Streptavidin derives its name from its bacterial source Streptomyces avidinii and from the hen egg-white protein, avidin, which has high affinity to biotin. Its homologous core shares 33% sequence similarity with avidin, as well as sharing a common tetrameric structure. It is a crystalline tetrameric protein, with a molecular weight of 4*15000Da. It binds four molecules of biotin. Streptavidin lacks carbohydrate and sulfur-containing amino acids.
Streptavidin is a crystalline protein isolated from the bacterium Streptomyces avidinii and possesses biotin-binding ability. It has four binding sites for biotin like avidin and binds four molecules of biotin. Streptavidin is now considered as a new type of biotin-binding protein.