Switchable Polypeptide Affinity Purification With Gentle SpyTag Elution
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Solution Overview
Problem
Existing affinity purification systems, such as SpyDock, require stringent conditions for elution that can destabilize proteins, and additional purification tags like His-tag introduce immunogenic sequences and increase cloning effort.
Innovation Solution
A modified SpyDock polypeptide, termed SpySwitch, with specific amino acid substitutions allows for selective and reversible binding of SpyTag peptides under mild conditions, including pH 5.0 and physiological temperatures, eliminating the need for additional tags and enabling efficient purification of sensitive proteins.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If SpyDock is used for affinity purification, then purification capability is achieved, but elution conditions become stringent and destabilize proteins
Solution Approach 1:
The patent applies parameter changes by modifying the binding interface between SpyDock and SpyTag through specific amino acid substitutions (E108Q, E108R, E108D, or E108N). These mutations alter the electrostatic and hydrogen bonding parameters of the interaction, enabling reversible binding under milder conditions (pH 5.0 and physiological temperatures) while maintaining purification capability. This resolves the contradiction by changing the binding parameters to allow gentle elution that doesn't destabilize proteins.
2Productivity
If additional purification tags like His-tag are used, then purification efficiency is improved, but immunogenic sequences are introduced and cloning effort increases
Solution Approach 1:
The patent extracts and eliminates the need for additional purification tags by engineering SpyDock itself to provide both the binding function and the purification function. Through the E108Q/R/D/N mutations, SpyDock becomes self-sufficient for affinity purification, removing the requirement for separate His-tags or other purification moieties. This resolves the contradiction by taking out the unnecessary additional tags that cause immunogenicity and cloning complexity while maintaining purification efficiency.
3Strength
If isopeptide bond formation is used, then stable covalent binding is achieved, but reversibility and gentle elution are lost
Solution Approach 1:
The patent inverts the binding mechanism from covalent isopeptide bond formation to non-covalent reversible binding. By mutating E108 to Q/R/D/N, the patent eliminates the isopeptide bond formation capability while creating a new reversible binding interface based on hydrogen bonding and electrostatic interactions. This allows the complex to form stably under physiological conditions but dissociate gently at pH 5.0, resolving the contradiction between binding strength and ease of reversible elution.
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
SpySwitch facilitates high-purity protein purification under gentle conditions, suitable for a wide range of target proteins, including viral glycoproteins, with improved stability and reusability of the immobilized substrate.
Implementation Method 1
capable of forming a stable and reversible non-covalent complex (i.e. a polypeptide:ligand complex) that can be dissociated under appropriate conditions
Implementation Method 2
selective and reversible binding of SpyTag peptides under mild conditions, including pH 5.0 and physiological temperatures
Implementation Method 3
selective and reversible binding of SpyTag peptides under mild conditions, including pH 5.0 and physiological temperatures
Data Source
Figure 1A~1B
Figure 2A~2B
Figure 2C
AI summary
The present invention relates to an affinity purification system comprising a polypeptide (protein) that binds selectively (e.g. specifically) and reversibly to its cognate peptide tag (ligand). In particular, the polypeptide comprises: (i) an amino acid sequence as set forth in SEQ ID NO: 1, wherein X at position 77 is selected from alanine, glycine, serine, asparagine, or threonine; (ii) a portion of (i) comprising an amino acid sequence as set forth in SEQ ID NO: 2, wherein X at position 56 is selected from alanine, glycine, serine, asparagine or threonine; (iii) an amino acid sequence with at least 80% sequence identity to a sequence as set forth in SEQ ID NO: 1, wherein the polypeptide comprises alanine, glycine, serine, asparagine or threonine at a position equivalent to position 77 of SEQ ID NO: 1, and wherein the polypeptide comprises histidine at positions equivalent to positions 30, 84 and 85 of SEQ ID NO: 1; or (iv) a portion of (iii) comprising an amino acid sequence with at least 80% sequence identity to a sequence as set forth in SEQ ID NO: 2, wherein the polypeptide comprises alanine, glycine, serine, asparagine or threonine at a position equivalent to position 56 of SEQ ID NO: 2, and wherein the polypeptide comprises histidine at positions equivalent to positions 9, 63 and 64 of SEQ ID NO: 2, wherein the polypeptide binds selectively and reversibly to a peptide comprising an amino acid sequence as set forth in SEQ ID NO: 3, 4 or 5.