Regulation of Chlamydia RsbU phosphatase activity by the enolase product, phosphoenolpyruvate

The intracellular pathogen Chlamydia temporally regulates the expression of its genes but the upstream signals that control transcription are not known. The best studied regulatory pathway is a partner switching mechanism that involves an anti-sigma factor RsbW, which inhibits transcription by binding and sequestering the sigma subunit of RNA polymerase. RsbW is itself regulated by an anti-anti-sigma factor RsbV whose phosyphorylation state is controlled by the phosphatase RsbU. In this study, we showed that Chlamydia trachomatis RsbU requires manganese or magnesium as a cofactor and dephosphorylates RsbV1 and RsbV2, which are the two chlamydial paralogs of RsbV. The gene for RsbU is adjacent to the enolase gene in a number of Chlamydia genomes, and we showed that eno and rsbU are co-transcribed from the same operon. In other bacteria, there is no known functional connection between the Rsb pathway and enolase, which is an enzyme in the glycolytic pathway. We found, however, that Chlamydia RsbU phosphatase activity was inhibited by phosphoenolpyruvate (PEP), the product of the enolase reaction, but not by 2-phosphoglycerate (2PGA), which is the substrate. These findings suggest that the enolase reaction, and more generally glucose metabolism, may provide an upstream signal that regulates transcription in Chlamydia through the RsbW pathway. IMPORTANCEThe RsbW pathway is a phosphorelay that regulates gene expression in Chlamydia but its upsteam signal has not been identified. We showed that RsbU, a phosphatase in this pathway is inhibited by phosphoenolpyruvate, which is the product of the enolase reaction. As enolase is an enzyme in the glycolytic pathway, these results reveal an unrecognized link between glucose metabolism and gene regulation in chlamydiae. Moreover, as these intracellular bacteria acquire gluose from the infected host cell, our findings suggest that glucose availability may be an external signal that controls chlamydial gene expression.