3chb
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(New page: 200px<br /><applet load="3chb" size="450" color="white" frame="true" align="right" spinBox="true" caption="3chb, resolution 1.25Å" /> '''CHOLERA TOXIN B-PENT...)
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Revision as of 17:27, 20 November 2007
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CHOLERA TOXIN B-PENTAMER COMPLEXED WITH GM1 PENTASACCHARIDE
Overview
Crystals of the 61 kDa complex of the cholera toxin B-pentamer with the, ganglioside GM1 receptor pentasaccharide diffract to near-atomic, resolution. We have refined the crystallographic model for this complex, using anisotropic displacement parameters for all atoms to a conventional, crystallographic residual R=0.129 for all observed Bragg reflections in, the resolution range 22 A to 1.25 A. Remarkably few residues show evidence, of discrete conformational disorder. A notable exception is a minority, conformation found for the Cys9 side-chain, which implies that the, Cys9-Cys86 disulfide linkage is incompletely formed. In all five, crystallographically independent instances, the peptide backbone in the, region of the receptor-binding site shows evidence of strain, including, unusual bond lengths and angles, and a highly non-planar (omega=153.7(7), degrees) peptide group between residues Gln49 and Val50. The location of, well-ordered water molecules at the protein surface is notable reproduced, among the five crystallographically independent copies of the peptide, chain, both at the receptor-binding site and elsewhere. The 5-fold, non-crystallographic symmetry of this complex allows an evaluation of the, accuracy, reproducibility, and derived error estimates from refinement of, large structures at near-atomic resolution. We find that blocked-matrix, treatment of parameter covariance underestimates the uncertainty of atomic, positions in the final model by approximately 10% relative to estimates, based either on full-matrix inversion or on the 5-fold, non-crystallographic symmetry.
About this Structure
3CHB is a Single protein structure of sequence from Vibrio cholerae with UNX and MES as ligands. Full crystallographic information is available from OCA.
Reference
The 1.25 A resolution refinement of the cholera toxin B-pentamer: evidence of peptide backbone strain at the receptor-binding site., Merritt EA, Kuhn P, Sarfaty S, Erbe JL, Holmes RK, Hol WG, J Mol Biol. 1998 Oct 9;282(5):1043-59. PMID:9753553
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