2bz3

File:2bz3.gif

spinqualitylabelsall models 2bz3, resolution 2.00Å Show:Asymmetric Unit Biological Assembly Drag the structure with the mouse to rotate   Export Animated Image

STRUCTURE OF E. COLI KAS I H298E MUTANT IN COMPLEX WITH C12 FATTY ACID

OverviewOverview

Beta-ketoacyl-acyl carrier protein (ACP) synthase enzymes join short, carbon units to construct fatty acyl chains by a three-step Claisen, condensation reaction. The reaction starts with a trans thioesterification, of the acyl primer substrate from ACP to the enzyme. Subsequently, the, donor substrate malonyl-ACP is decarboxylated to form a carbanion, intermediate, which in the third step attacks C1 of the primer substrate, giving rise to an elongated acyl chain. A subgroup of beta-ketoacyl-ACP, synthases, including mitochondrial beta-ketoacyl-ACP synthase, bacterial, plus plastid beta-ketoacyl-ACP synthases I and II, and a domain of human, fatty acid synthase, have a Cys-His-His triad and also a completely, conserved Lys in the active site. To examine the role of these residues in, catalysis, H298Q, H298E and six K328 mutants of Escherichia, colibeta-ketoacyl-ACP synthase I were constructed and their ability to, carry out the trans thioesterification, decarboxylation and/or, condensation steps of the reaction was ascertained. The crystal structures, of wild-type and eight mutant enzymes with and/or without bound substrate, were determined. The H298E enzyme shows residual decarboxylase activity in, the pH range 6-8, whereas the H298Q enzyme appears to be completely, decarboxylation deficient, showing that H298 serves as a catalytic base in, the decarboxylation step. Lys328 has a dual role in catalysis: its charge, influences acyl transfer to the active site Cys, and the steric restraint, imposed on H333 is of critical importance for decarboxylation activity., This restraint makes H333 an obligate hydrogen bond donor at Nepsilon, directed only towards the active site and malonyl-ACP binding area in the, fatty acid complex.

About this StructureAbout this Structure

2BZ3 is a Single protein structure of sequence from Escherichia coli with NH4, SO4 and DAO as ligands. Active as Beta-ketoacyl-acyl-carrier-protein synthase I, with EC number 2.3.1.41 Structure known Active Site: AC1. Full crystallographic information is available from OCA.

ReferenceReference

Fatty acid synthesis. Role of active site histidines and lysine in Cys-His-His-type beta-ketoacyl-acyl carrier protein synthases., von Wettstein-Knowles P, Olsen JG, McGuire KA, Henriksen A, FEBS J. 2006 Feb;273(4):695-710. PMID:16441657

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