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Interactions between Partner Switcher Orthologs BtrW and BtrV Regulate Type III Secretion in Bordetella

Natalia A. Kozak,¹ Seema Mattoo,^1, Amy K. Foreman-Wykert,¹ Julian P. Whitelegge,^2,4 and Jeff F. Miller^1,2,3*

Department of Microbiology, Immunology and Molecular Genetics, David Geffen School of Medicine,¹ The Molecular Biology Institute,² The California Nanosystems Institute,³ The Pasarow Mass Spectrometry Laboratory, Departments of Psychiatry and Biobehavioral Sciences, Chemistry and Biochemistry, and the Neuropsychiatric Institute, University of California, Los Angeles, California⁴

Received 4 March 2005/ Accepted 19 May 2005

We have recently described a multicomponent cascade that regulates type III secretion in Bordetella. This cascade includes a group of proteins, BtrU, BtrW, and BtrV, that contain an array of domains that define partner-switching complexes previously characterized in gram-positive bacteria. BtrU contains a PP2C-like serine phosphatase domain, BtrW contains a serine kinase/anti-sigma factor motif, and BtrV includes an anti-sigma factor antagonist domain. On the basis of genetic studies and sequence similarity with the RsbU-RsbW-RsbV and SpoIIE-SpoIIAB-SpoIIAA partner switchers of Bacillus subtilis, a series of interactions between Bordetella orthologs have been proposed. Bacterial two-hybrid analysis, tagged protein pull-downs, and in vitro phosphorylation assays were used to characterize interactions between BtrW and BtrV. In addition, BtrV mutants predicted to mimic a constitutively phosphorylated form of BtrV or to be nonphosphorylatable and BtrW mutants defective in serine kinase activity or the ability to bind BtrV were constructed and analyzed. Our results demonstrate that (i) BtrW and BtrV interact with each other, (ii) BtrW phosphorylates BtrV at serine S55, (iii) the conserved serine residue S55 of BtrV plays a key role in BtrV-BtrW interactions, and (iv) the ability of BtrW to phosphorylate BtrV and disrupt BtrV-BtrW binding is essential for the type III secretion process.

Present address: Department of Pharmacology, University of California, San Diego, School of Medicine, Leichtag Biomedical Research Bldg, Rm. 249, Bay M, 9500 Gilman Drive, Dept. 0721, La Jolla, CA 92093-0721.

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