2cga
From Proteopedia
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BOVINE CHYMOTRYPSINOGEN A. X-RAY CRYSTAL STRUCTURE ANALYSIS AND REFINEMENT OF A NEW CRYSTAL FORM AT 1.8 ANGSTROMS RESOLUTION
Overview
The X-ray structure of a new crystal form of chymotrypsinogen A grown from, ethanol/water has been determined at 1.8 A resolution using Patterson, search techniques. The crystals are of orthorhombic space group P212121, and contain two molecules in the asymmetric unit. Both independent, molecules (referred to as A and B) have been crystallographically refined, to a final R value of 0.173 with reflection data to 1.8 A resolution., Owing to different crystal contacts, both independent molecules show at, various sites conformational differences, especially in segments 33-38, 142-153 and 215-222. If these three loops are omitted in a comparison, the, root-mean-square (r.m.s.) deviation of the main-chain atoms of molecules A, and B is 0.32 A. If segments 70-79, 143-152 and 215-221 are omitted, a, comparison of either molecule A or molecule B with the chymotrypsinogen, model of Freer et al. (1970) reveals an r.m.s. deviation of the, alpha-carbon atoms of about 0.7 A. Compared with the active enzyme, four, spatially adjacent peptide segments, in particular, are differently, organized in the zymogen: the amino-terminal segment 11-19 runs in a rigid, but strained conformation along the molecular surface due to the covalent, linkage through Cys1; also segment 184-194 is in a rigid unique, conformation due to several mutually stabilizing interactions with the, amino-terminal segment; segment 216-222, which also lines the specificity, pocket, adapts to different crystal contacts and exists in both, chymotrypsinogen molecules in different, but defined conformations; in, particular, disulfide bridge 191-220, which covalently links both latter, segments, has opposite handedness in molecules A and B; finally, the, autolysis loop 142 to 153 is organized in a variety of ways and in its, terminal part is completely disordered. Thus, the allosteric activation, domain (Huber & Bode, 1978) is organized in defined although different, conformations in chymotrypsinogen molecules A and B, in contrast to, trypsinogen, where all four homologous segments of the activation domain, are disordered. This reflects the structural variability and deformability, of the activation domain in serine proteinase proenzymes. If the, aforementioned peptide segments are omitted, a comparison of our, chymotrypsinogen models with gamma-chymotrypsin (Cohen et al., 1981), yields an r.m.s. deviation for alpha-carbon atoms of about 0.5 A. The, residues of the "active site triad" are arranged similarly, but the, oxyanion hole is lacking in chymotrypsinogen.(ABSTRACT TRUNCATED AT 400, WORDS)
About this Structure
2CGA is a Single protein structure of sequence from Bos taurus. Full crystallographic information is available from OCA.
Reference
Bovine chymotrypsinogen A X-ray crystal structure analysis and refinement of a new crystal form at 1.8 A resolution., Wang D, Bode W, Huber R, J Mol Biol. 1985 Oct 5;185(3):595-624. PMID:4057257
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