JB Accepts, published online ahead of print on 4 January 2008

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J. Bacteriol. doi:10.1128/JB.01341-07
Copyright (c) 2008, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Protein subassemblies of the Helicobacter pylori Cag type IV secretion system revealed by localization and interaction studies

STEFAN KUTTER, RENATE BUHRDORF, JÜRGEN HAAS, WULF SCHNEIDER-BRACHERT, RAINER HAAS, and WOLFGANG FISCHER^*

Max von Pettenkofer-Institut für Hygiene und Medizinische Mikrobiologie, Ludwig-Maximilians-Universität, 80336 München, Germany, Abteilung Bakteriologie, and Abteilung Virologie; Division of Pathway Medicine, University of Edinburgh, UK; and Institut für Medizinische Mikrobiologie und Hygiene, Universität Regensburg, 93042 Regensburg, Germany

^* To whom correspondence should be addressed. Email: fischer{at}mvp.uni-muenchen.de.

Type IV secretion systems are possibly the most versatile protein transport systems in Gram-negative bacteria, with substrates ranging from small proteins to large nucleoprotein complexes. In many cases, such as the cag pathogenicity island of Helicobacter pylori, genes encoding components of a type IV secretion system have been identified due to their sequence similarities to prototypical systems such as the VirB system of Agrobacterium tumefaciens. The Cag type IV secretion system contains at least 14 essential apparatus components and several substrate translocation and auxiliary factors, but the functions of most components cannot be inferred from their sequences due to the lack of similarities. In this study, we have performed a comprehensive sequence analysis of all essential or auxiliary Cag components, and we have used antisera raised against a subset of components to determine their subcellular localization. The results suggest that the Cag system contains functional analogues to all VirB components except VirB5. Moreover, we have characterized mutual stabilization effects and performed a comprehensive yeast two-hybrid screening for potential protein-protein interactions. Immunoprecipitation studies resulted in identification of a secretion apparatus subassembly at the outer membrane. Combining these data, we provide a first low-resolution model of the Cag type IV secretion apparatus.

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