A Single-Domain Response Regulator Functions as an Integrating Hub To Coordinate General Stress Response and...

Area of Science:

• Microbiology
• Molecular Biology
• Bacterial Physiology

Background:

• The alphaproteobacterial general stress response relies on a conserved partner-switching mechanism initiated by PhyR phosphorylation.
• In Caulobacter crescentus, the histidine kinase PhyK was proposed to phosphorylate PhyR, but direct biochemical evidence was lacking.
• Two-component systems (TCSs) are crucial for bacterial signal transduction, generally considered insulated to prevent cross-talk.

Purpose of the Study:

• To elucidate the precise role of PhyK in the Caulobacter crescentus general stress response.
• To identify novel regulators involved in the stress response pathway.
• To investigate the phosphorylation network coordinating stress response with other cellular behaviors.

Main Methods:

• Identification and characterization of the response regulator MrrA.
• Biochemical assays to determine phosphorylation transfer between MrrA, PhyK, PhyR, and LovK.
• Phenotypic analysis of an mrrA mutant, including stress response activation and attachment assays.

Main Results:

• MrrA, a single-domain response regulator, is essential for activating the general stress response in C. crescentus.
• PhyK functions as a histidine phosphotransferase, accepting phosphate from MrrA and transferring it to PhyR, not as a direct kinase.
• MrrA acts as a promiscuous phosphorylation hub, interacting with multiple histidine kinases and redirecting phosphate flux, notably to LovK, influencing holdfast production.

Conclusions:

• MrrA serves as a central phosphorylation hub, integrating the general stress response with C. crescentus development and adaptive behaviors.
• The identified phosphorylation network challenges the notion of strictly insulated two-component systems, proposing a 'bow-tie' architecture for evolvability.
• FATGUY-type response regulators like MrrA likely evolved in alphaproteobacteria to broadly sample information and coordinate diverse cellular functions.