Tandem Affinity Tags for Full-Length Protein Selection
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Solution Overview
Problem
Existing protein purification methods struggle to selectively isolate full-length proteins over truncated forms and degraded proteins, which are common issues in protein expression and purification.
Innovation Solution
The use of a recombinant fusion protein system, TSGIT, which includes N-terminal and C-terminal purification tags, solubilization tags, and cleavage tags, allowing for the selection of full-length proteins through sequential affinity tag interactions and subsequent cleavage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single purification tag is used at either N- or C-terminus, then the purification process is simple, but truncated and degraded protein forms cannot be distinguished from full-length protein
Solution Approach 1:
The invention divides the purification system into two separate functional segments: an N-terminal affinity tag for initial capture and a C-terminal affinity tag for subsequent verification. This segmentation allows the system to first enrich for proteins with the N-terminal tag, then further purify by selecting only those proteins that also retain the C-terminal tag, thereby distinguishing full-length proteins from truncated forms.
Solution Approach 2:
The invention adds a second dimension of purification by introducing a second affinity tag at the opposite terminus of the protein. Instead of relying on a single purification step, the system performs sequential purification in two directions (N-terminus then C-terminus), creating a two-dimensional selection process that significantly improves the ability to isolate intact full-length proteins.
2Adaptability or versatility
If cleavable fusion tags are used to remove unwanted amino acids, then the protein function is improved, but the tags can only be placed at one terminus and may leave remaining amino acids
Solution Approach 1:
The invention introduces a self-cleaving peptide sequence (such as a furin recognition site or other protease cleavage site) as an intermediary element between the affinity tag and the protein of interest. This intermediary sequence serves as a recognition motif for specific proteases that can cleave the tag-protein junction, allowing clean removal of the affinity tag without leaving unwanted amino acid residues on the final protein product.
3Ease of operation
If standard protein purification methods are used, then the purification process is straightforward, but truncated and degraded protein forms are co-purified with full-length protein
Solution Approach 1:
The invention performs a preliminary enrichment step using the N-terminal affinity tag to capture all proteins containing that tag before the final purification step. This preliminary action creates a pre-enriched sample that contains both full-length and truncated proteins, which then undergoes a second purification step using the C-terminal tag to selectively isolate only the full-length proteins, thereby simplifying the overall process while improving precision.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enables the efficient purification of full-length proteins while removing unwanted truncated forms and degraded proteins, resulting in high yields of pure, native protein ready for further applications.
Implementation Method 1
The fusion protein is expressed as a three domain fusion, represented by formula I: A-[L1]-B-[L2]-C, where A is a first purification tag domain, C is the second purification tag domain and B is the target protein domain
Data Source
AI summary
Expression vectors and methods of protein purification, which allow for selection of full length protein over truncated forms of the protein being purified, are disclosed. The methods express a target protein as a three domain fusion, represented by formula I:A-[Li]-B-[L2]-C, where A is a first purification tag domain, C is the second purification tag domain and B is the target protein domain. A, B and C are preferably covalently linked by linkers, L1 and L2 may be optional. The purification tags at the N and C termini are different. The purification tags at the N and C termini are different. Expression vectors including nucleic acid sequences which encode the fusion protein represented by formula I are also disclosed. The vectors are used with host expression systems such as insect, yeast, or mammalian cells to express the target protein, which is subsequently purified as a function of the different affinity tags.