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Journal of Bacteriology, December 2009, p. 7343-7352, Vol. 191, No. 23
0021-9193/09/$08.00+0     doi:10.1128/JB.00946-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Cag3 Is a Novel Essential Component of the Helicobacter pylori Cag Type IV Secretion System Outer Membrane Subcomplex {triangledown} ,{dagger}

Delia M. Pinto-Santini1,2 and Nina R. Salama1*

Division of Human Biology, Fred Hutchinson Cancer Research Center, Seattle, Washington 98109,1 Molecular and Cellular Biology Graduate Program, University of Washington, Seattle, Washington 981952

Received 17 July 2009/ Accepted 22 September 2009

Helicobacter pylori strains harboring the cag pathogenicity island (PAI) have been associated with more severe gastric disease in infected humans. The cag PAI encodes a type IV secretion (T4S) system required for CagA translocation into host cells as well as induction of proinflammatory cytokines, such as interleukin-8 (IL-8). cag PAI genes sharing sequence similarity with T4S components from other bacteria are essential for Cag T4S function. Other cag PAI-encoded genes are also essential for Cag T4S, but lack of sequence-based or structural similarity with genes in existing databases has precluded a functional assignment for the encoded proteins. We have studied the role of one such protein, Cag3 (HP0522), in Cag T4S and determined Cag3 subcellular localization and protein interactions. Cag3 is membrane associated and copurifies with predicted inner and outer membrane Cag T4S components that are essential for Cag T4S as well as putative accessory factors. Coimmunoprecipitation and cross-linking experiments revealed specific interactions with HpVirB7 and CagM, suggesting Cag3 is a new component of the Cag T4S outer membrane subcomplex. Finally, lack of Cag3 lowers HpVirB7 steady-state levels, further indicating Cag3 makes a subcomplex with this protein.

* Corresponding author. Mailing address: FHCRC, 1100 Fairview Ave. N, Mailstop C3-168, Seattle, WA 98109-1024. Phone: (206) 667-1540. Fax: (206) 667-6524. E-mail: nsalama{at}fhcrc.org

{triangledown} Published ahead of print on 2 October 2009.

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

Journal of Bacteriology, December 2009, p. 7343-7352, Vol. 191, No. 23
0021-9193/09/$08.00+0     doi:10.1128/JB.00946-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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