7tim
From Proteopedia
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STRUCTURE OF THE TRIOSEPHOSPHATE ISOMERASE-PHOSPHOGLYCOLOHYDROXAMATE COMPLEX: AN ANALOGUE OF THE INTERMEDIATE ON THE REACTION PATHWAY
Overview
The glycolytic enzyme triosephosphate isomerase (TIM) catalyzes the, interconversion of the three-carbon sugars dihydroxyacetone phosphate, (DHAP) and D-glyceraldehyde 3-phosphate (GAP) at a rate limited by the, diffusion of substrate to the enzyme. We have solved the three-dimensional, structure of TIM complexed with a reactive intermediate analogue, phosphoglycolohydroxamate (PGH), at 1.9-A resolution and have refined the, structure to an R-factor of 18%. Analysis of the refined structure reveals, the geometry of the active-site residues and the interactions they make, with the inhibitor and, by analogy, the substrates. The structure is, consistent with an acid-base mechanism in which the carboxylate of Glu-165, abstracts a proton from carbon while His-95 donates a proton to oxygen to, form an enediol (or enediolate) intermediate. The conformation of the, bound substrate stereoelectronically favors proton transfer from substrate, carbon to the syn orbital of Glu-165. The crystal structure suggests that, His-95 is neutral rather than cationic in the ground state and therefore, would have to function as an imidazole acid instead of the usual, imidazolium. Lys-12 is oriented so as to polarize the substrate oxygens by, hydrogen bonding and/or electrostatic interaction, providing stabilization, for the charged transition state. Asn-10 may play a similar role.
About this Structure
7TIM is a Single protein structure of sequence from Saccharomyces cerevisiae with PGH as ligand. Active as Triose-phosphate isomerase, with EC number 5.3.1.1 Full crystallographic information is available from OCA.
Reference
Structure of the triosephosphate isomerase-phosphoglycolohydroxamate complex: an analogue of the intermediate on the reaction pathway., Davenport RC, Bash PA, Seaton BA, Karplus M, Petsko GA, Ringe D, Biochemistry. 1991 Jun 18;30(24):5821-6. PMID:2043623
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