1oxp
From Proteopedia
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ASPARTATE AMINOTRANSFERASE, H-ASP COMPLEX, CLOSED CONFORMATION
Overview
The interaction of mitochondrial aspartate aminotransferase with, hydroxylamine and five derivatives (in which the hydroxyl hydrogen is, replaced by the side chain of naturally occurring amino acids) was, investigated by X-ray diffraction as well as by kinetic and spectral, measurements with the enzyme in solution. The inhibitors react with, pyridoxal 5'-phosphate in the enzyme active site, both in solution and in, the crystalline state, in a reversible single-step reaction forming, spectrally distinct oxime adducts. Dissociation constants determined in, solution range from 10(-8) M to 10(-6) M depending on the nature of the, side-chain group. The crystal structures of the adducts of mitochondrial, aspartate aminotransferase with the monocarboxylic analogue of L-aspartate, in the open and closed enzyme conformation were determined at 0.23-nm and, 0.25-nm resolution, respectively. This inhibitor binds to both the open, and closed crystal forms of the enzyme without disturbing the crystalline, order. Small differences in the conformation of the cofactor pyridoxal, phosphate were detected between the omega-carboxylate of the inhibitor and, Arg292 of the neighbouring subunit is mainly responsible for the, attainment of near-coplanarity of the aldimine bond with the pyridine ring, in the oxime adducts. Studies with a fluorescent probe aimed to detect, shifts in the open/closed conformational equilibrium of the enzyme in, oxime complexes showed that the hydroxylamine-derived inhibitors, even, those containing a carboxylate group, do not induce the 'domain closure', in solution. This is probably due to the absence of the alpha-carboxylate, group in the monocarboxylic hydroxylamine-derived inhibitors, emphasizing, that both carboxylates of the substrates L-Asp and L-Glu are essential for, stabilizing the closed form of aspartate aminotransferase.
About this Structure
1OXP is a Single protein structure of sequence from Gallus gallus with IK2 as ligand. Active as Aspartate transaminase, with EC number 2.6.1.1 Full crystallographic information is available from OCA.
Reference
Crystal structures and solution studies of oxime adducts of mitochondrial aspartate aminotransferase., Markovic-Housley Z, Schirmer T, Hohenester E, Khomutov AR, Khomutov RM, Karpeisky MY, Sandmeier E, Christen P, Jansonius JN, Eur J Biochem. 1996 Mar 15;236(3):1025-32. PMID:8665890
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