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ß-Ketoacyl acyl carrier protein reductase (FabG) activity of the fatty acid biosynthetic pathway is a determining factor of 3-oxo-homoserine lactone acyl chain lengths

Department of Microbiology, Immunology and Pathology, Colorado State University, Fort Collins, CO 80523-1682A, USA¹

Author for correspondence: Herbert P. Schweizer. Tel: +1 970 491 3536. Fax: +1 970 491 1815. e-mail: herbert.schweizer{at}colostate.edu

The two acyl-homoserine lactones (AHLs) N-(butyryl)-L-homoserine lactone and N-[3-oxododecanoyl]-L-homoserine lactone (3-oxo-C₁₂-HSL) are required for quorum sensing in Pseudomonas aeruginosa. These AHLs derive their invariant lactone rings from S-adenosylmethionine and their variable acyl chains from the cellular acyl-acyl carrier protein (ACP) pool. This reaction is catalysed by specific AHL synthases, which exhibit acyl chain specificity. Culture supernatants of P. aeruginosa contain multiple 3-oxo-AHLs that differ in their acyl chain lengths but their physiological role, if any, remains unknown. An in vitro fatty acid-3-oxo-AHL synthesis system was established utilizing purified P. aeruginosa Fab proteins, ACP and the LasI 3-oxo-AHL synthase. In the presence of excess protein, substrates and cofactors, this system produced almost exclusively 3-oxo-C₁₂-HSL. When the ß-ketoacyl-ACP reductase (FabG) catalysed step was made rate-limiting by switching from the preferred NADPH cofactor to NADH, increased levels of short chain 3-oxo-AHLs were produced, presumably because shorter-chain ketoacyl-ACPs accumulated and thus became LasI substrates. Consistent with these in vitro observations, a fabG(Ts) mutant produced increased amounts of 3-oxo-AHLs in vivo. Thus, in vitro and in vivo evidence indicated that modulation of FabG activity of the fatty acid biosynthetic pathway may determine the acyl chain lengths of these 3-oxo-AHLs and that the LasI 3-oxo-AHL synthase is sufficient for their synthesis.

Keywords: Pseudomonas, homoserine lactone, fatty acid synthesis, synthase

Abbreviations: ACP, acyl carrier protein; AHL, acyl homoserine lactone; C₄-HSL, N-(butyryl)-L-homoserine lactone; Fab, fatty acid biosynthesis; HSL, homoserine lactone; SAM, S-adenosyl methionine

^a Present address: Department of Microbiology, University of Hawaii at Manoa, Honolulu, HI 96822, USA.

^b Present address: VWR International, 106 Gray Road, Suite D, Indianapolis, IN 46237, USA.

^c Present address: National Jewish Hospital, 1400 Jackson Street, Denver, CO 80206, USA.

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