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General Stress Signaling in the Alphaproteobacteria.

ABSTRACT: The Alphaproteobacteria uniquely integrate features of two-component signal transduction and alternative ? factor regulation to control transcription of genes that ensure growth and survival across a range of stress conditions. Research over the past decade has led to the discovery of the key molecular players of this general stress response (GSR) system, including the sigma factor ?(EcfG), its anti-? factor NepR, and the anti-anti-? factor PhyR. The central molecular event of GSR activation entails aspartyl phosphorylation of PhyR, which promotes its binding to NepR and thereby releases ?(EcfG) to associate with RNAP and direct transcription. Recent studies are providing a new understanding of complex, multilayered sensory networks that activate and repress this central protein partner switch. This review synthesizes our structural and functional understanding of the core GSR regulatory proteins and highlights emerging data that are defining the systems that regulate GSR transcription in a variety of species.

SUBMITTER: Fiebig A

PROVIDER: S-EPMC4710059 | biostudies-literature | 2015

REPOSITORIES: biostudies-literature

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General Stress Signaling in the Alphaproteobacteria.

Fiebig Aretha A Herrou Julien J Willett Jonathan J Crosson Sean S

Annual review of genetics 20151005

The Alphaproteobacteria uniquely integrate features of two-component signal transduction and alternative σ factor regulation to control transcription of genes that ensure growth and survival across a range of stress conditions. Research over the past decade has led to the discovery of the key molecular players of this general stress response (GSR) system, including the sigma factor σ(EcfG), its anti-σ factor NepR, and the anti-anti-σ factor PhyR. The central molecular event of GSR activation ent ...[more]

PMID: 26442844

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Complex two-component signaling regulates the general stress response in Alphaproteobacteria.

Project description:The general stress response (GSR) in Alphaproteobacteria was recently shown to be controlled by a partner-switching mechanism that is triggered by phosphorylation of the response regulator PhyR. Activation of PhyR ultimately results in release of the alternative extracytoplasmic function sigma factor ?(EcfG), which redirects transcription toward the GSR. Little is known about the signal transduction pathway(s) controlling PhyR phosphorylation. Here, we identified the single-domain response regulator (SDRR) SdrG and seven histidine kinases, PakA to PakG, belonging to the HWE/HisKA2 family as positive modulators of the GSR in Sphingomonas melonis Fr1. Phenotypic analyses, epistasis experiments, and in vitro phosphorylation assays indicate that Paks directly phosphorylate PhyR and SdrG, and that SdrG acts upstream of or in concert with PhyR, modulating its activity in a nonlinear pathway. Furthermore, we found that additional SDRRs negatively affect the GSR in a way that strictly requires PhyR and SdrG. Finally, analysis of GSR activation by thermal, osmotic, and oxidative stress indicates that Paks display different degrees of redundancy and that a specific kinase can sense multiple stresses, suggesting that the GSR senses a particular condition as a combination of, rather than individual, molecular cues. This study thus establishes the alphaproteobacterial GSR as a complex and interlinked network of two-component systems, in which multiple histidine kinases converge to PhyR, the phosphorylation of which is, in addition, subject to regulation by several SDRRs. Our finding that most HWE/HisKA2 kinases contribute to the GSR in S. melonis Fr1 opens the possibility that this notion might also be true for other Alphaproteobacteria.

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