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Egg-White Avidin in its functional complex with Biotin
Avidin is a glycoprotein made of four identical subunits. Biotin is a vitamin that is involved in carboxylation-decarboxylation reactions and forms a highly stable complex with Avidin. Two Avidin chains are contained in an asymmetric unit. Avidin's binding with biotin is one of the tightest binding intereactions known.
For more information see:
Chapter 5A: REVERSIBLE BINDING 1- MATHEMATICAL MODELS AND EXPERIMENTAL TECHNIQUES
Show Biotin Ligand
Backbone and sidechains
Cartoon showing hydrogen bonds
Cartoon and Wireframe
Dot surface and Wireframe
Each monomer also contains one disulfide bridge connecting Cys4 in the N-terminal region to Cys83 in strand six of the beta barrel.
Show Disulfide bridge
-Glu91 of strand 7 and Arg122 of strand 8. This bridge acts as a lid to the barrel and is located opposite the binding sight.
-Arg100 of strand 7 and Asp109 of loop 7-8.
-Asp108 and Lys111.
-Several polar residues are in the binding pocket are available for hydrogen bonding on biotin's ureidic ring. N-13 is bound to the oxygen on
. O-12 has strong interactions with OG of
and OH of Tyr33.
N-11 is bonded to oxygen of
-The aromatic residues of Phe79
surround biotin's tetrahydrothiophenic ring and stablize.
-Biotin's terminal carboxylate group is Hydrogen bonded to
Ser73, Ser 75.
-The avidin-biotin complex is extremely tight and stable, the complex is stable in 9 M Urea. Tryptophan residues 70, 97 and 110 are thought to be involved in recognition of biotin.
-In each chain of avidin, when biotin is bound it is in close contact with Trp 70 and Trp 97