferably A; ando the amino acid at position 182 of said amino acid sequence of the mutant (position165 in case of SEQ ID NO 52, position 181 in case of SEQ ID NO 55) is selected from thelist consisting of L, M, A, D, E, S, N, Q, T, R and K, preferably selected from the listconsisting of L, M, A, D, E, S, T, R and K, more preferably selected from the list consisting of L, M, A, S, T, D and E, even more preferably selected form the list consisting of L, M, A, S, T and D, even more preferably selected from the list consisting of L, M, A, S and T, even more preferably selected from the list consisting of L, M, S and T, most preferably S; ando the amino acid at position 324 of said amino acid sequence of the mutant (position307 in case of SEQ ID NO 52, position 323 in case of SEQ ID NO 55) is selected from thelist consisting of R, N, D, Q, E, H, K, S, T and Y, preferably selected from the list consistingof D, E, N, Q, S, T and Y, more preferably selected from the list consisting of D, E, N, Q, S and T, even more preferably selected from the list consisting of S, D, E and T, even more preferably selected form the list consisting of S, D and E, even more preferablyD or S, most preferably D; and othe amino acid at position 325 of said amino acid sequence of the mutant (position308 in case of SEQ ID NO 52, position 324 in case of SEQ ID NO 55) is selected from thelist consisting of R, N, D, Q, E, H, K, S, T and Y, preferably selected from the list consisting of D, E, N, Q, S, T and Y, more preferably selected from the list consisting of D, E, N, Q, S and T, even more preferably selected from the list consisting of S, D, E and T, even more preferably selected form the list consisting of S, D and E, even more preferably D or S, most preferably S;- SEQ ID NO 56, preferably SEQ ID NO 57, 58 or 59, more preferably SEQ ID NO 57, 58, 60 or 61,even more preferably SEQ ID NO 57 or 58, most preferably SEQ ID NO 57; and wherein:o the amino acid at position 339 of said amino acid sequence of the mutant (position322 in case of SEQ ID NO 58, position 338 in case of SEQ ID NO 61) is selected from thelist consisting of C, M, A, G, T, S, P, H, N, D, Q, E, K and R, preferably selected from the list consisting of A, G, N, Q, M, C, D, E, R and K, more preferably selected from the list consisting of A, G, N, Q, M, C, D, E, R and K, even more preferably selected from the list consisting of A, G, N, Q, M, D, E, R and K, even more preferably selected from the list consisting of A, G, N, Q, M, D and E, even more preferably selected from the list consisting of A, G, N, Q and M, even more preferably selected from the list consisting of A, G, N and M, even more preferably selected from the list consisting of A, N and M, even more preferably N or A, most preferably A; ando the amino acid at position 180 of said amino acid sequence of the mutant (position163 in case of SEQ ID NO 58, position 179 in case of SEQ ID NO 61) is selected from thelist consisting of D, E, S, N, Q, T, R, K, H and Y, more preferably selected from the list consisting of D, E, S, N, Q, T, R and K, even more preferably selected from the list consisting of D, E, S, T, R and K, even more preferably selected from the list consisting of S, T, R and K, even more preferably R or K, most preferably R; ando the amino acid at position 324 of said amino acid sequence of the mutant (position307 in case of SEQ ID NO 58, position 323 in case of SEQ ID NO 61) is selected from thelist consisting of R, N, D, Q, E, H, K, S, T and Y, preferably selected from the list consistingof D, E, N, Q, S, T and Y, more preferably selected from the list consisting of D, E, N, Q, S and T, even more preferably selected from the list consisting of S, D, E and T, even more preferably selected form the list consisting of S, D and E, even more preferably D or S, most preferably D; and othe amino acid at position 325 of said amino acid sequence of the mutant (position308 in case of SEQ ID NO 58, position 324 in case of SEQ ID NO 61) is selected from thelist consisting of R, N, D, Q, E, H, K, S, T and Y, preferably selected from the list consisting of D, E, N, Q, S, T and Y, more preferably selected from the list consisting of D, E, N, Q, S and T, even more preferably selected from the list consisting of S, D, E and T, even more preferably selected form the list consisting of S, D and E, even more preferably D or S, most preferably S; or- SEQ ID NO: 62, preferably SEQ ID NO 63, 64 or 65, more preferably SEQ ID NO 63, 64, 66 or 67,even more preferably SEQ ID NO 63 or 64, most preferably SEQ ID NO 63; and wherein:o the amino acid at position 339 of said amino acid sequence of the mutant (position322 in case of SEQ ID NO 64, position 338 in case of SEQ ID NO 67) is selected from thelist consisting of C, M, A, G, T, S, P, H, N, D, Q, E, K and R, preferably selected from the list consisting of A, G, N, Q, M, C, D, E, R and K, more preferably selected from the list consisting of A, G, N, Q, M, C, D, E, R and K, even more preferably selected from the list consisting of A, G, N, Q, M, D, E, R and K, even more preferably selected from the list consisting of A, G, N, Q, M, D and E, even more preferably selected from the list consisting of A, G, N, Q and M, even more preferably selected from the list consisting of A, G, N and M, even more preferably selected from the list consisting of A, N and M, even more preferably N or A, most preferably A; ando the amino acid at position 211 of said amino acid sequence of the mutant (position194 in case of SEQ ID NO 64, position 210 in case of SEQ ID NO 67) is selected from thelist consisting of A, G, N, Q, M, D, and E, more preferably selected from the list consisting of A, G, N, Q and M, even more preferably selected from the list consisting of A, G, N and M, even more preferably selected from the list consisting of A, N and M, most preferably M or N; ando the amino acid at position 324 of said amino acid sequence of the mutant (position307 in case of SEQ ID NO 64, position 323 in case of SEQ ID NO 67) is selected from thelist consisting of R, N, D, Q, E, H, K, S, T and Y, preferably selected from the list consistingof D, E, N, Q, S, T and Y, more preferably selected from the list consisting of D, E, N, Q, S and T, even more preferably selected from the list consisting of S, D, E and T, even more preferably selected form the list consisting of S, D and E, even more preferably D or S, most preferably D; and othe amino acid at position 325 of said amino acid sequence of the mutant (position308 in case of SEQ ID NO 64, position 324 in case of SEQ ID NO 67) is selected from the list consisting of R, N, D, Q, E, H, K, S, T and Y, preferably selected from the list consisting of D, E, N, Q, S, T and Y, more preferably selected from the list consisting of D, E, N, Q,S and T, even more preferably selected from the list consisting of S, D, E and T, even more preferably selected form the list consisting of S, D and E, even more preferably D or S, most preferably S; preferably with: -SEQ ID NO 50, preferably SEQ ID NO 51, 52 or 53, more preferably SEQ ID NO 51, 52, 54 or 55,even more preferably SEQ ID NO 51 or 52, most preferably SEQ ID NO 51; and wherein:o the amino acid at position 339 of said amino acid sequence of the mutant (position322 in case of SEQ ID NO 52, position 338 in case of SEQ ID NO 55) is selected from thelist consisting of C, M, A, G, T, S, P, H, N, D, Q, E, K and R, preferably selected from the list consisting of A, G, N, Q, M, C, D, E, R and K, more preferably selected from the list consisting of A, G, N, Q, M, C, D, E, R and K, even more preferably selected from the list consisting of A, G, N, Q, M, D, E, R and K, even more preferably selected from the list consisting of A, G, N, Q, M, D and E, even more preferably selected from the list consisting of A, G, N, Q and M, even more preferably selected from the list consisting of A, G, N and M, even more preferably selected from the list consisting of A, N and M, even more preferably N or A, most preferably A; ando the amino acid at position 182 of said amino acid sequence of the mutant (position165 in case of SEQ ID NO 52, position 181 in case of SEQ ID NO 55) is selected from thelist consisting of L, M, A, D, E, S, N, Q, T, R and K, preferably selected from the listconsisting of L, M, A, D, E, S, T, R and K, more preferably selected from the list consisting of L, M, A, S, T, D and E, even more preferably selected form the list consisting of L, M, A, S, T and D, even more preferably selected from the list consisting of L, M, A, S and T, even more preferably selected from the list consisting of L, M, S and T, most preferably S; and othe amino acid at position 324 of said amino acid sequence of the mutant (position307 in case of SEQ ID NO 52, position 323 in case of SEQ ID NO 55) is selected from thelist consisting of R, N, D, Q, E, H, K, S, T and Y, preferably selected from the list consistingof D, E, N, Q, S, T and Y, more preferably selected from the list consisting of D, E, N, Q, S and T, even more preferably selected from the list consisting of S, D, E and T, even more preferably selected form the list consisting of S, D and E, even more preferably D or S, most preferably D; and othe amino acid at position 325 of said amino acid sequence of the mutant (position308 in case of SEQ ID NO 52, position 324 in case of SEQ ID NO 55) is selected from thelist consisting of R, N, D, Q, E, H, K, S, T and Y, preferably selected from the list consisting of D, E, N, Q, S, T and Y, more preferably selected from the list consisting of D, E, N, Q, S and T, even more preferably selected from the list consisting of S, D, E and T, even more preferably selected form the list consisting of S, D and E, even more preferably Dor S, most preferably S; or- SEQ ID NO 56, preferably SEQ ID NO 57, 58 or 59, more preferably SEQ ID NO 57, 58, 60 or 61,even more preferably SEQ ID NO 57 or 58, most preferably SEQ ID NO 57; and wherein: othe amino acid at position 339 of said amino acid sequence of the mutant (position322 in case of SEQ ID NO 58, position 338 in case of SEQ ID NO 61) is selected from thelist consisting of C, M, A, G, T, S, P, H, N, D, Q, E, K and R, preferably selected from the list consisting of A, G, N, Q, M, C, D, E, R and K, more preferably selected from the list consisting of A, G, N, Q, M, C, D, E, R and K, even more preferably selected from the list consisting of A, G, N, Q, M, D, E, R and K, even more preferably selected from the list consisting of A, G, N, Q, M, D and E, even more preferably selected from the list consisting of A, G, N, Q and M, even more preferably selected from the list consisting of A, G, N and M, even more preferably selected from the list consisting of A, N and M, even more preferably N or A, most preferably A; ando the amino acid at position 180 of said amino acid sequence of the mutant (position163 in case of SEQ ID NO 58, position 179 in case of SEQ ID NO 61) is selected from thelist consisting of D, E, S, N, Q, T, R, K, H and Y, more preferably selected from the list consisting of D, E, S, N, Q, T, R and K, even more preferably selected from the list consisting of D, E, S, T, R and K, even more preferably selected from the list consisting of S, T, R and K, even more preferably R or K, most preferably R; and othe amino acid at position 324 of said amino acid sequence of the mutant (position307 in case of SEQ ID NO 58, position 323 in case of SEQ ID NO 61) is selected from thelist consisting of R, N, D, Q, E, H, K, S, T and Y, preferably selected from the list consistingof D, E, N, Q, S, T and Y, more preferably selected from the list consisting of D, E, N, Q, S and T, even more preferably selected from the list consisting of S, D, E and T, even more preferably selected form the list consisting of S, D and E, even more preferably D or S, most preferably D; and othe amino acid at position 325 of said amino acid sequence of the mutant (position308 in case of SEQ ID NO 58, position 324 in case of SEQ ID NO 61) is selected from thelist consisting of R, N, D, Q, E, H, K, S, T and Y, preferably selected from the list consisting of D, E, N, Q, S, T and Y, more preferably selected from the list consisting of D, E, N, Q, S and T, even more preferably selected from the list consisting of S, D, E and T, even more preferably selected form the list consisting of S, D and E, even more preferably D or S, most preferably S;most preferably with:- SEQ ID NO 56, preferably SEQ ID NO 57, 58 or 59, more preferably SEQ ID NO 57, 58, 60 or 61,even more preferably SEQ ID NO 57 or 58, most preferably SEQ ID NO 57; and wherein: othe amino acid at position 339 of said amino acid sequence of the mutant (position322 in case of SEQ ID NO 58, position 338 in case of SEQ ID NO 61) is selected from thelist consisting of C, M, A, G, T, S, P, H, N, D, Q, E, K and R, preferably selected from the list consisting of A, G, N, Q, M, C, D, E, R and K, more preferably selected from the list consisting of A, G, N, Q, M, C, D, E, R and K, even more preferably selected from the list consisting of A, G, N, Q, M, D, E, R and K, even more preferably selected from the list consisting of A, G, N, Q, M, D and E, even more preferably selected from the list consisting of A, G, N, Q and M, even more preferably selected from the list consisting of A, G, N and M, even more preferably selected from the list consisting of A, N and M, even more preferably N or A, most preferably A; ando the amino acid at position 180 of said amino acid sequence of the mutant (position163 in case of SEQ ID NO 58, position 179 in case of SEQ ID NO 61) is selected from thelist consisting of D, E, S, N, Q, T, R, K, H and Y, more preferably selected from the list consisting of D, E, S, N, Q, T, R and K, even more preferably selected from the list consisting of D, E, S, T, R and K, even more preferably selected from the list consisting of S, T, R and K, even more preferably R or K, most preferably R; and othe amino acid at position 324 of said amino acid sequence of the mutant (position307 in case of SEQ ID NO 58, position 323 in case of SEQ ID NO 61) is selected from thelist consisting of R, N, D, Q, E, H, K, S, T and Y, preferably selected from the list consistingof D, E, N, Q, S, T and Y, more preferably selected from the list consisting of D, E, N, Q, S and T, even more preferably selected from the list consisting of S, D, E and T, even more preferably selected form the list consisting of S, D and E, even more preferably D or S, most preferably D; and othe amino acid at position 325 of said amino acid sequence of the mutant (position308 in case of SEQ ID NO 58, position 324 in case of SEQ ID NO 61) is selected from thelist consisting of R, N, D, Q, E, H, K, S, T and Y, preferably selected from the list consisting of D, E, N, Q, S, T and Y, more preferably selected from the list consisting of D, E, N, Q, S and T, even more preferably selected from the list consisting of S, D, E and T, even more preferably selected form the list consisting of S, D and E, even more preferably D or S, most preferably S. For the sake of clarity, said “sequence similarity” and “sequence identity” are as defined earlier in the present Section “Mutant beta-1,3-N-acetylglucosaminyltransferase”.For the sake of clarity, SEQ ID NO 50 represents a F339+P182+A224+A225 mutant of the reference beta- 1,3-N-acetylglucosaminyltransferase represented with SEQ ID NO 01. The corresponding mutant amino sequence when the reference beta-1,3-N-acetylglucosaminyltransferase is represented with SEQ ID NO 03, 04, 05, 06 or 07 (it is referred to the Section “Reference beta-1,3-N-acetylglucosaminyltransferase”and also in particular Table 1), is SEQ ID NO 51, 52, 53, 54 or 55, respectively.For the sake of clarity, SEQ ID NO 56 represents a F339+G180+A224+A225 mutant of the reference beta-1,3-N-acetylglucosaminyltransferase represented with SEQ ID NO 01. The corresponding mutant aminosequence when the reference beta-1,3-N-acetylglucosaminyltransferase is represented with SEQ ID NO 03, 04, 05, 06 or 07 (it is referred to the Section “Reference beta-1,3-N-acetylglucosaminyltransferase” and also in particular Table 1), is SEQ ID NO 57, 58, 59, 60 or 61, respectively.For the sake of clarity, SEQ ID NO 62 represents a F339+Y211+A224+A225 mutant of the reference beta-1,3-N-acetylglucosaminyltransferase represented with SEQ ID NO 01. The corresponding mutant amino sequence when the reference beta-1,3-N-acetylglucosaminyltransferase is represented with SEQ ID NO 03, 04, 05, 06 or 07 (it is referred to the Section “Reference beta-1,3-N-acetylglucosaminyltransferase” and also in particular Table 1), is SEQ ID NO 63, 64, 65, 66 or 67, respectively.In an alternative even more preferred embodiment, the beta-1,3-N-acetylglucosaminyltransferasemutant according to the invention comprises an amino acid sequence that has at least 80.0% sequence similarity, preferably at least 80.0% sequence identity, with: -SEQ ID NO 68, preferably SEQ ID NO 69, 70 or 71, more preferably SEQ ID NO 69, 70, 72 or 73,even more preferably SEQ ID NO 69 or 70, most preferably SEQ ID NO 69; and wherein:o the amino acid at position 339 of said amino acid sequence of the mutant (position322 in case of SEQ ID NO 70, position 338 in case of SEQ ID NO 73) is selected from thelist consisting of C, M, A, G, T, S, P, H, N, D, Q, E, K and R, preferably selected from the list consisting of A, G, N, Q, M, C, D, E, R and K, more preferably selected from the list consisting of A, G, N, Q, M, C, D, E, R and K, even more preferably selected from the list consisting of A, G, N, Q, M, D, E, R and K, even more preferably selected from the list consisting of A, G, N, Q, M, D and E, even more preferably selected from the list consisting of A, G, N, Q and M, even more preferably selected from the list consisting of A, G, N and M, even more preferably selected from the list consisting of A, N and M, even more preferably N or A, most preferably A; ando the amino acid at position 182 of said amino acid sequence of the mutant (position165 in case of SEQ ID NO 70, position 181 in case of SEQ ID NO 73) is selected from thelist consisting of L, M, A, D, E, S, N, Q, T, R and K, preferably selected from the list consisting of L, M, A, D, E, S, T, R and K, more preferably selected from the list consisting of L, M, A, S, T, D and E, even more preferably selected form the list consisting of L, M, A, S, T and D, even more preferably selected from the list consisting of L, M, A, S and T, even more preferably selected from the list consisting of L, M, S and T, most preferably S; and othe amino acid at position 315 of said amino acid sequence of the mutant (position298 in case of SEQ ID NO 70, position 314 in case of SEQ ID NO 73) is selected from thelist consisting of R, N, D, Q, E, H, K, S, T and Y, preferably selected from the list consistingof D, E, S, N, Q and T, more preferably selected from the list consisting of D, E, S and T, even more preferably selected from the list consisting of D, E and S, even more preferably D or E, most preferably D; and othe amino acid at position 316 of said amino acid sequence of the mutant (position299 in case of SEQ ID NO 70, position 315 in case of SEQ ID NO 73) is selected from thelist consisting of R, N, D, Q, E, H, K, S, T and Y, preferably selected from the list consistingof D, E, S, N, Q and T, more preferably selected from the list consisting of D, E, S and T, even more preferably selected from the list consisting of D, E and S, most preferablyS; and othe amino acid at position 317 of said amino acid sequence of the mutant (position300 in case of SEQ ID NO 70, position 316 in case of SEQ ID NO 73) is selected from thelist consisting of R, N, D, Q, E, H, K, S, T and Y, preferably selected from the list consistingof D, E, N, Q, S, T and Y, more preferably selected from the list consisting of D, E, S, N, Q and T, even more preferably selected from the list consisting of D, E, S and T, even more preferably selected from the list consisting of D, E and S; even more preferablyD or E; most preferably E; and othe amino acid at position 318 of said amino acid sequence of the mutant (position301 in case of SEQ ID NO 70, position 317 in case of SEQ ID NO 73) is selected from thelist consisting of R, N, D, Q, E, H, K, S, T and Y, preferably selected from the list consistingof D, E, S, N, Q and T, more preferably selected from the list consisting of D, E, S and T, even more preferably selected from the list consisting of D, E and S, most preferablyS; and othe amino acid at position 319 of said amino acid sequence of the mutant (position302 in case of SEQ ID NO 70, position 318 in case of SEQ ID NO 73) is selected from thelist consisting of R, N, D, Q, E, H, K, S, T and Y, preferably selected from the list consistingof D, E, N, Q, S, T and Y, more preferably selected from the list consisting of D, E, S, N, Q and T, even more preferably selected from the list consisting of D, E, S and T, even more preferably selected from the list consisting of D, E and S; even more preferably D or E; most preferably E; or- SEQ ID NO 74, preferably SEQ ID NO 75, 76 or 77, more preferably SEQ ID NO 75, 76, 78 or 79,even more preferably SEQ ID NO 75 or 76, most preferably SEQ ID NO 75; and wherein:the amino acid at position 339 of said amino acid sequence of the mutant (position322 in case of SEQ ID NO 76, position 338 in case of SEQ ID NO 79) is selected from thelist consisting of C, M, A, G, T, S, P, H, N, D, Q, E, K and R, preferably selected from the list consisting of A, G, N, Q, M, C, D, E, R and K, more preferably selected from the list consisting of A, G, N, Q, M, C, D, E, R and K, even more preferably selected from the list consisting of A, G, N, Q, M, D, E, R and K, even more preferably selected from the list consisting of A, G, N, Q, M, D and E, even more preferably selected from the list consisting of A, G, N, Q and M, even more preferably selected from the list consisting of A, G, N and M, even more preferably selected from the list consisting of A, N and M,even more preferably N or A, most preferably A; andthe amino acid at position 180 of said amino acid sequence of the mutant (position163 in case of SEQ ID NO 76, position 179 in case of SEQ ID NO 79) is selected from thelist consisting of D, E, S, N, Q, T, R, K, H and Y, more preferably selected from the list consisting of D, E, S, N, Q, T, R and K, even more preferably selected from the list consisting of D, E, S, T, R and K, even more preferably selected from the list consisting of S, T, R and K, even more preferably R or K, most preferably R; andthe amino acid at position 315 of said amino acid sequence of the mutant (position298 in case of SEQ ID NO 76, position 314 in case of SEQ ID NO 79) is selected from thelist consisting of R, N, D, Q, E, H, K, S, T and Y, preferably selected from the list consisting of D, E, S, N, Q and T, more preferably selected from the list consisting of D, E, S and T, even more preferably selected from the list consisting of D, E and S, even more preferably D or E, most preferably D; andthe amino acid at position 316 of said amino acid sequence of the mutant (position299 in case of SEQ ID NO 76, position 315 in case of SEQ ID NO 79) is selected from thelist consisting of R, N, D, Q, E, H, K, S, T and Y, preferably selected from the list consisting of D, E, S, N, Q and T, more preferably selected from the list consisting of D, E, S and T,even more preferably selected from the list consisting of D, E and S, most preferablyS; andthe amino acid at position 317 of said amino acid sequence of the mutant (position300 in case of SEQ ID NO 76, position 316 in case of SEQ ID NO 79) is selected from thelist consisting of R, N, D, Q, E, H, K, S, T and Y, preferably selected from the list consisting of D, E, N, Q, S, T and Y, more preferably selected from the list consisting of D, E, S, N, Q and T, even more preferably selected from the list consisting of D, E, S and T, even more preferably selected from the list consisting of D, E and S; even more preferably D or E; most preferably E; ando the amino acid at position 318 of said amino acid sequence of the mutant (position301 in case of SEQ ID NO 76, position 317 in case of SEQ ID NO 79) is selected from thelist consisting of R, N, D, Q, E, H, K, S, T and Y, preferably selected from the list consisting of D, E, S, N, Q and T, more preferably selected from the list consisting of D, E, S and T, even more preferably selected from the list consisting of D, E and S, most preferablyS; and othe amino acid at position 319 of said amino acid sequence of the mutant (position302 in case of SEQ ID NO 76, position 318 in case of SEQ ID NO 79) is selected from thelist consisting of R, N, D, Q, E, H, K, S, T and Y, preferably selected from the list consisting of D, E, N, Q, S, T and Y, more preferably selected from the list consisting of D, E, S, N, Q and T, even more preferably selected from the list consisting of D, E, S and T, even more preferably selected from the list consisting of D, E and S; even more preferably D or E; most preferably E; or- SEQ ID NO: 80, preferably SEQ ID NO 81, 82 or 83, more preferably SEQ ID NO 81, 82, 84 or 85,even more preferably SEQ ID NO 81 or 82, most preferably SEQ ID NO 81; and wherein:o the amino acid at position 339 of said amino acid sequence of the mutant (position322 in case of SEQ ID NO 82, position 338 in case of SEQ ID NO 85) is selected from thelist consisting of C, M, A, G, T, S, P, H, N, D, Q, E, K and R, preferably selected from thelist consisting of A, G, N, Q, M, C, D, E, R and K, more preferably selected from the list consisting of A, G, N, Q, M, C, D, E, R and K, even more preferably selected from the list consisting of A, G, N, Q, M, D, E, R and K, even more preferably selected from the list consisting of A, G, N, Q, M, D and E, even more preferably selected from the list consisting of A, G, N, Q and M, even more preferably selected from the list consisting of A, G, N and M, even more preferably selected from the list consisting of A, N and M, even more preferably N or A, most preferably A; ando the amino acid at position 211 of said amino acid sequence of the mutant (position194 in case of SEQ ID NO 82, position 210 in case of SEQ ID NO 85) is selected from thelist consisting of A, G, N, Q, M, D, and E, more preferably selected from the list consisting of A, G, N, Q and M, even more preferably selected from the list consisting of A, G, N and M, even more preferably selected from the list consisting of A, N and M, most preferably M or N; and othe amino acid at position 315 of said amino acid sequence of the mutant (position298 in case of SEQ ID NO 82, position 314 in case of SEQ ID NO 85) is selected from thelist consisting of R, N, D, Q, E, H, K, S, T and Y, preferably selected from the list consisting of D, E, S, N, Q and T, more preferably selected from the list consisting of D, E, S and T, even more preferably selected from the list consisting of D, E and S, even more preferably D or E, most preferably D; and othe amino acid at position 316 of said amino acid sequence of the mutant (position299 in case of SEQ ID NO 82, position 315 in case of SEQ ID NO 85) is selected from thelist consisting of R, N, D, Q, E, H, K, S, T and Y, preferably selected from the list consisting of D, E, S, N, Q and T, more preferably selected from the list consisting of D, E, S and T, even more preferably selected from the list consisting of D, E and S, most preferablyS; and othe amino acid at position 317 of said amino acid sequence of the mutant (position300 in case of SEQ ID NO 82, position 316 in case of SEQ ID NO 85) is selected from thelist consisting of R, N, D, Q, E, H, K, S, T and Y, preferably selected from the list consisting of D, E, N, Q, S, T and Y, more preferably selected from the list consisting of D, E, S, N, Q and T, even more preferably selected from the list consisting of D, E, S and T, even more preferably selected from the list consisting of D, E and S; even more preferably D or E; most preferably E; and othe amino acid at position 318 of said amino acid sequence of the mutant (position301 in case of SEQ ID NO 82, position 317 in case of SEQ ID NO 85) is selected from thelist consisting of R, N, D, Q, E, H, K, S, T and Y, preferably selected from the list consisting of D, E, S, N, Q and T, more preferably selected from the list consisting of D, E, S and T, even more preferably selected from the list consisting of D, E and S, most preferablyS; and othe amino acid at position 319 of said amino acid sequence of the mutant (position302 in case of SEQ ID NO 82, position 318 in case of SEQ ID NO 85) is selected from thelist consisting of R, N, D, Q, E, H, K, S, T and Y, preferably selected from the list consisting of D, E, N, Q, S, T and Y, more preferably selected from the list consisting of D, E, S, N, Q and T, even more preferably selected from the list consisting of D, E, S and T, even more preferably selected from the list consisting of D, E and S; even more preferably D or E; most preferably E; preferably with: -SEQ ID NO 68, preferably SEQ ID NO 69, 70 or 71, more preferably SEQ ID NO 69, 70, 72 or 73,even more preferably SEQ ID NO 69 or 70, most preferably SEQ ID NO 69; and wherein:o the amino acid at position 339 of said amino acid sequence of the mutant (position322 in case of SEQ ID NO 70, position 338 in case of SEQ ID NO 73) is selected from thelist consisting of C, M, A, G, T, S, P, H, N, D, Q, E, K and R, preferably selected from the list consisting of A, G, N, Q, M, C, D, E, R and K, more preferably selected from the list consisting of A, G, N, Q, M, C, D, E, R and K, even more preferably selected from the list consisting of A, G, N, Q, M, D, E, R and K, even more preferably selected from the list consisting of A, G, N, Q, M, D and E, even more preferably selected from the list consisting of A, G, N, Q and M, even more preferably selected from the list consisting of A, G, N and M, even more preferably selected from the list consisting of A, N and M,even more preferably N or A, most preferably A; andthe amino acid at position 182 of said amino acid sequence of the mutant (position165 in case of SEQ ID NO 70, position 181 in case of SEQ ID NO 73) is selected from thelist consisting of L, M, A, D, E, S, N, Q, T, R and K, preferably selected from the list consisting of L, M, A, D, E, S, T, R and K, more preferably selected from the list consisting of L, M, A, S, T, D and E, even more preferably selected form the list consisting of L, M, A, S, T and D, even more preferably selected from the list consisting of L, M, A, S and T, even more preferably selected from the list consisting of L, M, S and T, most preferably S; andthe amino acid at position 315 of said amino acid sequence of the mutant (position298 in case of SEQ ID NO 70, position 314 in case of SEQ ID NO 73) is selected from thelist consisting of R, N, D, Q, E, H, K, S, T and Y, preferably selected from the list consisting of D, E, S, N, Q and T, more preferably selected from the list consisting of D, E, S and T, even more preferably selected from the list consisting of D, E and S, even more preferably D or E, most preferably D; andthe amino acid at position 316 of said amino acid sequence of the mutant (position299 in case of SEQ ID NO 70, position 315 in case of SEQ ID NO 73) is selected from thelist consisting of R, N, D, Q, E, H, K, S, T and Y, preferably selected from the list consisting of D, E, S, N, Q and T, more preferably selected from the list consisting of D, E, S and T,even more preferably selected from the list consisting of D, E and S, most preferablyS; andthe amino acid at position 317 of said amino acid sequence of the mutant (position300 in case of SEQ ID NO 70, position 316 in case of SEQ ID NO 73) is selected from thelist consisting of R, N, D, Q, E, H, K, S, T and Y, preferably selected from the list consisting of D, E, N, Q, S, T and Y, more preferably selected from the list consisting of D, E, S, N, Q and T, even more preferably selected from the list consisting of D, E, S and T, even more preferably selected from the list consisting of D, E and S; even more preferably D or E; most preferably E; andthe amino acid at position 318 of said amino acid sequence of the mutant (position301 in case of SEQ ID NO 70, position 317 in case of SEQ ID NO 73) is selected from thelist consisting of R, N, D, Q, E, H, K, S, T and Y, preferably selected from the list consisting of D, E, S, N, Q and T, more preferably selected from the list consisting of D, E, S and T,even more preferably selected from the list consisting of D, E and S, most preferablyS; and othe amino acid at position 319 of said amino acid sequence of the mutant (position302 in case of SEQ ID NO 70, position 318 in case of SEQ ID NO 73) is selected from thelist consisting of R, N, D, Q, E, H, K, S, T and Y, preferably selected from the list consisting of D, E, N, Q, S, T and Y, more preferably selected from the list consisting of D, E, S, N, Q and T, even more preferably selected from the list consisting of D, E, S and T, even more preferably selected from the list consisting of D, E and S; even more preferably Dor E; most preferably E; or- SEQ ID NO 74, preferably SEQ ID NO 75, 76 or 77, more preferably SEQ ID NO 75, 76, 78 or 79,even more preferably SEQ ID NO 75 or 76, most preferably SEQ ID NO 75; and wherein:o the amino acid at position 339 of said amino acid sequence of the mutant (position322 in case of SEQ ID NO 76, position 338 in case of SEQ ID NO 79) is selected from thelist consisting of C, M, A, G, T, S, P, H, N, D, Q, E, K and R, preferably selected from the list consisting of A, G, N, Q, M, C, D, E, R and K, more preferably selected from the list consisting of A, G, N, Q, M, C, D, E, R and K, even more preferably selected from the list consisting of A, G, N, Q, M, D, E, R and K, even more preferably selected from the list consisting of A, G, N, Q, M, D and E, even more preferably selected from the list consisting of A, G, N, Q and M, even more preferably selected from the list consisting of A, G, N and M, even more preferably selected from the list consisting of A, N and M, even more preferably N or A, most preferably A; ando the amino acid at position 180 of said amino acid sequence of the mutant (position163 in case of SEQ ID NO 76, position 179 in case of SEQ ID NO 79) is selected from thelist consisting of D, E, S, N, Q, T, R, K, H and Y, more preferably selected from the list consisting of D, E, S, N, Q, T, R and K, even more preferably selected from the list consisting of D, E, S, T, R and K, even more preferably selected from the list consisting of S, T, R and K, even more preferably R or K, most preferably R; and othe amino acid at position 315 of said amino acid sequence of the mutant (position298 in case of SEQ ID NO 76, position 314 in case of SEQ ID NO 79) is selected from thelist consisting of R, N, D, Q, E, H, K, S, T and Y, preferably selected from the list consisting of D, E, S, N, Q and T, more preferably selected from the list consisting of D, E, S and T, even more preferably selected from the list consisting of D, E and S, even more preferably D or E, most preferably D; and othe amino acid at position 316 of said amino acid sequence of the mutant (position299 in case of SEQ ID NO 76, position 315 in case of SEQ ID NO 79) is selected from thelist consisting of R, N, D, Q, E, H, K, S, T and Y, preferably selected from the list consisting of D, E, S, N, Q and T, more preferably selected from the list consisting of D, E, S and T, even more preferably selected from the list consisting of D, E and S, most preferablyS; and othe amino acid at position 317 of said amino acid sequence of the mutant (position300 in case of SEQ ID NO 76, position 316 in case of SEQ ID NO 79) is selected from thelist consisting of R, N, D, Q, E, H, K, S, T and Y, preferably selected from the list consisting of D, E, N, Q, S, T and Y, more preferably selected from the list consisting of D, E, S, N, Q and T, even more preferably selected from the list consisting of D, E, S and T, even more preferably selected from the list consisting of D, E and S; even more preferably D or E; most preferably E; and othe amino acid at position 318 of said amino acid sequence of the mutant (position301 in case of SEQ ID NO 76, position 317 in case of SEQ ID NO 79) is selected from thelist consisting of R, N, D, Q, E, H, K, S, T and Y, preferably selected from the list consisting of D, E, S, N, Q and T, more preferably selected from the list consisting of D, E, S and T, even more preferably selected from the list consisting of D, E and S, most preferablyS; and othe amino acid at position 319 of said amino acid sequence of the mutant (position302 in case of SEQ ID NO 76, position 318 in case of SEQ ID NO 79) is selected from thelist consisting of R, N, D, Q, E, H, K, S, T and Y, preferably selected from the list consisting of D, E, N, Q, S, T and Y, more preferably selected from the list consisting of D, E, S, N, Q and T, even more preferably selected from the list consisting of D, E, S and T, even more preferably selected from the list consisting of D, E and S; even more preferably D or E; most preferably E;most preferably with:- SEQ ID NO 74, preferably SEQ ID NO 75, 76 or 77, more preferably SEQ ID NO 75, 76, 78 or 79,even more preferably SEQ ID NO 75 or 76, most preferably SEQ ID NO 75; and wherein:o the amino acid at position 339 of said amino acid sequence of the mutant (position322 in case of SEQ ID NO 76, position 338 in case of SEQ ID NO 79) is selected from thelist consisting of C, M, A, G, T, S, P, H, N, D, Q, E, K and R, preferably selected from the list consisting of A, G, N, Q, M, C, D, E, R and K, more preferably selected from the list consisting of A, G, N, Q, M, C, D, E, R and K, even more preferably selected from the list consisting of A, G, N, Q, M, D, E, R and K, even more preferably selected from the list consisting of A, G, N, Q, M, D and E, even more preferably selected from the list consisting of A, G, N, Q and M, even more preferably selected from the list consisting of A, G, N and M, even more preferably selected from the list consisting of A, N and M, even more preferably N or A, most preferably A; andthe amino acid at position 180 of said amino acid sequence of the mutant (position163 in case of SEQ ID NO 76, position 179 in case of SEQ ID NO 79) is selected from thelist consisting of D, E, S, N, Q, T, R, K, H and Y, more preferably selected from the list consisting of D, E, S, N, Q, T, R and K, even more preferably selected from the list consisting of D, E, S, T, R and K, even more preferably selected from the list consisting of S, T, R and K, even more preferably R or K, most preferably R; andthe amino acid at position 315 of said amino acid sequence of the mutant (position298 in case of SEQ ID NO 76, position 314 in case of SEQ ID NO 79) is selected from thelist consisting of R, N, D, Q, E, H, K, S, T and Y, preferably selected from the list consisting of D, E, S, N, Q and T, more preferably selected from the list consisting of D, E, S and T, even more preferably selected from the list consisting of D, E and S, even more preferably D or E, most preferably D; andthe amino acid at position 316 of said amino acid sequence of the mutant (position299 in case of SEQ ID NO 76, position 315 in case of SEQ ID NO 79) is selected from thelist consisting of R, N, D, Q, E, H, K, S, T and Y, preferably selected from the list consisting of D, E, S, N, Q and T, more preferably selected from the list consisting of D, E, S and T,even more preferably selected from the list consisting of D, E and S, most preferablyS; andthe amino acid at position 317 of said amino acid sequence of the mutant (position300 in case of SEQ ID NO 76, position 316 in case of SEQ ID NO 79) is selected from thelist consisting of R, N, D, Q, E, H, K, S, T and Y, preferably selected from the list consisting of D, E, N, Q, S, T and Y, more preferably selected from the list consisting of D, E, S, N, Q and T, even more preferably selected from the list consisting of D, E, S and T, even more preferably selected from the list consisting of D, E and S; even more preferably D or E; most preferably E; andthe amino acid at position 318 of said amino acid sequence of the mutant (position301 in case of SEQ ID NO 76, position 317 in case of SEQ ID NO 79) is selected from thelist consisting of R, N, D, Q, E, H, K, S, T and Y, preferably selected from the list consisting of D, E, S, N, Q and T, more preferably selected from the list consisting of D, E, S and T,even more preferably selected from the list consisting of D, E and S, most preferablyS; andthe amino acid at position 319 of said amino acid sequence of the mutant (position302 in case of SEQ ID NO 76, position 318 in case of SEQ ID NO 79) is selected from thelist consisting of R, N, D, Q, E, H, K, S, T and Y, preferably selected from the list consisting of D, E, N, Q, S, T and Y, more preferably selected from the list consisting of D, E, S, N, Q and T, even more preferably selected from the list consisting of D, E, S and T, even more preferably selected from the list consisting of D, E and S; even more preferably D or E; most preferably E. For the sake of clarity, said “sequence similarity” and “sequence identity” are as defined earlier in the present Section “Mutant beta-1,3-N-acetylglucosaminyltransferase”.For the sake of clarity, SEQ ID NO 68 represents a F339+P182+positions 315-319 mutant of the referencebeta-1,3-N-acetylglucosaminyltransferase represented with SEQ ID NO 01. The corresponding mutant amino sequence when the reference beta-1,3-N-acetylglucosaminyltransferase is represented with SEQ ID NO 03, 04, 05, 06 or 07 (it is referred to the Section “Reference beta-1,3-N- acetylglucosaminyltransferase” and also in particular Table 1), is SEQ ID NO 69, 70, 71, 72 or 73, respectively.For the sake of clarity, SEQ ID NO 74 represents a F339+G180+ positions 315-319 mutant of the referencebeta-1,3-N-acetylglucosaminyltransferase represented with SEQ ID NO 01. The corresponding mutant amino sequence when the reference beta-1,3-N-acetylglucosaminyltransferase is represented with SEQ ID NO 03, 04, 05, 06 or 07 (it is referred to the Section “Reference beta-1,3-N- acetylglucosaminyltransferase” and also in particular Table 1), is SEQ ID NO 75, 76, 77, 78 or 79, respectively.For the sake of clarity, SEQ ID NO 80 represents a F339+Y211+ positions 315-319 mutant of the referencebeta-1,3-N-acetylglucosaminyltransferase represented with SEQ ID NO 01. The corresponding mutant amino sequence when the reference beta-1,3-N-acetylglucosaminyltransferase is represented with SEQ ID NO 03, 04, 05, 06 or 07 (it is referred to the Section “Reference beta-1,3-N- acetylglucosaminyltransferase” and also in particular Table 1), is SEQ ID NO 81, 82, 83, 84 or 85, respectively. In an even more preferred embodiment, the beta-1,3-N-acetylglucosaminyltransferase mutant according to the invention comprises an amino acid sequence that has at least 80.0% sequence similarity, preferablyat least 80.0% sequence identity, with SEQ ID NO 38, preferably SEQ ID NO 39, 40 or 41, more preferablySEQ ID NO 39, 40, 42 or 43, even more preferably SEQ ID NO 39 or 40, most preferably SEQ ID NO 39; and wherein: -the amino acid at position 339 of said amino acid sequence of the mutant (position 322 in caseof SEQ ID NO 40, position 338 in case of SEQ ID NO 43) is selected from the list consisting of C,M, A, G, T, S, P, H, N, D, Q, E, K and R, preferably selected from the list consisting of A, G, N, Q, M, C, D, E, R and K, more preferably selected from the list consisting of A, G, N, Q, M, C, D, E, R and K, even more preferably selected from the list consisting of A, G, N, Q, M, D, E, R and K, even more preferably selected from the list consisting of A, G, N, Q, M, D and E, even more preferably selected from the list consisting of A, G, N, Q and M, even more preferably selected from the list consisting of A, G, N and M, even more preferably selected from the list consisting of A, N and M, even more preferably N or A, most preferably A; and- the amino acid at position 180 of said amino acid sequence of the mutant (position 163 in caseof SEQ ID NO 40, position 179 in case of SEQ ID NO 43) is selected from the list consisting of D, E, S, N, Q, T, R, K, H and Y, more preferably selected from the list consisting of D, E, S, N, Q, T, R and K, even more preferably selected from the list consisting of D, E, S, T, R and K, even more preferably selected from the list consisting of S, T, R and K, even more preferably R or K, most preferably R; and- preferably wherein further:o one or more, preferably all, of the following is present:^ the amino acid at position 315 of said amino acid sequence of the mutant(position 298 in case of SEQ ID NO 40, position 314 in case of SEQ ID NO 43) isselected from the list consisting of R, N, D, Q, E, H, K, S, T and Y, preferably selected from the list consisting of D, E, S, N, Q and T, more preferably selected from the list consisting of D, E, S and T, even more preferably selected from the list consisting of D, E and S, even more preferably D or E, most preferably D; and ^the amino acid at position 316 of said amino acid sequence of the mutant(position 299 in case of SEQ ID NO 40, position 315 in case of SEQ ID NO 43) isselected from the list consisting of R, N, D, Q, E, H, K, S, T and Y, preferably selected from the list consisting of D, E, S, N, Q and T, more preferably selected from the list consisting of D, E, S and T, even more preferably selected from the listconsisting of D, E and S, most preferably S; and ^the amino acid at position 317 of said amino acid sequence of the mutant(position 300 in case of SEQ ID NO 40, position 316 in case of SEQ ID NO 43) isselected from the list consisting of R, N, D, Q, E, H, K, S, T and Y, preferably selected from the list consisting of D, E, N, Q, S, T and Y, more preferably selected from the list consisting of D, E, S, N, Q and T, even more preferably selected from the list consisting of D, E, S and T, even more preferably selected from the list consisting of D, E and S; even more preferably D or E; most preferably E; and ^the amino acid at position 318 of said amino acid sequence of the mutant(position 301 in case of SEQ ID NO 40, position 317 in case of SEQ ID NO 43) isselected from the list consisting of R, N, D, Q, E, H, K, S, T and Y, preferably selected from the list consisting of D, E, S, N, Q and T, more preferably selected from the list consisting of D, E, S and T, even more preferably selected from the listconsisting of D, E and S, most preferably S; and ^the amino acid at position 319 of said amino acid sequence of the mutant(position 302 in case of SEQ ID NO 40, position 318 in case of SEQ ID NO 43) isselected from the list consisting of R, N, D, Q, E, H, K, S, T and Y, preferably selected from the list consisting of D, E, N, Q, S, T and Y, more preferably selected from the list consisting of D, E, S, N, Q and T, even more preferably selected from the list consisting of D, E, S and T, even more preferably selected from the list consisting of D, E and S; even more preferably D or E; most preferably E; -or one or more, preferably all, of the following is present:^ the amino acid at position 324 of said amino acid sequence of the mutant(position 307 in case of SEQ ID NO 40, position 323 in case of SEQ ID NO 43) isselected from the list consisting of R, N, D, Q, E, H, K, S, T and Y, preferably selectedfrom the list consisting of D, E, N, Q, S, T and Y, more preferably selected from the list consisting of D, E, N, Q, S and T, even more preferably selected from the list consisting of S, D, E and T, even more preferably selected form the list consisting of S, D and E, even more preferably D or S, most preferably D; and ^the amino acid at position 325 of said amino acid sequence of the mutant(position 308 in case of SEQ ID NO 40, position 324 in case of SEQ ID NO 43) isselected from the list consisting of R, N, D, Q, E, H, K, S, T and Y, preferably selected from the list consisting of D, E, N, Q, S, T and Y, more preferably selected from the list consisting of D, E, N, Q, S and T, even more preferably selected from the list consisting of S, D, E and T, even more preferably selected form the list consisting of S, D and E, even more preferably D or S, most preferably S. In an alternative even more preferred embodiment, the beta-1,3-N-acetylglucosaminyltransferase mutant according to the invention comprises an amino acid sequence that has at least 80.0% sequence similarity, preferably at least 80.0% sequence identity, with SEQ ID NO 100, preferably SEQ ID NO 101,102 or 103, more preferably SEQ ID NO 101, 102, 104 or 105, even more preferably SEQ ID NO 101 or 102,most preferably SEQ ID NO 101; and wherein: -the amino acid at position 339 of said amino acid sequence of the mutant (position 322 in caseof SEQ ID NO 108, position 338 in case of SEQ ID NO 111) is selected from the list consisting of C, M, A, G, T, S, P, H, N, D, Q, E, K and R, preferably selected from the list consisting of A, G, N, Q, M, C, D, E, R and K, more preferably selected from the list consisting of A, G, N, Q, M, C, D, E, R and K, even more preferably selected from the list consisting of A, G, N, Q, M, D, E, R and K, even more preferably selected from the list consisting of A, G, N, Q, M, D and E, even more preferably selected from the list consisting of A, G, N, Q and M, even more preferably selected from the list consisting of A, G, N and M, even more preferably selected from the list consistingof A, N and M, even more preferably N or A, most preferably A; and- the amino acid at position 249 of said amino acid sequence of the mutant (position 232 in caseof SEQ ID NO 108, position 248 in case of SEQ ID NO 111) is selected from the list consisting of A, C, G, I, L, M, F, P, W and V, preferably selected from the list consisting of W, F, G and A, more preferably W or F, most preferably F; and -the amino acid at position 256 of said amino acid sequence of the mutant (position 239 in caseof SEQ ID NO 108, position 255 in case of SEQ ID NO 111) is selected from the list consisting of A, C, G, I, L, M, F, P, W and V, preferably selected from the list consisting of W, F, G and A, more preferably W or F, most preferably W. In an alternative even more preferred embodiment, the beta-1,3-N-acetylglucosaminyltransferase mutant according to the invention comprises an amino acid sequence that has at least 80.0% sequence similarity, preferably at least 80.0% sequence identity, with SEQ ID NO 106, preferably SEQ ID NO 107,108 or 109, more preferably SEQ ID NO 107, 108, 110 or 111, even more preferably SEQ ID NO 107 or 108,most preferably SEQ ID NO 107; and wherein: -the amino acid at position 339 of said amino acid sequence of the mutant (position 322 in caseof SEQ ID NO 108, position 338 in case of SEQ ID NO 111) is selected from the list consisting of C, M, A, G, T, S, P, H, N, D, Q, E, K and R, preferably selected from the list consisting of A, G, N, Q, M, C, D, E, R and K, more preferably selected from the list consisting of A, G, N, Q, M, C, D, E, R and K, even more preferably selected from the list consisting of A, G, N, Q, M, D, E, R and K, even more preferably selected from the list consisting of A, G, N, Q, M, D and E, even more preferably selected from the list consisting of A, G, N, Q and M, even more preferably selected from the list consisting of A, G, N and M, even more preferably selected from the list consisting of A, N and M, even more preferably N or A, most preferably A; and -the amino acid at position 158 of said amino acid sequence of the mutant (position 241 in caseof SEQ ID NO 108, position 157 in case of SEQ ID NO 111) is selected from the list consisting of A, C, G, I, L, M, F, P, W and V, preferably selected from the list consisting of W, F, G and A, more preferably W or F, most preferably W; and -the amino acid at position 249 of said amino acid sequence of the mutant (position 232 in caseof SEQ ID NO 108, position 248 in case of SEQ ID NO 111) is selected from the list consisting of A, C, G, I, L, M, F, P, W and V, preferably selected from the list consisting of W, F, G and A, more preferably W or F, most preferably F; and -the amino acid at position 256 of said amino acid sequence of the mutant (position 239 in caseof SEQ ID NO 108, position 255 in case of SEQ ID NO 111) is selected from the list consisting of A, C, G, I, L, M, F, P, W and V, preferably selected from the list consisting of W, F, G and A, more preferably W or F, most preferably W.In a most preferred embodiment, the beta-1,3-N-acetylglucosaminyltransferase mutant according to theinvention comprises an amino acid sequence that has at least 80.0% sequence similarity, preferably atleast 80.0% sequence identity, with SEQ ID NO 38, preferably SEQ ID NO 39, 40 or 41, more preferablySEQ ID NO 39, 40, 42 or 43, even more preferably SEQ ID NO 39 or 40, most preferably SEQ ID NO 39; and wherein: -the amino acid at position 339 of said amino acid sequence of the mutant (position 322 in caseof SEQ ID NO 40, position 338 in case of SEQ ID NO 43) is selected from the list consisting of C, M, A, G, T, S, P, H, N, D, Q, E, K and R, preferably selected from the list consisting of A, G, N, Q,M, C, D, E, R and K, more preferably selected from the list consisting of A, G, N, Q, M, C, D, E, R and K, even more preferably selected from the list consisting of A, G, N, Q, M, D, E, R and K, even more preferably selected from the list consisting of A, G, N, Q, M, D and E, even more preferably selected from the list consisting of A, G, N, Q and M, even more preferably selected from the list consisting of A, G, N and M, even more preferably selected from the list consisting of A, N and M, even more preferably N or A, most preferably A; ando the amino acid at position 180 of said amino acid sequence of the mutant (position 163 in caseof SEQ ID NO 40, position 179 in case of SEQ ID NO 43) is selected from the list consisting of D, E, S, N, Q, T, R, K, H and Y, more preferably selected from the list consisting of D, E, S, N, Q, T, R and K, even more preferably selected from the list consisting of D, E, S, T, R and K, even more preferably selected from the list consisting of S, T, R and K, even more preferably R or K, most preferably R; and opreferably wherein further:- one or more, preferably all, of the following is present:^ the amino acid at position 315 of said amino acid sequence of the mutant(position 298 in case of SEQ ID NO 40, position 314 in case of SEQ ID NO 43) isselected from the list consisting of R, N, D, Q, E, H, K, S, T and Y, preferably selected from the list consisting of D, E, S, N, Q and T, more preferably selected from the list consisting of D, E, S and T, even more preferably selected from the list consisting of D, E and S, even more preferably D or E, most preferably D; and ^the amino acid at position 316 of said amino acid sequence of the mutant(position 299 in case of SEQ ID NO 40, position 315 in case of SEQ ID NO 43) isselected from the list consisting of R, N, D, Q, E, H, K, S, T and Y, preferably selected from the list consisting of D, E, S, N, Q and T, more preferably selected from the list consisting of D, E, S and T, even more preferably selected from the listconsisting of D, E and S, most preferably S; and ^the amino acid at position 317 of said amino acid sequence of the mutant(position 300 in case of SEQ ID NO 40, position 316 in case of SEQ ID NO 43) is selected from the list consisting of R, N, D, Q, E, H, K, S, T and Y, preferably selected from the list consisting of D, E, N, Q, S, T and Y, more preferably selected from the list consisting of D, E, S, N, Q and T, even more preferably selected from the list consisting of D, E, S and T, even more preferably selected from the list consisting of D, E and S; even more preferably D or E; most preferably E; and ^the amino acid at position 318 of said amino acid sequence of the mutant(position 301 in case of SEQ ID NO 40, position 317 in case of SEQ ID NO 43) isselected from the list consisting of R, N, D, Q, E, H, K, S, T and Y, preferably selected from the list consisting of D, E, S, N, Q and T, more preferably selected from the list consisting of D, E, S and T, even more preferably selected from the listconsisting of D, E and S, most preferably S; and ^the amino acid at position 319 of said amino acid sequence of the mutant(position 302 in case of SEQ ID NO 40, position 318 in case of SEQ ID NO 43) isselected from the list consisting of R, N, D, Q, E, H, K, S, T and Y, preferably selected from the list consisting of D, E, N, Q, S, T and Y, more preferably selected from the list consisting of D, E, S, N, Q and T, even more preferably selected from the list consisting of D, E, S and T, even more preferably selected from the list consisting of D, E and S; even more preferably D or E; most preferably E; -or one or more, preferably all, of the following is present:^ the amino acid at position 324 of said amino acid sequence of the mutant(position 307 in case of SEQ ID NO 40, position 323 in case of SEQ ID NO 43) isselected from the list consisting of R, N, D, Q, E, H, K, S, T and Y, preferably selectedfrom the list consisting of D, E, N, Q, S, T and Y, more preferably selected from the list consisting of D, E, N, Q, S and T, even more preferably selected from the list consisting of S, D, E and T, even more preferably selected form the list consisting of S, D and E, even more preferably D or S, most preferably D; and ^the amino acid at position 325 of said amino acid sequence of the mutant(position 308 in case of SEQ ID NO 40, position 324 in case of SEQ ID NO 43) isselected from the list consisting of R, N, D, Q, E, H, K, S, T and Y, preferably selected from the list consisting of D, E, N, Q, S, T and Y, more preferably selected from the list consisting of D, E, N, Q, S and T, even more preferably selected from the list consisting of S, D, E and T, even more preferably selected form the list consisting of S, D and E, even more preferably D or S, most preferably S. Nucleic acid In a second aspect, the invention provides a nucleic acid encoding the beta-1,3-N- acetylglucosaminyltransferase mutant according to the first aspect of the invention. CellIn a third aspect, the invention provides a cell comprising a beta-1,3-N-acetylglucosaminyltransferasemutant according to the first aspect of the invention. In a third aspect, the invention also provides a cellcomprising a nucleic acid according to the second aspect of the invention.In a preferred embodiment, a cell according to the invention comprises a nucleic acid encoding the beta-1,3-N-acetylglucosaminyltransferase mutant according to the first aspect of the invention. Said nucleic acid is integrated into the genome of the cell or is present within a plasmid. In the context of the present invention, more than one nucleic acid encoding a beta-1,3-N-acetylglucosaminyltransferase mutant according to the first aspect of the invention can be present in the cell. Hence, a nucleic acid encoding a beta-1,3-N-acetylglucosaminyltransferas...

Claims

Claims 1. A beta-1,3-N-acetylglucosaminyltransferase mutant comprising an amino acid sequence that only differs from the full-length amino acid sequence of a reference beta-1,3-N- acetylglucosaminyltransferase represented by SEQ ID NO 01 in: (i) one or more non-conservative amino acid substitutions at 302-363 of SEQ ID NO 01(preferably at 302-349 or at 321-363 of SEQ ID NO 01, more preferably at 321-349 of SEQ ID NO 01); and (ii) optionally:- one or more non-conservative amino acid substitutions at 1-301 of SEQ ID NO 01,preferably at 17-301, more preferably at 89-301, even more preferably at 158-301, even more preferably at 171-301, even more preferably at 180-301, most preferably at 180-298, and / or -one or more conservative amino acid substitutions at 1-363 (preferably at 17-363,more preferably at 17-349) of SEQ ID NO 01, and / or -one or more amino acids missing at 340-349 of SEQ ID NO 01.

2. A beta-1,3-N-acetylglucosaminyltransferase mutant according to claim 1, wherein said non-conservative amino acid substitution is the substitution of: (i) an aromatic amino acid by a non-aromatic amino acid or vice versa;(ii) a non-polar amino acid by a polar amino acid or vice versa;(iii) a hydrophobic amino acid by a hydrophilic amino acid or vice versa;(iv) a positively charged amino acid by a negatively charged amino acid or uncharged aminoacid; or (v) a negatively charged amino acid by a positively charged amino acid or uncharged aminoacid.

3. A beta-1,3-N-acetylglucosaminyltransferase mutant according to claim 1 or 2, wherein said mutantcomprises an amino acid sequence that has at least 80.0% sequence similarity with the full-length amino acid sequence represented by SEQ ID NO 02.

4. A beta-1,3-N-acetylglucosaminyltransferase mutant according to any one of claims 1 to 3, whereinone or more of said non-conservative amino acid substitutions at 302-363 of SEQ ID NO 01 is the substitution of one or more aromatic amino acids into a non-aromatic amino acid.

5. A beta-1,3-N-acetylglucosaminyltransferase mutant according to claim 4, wherein said aromaticamino acid is selected from the list consisting of phenylalanine (F), tyrosine (Y) and tryptophan (W), preferably selected from the list consisting of phenylalanine (F) and tyrosine (Y), most preferably phenylalanine (F).

6. A beta-1,3-N-acetylglucosaminyltransferase mutant according to claim 4 or 5, wherein one or moreof said non-conservative amino acid substitutions at 302-363 of SEQ ID NO 01 is the substitution ofone or more amino acids selected from the list consisting of F339, F333, F323, F309, F304, Y338, Y306 and W320.

7. A beta-1,3-N-acetylglucosaminyltransferase mutant according to any one of claims 4 to 6, whereinsaid one or more aromatic amino acid substitutions at 302-363 of SEQ ID NO 01 is the substitution of at least F339.

8. A beta-1,3-N-acetylglucosaminyltransferase mutant according to any one of claims 4 to 7, whereinsaid non-aromatic amino acid is an amino acid with a side chain that is less hydrophobic than the side chain of said aromatic amino acid.

9. A beta-1,3-N-acetylglucosaminyltransferase mutant according to any one of claims 1 to 8, whereinone or more of said non-conservative amino acid substitutions at 302-363 of SEQ ID NO 01 is the substitution of one or more non-polar amino acids into a polar amino acid.

10. A beta-1,3-N-acetylglucosaminyltransferase mutant according to claim 9, wherein said non-polaramino acid is selected from the list consisting of P315 (or L315), P316, A317 (unless S is present at position 317), G318, A319, A324, A325, L332 and G340, preferably selected from the list consisting of P315 (or L315), P316, A317 (unless S is present at position 317), G318, A319, A324, A325 and G340, most preferably selected from the list consisting of P315 (or L315), P316, A317 (unless S is present at position 317), G318, A319, A324 and A325.

11. A beta-1,3-N-acetylglucosaminyltransferase mutant according to any one of claims 1 to 10, whereinone or more of said non-conservative amino acid substitutions at 302-363 of SEQ ID NO 01 is the substitution of one or more amino acids having a side chain that is positively charged at physiological pH into an amino acid having a side chain that is uncharged or negatively charged at physiological pH, preferably into an amino acid having a side chain that is negatively charged at physiological pH.

12. A beta-1,3-N-acetylglucosaminyltransferase mutant according to any one of claims 1 to 11, whereinone or more of said non-conservative amino acid substitutions at 1-301 of SEQ ID NO 01 is thesubstitution of one or more amino acids selected from the list consisting of A27, P89, W141, K149, D150, G151, N152, R153, L154, A155, R156, H157, H158, W164, E171, F176, F177, P178, F179, G180, N181, P182, I183, H184, N186, T187, M188, Y201, W207, A208, Y211, Q212, F213, W214, Y215, V217, Y225, Y226, L230, V231, Y233, R234, H236, S241, S242, K243, H244, Y244, S245, Q248, H249, I251, A252, I255, Q256, A259, F263, S266, F269, F273, Y278, N181, K291, P294, E295, F298, E299, R300 and A301.

13. A beta-1,3-N-acetylglucosaminyltransferase mutant according to any one of claims 1 to 12, whereinone or more of said non-conservative amino acid substitutions at 1-301 of SEQ ID NO 01 is the substitution of one or more amino acids selected from the list consisting of G180 and P182.

14. A beta-1,3-N-acetylglucosaminyltransferase mutant according to any one of claims 1 to 13, whereinone or more of said non-conservative amino acid substitutions at 1-301 of SEQ ID NO 01 is the substitution of one or more amino acids selected from the list consisting of H158, H249 and Q256.

15. A beta-1,3-N-acetylglucosaminyltransferase mutant according to any one of claims 1 to 14, whereinone or more of said non-conservative amino acid substitutions at 1-301 of SEQ ID NO 01 is the substitution of: -one or more amino acids selected from the list consisting of W141, G180, P182, N186, M188,Y201, Y211, Q212, Y215, Y225, Y226, L230, and A259; preferably selected from the list consisting of G180, P182 and Y211; more preferably G180 and / or P182; even more preferably G180 or P182; most preferably G180; and -preferably one or more selected form the list consisting of A27, P89, E171, I183, V217, V231,S245, A285, K291, E295, E299, R300 and A301, more preferably selected from the list consisting of A27, P89, E171, I183, V217, V231, S245, A285 and K291, even more preferablyselected from the list consisting of P89, E171, I183, V217 and K291.

16. A beta-1,3-N-acetylglucosaminyltransferase mutant according to any one of claims 1 to 14, whereinone or more of said non-conservative amino acid substitutions at 1-301 of SEQ ID NO 01 is the substitution of: -one or more amino acids selected from the list consisting of H158, H249 and Q256, preferablyH249, Q256 and optionally H158, more preferably H158, H249 and Q256; and -preferably G180 and / or P182, more preferably G180 or P182, most preferably G180.

17. A beta-1,3-N-acetylglucosaminyltransferase mutant according to any one of claims 1 to 16, whereinsaid mutant comprises an amino acid sequence that has at least 80.0% sequence similarity, preferably at least 80.0% sequence identity, with: -SEQ ID NO 08; and wherein the amino acid at position 339 of said amino acid sequence ofthe mutant is selected from the list consisting of C, M, A, G, T, S, P, H, N, D, Q, E, K and R; or -SEQ ID NO 14; and wherein the amino acid at position 333 of said amino acid sequence ofthe mutant is selected from the list consisting of C, M, A, G, T, S, P, H, N, D, Q, E, K and R; or -SEQ ID NO: 20; and wherein the amino acid at position 323 of said amino acid sequence ofthe mutant is selected from the list consisting of C, M, A, G, T, S, P, H, N, D, Q, E, K and R; or -SEQ ID NO: 26; and wherein the amino acid at position 304 of said amino acid sequence ofthe mutant is selected from the list consisting of C, M, A, G, T, S, P, H, N, D, Q, E, K and R.

18. A beta-1,3-N-acetylglucosaminyltransferase mutant according to any one of claims 1 to 16, whereinsaid mutant comprises an amino acid sequence that has at least 80.0% sequence similarity, preferably at least 80.0% sequence identity, with: -SEQ ID NO 32; and wherein:o the amino acid at position 339 of said amino acid sequence of the mutant is selectedfrom the list consisting of C, M, A, G, T, S, P, H, N, D, Q, E, K and R; and othe amino acid at position 182 of said amino acid sequence of the mutant is selectedfrom the list consisting of L, M, A, D, E, S, N, Q, T, R and K; or- SEQ ID NO 38; and wherein:o the amino acid at position 339 of said amino acid sequence of the mutant is selectedfrom the list consisting of C, M, A, G, T, S, P, H, N, D, Q, E, K and R; and othe amino acid at position 180 of said amino acid sequence of the mutant is selectedfrom the list consisting of D, E, S, N, Q, T, R, K, H and Y; or- SEQ ID NO: 44; and wherein:o the amino acid at position 339 of said amino acid sequence of the mutant is selectedfrom the list consisting of C, M, A, G, T, S, P, H, N, D, Q, E, K and R; and othe amino acid at position 211 of said amino acid sequence of the mutant is selectedfrom the list consisting of A, G, N, Q, M, D, and E; or -SEQ ID NO 100; and wherein:o the amino acid at position 339 of said amino acid sequence of the mutant is selectedfrom the list consisting of C, M, A, G, T, S, P, H, N, D, Q, E, K and R; and othe amino acid at position 249 of said amino acid sequence of the mutant is selectedfrom the list consisting of A, C, G, I, L, M, F, P, W and V; and othe amino acid at position 256 of said amino acid sequence of the mutant is selectedfrom the list consisting of A, C, G, I, L, M, F, P, W and V; or -SEQ ID NO 106; and wherein:o the amino acid at position 339 of said amino acid sequence of the mutant is selectedfrom the list consisting of C, M, A, G, T, S, P, H, N, D, Q, E, K and R; and othe amino acid at position 158 of said amino acid sequence of the mutant is selectedfrom the list consisting of A, C, G, I, L, M, F, P, W and V; and othe amino acid at position 249 of said amino acid sequence of the mutant is selectedfrom the list consisting of A, C, G, I, L, M, F, P, W and V; and othe amino acid at position 256 of said amino acid sequence of the mutant is selectedfrom the list consisting of A, C, G, I, L, M, F, P, W and V.

19. A beta-1,3-N-acetylglucosaminyltransferase mutant according to any one of claims 1 to 16, whereinsaid mutant comprises an amino acid sequence that has at least 80.0% sequence similarity, preferably at least 80.0% sequence identity, with: -SEQ ID NO 50; and wherein:o the amino acid at position 339 of said amino acid sequence of the mutant is selectedfrom the list consisting of C, M, A, G, T, S, P, H, N, D, Q, E, K and R; and othe amino acid at position 182 of said amino acid sequence of the mutant is selectedfrom the list consisting of L, M, A, D, E, S, N, Q, T, R and K; and othe amino acid at position 324 of said amino acid sequence of the mutant is selectedfrom the list consisting of R, N, D, Q, E, H, K, S, T and Y; ando the amino acid at position 325 of said amino acid sequence of the mutant is selectedfrom the list consisting of R, N, D, Q, E, H, K, S, T and Y; or -SEQ ID NO 56; and wherein:o the amino acid at position 339 of said amino acid sequence of the mutant is selectedfrom the list consisting of C, M, A, G, T, S, P, H, N, D, Q, E, K and R; and othe amino acid at position 180 of said amino acid sequence of the mutant is selectedfrom the list consisting of D, E, S, N, Q, T, R, K, H and Y; and othe amino acid at position 324 of said amino acid sequence of the mutant is selectedfrom the list consisting of R, N, D, Q, E, H, K, S, T and Y; and othe amino acid at position 325 of said amino acid sequence of the mutant is selectedfrom the list consisting of R, N, D, Q, E, H, K, S, T and Y; or -SEQ ID NO: 62; and wherein:o the amino acid at position 339 of said amino acid sequence of the mutant is selectedfrom the list consisting of C, M, A, G, T, S, P, H, N, D, Q, E, K and R; and othe amino acid at position 211 of said amino acid sequence of the mutant is selectedfrom the list consisting of A, G, N, Q, M, D, and E; and othe amino acid at position 324 of said amino acid sequence of the mutant is selectedfrom the list consisting of R, N, D, Q, E, H, K, S, T and Y; and othe amino acid at position 325 of said amino acid sequence of the mutant is selectedfrom the list consisting of R, N, D, Q, E, H, K, S, T and Y.

20. A beta-1,3-N-acetylglucosaminyltransferase mutant according to any one of claims 1 to 16, whereinsaid mutant comprises an amino acid sequence that has at least 80.0% sequence similarity, preferably at least 80.0% sequence identity, with: -SEQ ID NO 68; and wherein:o the amino acid at position 339 of said amino acid sequence of the mutant is selectedfrom the list consisting of C, M, A, G, T, S, P, H, N, D, Q, E, K and R; and othe amino acid at position 182 of said amino acid sequence of the mutant is selectedfrom the list consisting of L, M, A, D, E, S, N, Q, T, R and K; and othe amino acid at position 315 of said amino acid sequence of the mutant is selectedfrom the list consisting of R, N, D, Q, E, H, K, S, T and Y; and othe amino acid at position 316 of said amino acid sequence of the mutant is selectedfrom the list consisting of R, N, D, Q, E, H, K, S, T and Y; and othe amino acid at position 317 of said amino acid sequence of the mutant is selectedfrom the list consisting of R, N, D, Q, E, H, K, S, T and Y; and othe amino acid at position 318 of said amino acid sequence of the mutant is selectedfrom the list consisting of R, N, D, Q, E, H, K, S, T and Y; ando the amino acid at position 319 of said amino acid sequence of the mutant is selectedfrom the list consisting of R, N, D, Q, E, H, K, S, T and Y; or -SEQ ID NO 74; and wherein:o the amino acid at position 339 of said amino acid sequence of the mutant is selectedfrom the list consisting of C, M, A, G, T, S, P, H, N, D, Q, E, K and R; and othe amino acid at position 180 of said amino acid sequence of the mutant is selectedfrom the list consisting of D, E, S, N, Q, T, R, K, H and Y; and othe amino acid at position 315 of said amino acid sequence of the mutant is selectedfrom the list consisting of R, N, D, Q, E, H, K, S, T and Y; and othe amino acid at position 316 of said amino acid sequence of the mutant is selectedfrom the list consisting of R, N, D, Q, E, H, K, S, T and Y; and othe amino acid at position 317 of said amino acid sequence of the mutant is selectedfrom the list consisting of R, N, D, Q, E, H, K, S, T and Y; and othe amino acid at position 318 of said amino acid sequence of the mutant is selectedfrom the list consisting of R, N, D, Q, E, H, K, S, T and Y; and othe amino acid at position 319 of said amino acid sequence of the mutant is selectedfrom the list consisting of R, N, D, Q, E, H, K, S, T and Y; or -SEQ ID NO: 80; and wherein:o the amino acid at position 339 of said amino acid sequence of the mutant is selectedfrom the list consisting of C, M, A, G, T, S, P, H, N, D, Q, E, K and R; and othe amino acid at position 211 of said amino acid sequence of the mutant is selectedfrom the list consisting of A, G, N, Q, M, D, and E; and othe amino acid at position 315 of said amino acid sequence of the mutant is selectedfrom the list consisting of R, N, D, Q, E, H, K, S, T and Y; and othe amino acid at position 316 of said amino acid sequence of the mutant is selectedfrom the list consisting of R, N, D, Q, E, H, K, S, T and Y; and othe amino acid at position 317 of said amino acid sequence of the mutant is selectedfrom the list consisting of R, N, D, Q, E, H, K, S, T and Y; and othe amino acid at position 318 of said amino acid sequence of the mutant is selectedfrom the list consisting of R, N, D, Q, E, H, K, S, T and Y; and othe amino acid at position 319 of said amino acid sequence of the mutant is selectedfrom the list consisting of R, N, D, Q, E, H, K, S, T and Y.

21. A beta-1,3-N-acetylglucosaminyltransferase mutant according to any one of claims 1 to 16, whereinsaid mutant comprises an amino acid sequence that has at least 80.0% sequence similarity, preferably at least 80.0% sequence identity, with SEQ ID NO 38; and wherein: -the amino acid at position 339 of said amino acid sequence of the mutant is selected fromthe list consisting of C, M, A, G, T, S, P, H, N, D, Q, E, K and R; and -the amino acid at position 180 of said amino acid sequence of the mutant is selected fromthe list consisting of D, E, S, N, Q, T, R, K, H and Y; and -preferably wherein further:o one or more, preferably all, of the following is present:^ the amino acid at position 315 of said amino acid sequence of the mutant isselected from the list consisting of R, N, D, Q, E, H, K, S, T and Y; and ^the amino acid at position 316 of said amino acid sequence of the mutant isselected from the list consisting of R, N, D, Q, E, H, K, S, T and Y; and ^the amino acid at position 317 of said amino acid sequence of the mutant isselected from the list consisting of R, N, D, Q, E, H, K, S, T and Y; and ^the amino acid at position 318 of said amino acid sequence of the mutant isselected from the list consisting of R, N, D, Q, E, H, K, S, T and Y; and ^the amino acid at position 319 of said amino acid sequence of the mutant isselected from the list consisting of R, N, D, Q, E, H, K, S, T and Y; oor one or more, preferably all, of the following is present:^ the amino acid at position 324 of said amino acid sequence of the mutant isselected from the list consisting of R, N, D, Q, E, H, K, S, T and Y; and ^the amino acid at position 325 of said amino acid sequence of the mutant isselected from the list consisting of R, N, D, Q, E, H, K, S, T and Y.

22. A beta-1,3-N-acetylglucosaminyltransferase mutant according to any one of claims 1 to 16, whereinsaid mutant comprises an amino acid sequence that has at least 80.0% sequence similarity, preferably at least 80.0% sequence identity, with SEQ ID NO 100; and wherein: -the amino acid at position 339 of said amino acid sequence of the mutant is selected fromthe list consisting of C, M, A, G, T, S, P, H, N, D, Q, E, K and R; and -the amino acid at position 249 of said amino acid sequence of the mutant is selected fromthe list consisting of A, C, G, I, L, M, F, P, W and V; and -the amino acid at position 256 of said amino acid sequence of the mutant is selected fromthe list consisting of A, C, G, I, L, M, F, P, W and V.

23. A beta-1,3-N-acetylglucosaminyltransferase mutant according to any one of claims 1 to 16, whereinsaid mutant comprises an amino acid sequence that has at least 80.0% sequence similarity, preferably at least 80.0% sequence identity, with SEQ ID NO 106; and wherein: -the amino acid at position 339 of said amino acid sequence of the mutant is selected fromthe list consisting of C, M, A, G, T, S, P, H, N, D, Q, E, K and R; and -the amino acid at position 158 of said amino acid sequence of the mutant is selected fromthe list consisting of A, C, G, I, L, M, F, P, W and V; and- the amino acid at position 249 of said amino acid sequence of the mutant is selected fromthe list consisting of A, C, G, I, L, M, F, P, W and V; and -the amino acid at position 256 of said amino acid sequence of the mutant is selected fromthe list consisting of A, C, G, I, L, M, F, P, W and V.

24. A beta-1,3-N-acetylglucosaminyltransferase mutant according to any one of claims 1 to 23, whereinthe full-length amino acid sequence of the reference beta-1,3-N-acetylglucosaminyltransferase is represented by SEQ ID NO 03, 04 or 05, preferably by SEQ ID NO 03 or 04, most preferably by SEQ ID NO 03.

25. A beta-1,3-N-acetylglucosaminyltransferase mutant according to any one of claims 1 to 24, whereinsaid beta-1,3-N-acetylglucosaminyltransferase mutant exhibits a higher activity compared to said reference beta-1,3-N-acetylglucosaminyltransferase.

26. A beta-1,3-N-acetylglucosaminyltransferase mutant according to claim 25, wherein said activity is theconversion of lactose into a lacto-N-triose II (LN3)-containing oligosaccharide, preferably LNnT.

27. A beta-1,3-N-acetylglucosaminyltransferase mutant according to any one of claims 1 to 26, whereinsaid beta-1,3-N-acetylglucosaminyltransferase mutant has an increased substrate specificity for lactose over a longer-chain oligosaccharide compared to said reference beta-1,3-N- acetylglucosaminyltransferase, wherein said longer-chain oligosaccharide is preferably selected form the list consisting of LNnT, pLNnH, GlcNAc-beta-1,6-LNnT, LNT, LNH, pLNH, pLNH II, pLNnH II and GlcNAc-beta-1,6-LNT, optionally wherein said longer-chain oligosaccharide further consists of one or more fucose residues (preferably alpha-1-3-linked fucose residues).

28. A nucleic acid encoding the beta-1,3-N-acetylglucosaminyltransferase mutant according to any oneof claims 1 to 27.

29. A cell comprising a beta-1,3-N-acetylglucosaminyltransferase mutant according to any one of claims1 to 27.

30. A cell comprising a nucleic acid according to claim 28.

31. A cell according to claim 29 or 30, comprising two or more nucleic acids encoding the same beta-1,3-N-acetylglucosaminyltransferase mutant or wherein one or more nucleic acids encode a different beta-1,3-N-acetylglucosaminyltransferase mutant.

32. A cell according to any one of claims 29 to 31, wherein said cell is capable of producing a lacto-Ntriose II (LN3)-containing oligosaccharide or a mixture of at least two different LN3-containing oligosaccharides.

33. A method for the production of a lacto-N-triose II (LN3)-containing oligosaccharide or a mixturecomprising at least two different LN3-containing oligosaccharides, the method comprising the steps of: -providing (i) an acceptor saccharide or a mixture of at least two different acceptorsaccharides, (ii) UDP-N-acetylglucosamine (UDP-GlcNAc) and (iii) a beta-1,3-N-acetylglucosaminyltransferase mutant according to any one of claims 1 to 27; -bringing said (i), (ii) and (iii) into contact with each other under conditions such that said beta-1,3-N-acetylglucosaminyltransferase mutant transfers a N-acetylglucosamine (GlcNAc) form UDP-GlcNAc to one or more of said acceptor saccharides as to produce a LN3-containing oligosaccharide or a mixture comprising at least two different LN3-containing oligosaccharides.

34. A method for the production of a lacto-N-triose II (LN3)-containing oligosaccharide or a mixturecomprising at least two different LN3-containing oligosaccharides, the method comprising the step of: (a) cultivating a cell according to any one of claims 29 to 32, in a suitable cultivation medium toform a cultivation broth and under conditions permissive for the production of said LN3- containing oligosaccharide or said mixture comprising at least two different LN3-containing oligosaccharides; (b) optionally separating said LN3-containing oligosaccharide from the cultivation broth orseparating any one, preferably at least two, more preferably at least three, even more preferably at least four, most preferably all, of the LN3-containing oligosaccharides in said mixture from the cultivation broth.

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