Recombinant Streptavidin 2 ( r-SA2)

Streptavidin (SA) has a strong affinity with biotin. The affinity constant Kd can generally reach 10-15M. Active SA usually exists as a tetramer. Because SA does not contain glycosyl, SA has a lower level of non-specific binding than avidin in detection applications. It has been widely used in enzyme linked immunosorbent assay (ELISA), immunohistochemistry, time-resolved immunofluorescence technology (TRFIA), quantitative PCR, single-stranded DNA preparation, purification of biomolecules, the preparation of monoclonal antibodies and other biotechnological fields.

However, the very high affinity of SA and biotin generally makes it difficult to separate the combined SA from biotin by a gentle method. Conditions that can be separated generally render SA inactive, as well as biotin-labeled antibodies and antigens. Therefore, it is generally considered that the combination of SA and biotin is irreversible. Recombinant streptavidin 2 (r-SA2) is modified from native streptavidin at the molecular level by removing the binding force to form tetramers. r-SA2 is an active monomer, but its affinity for biotin is strongly weakened (Kd≈10-7M), achieving reversible binding and dissociation. Thus, it can be used for the gentle separation and purification of proteins, antibodies, nucleic acids and other biotinylated materials.