Escherichia coliS2P family intramembrane protease RseP is engaged in the regulated sequential cleavages of FecR in the ferric citrate signaling

Abstract

Escherichia coli RseP, a member of the S2P family of intramembrane proteases, is involved in the activation of the σE extracytoplasmic stress response and elimination of remnant signal peptides. However, whether RseP has additional cellular functions is unclear. In this study, we attempted to identify new RseP substrates to explore still unknown physiological roles of this protease. Our mass spectrometry-based quantitative proteomic analysis revealed that the levels of several Fec system proteins encoded by the fecABCDE operon (fec operon) were significantly decreased in an RseP-deficient strain. The Fec system is responsible for the uptake of ferric citrate, and the transcription of the fec operon is controlled by FecI, an alternative sigma factor, and its regulator FecR, a single-pass transmembrane protein. Assays with the fec operon expression reporter demonstrated that the proteolytic activity of RseP is essential for the ferric citrate-dependent upregulation of the fec operon. Analysis using the FecR protein and FecR-derived model proteins showed that FecR undergoes sequential processing at the membrane and that RseP participates in the last step of this sequential processing to generate the N-terminal cytoplasmic fragment of FecR that participates in the transcription of the fec operon with FecI. Ferric citrate signal-dependent generation of this cleavage product is the essential and sufficient role of RseP in the transcriptional activation of the fec operon. Our study unveiled that E. coli RseP performs the intramembrane proteolysis of FecR, a novel physiological role that is essential for regulating iron uptake by the ferric citrate transport system.

Transcription regulation of iron carrier transport genes by ECF sigma factors through signaling from the cell surface into the cytoplasm

“…In a recent study aimed at identifying additional cellular functions of the RseP protease, mass-spectrometry revealed lower levels of the FecA, FecB and FecD proteins in an inactive rseP point mutant relative to the levels in the rseP wild type (Yokoyama et al . 2021 ). In the rseP mutant, fecA-lacZ transcription was not elevated in response to FeCit, in contrast to the ten-fold higher induction of LacZ activity in the rseP wild-type.…”