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Journal of Bacteriology, February 2001, p. 951-958, Vol. 183, No. 3
0021-9193/01/$04.00+0   DOI: 10.1128/JB.183.3.951-958.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.

Periplasmic Transit and Disulfide Bond Formation of the Autotransported Shigella Protein IcsA

Lauren D. Brandon and Marcia B. Goldberg*

Infectious Disease Division, Massachusetts General Hospital, Boston, Massachusetts 02114

Received 15 August 2000/Accepted 9 November 2000

The Shigella outer membrane protein IcsA belongs to the family of type V secreted (autotransported) virulence factors. Members of this family mediate their own translocation across the bacterial outer membrane: the carboxy-terminal beta  domain forms a beta  barrel channel in the outer membrane through which the amino-terminal alpha  domain passes. IcsA, which is localized at one pole of the bacterium, mediates actin assembly by Shigella, which is essential for bacterial intracellular movement and intercellular dissemination. Here, we characterize the transit of IcsA across the periplasm during its secretion. We show that an insertion in the dsbB gene, whose gene product mediates disulfide bond formation of many periplasmic intermediates, does not affect the surface expression or unipolar targeting of IcsA. However, IcsA forms one disulfide bond in the periplasm in a DsbA/DsbB-dependent fashion. Furthermore, cellular fractionation studies reveal that IcsA has a transient soluble periplasmic intermediate. Our data also suggest that IcsA is folded in a proteinase K-resistant state in the periplasm. From these data, we propose a novel model for the secretion of IcsA that may be applicable to other autotransported proteins.

* Corresponding author. Mailing address: Infectious Disease Division, Massachusetts General Hospital, 55 Fruit St., GRJ504, Boston, MA 02114. Phone: (617) 726-3812. Fax: (617) 726-7416. E-mail: mgoldberg1{at}partners.org.

Journal of Bacteriology, February 2001, p. 951-958, Vol. 183, No. 3
0021-9193/01/$04.00+0   DOI: 10.1128/JB.183.3.951-958.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.


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