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Journal of Bacteriology, March 2008, p. 2161-2171, Vol. 190, No. 6
0021-9193/08/$08.00+0     doi:10.1128/JB.01341-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Protein Subassemblies of the Helicobacter pylori Cag Type IV Secretion System Revealed by Localization and Interaction Studies{triangledown} ,{dagger}

Stefan Kutter,1 Renate Buhrdorf,1,{ddagger} Jürgen Haas,2,3 Wulf Schneider-Brachert,4 Rainer Haas,1 and Wolfgang Fischer1*

Abteilung Bakteriologie,1 Abteilung Virologie, Max von Pettenkofer Institut für Hygiene und Medizinische Mikrobiologie, Ludwig Maximilians Universität, 80336 München, Germany,2 Division of Pathway Medicine, University of Edinburgh, Edinburgh, United Kingdom,3 Institut für Medizinische Mikrobiologie und Hygiene, Universität Regensburg, 93042 Regensburg, Germany4

Received 17 August 2007/ Accepted 23 December 2007

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.

* Corresponding author. Mailing address: Max von Pettenkofer Institut, Pettenkoferstr. 9a, D-80336 München, Germany. Phone: 49 89 51605277. Fax: 49 89 51605223. E-mail: fischer{at}mvp.uni-muenchen.de

{triangledown} Published ahead of print on 4 January 2008.

{dagger} Supplemental material for this article may be found at http://jb.asm.org/.

{ddagger} Present address: 4SC AG, Am Klopferspitz 19a, 82152 Martinsried, Germany.

Journal of Bacteriology, March 2008, p. 2161-2171, Vol. 190, No. 6
0021-9193/08/$08.00+0     doi:10.1128/JB.01341-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.





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