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IcsA Surface Presentation in Shigella flexneri Requires the Periplasmic Chaperones DegP, Skp, and SurA

Georgiana E. Purdy, Carolyn R. Fisher, and Shelley M. Payne^*

Institute for Cellular and Molecular Biology and Section of Molecular Genetics and Microbiology, The University of Texas at Austin, Austin, Texas 78712

Received 30 March 2007/ Accepted 10 May 2007

A Shigella flexneri degP mutant, which was defective for plaque formation in Henle cell monolayers, had a reduced amount of IcsA detectable on the bacterial surface with antibody. However, the mutant secreted IcsA to the outer membrane at wild-type levels. This suggests that IcsA adopts an altered conformation in the outer membrane of the degP mutant with reduced exposure on the cell surface. IcsA is, therefore, unlikely to be accessible to actin-nucleating proteins within the eukaryotic cell cytoplasm, which is required for bacterial movement within the host cell and cell-to-cell spread. The degP mutant was somewhat more sensitive to detergents, antibiotics, and the antimicrobial peptide magainin, indicating that the degP phenotype was not limited to IcsA surface presentation. The plaque defect of the degP mutant, which is independent of DegP protease activity, was suppressed by overexpression of the periplasmic chaperone Skp but not by SurA. S. flexneri skp and surA mutants failed to form plaques in Henle cell monolayers and were defective in cell surface presentation and polar localization of IcsA. Therefore, the three periplasmic folding factors DegP, Skp, and SurA were all required for IcsA localization and plaque formation by S. flexneri.

Published ahead of print on 25 May 2007.

Present address: Cornell University, College of Veterinary Medicine, Department of Microbiology and Immunology, Ithaca, NY 14853.

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