Transcriptional Regulation by the Short-Chain Fatty Acyl Coenzyme A Regulator (ScfR) PccR Controls Propionyl Coenzyme A Assimilation by Rhodobacter sphaeroides

Abstract

Propionyl coenzyme A (propionyl-CoA Rhodobacter sphaeroides belongs to the purple nonsulfur bacteria, a physiologically related group of phototrophic bacteria known for their metabolic versatility (1). Given their natural abundance in anaerobic portions of stagnant water, purple nonsulfur bacteria are adept at using light as a source of energy during anaerobic growth while acquiring carbon from fermentation products, such as propionate. Despite the abundance of propionate in its natural environment, R. sphaeroides was originally classified uniquely among the purple nonsulfur bacteria to be unable to use propionate as a carbon source for growth (1). A recent edition of Bergey's Manual of Systematic Bacteriology, however, recognizes that the type strain, R. sphaeroides 2.4.1, does grow with propionate (2).As a growth substrate, propionate is directly activated to propionyl coenzyme A (propionyl-CoA). Propionyl-CoA is also an intermediate of pathways responsible for the degradation of endogenously derived or exogenously supplied branched-chain amino acids as well as branched-chain and odd-numbered-chain fatty acids (3-6). In addition, propionylCoA is formed during the metabolism of 3-hydroxypropionate and during acetyl-CoA assimilation via the ethylmalonyl-CoA pathway (see Fig. S1 in the supplemental material) (7,8). The ethylmalonyl-CoA pathway substitutes for the glyoxylate bypass in many bacteria and is required for replenishing intermediates of the citric acid cycle for growth with substrates that enter central carbon metabolism at the level of acetyl-CoA (9).Propionyl-CoA is an inhibitor of several key metabolic enzymes, and therefore, the metabolism of propionyl-CoA needs to

TetR Family Transcriptional Regulator PccD Negatively Controls Propionyl Coenzyme A Assimilation in Saccharopolyspora erythraea

“…The pccBC and pccA operons are induced by propanol and propionate in S. erythraea. It was reported that propionyl-CoA carboxylases were upregulated when propanol or propionate was added to microorganisms (18,19). Propanol is converted into propionate, which is subsequently metabolized to propionyl-phosphate or propionyl-CoA by propionate kinase or acetyl/propionyl-CoA synthetase (Fig.…”

“…The transcriptional regulation of the genes encoding enzymes of the PCC pathway in bacteria remains unknown. Recently, Carter and Alber found that RSP_2186 (designated PccR) controls the transcription of the propionyl-CoA carboxylase gene in Rhodobacter sphaeroides (19). They defined a novel family of short-chain fatty acyl-CoA regulators (ScfRs) that modulate pathways for short-chain acyl-CoA assimilation in microorganisms, including PccR (PCC pathway for propionyl-CoA assimilation), MccR (MCC for propionyl-CoA assimilation), RamB (glyoxylate bypass for acetyl-CoA assimilation), and IbcR (for isobutyryl-CoA assimilation) (19).…”

“…Recently, Carter and Alber found that RSP_2186 (designated PccR) controls the transcription of the propionyl-CoA carboxylase gene in Rhodobacter sphaeroides (19). They defined a novel family of short-chain fatty acyl-CoA regulators (ScfRs) that modulate pathways for short-chain acyl-CoA assimilation in microorganisms, including PccR (PCC pathway for propionyl-CoA assimilation), MccR (MCC for propionyl-CoA assimilation), RamB (glyoxylate bypass for acetyl-CoA assimilation), and IbcR (for isobutyryl-CoA assimilation) (19). ScfRs typically belong to the xenobiotic response element (XRE) family and have a helix-turn-helix N-terminal domain for DNA binding and a C-terminal domain of unknown function (DUF2083) as common features.…”

“…In this study, we found that the TetR/AcrR family transcriptional regulator PccD negatively controlled propionyl-CoA assimilation. S. erythraea PccD is a novel ScfR, as it does not belong to the XRE family regulator described by Carter and Alber (19).…”

PccD Regulates Branched-Chain Amino Acid Degradation and Exerts a Negative Effect on Erythromycin Production in Saccharopolyspora erythraea

“…For example, BkdR (21,23,26) takes part in regulating BCAA degradation. LrpG (33), PrpR (34), PccR (35), and PccD (29) participated in propionyl-CoA assimilation. In Mycobacterium, acetyl/propionyl-CoA carboxylase (accD1A1) and branched-chain ␣-keto acid dehydrogenase (bkdABC) exist in the same operon and are regulated by a regulator, BkaR, simultaneously (36).…”