How streptavidin's utility in bionanotechnology was increased: pushing the limits of a non‐covalent interaction

Streptavidin is a widely used tool in many areas of bionanotechnology. Some key features of streptavidin include: its extremely high biotin binding affinity, allowing stable binding of biotinylated species; its tetravalency, allowing it to act as a bridge between biotinylated species as well as enabling amplification; and its ability to bind many ligands, such as biotin, desthiobiotin and Strep‐tag. However, the stability of biotin‐binding is limiting in certain applications, and to address this, we engineered a mutant streptavidin, named traptavidin, with more than ten‐fold slower biotin dissociation as well as higher thermal and mechanical stability. We have solved the crystal structures of both apo‐ and biotin‐bound traptavidin at high resolution, which revealed a striking difference in the conformation of traptavidin compared to streptavidin, shedding light on the molecular basis of the mutant's increased stability. We are now utilizing both streptavidin and traptavidin to engineer ‘molecular hubs', producing controlled valency proteins that have a use in ‘bottom‐up’ nanofabrication procedures. Funding was provided by the Wellcome Trust, the Biotechnology and Biological Sciences Research Council Chemical Biology DPhil programme and Somerville College Oxford.