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Recombinant Core Streptavidin 3 (r-cSA3 )

DjoumanaSeptember 5, 2021

Streptavidin (SA) has a strong affinity with biotin. The affinity constant Kd can generally be as high as 10-15 M. Active SA usually exists as a tetramer. Because SA does not contain sugar groups, SA has a lower level of non-specific binding than avidin in detection applications. It has been widely used in enzyme-linked immunosorbent assay, immunohistochemistry, time-resolved immunofluorescence technology (TRFIA), quantitative PCR, single-stranded DNA preparation, biomolecule-purification, preparation of monoclonal antibodies, and other biotechnology 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 central streptavidin 3 (r-cSA3) is modified from native streptavidin at the molecular level by removing the binding force to form tetramers. r-cSA3 is an active monomer, but its affinity for biotin is strongly weakened (Kd≈10-7M), achieving reversible binding and dissociation. It can be used for gentle separation and purification of proteins, antibodies, nucleic acids, and other biotinylated materials.

Streptavidin-based amplification techniques are widely used in flow cytometry, fluorescent imaging, western blotting, and microplate-based detection for increased signal output and greater sensitivity. Fluorescent conjugates of streptavidin are used to detect biotinylated biomolecules such as primary and secondary antibodies, ligands and toxins, or DNA probes for in situ hybridization or bead-based detection. Enzyme conjugates of streptavidin, such as HRP and AP, are commonly used in western blotting, ELISA, and in situ hybridization imaging applications. Streptavidin-conjugated magnetic beads and resins can be used to isolate proteins, cells, and DNA, or they can be used in immunoassays or bio-panning.

Our family of biotin-binding proteins includes streptavidin, avidin, and NeutrAvidin protein. Each protein binds four biotins per molecule with high affinity and selectivity.

• Streptavidin is most commonly used—it is non-glycosylated and exhibits low levels of nonspecific binding
• Avidin is a highly cationic glycoprotein with an isoelectric point of about 10.5—it can cause nonspecific background staining in some applications due to its positively charged residues and oligosaccharide components
• NeutrAvidin Protein has been processed to remove the carbohydrate and lower its isoelectric point, resulting in reduced nonspecific background staining.