The Enterococcus faecalis FabT Transcription Factor Regulates Fatty Acid Biosynthesis in Response to Exogeneous Fatty Acids

Abstract

The phospholipid acyl chains of Enterococcus faecalis can be derived either by de novo synthesis or by incorporation of exogenous fatty acids through the fatty acid kinase complex (Fak)-phosphate acyltransferase (PlsX) pathway. Exogenous fatty acids suppress fatty acid synthesis through the transcriptional repressor FabT, the loss of which eliminated regulation of de novo fatty acid biosynthesis and resulted in decreased incorporation of exogenous unsaturated fatty acids. Purified FabT bound to the promoters of several fatty acid synthesis genes that contain a specific palindromic sequence and binding was enhanced by acylated derivatives of acyl carrier protein B (acyl-AcpB). The loss of the PlsX pathway blocked FabT-dependent transcriptional repression in the presence of oleic acid. Transcriptional repression was partially retained in a E. faecalis ΔacpB strain which showed decreased fatty acid biosynthesis in the presence of exogenous unsaturated fatty acids. The FabT-dependent activity remaining in the ΔacpB strain indicates that acylated derivatives of AcpA were weak enhancers of FabT binding although AcpA is believed to primarily function in de novo fatty acid synthesis.

FabT, a Bacterial Transcriptional Repressor That Limits Futile Fatty Acid Biosynthesis

“…Consistent with the above observations, a recent report clarified that the role of AcpB in controlling FabT repression was minor, compared to earlier conclusions that the acpB mutant exerted a dominant effect on FabT repression; a secondary mutation in fabT was identified, which accounted for this revised explanation (14,36). In a reconstructed E. faecalis acpB deletion strain, addition of exogenous FA showed just partial repression of fabT promoter expression (36).…”

“…In a reconstructed E. faecalis acpB deletion strain, addition of exogenous FA showed just partial repression of fabT promoter expression (36). Also, and in contrast to the situation in S. pneumoniae, in E. faecalis, acyl-AcpA enhances FabT binding to the fabT promoter in vitro (32,36). This confirms that in E. faecalis, AcpA is also a FabT corepressor.…”

“…This suggested that chain length, and/or saturation status of the bound fatty acid might determine FabT-DNA binding affinity. In E. faecalis, FabT-mediated repression of FA synthesis is similarly exacerbated by C16:1 and C18:1 (cis-9), but less so in C18:1 (trans-9) and even less so in C16:0 (36). This argues in the favor of cis unsaturated FA maximizing FabT-DNA binding affinity.…”

“…Acyl-AcpB could additionally be a precursor for phospholipid synthesis that favors entry of exogenous fatty acids (14). Altogether, this suggested that AcpA is the main FASII enzyme needed for FA de novo synthesis, but may also regulate FASII repression in the presence of exogenous FA; AcpB which is encoded in the same operon as plsX and is nonessential, may only have a role in facilitating exogenous FA utilization for phospholipid synthesis (14,36). However, part of these conclusions were recently revised ((36); see below).…”

Unsaturated fatty acid synthesis in Enterococcus faecalis requires a specific enoyl‐ACP reductase

“…The E. faecalis deletion strain was constructed using the methods described before Zou et al, 2022) and the PCR F I G U R E 7 In vitro comparisons of FabN with FabA and of FabO with FabB. Lanes 1 and 2 are standards, lanes 3 and 4 compare the dehydration/isomerization activities of FabA (lane 3) and FabN (lane 4).…”