6cha
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(New page: 200px<br /><applet load="6cha" size="450" color="white" frame="true" align="right" spinBox="true" caption="6cha, resolution 1.8Å" /> '''STRUCTURE OF A TETRAH...)
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Revision as of 13:23, 20 November 2007
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STRUCTURE OF A TETRAHEDRAL TRANSITION STATE COMPLEX OF ALPHA-*CHYMOTRYPSIN AT 1.8-*ANGSTROMS RESOLUTION
Overview
A 1.8-A resolution x-ray crystallographic restrained least squares, refinement has been carried out on the phenylethane boronic acid (PEBA), complex of alpha-chymotrypsin dimer (alpha-CHT), and it has been compared, to the 1.67-A resolution structure of the native enzyme. PEBA has a high, binding affinity for alpha-CHT, and the boronate forms a tetrahedral, complex with Ser-195 OG of one molecule of the dimer; the boronate in the, other molecule is severely disordered and does not form a tetrahedral, complex. The former could be a model of the transition state of catalysis., The complex of PEBA X alpha-CHT displays significant nonequivalence in, conformation of side chains between the independent molecules comparable, to the native enzyme, but, like the latter, shows a high degree of, fidelity in the folding of the main chain. The orientation of the phenyl, ring, CA and CB of PEBA, in the specificity sites of the two molecules is, similar, suggesting that recognition is fairly insensitive to small, departures from local symmetry; the same does not apply to the boronate, functionalities suggesting that greater precision is required for, catalysis. The folding of the molecule remains the same upon PEBA binding, but some of the side chains respond nonequivalently. The latter is a, consequence of the inherent nonequivalence of the native dimer and the, asymmetrical nature of the PEBA binding.
About this Structure
6CHA is a Protein complex structure of sequences from Bos taurus with PBA as ligand. Active as Chymotrypsin, with EC number 3.4.21.1 Full crystallographic information is available from OCA.
Reference
Structure of a tetrahedral transition state complex of alpha-chymotrypsin dimer at 1.8-A resolution., Tulinsky A, Blevins RA, J Biol Chem. 1987 Jun 5;262(16):7737-43. PMID:3584139
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