IraM Remodels the RssB Segmented Helical Linker to Stabilize σ^sagainst Degradation by ClpXP

Abstract

Upon Mg2+starvation, a condition often associated with virulence, enterobacteria inhibit the ClpXP-dependent proteolysis of the master transcriptional regulator, σs, via IraM, a poorly understood anti-adaptor that prevents RssB-dependent loading of σsonto ClpXP. This inhibition results in σsaccumulation, and expression of stress resistance genes. Here we report on the structural analysis of RssB bound to IraM, which reveals that IraM induces two folding transitions within RssB, which are amplified via a segmental helical linker. This work highlights the remarkable structural plasticity of RssB and reveals how a stress-specific RssB antagonist modulates a core stress response pathway that could be leveraged to control biofilm formation, virulence, and the development of antibiotic resistance.

A General Mechanism for the General Stress Response in Bacteria

“…The C-terminal pseudo-phosphatase domain of RssB is joined to its N-terminal σ S binding response-receiver domain by a predominantly α-helical linker (termed the segmented helical linker, or SHL) of similar length to the linker of RsbU (Dorich et al 2019). The SHL folds to occlude the σ S interacting face of the response-receiver domain when bound to anti-adapters or when the response-receiver domain is phosphorylated (Brugger, Schwartz, et al 2023;Brugger, Srirangam, et al 2023;Dorich et al 2019). Supporting the hypothesis that the SHL is mechanistically related to the RsbU linker, substitution of W143, the homologous residue to Q94 of B. subtilis RsbU, blocks regulation by IraD and IraP (Battesti et al 2013).…”

“…Our findings reveal that E. coli RssB and B. subtilis RsbU use three shared regulatory features to control GSR activation through their distinct downstream mechanisms. First, the positioning of analogous flexible linkers controls GSR activation by RssB and RsbU (Brugger, Schwartz, et al 2023;Brugger, Srirangam, et al 2023;Dorich et al 2019). The C-terminal pseudo-phosphatase domain of RssB is joined to its N-terminal σ S binding response-receiver domain by a predominantly α-helical linker (termed the segmented helical linker, or SHL) of similar length to the linker of RsbU (Dorich et al 2019).…”