Streptavidin (SA)

Streptavidin is a 52.8 kDa protein purified from the bacterium Streptomyces avidinii.  Streptavidin homo-tetramers have an extraordinarily high affinity for biotin.  With a dissociation constant (Kd) on the order of ≈10−14 mol/L, the binding of biotin to streptavidin is one of the strongest non-covalent interactions known in nature.  Streptavidin is used extensively in molecular biology and bionanotechnology due to the streptavidin-biotin complex's resistance to organic solvents, denaturants, detergents, proteolytic enzymes, and extremes of temperature and pH. The crystal structure of streptavidin with biotin bound was reported by two groups in 1989. The structure was solved using multi wavelength anomalous diffraction by Hendrickson et al.