3s23

Publication Abstract from PubMed

OleA is a thiolase superfamily enzyme which has been shown to catalyze the condensation of two long-chain fatty-acyl-Coenzyme A (CoA) substrates. The enzyme is part of a larger gene cluster responsible for generating long-chain olefin products - a potential biofuel precursor. In thiolase superfamily enzymes, catalysis is achieved via a ping-pong mechanism. The first substrate forms a covalent intermediate with an active site cysteine which is followed by reaction with the second substrate. For OleA, this conjugation proceeds by a non-decarboxylative Claisen condensation. The OleA from Xanthomonas campestris has been crystallized and its structure solved, along with inhibitor bound and xenon derivatized structures, to better understand substrate positioning in the context of enzyme turnover. OleA is the first characterized thiolase superfamily member that has two long-chain alkyl substrates that need to be bound simultaneously, and therefore uniquely requires an additional alkyl binding channel. The location of the fatty acid biosynthesis inhibitor, cerulenin, that possesses an alkyl chain length in the range of known OleA substrates, in conjunction with a single xenon binding site, leads to the putative assignment of this novel alkyl binding channel. Structural overlays between the OleA homologs, 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) synthase and the fatty acid biosynthesis enzyme FabH, allow assignment of the remaining two channels; one for the thioester-containing pantetheinate arm and the second for the alkyl group of one substrate. A short beta-hairpin region is ordered in only one of the crystal forms and that may suggest open and closed states relevant for substrate binding. Cys143 is the conserved catalytic cysteine within the superfamily, and the site of alkylation by cerulenin. The alkylated structure suggests that a glutamic acid residue (Glu117beta) likely promotes Claisen condensation by acting as the catalytic base. Unexpectedly Glu117beta comes from the other monomer of the physiological dimer.

Crystal Structures of Xanthomonas Campestris OleA Reveal Features That Promote Head-to-Head Condensation of Two Long-Chain Fatty Acids.,Goblirsch BR, Frias JA, Wackett LP, Wilmot CM Biochemistry. 2012 Apr 23. PMID:22524624^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.