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2vsu
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Revision as of 06:17, 28 May 2008
A TERNARY COMPLEX OF HYDROXYCINNAMOYL-COA HYDRATASE-LYASE (HCHL) WITH ACETYL-COENZYME A AND VANILLIN GIVES INSIGHTS INTO SUBSTRATE SPECIFICITY AND MECHANISM.
Overview
Hydroxycinnamoyl-CoA Hydratase-Lyase (HCHL) catalyses the biotransformation of feruloyl-CoA to acetyl-CoA and the important flavour-fragrance compound vanillin (4-hydroxy 3-methoxybenzaldehyde) and is exploited in whole-cell systems for the bioconversion of ferulic acid to natural-equivalent vanillin. The reaction catalysed by HCHL has been thought to proceed by a two-step process involving first the hydration of the double bond of feruloyl-CoA, then the cleavage of the resultant beta-hydroxy thioester by retro-aldol reaction to yield the products. Kinetic analysis of active site residues identified using the crystal structure of HCHL revealed that whilst Glu-143 was essential for activity, Ser-123 played no major role in catalysis. However, mutation of Tyr-239 to Phe greatly increased the KM for the substrate ferulic acid, fulfilling its anticipated role as a factor in substrate binding. Structures of wild-type HCHL and of the Ser123Ala mutant, each of which had been co-crystallised with feruloyl-CoA, reveal a subtle helix movement upon ligand binding, the consequence of which is to bring the phenolic hydroxyl of Tyr-239 into close proximity with Tyr-75 from a neighbouring subunit in order to bind the phenolic hydroxyl of the product vanillin, for which electron density was observed. The active site residues of ligand-bound HCHL display a remarkable three-dimensional overlap with those of a structurally unrelated enzyme, vanillyl alcohol oxidase, that also recognises para-hydroxylated aromatic substrates related to vanillin. The data both explain the observed substrate specificity of HCHL for para-hydroxylated cinnamate derivatives and illustrate a remarkable convergence of the molecular determinants of ligand recognition between two otherwise unrelated enzymes.
About this Structure
2VSU is a Single protein structure of sequence from Pseudomonas fluorescens. Full crystallographic information is available from OCA.
Reference
A ternary complex of Hydroxycinnamoyl-CoA Hydratase-Lyase (HCHL) with acetyl-Coenzyme A and vanillin gives insights into substrate specificity and mechanism., Bennett JP, Bertin L, Moulton B, Fairlamb IJ, Brzozowski AM, Walton NJ, Grogan G, Biochem J. 2008 May 14;. PMID:18479250 Page seeded by OCA on Wed May 28 09:17:01 2008
