Structure-based design of a streptavidin mutant specific for an artificial biotin analogue

Abstract

For a multistep pre-targeting method using antibodies, a streptavidin mutant with low immunogenicity, termed low immunogenic streptavidin mutant No. 314 (LISA-314), was produced previously as a drug delivery tool. However, endogenous biotins (BTNs) with high affinity (Kd < 10(-10) M) for the binding pocket of LISA-314 prevents access of exogenous BTN-labelled anticancer drugs. In this study, we improve the binding pocket of LISA-314 to abolish its affinity for endogenous BTN species, therefore ensuring that the newly designed LISA-314 binds only artificial BTN analogue. The replacement of three amino acid residues was performed in two steps to develop a mutant termed V212, which selectively binds to 6-(5-((3aS,4S,6aR)-2-iminohexahydro-1H-thieno[3,4-d]imidazol-4-yl)pentanamido)hexanoic acid (iminobiotin long tail, IMNtail). Surface plasmon resonance results showed that V212 has a Kd value of 5.9 × 10(-7) M towards IMNtail, but no binding affinity for endogenous BTN species. This V212/IMNtail system will be useful as a novel delivery tool for anticancer therapy.