1avd
THREE-DIMENSIONAL STRUCTURE OF THE TETRAGONAL CRYSTAL FORM OF EGG-WHITE AVIDIN IN ITS FUNCTIONAL COMPLEX WITH BIOTIN AT 2.7 ANGSTROMS RESOLUTION
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OverviewOverview
The three-dimensional structure of hen egg-white avidin, crystallized in a, tetragonal crystal form, has been solved at 2.7 A resolution by molecular, replacement methods. After refinement the crystallographic R-factor is, 16.8%, for the 7255 reflections in the 10.0 to 2.7 A resolution range. The, asymmetric unit contains two avidin polypeptide chains (M(r) 2 x 15,600), which build up the functional tetramer through a crystallographic 2-fold, axis parallel to the c unit cell direction. The avidin tetramer has almost, exact 222 molecular symmetry; the three possible dimers display quite, distinct packing interfaces. Each protomer is organized in an, eight-stranded antiparallel orthogonal beta-barrel, with extended loop, regions. The avidin binding site within each promoter is located in a deep, pocket, at the center of the barrel, displaying both hydrophobic and polar, residues for recognition of the tightly bound vitamin. Two Trp residues, Trp70 and Trp97, and Phe79 are in close contact with biotin. Moreover, the, binding pocket is partly closed in its outer rim by residue Trp110 of a, neighboring subunit. Once bound, biotin is almost completely buried in the, protein core, with the exception of the valeryl side-chain carboxylate, group which is exposed to solvent, hydrogen bonds to residues Ala39, Thr40, and Ser75, and triggers the formation of a network of hydrogen bonded, water molecules. Modeling of synthetic biotin analogues allows us to, rationalize functional data available for the binding of these compounds, and to analyze them in terms of biotin recognition mechanism. Hen, egg-white avidin shows clear structural homology to streptavidin, from, Streptomyces avidinii, but significant deviations can be observed in some, regions.
About this StructureAbout this Structure
1AVD is a Single protein structure of sequence from Gallus gallus with NAG and BTN as ligands. Full crystallographic information is available from OCA.
ReferenceReference
Three-dimensional structure of the tetragonal crystal form of egg-white avidin in its functional complex with biotin at 2.7 A resolution., Pugliese L, Coda A, Malcovati M, Bolognesi M, J Mol Biol. 1993 Jun 5;231(3):698-710. PMID:8515446
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