1gc8
From Proteopedia
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THE CRYSTAL STRUCTURE OF THERMUS THERMOPHILUS 3-ISOPROPYLMALATE DEHYDROGENASE MUTATED AT 172TH FROM ALA TO PHE
Overview
The relationship between the structure and the thermostability of the, 3-isopropylmalate dehydrogenase from Thermus thermophilus was studied by, site-directed mutation of a single Ala residue located at the domain, interface. The crystal structures of three mutant enzymes, replacing, Ala172 with Gly, Val and Phe, were successfully determined at 2.3, 2.2 and, 2.5 A resolution, respectively. Substitution of Ala172 by relatively, 'short' residues (Gly, Val or Ile) enlarges or narrows the cavity in the, vicinity of the C(beta) atom of Ala172 and the thermostablity of the, enzyme shows a good correlation with the hydrophobicity of the substituted, residues. Substitution of Ala172 by the 'longer' residues Leu or Phe, causes a rearrangement of the domain structure, which leads to a higher, thermostability of the enzymes than that expected from the hydrophobicity, of the substituted residues. Mutation of Ala172 to negatively charged, residues gave an unexpected result: the melting temperature of the Asp, mutant enzyme was reduced by 2.7 K while that of the Glu mutant increased, by 1.8 K. Molecular-modelling studies indicated that the glutamate side, chain was sufficiently long that it did not act as a buried charge as did, the aspartate, but instead protruded to the outside of the hydrophobic, cavity and contributed to the stability of the enzyme by enhancing the, packing of the local side chains and forming an extra salt bridge with the, side chain of Lys175.
About this Structure
1GC8 is a Single protein structure of sequence from Thermus thermophilus. Active as 3-isopropylmalate dehydrogenase, with EC number 1.1.1.85 Full crystallographic information is available from OCA.
Reference
Design, X-ray crystallography, molecular modelling and thermal stability studies of mutant enzymes at site 172 of 3-isopropylmalate dehydrogenase from Thermus thermophilus., Qu C, Akanuma S, Tanaka N, Moriyama H, Oshima T, Acta Crystallogr D Biol Crystallogr. 2001 Feb;57(Pt 2):225-32. PMID:11173468
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