What is Streptavidin from Streptomyces avidinii?

Streptavidin is a 60000 dalton protein purified from the bacterium Streptomyces avidinii. Streptavidin homo-tetramers have an extraordinarily high affinity for biotin (also known as vitamin B7). With a dissociation constant (Kd) on the order of ≈10-14 mol/L, the binding of biotin to streptavidin is one of the strongest non-covalent interactions known in nature. Streptavidin is used extensively in molecular biology and bionanotechnology due to the streptavidin-biotin complex's resistance to organic solvents, denaturants (e.g. guanidinium chloride), detergents (e.g. SDS, Triton), proteolytic enzymes, and extremes of temperature and pH.
Structure
The crystal structure of streptavidin with biotin bound was first solved in 1989 by Hendrickson et al. and as of February 2012, there are 135 structures deposited in the Protein Data Bank. See this link for a complete list. The N and C termini of the 159 residue full-length protein are processed to give a shorter ‘core’ streptavidin, usually composed of residues 13 - 139; removal of the N and C termini is necessary for the high biotin-binding affinity. The secondary structure of a streptavidin monomer is composed of eight antiparallel β-strands, which fold to give an antiparallel beta barrel tertiary structure. A biotin binding-site is located at one end of each β-barrel. Four identical Streptavidin monomers (i.e. four identical β-barrels) associate to give streptavidin’s tetrameric quaternary structure. The biotin binding-site in each barrel consists of residues from the interior of the barrel, together with a conserved Trp120 from neighbouring subunit. In this way, each subunit contributes to the binding site on the neighbouring subunit, and so the tetramer can also be considered a dimer of functional dimers.
Uses in Biotechnology
Among the most common uses are the purification or detection of various biomolecules. The strong streptavidin-biotin bond can be used to attach various biomolecules to one another or onto a solid support. Harsh conditions are needed to break the streptavidin-biotin interaction, which often denatures the protein of interest being purified. However, it has been shown that a short incubation in water above 70°C will reversibly break the interaction without denaturing streptavidin, allowing re-use of the streptavidin solid support. A further application is the so called Strep-tag, which is an optimized system for the purification and detection of proteins. Streptavidin is widely used in Western blotting and immunoassays conjugated to some reporter molecule, such as horseradish peroxidase.
More about: Streptavidin from Streptomyces avidinii sale
Read more: Biochemical Reagent