Streptavidin is a tetrameric protein purified from Streptomyces sp. that binds very tightly to the vitamin biotin with a Kd of ~ 10-14 mol/l. The high affinity recognition of biotin and biotinylated molecules has made streptavidin one of the most important components in diagnostics and laboratory kits.

Streptavidin is a 53 kDa homotetramer isolated from Streptomyces avidinii for use in isolation and detection bioassays. Each streptavidin subunit forms high affinity non-covalent bonds with the vitamin biotin. Because of its strong non-covalent interaction with biotin, streptavidin can be used to detect and isolate biotinylated proteins.