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Science 26 September 2003:
Vol. 301. no. 5641, pp. 1918 - 1921
DOI: 10.1126/science.1088433
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Reports

Salmonella SipA Polymerizes Actin by Stapling Filaments with Nonglobular Protein Arms

Mirjana Lilic,1 Vitold E. Galkin,2 Albina Orlova,2 Margaret S. VanLoock,2 Edward H. Egelman,2 C. Erec Stebbins1*

Like many bacterial pathogens, Salmonella spp. use a type III secretion system to inject virulence proteins into host cells. The Salmonella invasion protein A (SipA) binds host actin, enhances its polymerization near adherent extracellular bacteria, and contributes to cytoskeletal rearrangements that internalize the pathogen. By combining x-ray crystallography of SipA with electron microscopy and image analysis of SipA-actin filaments, we show that SipA functions as a "molecular staple," in which a globular domain and two nonglobular "arms" mechanically stabilize the filament by tethering actin subunits in opposing strands. Deletion analysis of the tethering arms provides strong support for this model.

1 Laboratory of Structural Microbiology, Rockefeller University, New York, NY 10021, USA.
2 Department of Biochemistry and Molecular Genetics, University of Virginia Health Sciences Center, Charlottesville, VA 22908, USA.

* To whom correspondence should be addressed. E-mail: stebbins{at}rockefeller.edu

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Science. ISSN 0036-8075 (print), 1095-9203 (online)