Streptavidin is a glycoprotein comprised of four polypeptides that are connected with carbohydrates via glycosidic bonds. Streptavidin and Neutravidin are tetrameric proteins which form a highly specific binding site for Biotin. Neutravidin is a deglycosylated form of avidin.
The Avidin (Streptavidin/Neutravidin) -Biotin-bond is one of the strongest known, non-covalent bond in biology/ biochemistry (KD= 10-15 mol/l*). The binding site for Biotin is formed by various amino acids (see adjacent figure: binding site). When using covalently attached Avidin, Streptavidin or Neutravidin the molecules are less susceptible for desorption in the presence of alkaline, acids, in solutions of high ionic strength or at high temperatures. Biotin affine proteins can be distinguished by their isoelectric point, specificity and nonspecific binding as illustrated in the following table.