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J. Biol. Chem., Vol. 283, Issue 22, 15287-15299, May 30, 2008

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Evidence That the Bacillus subtilis SpoIIGA Protein Is a Novel Type of Signal-transducing Aspartic Protease^*

Daisuke Imamura¹, Ruanbao Zhou, Michael Feig, and Lee Kroos²

From the Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, Michigan 48824 and Faculty of Pharmaceutical Sciences, Setsunan University, Osaka 573-0101, Japan

The bacterium Bacillus subtilis undergoes endospore formation in response to starvation. factors play a key role in spatiotemporal regulation of gene expression during development. Activation of factors is coordinated by signal transduction between the forespore and the mother cell. ^E is produced as pro-^E, which is activated in the mother cell by cleavage in response to a signal from the forespore. We report that expression of SpoIIR, a putative signaling protein normally made in the forespore, and SpoIIGA, a putative protease, is necessary and sufficient for accurate, rapid, and abundant processing of pro-^E to ^E in Escherichia coli. Modeling and mutational analyses provide evidence that SpoIIGA is a novel type of aspartic protease whose C-terminal half forms a dimer similar to the human immunodeficiency virus type 1 protease. Previous studies suggest that the N-terminal half of SpoIIGA is membrane-embedded. We found that SpoIIGA expressed in E. coli is membrane-associated and that after detergent treatment SpoIIGA was self-associated. Also, SpoIIGA interacts with SpoIIR. The results support a model in which SpoIIGA forms inactive dimers or oligomers, and interaction of SpoIIR with the N-terminal domain of SpoIIGA on one side of a membrane causes a conformational change that allows formation of active aspartic protease dimer in the C-terminal domain on the other side of the membrane, where it cleaves pro-^E.

Received for publication, October 31, 2007 , and in revised form, March 25, 2008.

^* This work was supported, in whole or in part, by National Institutes of Health Grant GM43585 (to L. K.). This work was also supported by National Science Foundation Grant 0447799, a grant from the Alfred P. Sloan Foundation (to M. F.), and by the Michigan Agricultural Experiment Station. 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.

The on-line version of this article (available at http://www.jbc.org) contains supplemental Tables S1–S3, Figs. 1–3, and additional references.

¹ Supported in part by a fellowship from the Naito Foundation.

² To whom correspondence should be addressed. Fax: 517-353-9334; E-mail: kroos{at}msu.edu.

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