Avidin

Title: Avidin
Literature References: Basic glycoprotein isolated from raw egg white. Exhibits high binding affinity for biotin and is capable of producing biotin deficiency in rats and chicks. Occurs in the white portion of eggs and the oviducts of birds and amphibia. Destroyed by cooking or irradiation. Isoln: Eakin et al., J. Biol. Chem. 136, 801 (1940); Pennington et al., J. Am. Chem. Soc. 64, 469 (1942); Fraenkel-Conrat et al., Arch. Biochem. Biophys. 39, 80, 97 (1952). Improved purification and crystallization: Green et al., Biochem. J. 118, 67, 71 (1970). Structure is a glycoprotein containing four essentially identical subunits: Green, ibid. 92, 16c (1964). The combined mol wt of the subunits is about 66,000. Each subunit is a single polypeptide chain containing 128 amino acid residues with alanine at the N-terminal, glutamic acid at the C-terminal, and a carbohydrate moiety attached at the asparaginyl residue, position 17. Complete amino acid sequence of the protein subunit: DeLange, Huang, J. Biol. Chem. 246, 698 (1971). Studies on biotin inactivation by avidin: Becker, Wilchek, Biochim. Biophys. Acta 264, 165 (1972). Review of chemistry and binding properties: N. M. Green, Adv. Protein Chem. 29, 85-133 (1975). Review of use of avidin-biotin complex in molecular biology: E. A. Bayer, M. Wilchek, Methods Biochem. Anal. 26, 1-45 (1980); in immunoassays: M. Wilchek, E. A. Bayer, Immunol. Today 5, 39-43 (1984).
Use: Biochemical tool for affinity chromatography, affinity cytochemistry and immunoassay.
Avilamycin Avoparcin Azacitidine Azaconazole Azacosterol

Avidin
PDB 1sws EBI.jpg
core-streptavidin mutant d128a at pH 4.5
Identifiers
Symbol Avidin
Pfam PF01382
InterPro IPR005468
PROSITE PDOC00499
SCOP 1slf
SUPERFAMILY 1slf
Biotin - Avidin can bind up to four molecules of biotin simultaneously with a high degree of affinity and specificity

Avidin is a tetrameric or dimeric[1] biotin-binding protein produced in the oviducts of birds, reptiles and amphibians and deposited in the whites of their eggs. In chicken egg white, avidin makes up approximately 0.05% of total protein (approximately 1.8 mg per egg). The tetrameric protein contains four identical subunits (homotetramer), each of which can bind to biotin (Vitamin B7, vitamin H) with a high degree of affinity and specificity. The dissociation constant of avidin is measured to be KD ≈ 10−15 M, making it one of the strongest known non-covalent bonds.[2]

In its tetrameric form, avidin is estimated to be between 66–69 kDa in size.[3] 10% of the molecular weight is attributed to carbohydrate content composed of four to five mannose and three N-acetylglucosamine residues.[4] The carbohydrate moieties of avidin contain at least three unique oligosaccharide structural types that are similar in structure and composition.[5]

Functional avidin is found only in raw egg, as the biotin avidity of the protein is destroyed by cooking. The natural function of avidin in eggs is not known, although it has been postulated to be made in the oviduct as a bacterial growth-inhibitor, by binding biotin the bacteria need. As evidence for this, streptavidin, a loosely related protein with equal biotin affinity and a very similar binding site, is made by certain strains of Streptomyces bacteria, and is thought to serve to inhibit the growth of competing bacteria, in the manner of an antibiotic.[6]

A non-glycosylated form of avidin has been isolated from commercially prepared product; however, it is not conclusive as to whether the non-glycosylated form occurs naturally or is a product of the manufacturing process.[7]