1csh
From Proteopedia
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A VERY SHORT HYDROGEN BOND PROVIDES ONLY MODERATE STABILIZATION OF AN ENZYME: INHIBITOR COMPLEX OF CITRATE SYNTHASE
Overview
Two extremely potent inhibitors of citrate synthase, carboxyl and primary, amide analogues of acetyl coenzyme A, have been synthesized. The ternary, complexes of these inhibitors with oxaloacetate and citrate synthase have, been crystallized and their structures analyzed at 1.70- and 1.65-A, resolution, respectively. The inhibitors have dissociation constants in, the nanomolar range, with the carboxyl analogue binding more tightly (Ki =, 1.6 nM at pH 6.0) than the amide analogue (28 nM), despite the unfavorable, requirement for proton uptake by the former. The carboxyl group forms a, shorter hydrogen bond with the catalytic Asp 375 (distance < 2.4 A) than, does the amide group (distance approximately 2.5 A). Particularly with the, carboxylate inhibitor, the very short hydrogen bond distances measured, suggest a low barrier or short strong hydrogen bond. However, the binding, constants differ by only a factor of 20 at pH 6.0, corresponding to an, increase in binding energy for the carboxyl analogue on the enzyme of, about 2 kcal/mol more than the amide analogue, much less than has been, proposed for short strong hydrogen bonds based on gas phase measurements, [> 20 kcal/mol (Gerlt & Gassman, 1993a,b)]. The inhibitor complexes, support proposals that Asp 375 and His 274 work in concert to form an, enolized form of acetyl-coenzyme A as the first step in the reaction.
About this Structure
1CSH is a Single protein structure of sequence from Gallus gallus with OAA and AMX as ligands. Active as Citrate (Si)-synthase, with EC number 2.3.3.1 Full crystallographic information is available from OCA.
Reference
A very short hydrogen bond provides only moderate stabilization of an enzyme-inhibitor complex of citrate synthase., Usher KC, Remington SJ, Martin DP, Drueckhammer DG, Biochemistry. 1994 Jun 28;33(25):7753-9. PMID:8011640
Page seeded by OCA on Tue Nov 20 12:43:23 2007
