1ama

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spinqualitylabelsall models 1ama, resolution 2.3Å Show:Asymmetric Unit Biological Assembly Drag the structure with the mouse to rotate   Export Animated Image

DOMAIN CLOSURE IN MITOCHONDRIAL ASPARTATE AMINOTRANSFERASE

Overview

The subunits of the dimeric enzyme aspartate aminotransferase have two, domains: one large and one small. The active site lies in a cavity that is, close to both the subunit interface and the interface between the two, domains. On binding the substrate the domains close together. This closure, completely buries the substrate in the active site and moves two arginine, side-chains so they form salt bridges with carboxylate groups of the, substrate. The salt bridges hold the substrate close to the pyridoxal, 5'-phosphate cofactor and in the right position and orientation for the, catalysis of the transamination reaction. We describe here the structural, changes that produce the domain movements and the closure of the active, site. Structural changes occur at the interface between the domains and, within the small domain itself. On closure, the core of the small domain, rotates by 13 degrees relative to the large domain. Two other regions of, the small domain, which form part of the active site, move somewhat, differently. A loop, residues 39 to 49, above the active site moves about, 1 A less than the core of the small domain. A helix within the small, domain forms the "door" of the active site. It moves with the core of the, small domain and, in addition, shifts by 1.2 A, rotates by 10 degrees, and, switches its first turn from the alpha to the 3(10) conformation. This, results in the helix closing the active site. The domain movements are, produced by a co-ordinated series of small changes. Within one subunit the, polypeptide chain passes twice between the large and small domains. One, link involves a peptide in an extended conformation. The second link is in, the middle of a long helix that spans both domains. At the interface this, helix is kinked and, on closure, the angle of the kink changes to, accommodate the movement of the small domain. The interface between the, domains is formed by 15 residues in the large domain packing against 12, residues in the small domain and the manner in which these residues pack, is essentially the same in the open and closed structures. Domain, movements involve changes in the main-chain and side-chain torsion angles, in the residues on both sides of the interface. Most of these changes are, small; only a few side-chains switch to new conformations.(ABSTRACT, TRUNCATED AT 400 WORDS)

About this Structure

1AMA is a Single protein structure of sequence from Gallus gallus with PLA as ligand. Active as Aspartate transaminase, with EC number 2.6.1.1 Full crystallographic information is available from OCA.

Reference

Domain closure in mitochondrial aspartate aminotransferase., McPhalen CA, Vincent MG, Picot D, Jansonius JN, Lesk AM, Chothia C, J Mol Biol. 1992 Sep 5;227(1):197-213. PMID:1522585

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