The biochemical regulation of type II fatty acid synthesis (FASII) in bacteria is most completely studied in Escherichia coli[2–4]. The scheme that has emerged places the first committed step in membrane phospholipid synthesis, sn-glycerol-3-phosphate (glycerol-PO4) acyltransferase (PlsB), as a key regulatory point. How PlsB senses the requirement for new phospholipid is not completely understood, but one biochemical ISRIB datasheet regulator TPCA-1 order is ppGpp [5], a global regulator of gene expression [6]. The consequences of regulation at the PlsB step are relayed to FASII by long-chain acyl-acyl carrier protein (ACP), a crucial allosteric regulator of two steps in initiation. The importance of acyl-ACP was first recognized by

the expression of acyl-ACP thioesterases in E. coli, which leads to run-away FASII activity and the secretion of copious amounts of free fatty acids [7–9]. Long-chain acyl-ACPs act as potent feedback inhibitors of FASII by blocking the initiation of new acyl chains at the FabH step [10, 11] and slowing the elongation of acyl chains by inhibiting acetyl-CoA carboxylase [12]. It is not clear whether this regulatory model for membrane lipid homeostasis in E. coli can be extended SAHA to Gram-positive bacteria. Notably, these organisms do not have a PlsB acyltransferase, but rather

use a novel activated acyl donor, acyl-phosphate (acyl-PO4), produced by PlsX from the acyl-ACP end-products of FASII, and have a unique glycerol-PO4 acyltransferase, PlsY, which only uses acyl-PO4[13]. Precise control over fatty acid synthesis appears even more important for Gram-positive pathogens like S. aureus, because unlike E. coli, they lack a fatty acid catabolic Casein kinase 1 pathway [14]. Expression of the genes responsible for phosphatidic acid biosynthesis in Bacillus subtilis and S. aureus is controlled by FapR [15], which releases from its DNA

binding sites within the regulons multiple promoters when bound to malonyl-CoA [16, 17]. Although the transcriptional regulation of lipid synthesis is understood in considerable detail, much less is known about the biochemical regulation of FASII or the coupling of fatty acid and phospholipid synthesis. Glycerol-PO4 is the substrate for PlsY and a required precursor for membrane phospholipid synthesis, and is produced from dihydroxyacetone phosphate by glycerol-PO4 synthase (GpsA) [18]. Forty years ago Mindich [19] isolated a S. aureus glycerol auxotroph and demonstrated that phospholipid synthesis from [14C]acetate ceased abruptly following removal of the glycerol growth supplement, although free fatty acids continued to accumulate. Subsequent work revealed that the free fatty acids consisted primarily of 21-carbon branched-chain species that are longer than the normal 15–17 carbon fatty acids in normally growing cells [20]. Total protein synthesis continued following the removal of glycerol resulting in denser cells [20].