Avidin (AVD)

Avidin is a tetrameric glycoprotein primarily found in the egg whites of birds, reptiles, and amphibians, while streptavidin is a homologous protein derived from the bacterium Streptomyces avidinii (UniProt P02701, P22629). Both proteins are characterized by their extraordinarily high affinity for biotin (vitamin B7), forming one of the strongest known non-covalent biological interactions with a dissociation constant (Kd) of approximately 10^-15 M (Green, N. M., 1975, Advances in Protein Chemistry). In a therapeutic context, these proteins are utilized as components in "pre-targeting" strategies, particularly for cancer imaging and radioimmunotherapy (Boerman, O. C., et al., 2003, Journal of Nuclear Medicine). In these applications, a biotinylated antibody is first administered to localize at a tumor site, followed by the administration of avidin or streptavidin, and finally a radiolabeled biotin molecule (Paganelli, G., et al., 1991, European Journal of Nuclear Medicine). This approach minimizes the exposure of healthy tissues to radiation by decoupling the slow-circulating antibody from the fast-clearing effector molecule. Despite their utility, the clinical use of avidin and streptavidin is limited by their potential immunogenicity in humans, which can lead to the development of anti-protein antibodies (Meyer, D. L., et al., 2001, Protein Science). Additionally, high levels of endogenous biotin in the blood can compete with the therapeutic biotinylated ligands, potentially reducing the efficacy of the system.

Other names

StreptavidinEgg white avidinBiotin-binding proteinStreptomyces avidinii streptavidin

High-affinity non-covalent binding to biotinylated ligands to facilitate localized delivery of therapeutic or diagnostic agents in pre-targeting protocols.