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P.3 left column top paragraph: "Avidin and streptavidin are two additional affinity proteins, commonly used in biomedical applications. Avidin is a 66–69-kDa tetrameric protein found in the egg white of birds, reptiles, and amphibians [refs 44, 46, primary source]. Streptavidin is found in Streptomyces avidinii, and both avidin and streptavidin show affinity for biotin, also known as vitamin B7 or vitamin H [ref 44, primary source]. Streptavidin is a tetrameric protein with eight antiparallel β-strands and each subunit contains a biotin-binding site [refs 47,48]. Based on thise structural consideration, a monomeric streptavidin was developed with similar binding affinity to biotin [refs 49,50]. The dissociation constant of the streptavidin and biotin interaction is 10^13–10^16 M and shows the highest affinity among naturally occurring non-covalent bonds [primary source]. This interaction is mediated not only by hydrogen bonds, but also included a substantial portion of hydrophobic interactions [ref 48]. This strong binding is pseudo-irreversible as well as durable in the presence of organic solvents, detergents, pH, and high temperature. To exploit the strong bonding between biotin-streptavidin, various biotinylation strategies were developed [refs 51–54]." |