Alteration of the fatty acid profile of Streptomyces coelicolor by replacement of the initiation enzyme 3-ketoacyl acyl carrier protein synthase III (FabH).
The first elongation step of fatty acid biosynthesis by a type II dissociated fatty acid synthases is catalyzed by 3-ketoacyl-acyl carrier protein (ACP) synthase III (KASIII, FabH). This enzyme, encoded by the fabH gene, catalyzes a decarboxylative condensation between an acyl coenzyme A (CoA) primer and malonyl-ACP. In organisms such as Escherichia coli, which generate only straight-chain fatty acids (SCFAs), FabH has a substrate preference for acetyl-CoA. In streptomycetes and other organisms which produce a mixture of both SCFAs and branched-chain fatty acids (BCFAs), FabH has been shown to utilize straight- and branched-chain acyl-CoA substrates. We report herein the generation of a Streptomyces coelicolor mutant (YL/ecFabH) in which the chromosomal copy of the fabH gene has been replaced and the essential process of fatty acid biosynthesis is initiated by plasmid-based expression of the E. coli FabH (bearing only 35% amino acid identity to the Streptomyces enzyme). The YL/ecFabH mutant produces predominantly SCFAs (86%). In contrast, BCFAs predominate (approximately 70%) in both the S. coelicolor parental strain and S. coelicolor YL/sgFabH (a deltafabH mutant carrying a plasmid expressing the Streptomyces glaucescens FabH). These results provide the first unequivocal evidence that the substrate specificity of FabH observed in vitro is a determinant of the fatty acid made in an organism. The YL/ecFabH strain grows significantly slower on both solid and liquid media. The levels of FabH activity in cell extracts of YL/ecFabH were also significantly lower than those in cell extracts of YL/sgFabH, suggesting that a decreased rate of fatty acid synthesis may account for the observed decreased growth rate. The production of low levels of BCFAs in YL/ecFabH suggests either that the E. coli FabH is more tolerant of different acyl-CoAs substrates than previously thought or that there is an additional pathway for initiation of BCFA biosynthesis in Streptomyces coelicolor.
Li
Yongli
Y
Department of Medicinal Chemistry and Institute of Structural Biology and Drug Discovery, School of Pharmacy, Virginia Commonwealth University, Richmond, Virginia 23219, USA.
Florova
Galina
G
Reynolds
Kevin A
KA
D015099:3-Oxoacyl-(Acyl-Carrier-Protein) Synthase / Q000235:genetics* / Q000378:metabolism*; D004926:Escherichia coli / Q000201:enzymology / Q000235:genetics; D005227:Fatty Acids / Q000096:biosynthesis* / Q000378:metabolism; D017353:Gene Deletion; D005818:Genetic Engineering; D016296:Mutagenesis; D010957:Plasmids; D048372:Streptomyces coelicolor / Q000201:enzymology* / Q000235:genetics* / Q000254:growth & development
D005227:Fatty Acids; C077402:3-ketoacyl-acyl carrier protein synthase III; D015099:3-Oxoacyl-(Acyl-Carrier-Protein) Synthase