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J. Biol. Chem., Vol. 279, Issue 52, 54573-54580, December 24, 2004

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Chemotaxis in Rhodobacter sphaeroides Requires an Atypical Histidine Protein Kinase^*

Steven L. Porter and Judith P. Armitage

From the Microbiology Unit, Department of Biochemistry, University of Oxford, South Parks Road, Oxford OX1 3QU, United Kingdom

Rhodobacter sphaeroides has a complex chemosensory system comprising two classic CheAs, two atypical CheAs, and eight response regulators (six CheYs and two CheBs). The classic CheAs, CheA₁ and CheA₂, have similar domain structures to Escherichia coli CheA, whereas the atypical CheAs, CheA₃ and CheA₄, lack some of the domains found in E. coli CheA. CheA₂, CheA₃, and CheA₄ are all essential for chemotaxis. Here we demonstrate that CheA₃ and CheA₄ are both unable to undergo ATP-dependent autophosphorylation, however, CheA₄ is able to phosphorylate CheA₃. The in vitro kinetics of this phosphorylation reaction were consistent with a reaction mechanism in which CheA₃ associates with a CheA₄ dimer forming a complex, CheA₃A₄. To the best of our knowledge, CheA₃A₄ is the first characterized histidine protein kinase where the subunits are encoded by distinct genes. Selective phosphotransfer was observed from CheA₃-P to the response regulators CheY₁, CheY₆, and CheB_2. Using phosphorylation site and kinase domain mutants of CheA we show that phosphosignaling involving CheA₂, CheA₃, and CheA₄ is essential for chemotaxis in R. sphaeroides. Interestingly, CheA₃ was not phosphorylated in vitro by CheA₁ or CheA₂, although CheA₁ and CheA₂ mutants with defective kinase domains were phosphorylated by CheA₄. Because in vivo CheA₃ and CheA₄ localize to the cytoplasmic chemotaxis cluster, while CheA₂ localizes to the polar chemotaxis cluster, it is likely that the physical separation of CheA₂ and CheA₄ prevents unwanted cross-talk between these CheAs.

Received for publication, August 3, 2004 , and in revised form, September 20, 2004.

^* This work was funded by the Oxford Bionanotechnology Interdisciplinary Research Consortium, the Biotechnology and Biological Sciences and Research Council, and a British Tar Products research fellowship from Pembroke College, Oxford. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

To whom correspondence should be addressed. Tel.: 44-1865-275-297; Fax: 44-1865-275-299; E-mail: armitage{at}bioch.ox.ac.uk.

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				S. L. Porter, M. A. J. Roberts, C. S. Manning, and J. P. Armitage A bifunctional kinase-phosphatase in bacterial chemotaxis PNAS, November 25, 2008; 105(47): 18531 - 18536. [Abstract] [Full Text] [PDF]

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