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PROTEIN STRUCTURE REPORT

Crystal structures of RsbQ, a stress-response regulator in Bacillus subtilis

Department of Life Science, Graduate School of Bioscience and Biotechnology, Tokyo Institute of Technology, Midori-ku, Yokohama 226-8501, Japan

(RECEIVED October 7, 2004; FINAL REVISION October 7, 2004; ACCEPTED October 8, 2004)

Growth-limiting stresses in bacteria induce the general stress response to protect the cells against future stresses. Energy stress caused by starvation conditions in Bacillus subtilis is transmitted to the ^B transcription factor by stress-response regulators. RsbP, a positive regulator, is a phosphatase containing a PAS (Per-ARNT-Sim) domain and requires catalytic function of a putative / hydrolase, RsbQ, to be activated. These two proteins have been found to interact with each other. We determined the crystal structures of RsbQ in native and inhibitor-bound forms to investigate why RsbP requires RsbQ. These structures confirm that RsbQ belongs to the / hydrolase superfamily. Since the catalytic triad is buried inside the molecule due to the closed conformation, the active site is constructed as a hydrophobic cavity that is nearly isolated from the solvent. This suggests that RsbQ has specificity for a hydrophobic small compound rather than a macromolecule such as RsbP. Moreover, structural comparison with other / hydrolases demonstrates that a unique loop region of RsbQ is a likely candidate for the interaction site with RsbP, and the interaction might be responsible for product release by operating the hydrophobic gate equipped between the cavity and the solvent. Our results support the possibility that RsbQ provides a cofactor molecule for the mature functionality of RsbP.

Keywords: / hydrolase superfamily; energy stress; stress response; factor; PAS domain; cavity; phenylmethanesulfonyl fluoride (PMSF); catalytic triad

Abbreviations: PAS domain, Per-ARNT-Sim domain • PMSF, phenyl-methanesulfonyl fluoride • FMN, flavin mononucleotide • FAD, flavin adenine dinucleotide

Article published online ahead of print. Article and publication date are at http://www.proteinscience.org/cgi/doi/10.1110/ps.041170005.

Reprint requests to: Takashi Kumasaka, Tokyo Institute of Technology, 4259 Nagatsuta-cho, Midori-ku, Yokohama 226-8501, Japan; e-mail: tkumasak{at}bio.titech.ac.jp; fax: +81-45-924-5707.

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