A novel approach to make homogeneous protease-stable monovalent streptavidin.

The interaction between the tetramer streptavidin and biotin is recognized as one of the strongest non-covalent associations. Owing to the tight and specific binding, the streptavidin-biotin system has been used widely for bimolecular labeling, purification, immobilization, and even for targeted delivery of therapeutics drugs. Here, we report a novel approach to make homogeneous monovalent tetramer streptavidin. The purified monovalent protein showed both thermal stability and protease stability. Unexpectedly, we found that two proteases, Proteinase K (PK) and Subtilisin (SU), can efficiently remove the His8-tag from the wild-type subunit without affecting the tetramer architecture of monovalent streptavidin, thus making it more homogeneous. In addition, crystallization was performed to assure the homogeneity of the monovalent protein prepared. Overall, monovalent streptavidin shows increased homogeneity and will likely be valuable for many future applications in a wide range of research areas.