Journal of Biological Chemistry
Volume 279, Issue 39, 24 September 2004, Pages 40927-40937
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Protein Structure and Folding
Functional and Structural Characterization of RsbU, a Stress Signaling Protein Phosphatase 2C*

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RsbU is a positive regulator of the activity of σB, the general stress-response σ factor of Gram+ microorganisms. The N-terminal domain of this protein has no significant sequence homology with proteins of known function, whereas the C-terminal domain is similar to the catalytic domains of PP2C-type phosphatases. The phosphatase activity of RsbU is stimulated greatly during the response to stress by associating with a kinase, RsbT. This association leads to the induction of σB activity. Here we present data on the activation process and demonstrate in vivo that truncations in the N-terminal region of RsbU are deleterious for the activation of RsbU. This conclusion is supported by comparisons of the phosphatase activities of full-length and a truncated form of RsbU in vitro. Our determination of the crystal structure of the N-terminal domain of RsbU from Bacillus subtilis reveals structural similarities to the regulatory domains from ubiquitous protein phosphatases and a conserved domain of σ-factors, illuminating the activation processes of phosphatases and the evolution of “partner switching.” Finally, the molecular basis of kinase recruitment by the RsbU phosphatase is discussed by comparing RsbU sequences from bacteria that either possess or lack RsbT.

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The atomic coordinates and structure factors (code 1W53) have been deposited in the Protein Data Bank, Research Collaboratory for Structural Bioinformatics, Rutgers University, New Brunswick, NJ (http://www.rcsb.org/).

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This work was supported by a research grant (to M. D. Y.) and a studentship award (to R. J. L.) from the Biotechnology and Biological Sciences Research Council, a Wellcome Trust Research Career Development Fellowship (to R. J. L.), “headroom” funds from the University of Newcastle (to R. J. L.), and grants from the Max-Planck-Society and the Deutsche Forschungsgemeinschaft (to U. V.) for research in the Laboratory for Functional Genomics. 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.

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Current address: Institute of Cell and Molecular Biosciences, Faculty of Medical Sciences, University of Newcastle, Newcastle upon Tyne, NE2 4HH, United Kingdom.

Current address: National Institute for Medical Research, Protein Structure, The Ridgeway, Mill Hill, London NW7 1AA, United Kingdom.

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Current address: Institute for Cytobiology, Philipps-University, D-35037 Marburg, Germany.