Avidin

Original Settings - Two subunits shown at right.               

Restrict to only one subunit .   Each subunit is organized in an orthogonal eight-stranded antiparallel β-barrel.

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Biotin Ligand 

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Avidin Structure Show single monomer in cartoon form (Click twice)

Each monomer of avidin is organized into an orthogonal eight-stranded antiparallel β-barrel.      Move around β-barrel

Each monomer also contains one disulfide brigde connecting Cys4 in the N-terminal region to Cys83 in strand six of the beta barrel.      Show disulfide bond

Three salt bridges are also present in each monomer:

    -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.  Show

    -Arg100 of strand 7 and Asp109 of loop 7-8.  Show

    -Asp108 and Lys111. Show

Biotin Binding

Show Binding Site - (Click twice) Biotin is shown.

    - 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 Asn118.  O-12 has strong interactions with OG of Ser16 and OH of Tyr33. N-11 is bonded to oxygen of Thr35.    Show

    -The aromatic residues of Phe79 and Trp97 surround biotin's tetrahydrothiophenic ring and stablize. Show

    -Biotin's terminal carboxylate group is Hydrogen bonded to Ala39, Thr40, Ser73, Ser 75.           Show

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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.  Show these amino acids.

In each chain of avidin, when biotin is bound it is in close contact with Trp 70 and Trp 97.  Show these amino acids.

Created By Jeff Flynn & Nick Menth