A Novel Role of the PrpR as a Transcription Factor Involved in the Regulation of Methylcitrate Pathway in Mycobacterium tuberculosis

Abstract

Mycobacterium tuberculosis, the pathogen that causes tuberculosis, presumably utilizes fatty acids as a major carbon source during infection within the host. Metabolism of even-chain-length fatty acids yields acetyl-CoA, whereas metabolism of odd-chain-length fatty acids additionally yields propionyl-CoA. Utilization of these compounds by tubercle bacilli requires functional glyoxylate and methylcitrate cycles, respectively. Enzymes involved in both pathways are essential for M. tuberculosis viability and persistence during growth on fatty acids. However, little is known about regulatory factors responsible for adjusting the expression of genes encoding these enzymes to particular growth conditions. Here, we characterized the novel role of PrpR as a transcription factor that is directly involved in regulating genes encoding the key enzymes of methylcitrate (methylcitrate dehydratase [PrpD] and methylcitrate synthase [PrpC]) and glyoxylate (isocitrate lyase [Icl1]) cycles. Using cell-free systems and intact cells, we demonstrated an interaction of PrpR protein with prpDC and icl1 promoter regions and identified a consensus sequence recognized by PrpR. Moreover, we showed that an M. tuberculosis prpR-deletion strain exhibits impaired growth in vitro on propionate as the sole carbon source. Real-time quantitative reverse transcription-polymerase chain reaction confirmed that PrpR acts as a transcriptional activator of prpDC and icl1 genes when propionate is the main carbon source. Similar results were also obtained for a non-pathogenic Mycobacterium smegmatis strain. Additionally, we found that ramB, a prpR paralog that controls the glyoxylate cycle, is negatively regulated by PrpR. Our data demonstrate that PrpR is essential for the utilization of odd-chain-length fatty acids by tubercle bacilli. Since PrpR also acts as a ramB repressor, our findings suggest that it plays a key role in regulating expression of enzymes involved in both glyoxylate and methylcitrate pathways.

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

“…It is worthwhile to note that the TTTGCAAA identified by Masiewicz et al (27) within the M. tuberculosis MccR binding site is more similar to the motif that we identified for PccR than to the motif represented in the logo for the putative MccR binding site in Fig. 5.…”

“…The analysis presented here replaces the PrpQ* nomenclature with the MccR and PccR classes. (27). Given that PrpR was the name given to the 54 -dependent regulator of the prp operon of enterobacteria (18,19), Masiewicz et al (27) used the same nomenclature for Rv1129c, despite its dissimilarity in amino acid sequence to PrpR.…”

“…The transcriptional regulator has been named LrpG (26), PrpR (27), and Rv1129c (28) in M. tuberculosis and PrpR in C. glutamicum (29). It is important to note that the transcriptional regulator from M. tuberculosis and the so-called PrpR regulator from C. glutamicum are unrelated to PrpRs described for enterobacteria like S. enterica.…”

“…The expression of both genes is activated by the transcriptional activator RamA (42), a LuxR-type regulator, and is repressed by RamB (30). A homolog of RamB also controls the transcription of genes required for propionyl-CoA assimilation via the methylcitrate cycle for C. glutamicum and M. tuberculosis (see above) (26)(27)(28)(29).…”

Intracellular Concentrations of 65 Species of Transcription Factors with Known Regulatory Functions in Escherichia coli

“…Two key regulators, pyrimidine utilization regulator (RutR) (51) and allantoin repressor (AllR) (52), which are involved in control of pyrimidine and purine degradation, respectively, are also abundant (see Table S1 in the supplemental material), presumably because nucleotides are degraded for reutilization as nitrogen sources under the culture conditions employed. An abundant protein, propionate regulator (PrpR), might also be involved in degradation and utilization of fatty acids (53).…”