Laboratoire des Systèmes Macromoléculaires et Signalisation

Bacteria use complex transporters to secrete functionally relevant proteins to the extracellular medium. The type 2 secretion system (T2SS) translocates folded proteins involved in bacterial nutrient acquisition, virulence and adaptation. The T2SS pseudopilus is a periplasmic filament, assembled by the polymerization of PulG subunits, the major pseudopilin. Pseudopilin proteins have a conserved N-terminal hydrophobic segment followed by a more variable C-terminal periplasmic and globular domain. To better understand the mechanism of assembly and function of the T2SS, we have been studying the structure and dynamics of PulG by NMR, as well as its interaction with other components of the secretion machinery. As a first step on this study, here we reported the chemical shift assignments of PulG C-terminal domain and its secondary structure prediction based on NMR data.

The general stress response in Enterobacteria, like Escherichia coli or Salmonella, is controlled by the transcription factor σ(S), encoded by the rpoS gene, which accumulates during stationary phase growth and associates with the core RNA polymerase enzyme (E) to promote transcription of genes involved in cell survival. Tight regulation of σ(S) is essential to preserve the balance between self-preservation under stress conditions and nutritional competence in the absence of stress. Whereas σ factors are generally inactivated upon interaction with anti-sigma proteins, σ(S) binding by the Crl protein facilitates the formation of the holoenzyme Eσ(S), and therefore σ(S)-controlled transcription. Previously, critical residues in both Crl and σ(S) were identified and assigned to the binding interface in the Crl-σ(S) complex. However, high-resolution structural data are missing to fully understand the molecular mechanisms underlying σ(S) activation by Crl, in particular the possible role of Crl in triggering domain rearrangements in the multi-domain protein σ(S). Here we provide the (1)H, (13)C and (15)N resonance assignments of Salmonella enterica serovar Typhimurium Crl, as a starting point for CrlSTM structure determination and further structural investigation of the CrlSTM-σ STM (S) complex.