1ajs
From Proteopedia
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REFINEMENT AND COMPARISON OF THE CRYSTAL STRUCTURES OF PIG CYTOSOLIC ASPARTATE AMINOTRANSFERASE AND ITS COMPLEX WITH 2-METHYLASPARTATE
Overview
Two high resolution crystal structures of cytosolic aspartate, aminotransferase from pig heart provide additional insights into the, stereochemical mechanism for ligand-induced conformational changes in this, enzyme. Structures of the homodimeric native structure and its complex, with the substrate analog 2-methylaspartate have been refined, respectively, with 1.74-A x-ray diffraction data to an R value of 0.170, and with 1.6-A data to an R value of 0.173. In the presence of, 2-methylaspartate, one of the subunits (subunit 1) shows a ligand-induced, conformational change that involves a large movement of the small domain, (residues 12-49 and 327-412) to produce a "closed" conformation. No such, transition is observed in the other subunit (subunit 2), because crystal, lattice contacts lock it in an "open" conformation like that adopted by, subunit 1 in the absence of substrate. By comparing the open and closed, forms of cAspAT, we propose a stereochemical mechanism for the, open-to-closed transition that involves the electrostatic neutralization, of two active site arginine residues by the negative charges of the, incoming substrate, a large change in the backbone (phi,psi), conformational angles of two key glycine residues, and the entropy-driven, burial of a stretch of hydrophobic residues on the N-terminal helix. The, calculated free energy for the burial of this "hydrophobic plug" appears, to be sufficient to serve as the driving force for domain closure.
About this Structure
1AJS is a Protein complex structure of sequences from Sus scrofa with PLA as ligand. Active as Aspartate transaminase, with EC number 2.6.1.1 Structure known Active Sites: ACT and AXT. Full crystallographic information is available from OCA.
Reference
Refinement and comparisons of the crystal structures of pig cytosolic aspartate aminotransferase and its complex with 2-methylaspartate., Rhee S, Silva MM, Hyde CC, Rogers PH, Metzler CM, Metzler DE, Arnone A, J Biol Chem. 1997 Jul 11;272(28):17293-302. PMID:9211866
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