Cyclic-di-GMP binds to histidine kinase RavS to control RavS-RavR phosphotransfer and regulates the bacterial lifestyle transition between virulence and swimming.

Shou-Ting Cheng,Fang-Fang Wang,Wei Qian,Nian Wang

doi:10.1371/journal.ppat.1007952

Shou-Ting Cheng, Fang-Fang Wang + Show 2 more

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https://doi.org/10.1371/journal.ppat.1007952

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Abstract

The two-component signalling system (TCS) comprising a histidine kinase (HK) and a response regulator (RR) is the predominant bacterial sense-and-response machinery. Because bacterial cells usually encode a number of TCSs to adapt to various ecological niches, the specificity of a TCS is in the centre of regulation. Specificity of TCS is defined by the capability and velocity of phosphoryl transfer between a cognate HK and a RR. Here, we provide genetic, enzymology and structural data demonstrating that the second messenger cyclic-di-GMP physically and specifically binds to RavS, a HK of the phytopathogenic, gram-negative bacterium Xanthomonas campestris pv. campestris. The [c-di-GMP]-RavS interaction substantially promotes specificity between RavS and RavR, a GGDEF–EAL domain-containing RR, by reinforcing the kinetic preference of RavS to phosphorylate RavR. [c-di-GMP]-RavS binding effectively decreases the phosphorylation level of RavS and negatively regulates bacterial swimming. Intriguingly, the EAL domain of RavR counteracts the above regulation by degrading c-di-GMP and then increasing the level of phosphorylated RavS. Therefore, RavR acts as a bifunctional phosphate sink that finely controls the level of phosphorylated RavS. These biochemical processes interactively modulate the phosphoryl flux between RavS-RavR and bacterial lifestyle transition. Our results revealed that c-di-GMP acts as an allosteric effector to dynamically modulate specificity between HK and RR.

Highlights

The two-component signalling system (TCS) is one of the predominant molecular machineries used by almost all bacteria to monitor and adaptively respond to environmental cues [1, 2]
RavA does not contain a recognisable transmembrane helix, repeated experiments showed that RavA is located in both the membrane and cytoplasm (Fig 1B), which suggests that the histidine kinase (HK) has a membraneanchored peptide or that the protein contains an unrecognised transmembrane region
Together with the biochemical results demonstrating that c-di-GMP did not bind ravSR656A and that the phosphorylation level of RavSR656A is insensitive to c-di-GMP inhibition, these findings suggest that c-di-GMP associates with the Arg656 residue to negatively regulate the RavS phosphotransferase activity towards RavR

Summary

Introduction

The two-component signalling system (TCS) is one of the predominant molecular machineries used by almost all bacteria to monitor and adaptively respond to environmental cues [1, 2]. HK autophosphorylates an invariant histidine residue within its dimerization and histidine phosphotransfer (DHp) domain and catalyses the transfer of the phosphoryl group onto a conserved aspartic acid within the receiver (REC) domain of the cognate RR [3]. The activated RR modulates bacterial adaptation by controlling gene transcription or cellular behaviour [4, 5]. There is a high level of specificity between a HK and its cognate RR, which is quantified by the kinetic preference during phosphotransfer [6, 7]. Bacterial cells dynamically and elegantly regulate time, rhythm, space and flux of the phosphotransfer between the HK and RR to adapt to diverse ecological niches [8]. Hybrid-type HK-mediated phosphorelay, phosphatases, auxiliary proteins and small RNAs are involved in TCS regulation [9,10,11,12,13]

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