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1pb3
From Proteopedia
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Sites of binding and orientation in a four location model for protein stereospecificity.
Overview
The stereospecificity of the enzyme isocitrate dehydrogenase was examined, by steady-state kinetics and x-ray crystallography. The enzyme has the, intriguing property that the apoenzyme in the absence of divalent metal, showed a selectivity for the inactive l-enantiomer of the substrate, isocitrate, whereas the enzyme containing magnesium showed selectivity for, the physiologically active d-enantiomer. The hydrogen atom on the C2, carbon that is transferred during the reaction was, in both the d- and, l-isocitrate complexes, in an orientation very close to that expected for, delivery of a hydride ion to the cosubstrate NADP+. The beta-carboxylate, that is eliminated as a CO2 molecule during the reaction occupied the same, site on the protein in both the d- and l-isocitrate complexes. In, addition, the C3 carbon was in the same protein site in both the d- and, l-enantiomers. Only the fourth group, the OH atom, was in a very different, position in the apo enzyme and in the metal-containing complexes. A, four-location model is necessary to explain the enantiomeric specificity, of IDH in contrast to the conventional three-point attachment model. The, thermodynamic and kinetic ramifications of this model are explored.
About this Structure
1PB3 is a Single protein structure of sequence from Escherichia coli with SO4 and GOL as ligands. Active as Isocitrate dehydrogenase (NADP(+)), with EC number 1.1.1.42 Full crystallographic information is available from OCA.
Reference
Sites of binding and orientation in a four-location model for protein stereospecificity., Mesecar AD, Koshland DE Jr, IUBMB Life. 2000 May;49(5):457-66. PMID:10902579
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