avidin

Avidin is a highly basic, tetrameric glycoprotein found in the egg white (albumen) of birds, most notably in chickens. It consists of four identical subunits and binds up to four biotin molecules with exceptionally high affinity. The overall biotin-binding interaction is among the strongest noncovalent associations known, with dissociation constants in the range of picomolar to femtomolar order. Each subunit contributes a biotin-binding site, and the pockets are highly specific for biotin, allowing selective capture and detection in various biochemical applications.

Biotin avidin systems are widely used in molecular biology and biochemistry because of their robustness and the strength of binding. Avidin’s tetramer can be employed to purify biotinylated proteins, immobilize biotinylated ligands, or serve as a detection scaffold in assays such as ELISA and Western blotting. The interaction can be modulated by competing biotin or biotin analogs, and by extreme conditions that disrupt protein structure or biotin binding.

Avidin is a glycoprotein with a relatively high isoelectric point, and it exhibits stability under regular laboratory conditions and moderate heat. It is often contrasted with streptavidin, a non-glycosylated bacterial protein that also binds biotin with very high affinity, but lacks glycosylation and has different stability properties.

In practice, the strong avidin–biotin interaction enables a wide range of affinity capture, labeling, and detection techniques, making avidin a standard tool in biotechnology and research. Caution is advised when biotin is present in samples, as it can competitively inhibit avidin binding and affect assay results.