Streptavidin is a homotetrameric protein with a molecular weight of 55 kDa found in the culture broth of Streptomyces avidinii. Similar to avidin, one mole of streptavidin can bind 4 moles of biotin with a high affinity virtually unmatched in nature.
Streptavidin lacks carbohydrate side chains present on avidin and has an isoelectric point close to neutrality. Therefore it has a reducing nonspecific binding level as compared to avidin. Streptavidin has been extensively applied in various biological fields, such as ELISA, IHC, TRFIA, quantifying PCR, isolation of single-stranded nucleotide, purification of biomolecule, and monoclonal antibody production as well.