The stressosome complex regulates downstream effectors in response to environmental signals. In Bacillus subtilis, it activates the alternative sigma factor σ B, leading to the upregulation of the general stress regulon. Herein, we characterize a stressosome-regulated biochemical pathway in Moorella thermoacetica. We show that the presumed sensor, MtR, and the scaffold, MtS, form a pseudo-icosahedral structure like that observed in B. subtilis. The N-terminal domain of MtR is structurally homologous to B. subtilis RsbR, despite low sequence identity. The affinity of the switch kinase, MtT, for MtS decreases following MtS phosphorylation and not because of structural reorganization. Dephosphorylation of MtS by the PP2C type phosphatase MtX permits the switch kinase to rebind the stressosome to reset the response. We also show that MtT regulates cyclic di-GMP biosynthesis through inhibition of a GG(D/E)EF-type diguanylate cyclase, demonstrating that secondary messenger levels are regulated by the stressosome.
Bibliographical noteFunding Information:
This work was supported by grants from the BBSRC (BBG001553 and BBF001533). We would like to thank Dr. S. Ragsdale for the kind gift of M. thermoacetica genomic DNA and Dr. T. Schirmer for the kind gift of an expression plasmid containing E. coli ydeH . We thank the staff and beamline scientists at Diamond Light Source and the ESRF for their help with data collection and members of the Lewis laboratory for critical reading of the manuscript.