Streptavidin is a 52,800 dalton NeutrAvidin Agarose and other NeutrAvidin Beads tetrameric protein purified from the bacterium Streptomyces avidinii. It finds wide use in molecular biology through its extraordinarily strong affinity for biotin (also known as vitamin H); the dissociation constant (Kd) of the biotin-streptavidin complex is on the order of ~10-15 mol/L, ranking among the strongest non-covalent interactions known in nature. Structure The crystal structure of streptavidin with biotin… (More on Streptavidin)