Avidin

Avidin is a tetrameric biotin-binding protein that is produced in the oviducts of birds, reptiles, and amphibians and deposited in the whites of their eggs. In chickens, the most studied source, avidin consists of four identical subunits, each capable of binding biotin (vitamin B7) with a high degree of affinity and specificity. The strong binding of avidin to biotin is exploited in various biotechnological and diagnostic applications, making it a tool of significant interest in the fields of biochemistry and molecular biology.

Structure and Function

Avidin is a glycoprotein with a molecular weight of approximately 66-69 kDa. Each subunit of avidin is composed of 128 amino acid residues and binds to biotin with a dissociation constant (Kd) in the order of 10^-15 M, which is among the strongest non-covalent interactions known in nature. This high-affinity binding is utilized in affinity chromatography for the purification of biotinylated compounds, among other applications.

The primary function of avidin in nature is thought to be the sequestration of biotin, a vital nutrient, as a defense mechanism against bacteria and fungi in the egg white. The high affinity of avidin for biotin can lead to dietary biotin deficiency if raw egg whites are consumed in large quantities over time, a condition known as "avidin-induced biotin deficiency."

Biotechnological Applications

Due to its strong binding to biotin, avidin and its derivatives, such as streptavidin and neutravidin, are widely used in biotechnological applications. These include:

• Enzyme-linked immunosorbent assay (ELISA): Avidin-biotin complexes are used to enhance the sensitivity of this assay.
• Western blotting and immunohistochemistry: For the detection of proteins, where biotinylated antibodies are used.
• Affinity chromatography: For the purification of biotinylated molecules.
• Nucleic acid detection: In the labeling and detection of DNA and RNA.

Avidin-Biotin Technology

The avidin-biotin complex (ABC) technology exploits the high-affinity interaction between avidin and biotin for various applications in life sciences. This technology is used in the detection and quantification of various biomolecules, including proteins, carbohydrates, and nucleic acids. The versatility and high sensitivity of ABC technology have made it a valuable tool in research and diagnostic laboratories.

Health Implications

While avidin's biotin-binding property is beneficial in scientific applications, it can pose health risks when consumed in raw egg whites over prolonged periods. The binding of avidin to biotin in the gastrointestinal tract can prevent the absorption of biotin, leading to deficiency. Cooking egg whites denatures avidin, rendering it unable to bind biotin and mitigating this risk.

See Also

• Biotin
• Enzyme-linked immunosorbent assay (ELISA)
• Western blot
• Immunohistochemistry
• Affinity chromatography