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1ami
From Proteopedia
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STERIC AND CONFORMATIONAL FEATURES OF THE ACONITASE MECHANISM
Overview
Crystal structures of mitochondrial aconitase with alpha-methylisocitrate, and with sulfate bound have been solved and refined at 2.0 A resolution, with R factors of 18.2 and 16.8%, respectively. The steric factors and, conformational effects observed in both new structures support the, proposed mechanism for the overall reaction catalyzed by aconitase. The, alternate substrate alpha-methylisocitrate is derived from, alpha-methyl-cis-aconitate during crystallization and is observed to bind, in the active site in a manner very similar to that observed for, isocitrate. The methyl group is accommodated by favorable contact with, Ile-425. However, the other potential hydration product of, alpha-methyl-cis-aconitate, alpha-methylcitrate, cannot be accommodated in, the active site due to steric conflict of the methyl group with Asp-165., The results are consistent with the requirement that cis-aconitate must, bind in two ways, in the citrate mode and in the isocitrate mode. Crystals, of aconitase with sulfate bound are isomorphous to those with isocitrate, bound. However, the structure displays significant conformational changes, providing a model for the substrate-free state of enzyme. Three water, molecules bind in place of the C alpha- and C beta-hydroxyl and carboxyl, groups of isocitrate, while sulfate binds in place of the C gamma-carboxyl, group. Side chains of Ser-642 and Arg-447 in the active site rotate to, pair with other side chains in the absence of substrate. The new, conformation of Arg-447 triggers a concerted set of shifts which transmits, conformational change to the surface of the protein, 30 A from the active, site. In the absence of substrate, a chain segment containing the [4Fe-4S], ligand Cys-358 also shifts, resulting in the net translation and, reorientation of the Fe-S cluster.
About this Structure
1AMI is a Single protein structure of sequence from Bos taurus with SF4 and MIC as ligands. Active as Aconitate hydratase, with EC number 4.2.1.3 Full crystallographic information is available from OCA.
Reference
Steric and conformational features of the aconitase mechanism., Lauble H, Stout CD, Proteins. 1995 May;22(1):1-11. PMID:7675781
Page seeded by OCA on Tue Nov 20 10:57:36 2007
