Team:LMU-TUM Munich/Proteins
Streptavidin – Biotin
General
Streptavidin is a tetrameric protein with a molecular weight of 4 x 13,33 kDa[1], it can be isolated from Streptomyces avidinii. Each subunit is able to bind one molecule of biotin (molecular weight = 244.3 Da). This specific, non-covalent bondage with a femto molar dissociation constant (kD = 10-15 M) is one of the strongest known biological affinities. Antibodies, in comparison, have lower dissociation constants with 10-7 – 10-11 M.
One subunit of streptavidin is organized as eight stranded antiparallel beta sheets of coiled polypeptide chains which form a hydrogen bonded barrel with extended hydrogen loops�[2]�. The biotin binding pocket consists of primarily aromatic or polar side chains. These interact with the hetero atoms of biotin.
Due to its low unspecific binding, Streptavidin is primarily used in protein-purification and imaging. Biotinylation does not interrupt functions of a biomolecule. Biotin ligases can attach biotin to specific lysine residues in vitro and in vivo.
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