Streptavidin is a tetrameric protein composed of identical subunits. Each subunit binds one biotin molecule with a KD of ~1×10^-15 M. The preparation contains an N- and C-terminal shortened variant (core streptavidin) with improved properties concerning homogeneity, solubility, resistance towards proteolytic degradation and accessibility of the biotin binding pocket as compared to native streptavidin.
