Regulation of σ factors by conserved partner switches controlled by divergent signalling systems

Abstract

Partner-Switching Systems (PSS) are widespread regulatory systems, each comprising a kinase-anti-σ, a phosphorylatable anti-σ antagonist and a phosphatase module. The anti-σ domain quickly sequesters or delivers the target σ factor according to the phosphorylation state of the anti-σ antagonist induced by environmental signals. The PSS components are proteins alone or merged to other domains probably to adapt to the input signals. PSS are involved in major cellular processes including stress response, sporulation, biofilm formation and pathogenesis. Surprisingly, the target σ factors are often unknown and the sensing modules acting upstream from the PSS diverge according to the bacterial species. Indeed, they belong to either two-component systems or complex pathways as the stressosome or Chemosensory Systems (CS). Based on a phylogenetic analysis, we propose that the sensing module in Gram-negative bacteria is often a CS.

The Partner Switching System of the SigF Sigma Factor in Mycobacterium smegmatis and Induction of the SigF Regulon Under Respiration-Inhibitory Conditions

“…Western blotting analysis revealed that the WT and mutant forms of RsfB were expressed at similar levels in the M. smegmatis strains used in the experiment. These results suggest the followings: (i) unphosphorylated RsfB is the active form of RsfB as an anti-SigF antagonist, (ii) phosphorylation of RsfB on Ser-63 decreases the functionality of RsfB as in the RsfB homologs such as RsbV and SpoIIAA of B. subtilis (Bouillet et al, 2018), (iii) Thr-32 is important for anti-SigF antagonist activity of RsfB.…”

“…SigF belongs to group III sigma factors and is dispensable for growth of M. tuberculosis and M. smegmatis (Chen et al, 2000;Williams et al, 2007;Provvedi et al, 2008;Singh et al, 2015). SigF is phylogenetically and functionally in close relation to the well-studied stress sigma factor SigB in Bacillus species (DeMaio et al, 1996(DeMaio et al, , 1997Hecker and Volker, 2001;Hecker et al, 2007;Bouillet et al, 2018).…”

“…The functionality of SigF is regulated by the so-called partner switching system (PSS) including its cognate anti-sigma factor (anti-SigF) and anti-anti-sigma factors (anti-SigF antagonists) (Figure 1; DeMaio et al, 1997;Singh et al, 2015;Bouillet et al, 2018). Under non-stress (SigF-non-activating) conditions, SigF is held in an inactive state in complex with the anti-SigF (RsbW or UsfX).…”

Control of pellicle biogenesis involves the diguanylate cyclases PdgA and PdgB, the c‐di‐GMP binding protein MxdA and the chemotaxis response regulator CheY3 in Shewanella oneidensis

“…The two other Che systems of S. oneidensis are not involved in chemotaxis control. Indeed, one is probably non‐functional due to an IS insertion in the corresponding cheA gene (Che2), while the other controls a partner‐switch system involved in σ S sequestration/release (Che1) (Armitano et al ., ; Bouillet et al ., , ).…”

A partner‐switching system controls activation of mixed‐linkage β‐glucan synthesis by c‐di‐GMP in Sinorhizobium meliloti

“…PSS that regulate other traits have been described in diverse bacteria, such as biofilm formation in Vibrio fischeri (Morris and Visick, 2010), type III secretion system in Bordetella (Mattoo et al, 2004), biofilm formation and motility in Pseudomonas aeruginosa (Bordi et al, 2010;Bhuwan et al, 2012) or hormogonium development in Nostoc punctiforme (Riley et al, 2018). Proteins containing specific domains are shared by all these systems: a C-terminal phosphatase 2C (PP2C phosphatase) like in RsbU, an ATPase/kinase domain (GHKL domain) like in RsbW and a sulfate transporter and anti-sigma factor antagonist (STAS) domain protein like in RsbV (Sharma et al, 2011;Bouillet et al, 2018). In some cases like in V. fischeri and Bordetella, the target proteins of the PSS are not yet identified (Kozak et al, 2005;Thompson and Visick, 2015).…”