In Salmonella enterica, OatA (Formerly YjgM) Uses O-Acetyl-Serine and Acetyl-CoA to Synthesize N,O-Diacetylserine, Which Upregulates Cysteine Biosynthesis

L-Cysteine biosynthesis has been extensively analyzed in Salmonella enterica. The cysteine regulon contains the genes whose protein products are necessary to convert sulfate to sulfide, which is eventually reacted with O-acetyl-serine (OAS) to generate cysteine. The LysR type regulator, CysB, is required for activation of the cysteine regulon, and its interaction with various cys genes has been thoroughly characterized. Results from previous studies by others, suggested that OAS undergoes a spontaneous O- to N- migration to produce N-acetyl-serine (NAS), and that NAS is the true signal sensed by CysB. It was unclear, however, whether such migration occurred spontaneously in vivo or if NAS was generated enzymatically. Work reported herein characterizes a S. enterica N-acetyltransferase, OatA (formerly YjgM), which acetylates the Nα-amino group of OAS, producing N,O-diacetyl-serine (DAS) at the expense of acetyl-CoA. We isolated OatA to homogeneity and performed its initial biochemical characterization. The product of the OatA reaction was isolated by HPLC and confirmed by mass spectrometry to be DAS; OatA did not acetylate NAS, consistent with the conclusion that OatA is an N-acetyltransferase, not an O-acetyltransferase. Binding of OAS to OatA appears to be positively cooperative with the apparent K0.5 for OAS determined to be 0.74 mM, the kcat was 1.05 s-1, and the catalytic efficiency of the enzyme (kcat/K0.5) was 1.4 × 103 M-1 s-1. Size exclusion chromatography indicated that OatA was a monomer in solution. In S. enterica, overexpression of oatA led to shorter lag times on sulfate-limiting medium and that these delayed lag times were due to increased expression of the cysteine regulon, as indicated by RT-qPCR results. OatA is the first Gcn5-related N-acetyltransferase (aka GNAT) involved in the regulation of amino acid biosynthetic genes in Salmonella. On the basis of results of transcriptomics studies performed by other investigators, we hypothesize that DAS may play a role in biofilm formation in S. enterica and other bacteria

In Salmonella enterica, OatA (Formerly YjgM) Uses O-Acetyl-Serine and Acetyl-CoA to Synthesize N,O-Diacetylserine, Which Upregulates Cysteine Biosynthesis

L-Cysteine biosynthesis has been extensively analyzed in Salmonella enterica. The cysteine regulon contains the genes whose protein products are necessary to convert sulfate to sulfide, which is eventually reacted with O-acetyl-serine (OAS) to generate cysteine. The LysR type regulator, CysB, is required for activation of the cysteine regulon, and its interaction with various cys genes has been thoroughly characterized. Results from previous studies by others, suggested that OAS undergoes a spontaneous O- to N- migration to produce N-acetyl-serine (NAS), and that NAS is the true signal sensed by CysB. It was unclear, however, whether such migration occurred spontaneously in vivo or if NAS was generated enzymatically. Work reported herein characterizes a S. enterica N-acetyltransferase, OatA (formerly YjgM), which acetylates the N_α-amino group of OAS, producing N,O-diacetyl-serine (DAS) at the expense of acetyl-CoA. We isolated OatA to homogeneity and performed its initial biochemical characterization. The product of the OatA reaction was isolated by HPLC and confirmed by mass spectrometry to be DAS; OatA did not acetylate NAS, consistent with the conclusion that OatA is an N-acetyltransferase, not an O-acetyltransferase. Binding of OAS to OatA appears to be positively cooperative with the apparent K_(0.5) for OAS determined to be 0.74 mM, the k_(cat) was 1.05 s^(-1), and the catalytic efficiency of the enzyme (k_(cat)/K_(0.5)) was 1.4 × 10^3M^(-1) s^(-1). Size exclusion chromatography indicated that OatA was a monomer in solution. In S. enterica, overexpression of oatA led to shorter lag times on sulfate-limiting medium and that these delayed lag times were due to increased expression of the cysteine regulon, as indicated by RT-qPCR results. OatA is the first Gcn5-related N-acetyltransferase (aka GNAT) involved in the regulation of amino acid biosynthetic genes in Salmonella. On the basis of results of transcriptomics studies performed by other investigators, we hypothesize that DAS may play a role in biofilm formation in S. enterica and other bacteria

New AMP-forming acid:CoA ligases from Streptomyces lividans, some of which are posttranslationally regulated by reversible lysine acetylation

In nature, organic acids are a commonly used source of carbon and energy. Many bacteria use AMP‐forming acid:CoA ligases to convert organic acids into their corresponding acyl‐CoA derivatives, which can then enter metabolism. The soil environment contains a broad diversity of organic acids, so it is not surprising that bacteria such as Streptomyces lividans can activate many of the available organic acids. Our group has shown that the activity of many acid:CoA ligases is posttranslationally controlled by acylation of an active‐site lysine. In some cases, the modification is reversed by deacylases of different types. We identified eight new acid:CoA ligases in S. lividans TK24. Here, we report the range of organic acids that each of these enzymes can activate, and determined that two of the newly identified CoA ligases were under NAD⁺‐dependent sirtuin deacylase reversible lysine (de)acetylation control, four were not acetylated by two acetyltransferases used in this work, and two were acetylated but not deacetylated by sirtuin. This work provides insights into the broad organic‐acid metabolic capabilities of S. lividans, and sheds light into the control of the activities of CoA ligases involved in the activation of organic acids in this bacterium

Small-Molecule Acetylation Controls the Degradation of Benzoate and Photosynthesis in Rhodopseudomonas palustris

This work shows that the BadL protein of Rhodopseudomonas palustris has N-acetyltransferase activity and that this activity is required for the catabolism of benzoate under photosynthetic conditions in this bacterium. R. palustris occupies lignin-rich habitats, making its benzoate-degrading capability critical for the recycling of this important, energy-rich biopolymer. This work identifies the product of the BadL enzyme as acetamidobenzoates, which were needed to derepress genes encoding benzoate-degrading enzymes and proteins of the photosynthetic apparatus responsible for the generation of the proton motive force under anoxia in the presence of light. In short, acetamidobenzoates potentially coordinate the use of benzoate as a source of reducing power and carbon with the generation of a light-driven proton motive force that fuels ATP synthesis, motility, transport, and many other processes in the metabolically versatile bacterium R. palustris.The degradation of lignin-derived aromatic compounds such as benzoate has been extensively studied in Rhodopseudomonas palustris, and the chemistry underpinning the conversion of benzoate to acetyl coenzyme A (acetyl-CoA) is well understood. Here we characterize the last unknown gene, badL, of the bad (benzoic acid degradation) cluster. BadL function is required for growth under photoheterotrophic conditions with benzoate as the organic carbon source (i.e., light plus anoxia). On the basis of bioinformatics and in vivo and in vitro data, we show that BadL, a Gcn5-related N-acetyltransferase (GNAT) (PF00583), acetylates aminobenzoates to yield acetamidobenzoates. The latter relieved repression of the badDEFGAB operon by binding to BadM, triggering the synthesis of enzymes that activate and dearomatize the benzene ring. We also show that acetamidobenzoates are required for the expression of genes encoding the photosynthetic reaction center light-harvesting complexes through a BadM-independent mechanism. The effect of acetamidobenzoates on pigment synthesis is new and different than their effect on the catabolism of benzoate