Streptavidin is one of the most well understood ligand-protein binding complex. It is naturally composed of 4 separate chains arranged into 2 dimers. The attempt to make a stable single chain dimer of streptavidin for amendability to phage and chip display has long remained unsuccessful because of the streptavidin binding site is made up of portions of both dimers therefore when the tetrameric complex is disrupted, the biotin binding pocket is lost.
Charle Cantor and his group in Boston University, MA just discovered a really interesting story about the mutant streptavidin dimer in that despite significant reduction in biotin binding affinity, the mutant is able to bind B4F (biotin-4-fluorescein) at 100000-fold higher than the ability to bind biotin.
Moreover, though the B4F binding is at a very high affinity, it is reversible unlike the traditional streptavidin-biotin system that binds very tightly so that draconean condition will be required for releasing of biotin.
Reference:
- Allison D, Nature Methods 2005 July 22;2(8):573
- Aslan FM, Yu Y, Mohr SC, Cantor CR.,Proc Natl Acad Sci USA. 2005 Jun 14;102(24):8507-12.
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