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Journal of Bacteriology, January 2007, p. 325-335, Vol. 189, No. 2
0021-9193/07/$08.00+0     doi:10.1128/JB.01326-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Phosphotransfer Reactions of the CbbRRS Three-Protein Two- Component System from Rhodopseudomonas palustris CGA010 Appear To Be Controlled by an Internal Molecular Switch on the Sensor Kinase{triangledown}

Simona Romagnoli and F. Robert Tabita*

Department of Microbiology, The Ohio State University, 484 West 12th Avenue, Columbus, Ohio 43210

Received 21 August 2006/ Accepted 17 October 2006

The CbbRRS system is an atypical three-protein two-component system that modulates the expression of the cbbI CO2 fixation operon of Rhodopseudomonas palustris, possibly in response to a redox signal. It consists of a membrane-bound hybrid sensor kinase, CbbSR, with a transmitter and receiver domain, and two response regulator proteins, CbbRR1 and CbbRR2. No detectable helix-turn-helix DNA binding domain is associated with either response regulator, but an HPt domain and a second receiver domain are predicted at the C-terminal region of CbbRR1 and CbbRR2, respectively. The abundance of conserved residues predicted to participate in a His-Asp phosphorelay raised the question of their de facto involvement. In this study, the role of the multiple receiver domains was elucidated in vitro by generating site-directed mutants of the putative conserved residues. Distinct phosphorylation patterns were obtained with two truncated versions of the hybrid sensor kinase, CbbSRT189 and CbbSRR96 (CbbSR beginning at residues T189 and R96, respectively). These constructs also exhibited substantially different affinities for ATP and phosphorylation stability, which was found to be dependent on a conserved Asp residue (Asp-696) within the kinase receiver domain. Asp-696 also played an important role in defining the specificity of phosphorylation for response regulators CbbRR1 or CbbRR2, and this residue appeared to act in conjunction with residues within the region from Arg-96 to Thr-189 at the N terminus of the sensor kinase. The net effect of concerted interactions at these distinct regions of CbbSR created an internal molecular switch that appears to coordinate a unique branched phosphorelay system.

* Corresponding author. Mailing address: Department of Microbiology, The Ohio State University, 484 West 12th Avenue, Columbus, OH 43210-1292. Phone: (614) 292-4297. Fax: (614) 292-6337. E-mail: tabita.1{at}osu.edu.

{triangledown} Published ahead of print on 27 October 2006.

Journal of Bacteriology, January 2007, p. 325-335, Vol. 189, No. 2
0021-9193/07/$08.00+0     doi:10.1128/JB.01326-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

  • Joshi, G. S., Romagnoli, S., VerBerkmoes, N. C., Hettich, R. L., Pelletier, D., Tabita, F. R. (2009). Differential Accumulation of Form I RubisCO in Rhodopseudomonas palustris CGA010 under Photoheterotrophic Growth Conditions with Reduced Carbon Sources. J. Bacteriol. 191: 4243-4250 [Abstract] [Full Text]  


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