Avidin–biotin complex (ABC)

The avidin-biotin interface represents one of the strongest known non-covalent biological interactions, characterized by a dissociation constant (Kd) of approximately 10^-15 M. Avidin is a tetrameric glycoprotein primarily found in avian egg whites, while biotin (Vitamin B7) is a small essential cofactor. This interface is widely exploited in biotechnology and medicine for its stability and specificity, remaining intact under extremes of pH, temperature, and organic solvents (Green, 1975, Advances in Protein Chemistry). In therapeutic contexts, it is the cornerstone of "pre-targeting" strategies, particularly in oncology, where an avidin-conjugated antibody is first localized to a tumor, followed by the administration of a small, biotinylated drug or radioisotope. This approach minimizes systemic toxicity by ensuring the effector molecule rapidly binds to the pre-localized avidin at the disease site while unbound molecules are quickly cleared from circulation (Laitinen et al., 2007, Trends in Biotechnology). However, the clinical utility is sometimes limited by the immunogenicity of avidin and streptavidin, which are foreign proteins to the human immune system, and potential competition from endogenous biotin.

Other names

Avidin-biotin systemStreptavidin-biotin systemBiotin-binding interfaceAvidin-biotin technology

The system utilizes the exceptionally high non-covalent affinity between avidin (or streptavidin) and biotin (Kd ~10^-15 M) to localize therapeutic or diagnostic agents to specific sites. In pre-targeting strategies, an avidin-conjugated primary agent binds to a disease-specific antigen, followed by the administration of a small biotinylated effector molecule that rapidly binds to the pre-localized avidin (Paganelli et al., 1991, Cancer Research).