Scalable production of monovalent streptavidin with high yield and purity.

The tetrameric protein streptavidin has found ubiquitous use in a wide variety of applications due to its ability to bind biotin molecules with remarkable affinity (Kd of 10- 14 M). However, for applications that require equimolar conjugation, streptavidin and its four active biotin-binding sites can be difficult to employ. To address this need, a monovalent variant of streptavidin comprising one wild-type (biotin binding) and three mutant (non-binding) streptavidin monomers has emerged that conserves the characteristic binding affinity of the wild-type protein but with only a single biotin recognition pocket. While monovalent streptavidin has found broad utility in biotechnology, the difficult nature of its production-involving its retrieval from insoluble inclusion bodies upon recombinant expression-has limited its availability as a powerful biological tool. Here, we present an improved method for monovalent streptavidin production that circumvents critical challenges by implementing a protein solubility partner to streamline isolation, minimize laborious hands-on procedures, and achieve exceptional protein purity and yield. First, we describe plasmid design and recombinant expression of maltose binding protein fusions with both wild-type and mutant streptavidin monomers. Next, we outline the chromatographic steps to isolate these products independently from cell lysate and cleave the monomers enzymatically from their fusion partner. Finally, we detail the folding, purification, and functional validation of the resulting tetrameric streptavidin consisting of one wild-type and three mutant monomers. This scalable workflow achieves exceptional yield (7 mg per L of culture) and purity (approximately 95%) of monovalent streptavidin.