Circularly Permuted Avidin for Independent Biotin Binding Control
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Solution Overview
Problem
Existing methods for modifying avidin proteins to alter biotin-binding affinity across subunits are limited, as simple fusion strategies fail due to the distant N- and C-termini in avidin tetramers, leading to inconsistent refolding and alternative forms with varying affinities.
Innovation Solution
The creation of dual-chain and single-chain avidin proteins through circular permutation, where two circularly permuted avidin monomers are fused to form a pseudo-tetramer with two polypeptide chains, allowing for the generation of avidins with two different biotin-binding affinities and the ability to modify each binding site independently.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If simple fusion strategies are used to modify avidin proteins, then the structure can be altered, but the N- and C-termini are too distant in avidin tetramers leading to inconsistent refolding and alternative forms with varying affinities
Solution Approach 1:
The avidin tetramer is segmented into two distinct polypeptide chains (first and second chains), each containing two biotin-binding sites. This segmentation allows independent modification of each chain while maintaining overall structural integrity and consistent refolding behavior.
Solution Approach 2:
Different binding affinities are introduced at local levels within the protein structure. The first and second chains can have different biotin-binding affinities, allowing site-specific modification without affecting the entire tetramer uniformly. This enables precise control over binding properties at specific locations.
2Manufacturing precision
If site-directed mutagenesis is used to alter biotin-binding affinity, then affinity can be fine-tuned, but all four subunits are affected concurrently as single gene products
Solution Approach 1:
The protein is divided into two separate polypeptide chains encoded by different gene sequences, allowing independent mutagenesis and modification of each chain. This enables different binding affinities to be introduced in specific chains without affecting all subunits uniformly.
Solution Approach 2:
The tetramer structure is made asymmetric by having two different polypeptide chains instead of four identical subunits. The first and second chains can have different amino acid sequences and binding properties, breaking the perfect symmetry of wild-type avidin to enable differential affinity control.
3Adaptability or versatility
If circular permutation is used to create dual-chain avidin, then independent modification of binding sites is enabled, but the protein structure becomes more complex
Solution Approach 1:
The circularly permuted avidin is segmented into two chains connected by a peptide linker. Each chain contains two biotin-binding sites and can be independently modified. The segmentation is achieved through strategic breaking and rejoining of the polypeptide backbone at specific locations.
Solution Approach 2:
A peptide linker acts as an intermediary element connecting the first and second polypeptide chains. This linker facilitates the formation of the dual-chain structure while allowing independent folding and modification of each chain, managing the complexity through a modular connecting element.
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 results in avidins with preserved high-affinity biotin-binding sites and adjustable lower-affinity sites, enabling novel applications in bioseparation and nanoscale technologies by maintaining structural and functional properties similar to wild-type avidin.
Implementation Method 1
two circularly permuted avidin monomers were fused to a dual-chain avidin (dcAvd) leading to a dual-chain pseudo-tetrameric avidin containing two polypeptides instead of four in the native protein
Implementation Method 2
two dcAvd-molecules are fused together via a linker to form a single polypeptide with four binding sites for biotin
Implementation Method 3
Avidin, a glycoprotein found in chicken egg white as well as its distant relative, streptavidin from Streptomyces bacteria, have high affinity for biotin. This firm interaction has been utilized in countless applications
Data Source
AI summary
Two circularly permuted avidin monomers arc designed. The circularly permuted monomers are fused and the resulting fusion peptides (dcAvd) form a pseudo-tetrameric dual-chain avidin, which is biologically active in biotin binding and shows similar structural characteristics as wild-type avidin. The dcAvd makes the development of dual-affinity avidins possible by allowing the adjustment of the ligand binding properties in the half of the binding sites differently than in the rest of the sites. The present invention provides further a single-chain avidin (scAvd) where two dcAvd-molecules are fused together via a linker to form a single polypeptide with four binding sites for biotin or other ligand.