Avidin

Avidin family
Tetrameric structure of streptavidin with 2 bound biotins
Identifiers
SymbolAvidin
PfamPF01382
InterProIPR005468
PROSITEPDOC00499
CATH1slf
SCOP21slf / SCOPe / SUPFAM
Available protein structures:
Pfam  structures / ECOD  
PDBRCSB PDB; PDBe; PDBj
PDBsumstructure summary
Biotin - Avidin can bind up to four molecules of biotin simultaneously with a high degree of affinity and specificity

Avidin is a tetrameric biotin-binding protein produced in the oviducts of birds, reptiles and amphibians and deposited in the whites of their eggs. Dimeric members of the avidin family are also found in some bacteria.[1] In chicken egg white, avidin makes up approximately 0.05% of total protein (approximately 1800 μg 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 the avidin-biotin complex 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 66–69 kDa in size.[3] 10% of the molecular weight is contributed by carbohydrate, 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 in raw egg, but depending on the amount of heat it is exposed to during cooking, the quantity of molecules available for binding biotin can change. 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 helpful for bacterial growth. As evidence for this, streptavidin, a 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]

  1. ^ Cite error: The named reference Helppolainen_2007 was invoked but never defined (see the help page).
  2. ^ Cite error: The named reference Green_1963 was invoked but never defined (see the help page).
  3. ^ Cite error: The named reference Korpela_1984 was invoked but never defined (see the help page).
  4. ^ Cite error: The named reference Green_1975 was invoked but never defined (see the help page).
  5. ^ Cite error: The named reference Bruch_1982 was invoked but never defined (see the help page).
  6. ^ Cite error: The named reference Hendrickson_1989 was invoked but never defined (see the help page).
  7. ^ Cite error: The named reference Hiller_1987 was invoked but never defined (see the help page).