CLOSE SIMILARITY AMONG STREPTAVIDIN-LIKE, BIOTIN-BINDING PROTEINS FROM STREPTOMYCES

Two strains of Streptomyces venezuelae were found to produce high-affinity, biotin-binding proteins, termed streptavidin vl and v2, respectively. Both proteins were isolated to purity, and their corresponding genes were cloned and sequenced. Compared to streptavidin from S. avidinii, streptavidin v1 had only a single amino acid substitution and streptavidin v2 showed 9 such differences. The substitutions were remarkably conservative, none of which affected the amino acid residues known to be important to the biotin-binding properties or to the structure of the tetrameric protein. The results also indicate that the biosynthesis of such biotin-binding proteins is not simply a curious anomaly in a single species of Streptomyces. It is suggested that the classification of S, avidinii as a unique species should be reconsidered. The occurrence of these proteins appears to be linked to the production of an unusual synergistic antibiotic complex.