Source : E.coli.
Streptavidin Recombinant produced in E. coli is a single polypeptide chain containing 148 amino acids (37-159) and having a molecular mass of 15.6kDa. Streptavidin is fused to a 25 amino acid His-tag at N-terminus & purified by proprietary chromatographic techniques.
Streptavidin is a tetrameric protein secreted by Streptomyces avidinii which binds firmly to biotin. Streptavidin is widely used in molecular biology through its unique high affinity for the vitamin biotin. The dissociation constant (Kd) of the biotin-streptavidin complex is about ~10-15 mol/L. The strong affinity recognition of biotin and biotinylated molecules has made streptavidin one of the most important components in diagnostics and laboratory kits. The streptavidin/biotin system has one of the biggest free energies of association of yet observed for noncovalent binding of a protein and small ligand in aqueous solution (K_assoc = 10**14). The complexes are also extremely stable over a wide range of temperature and pH.
