Research Interests - Edith Gouin
Engineer, Pasteur Institute
The RickA Protein of Rickettsia conorii is a novel activator of Arp2/3 complex
Vérinique Villiers and Edith Gouin work together on the Rickettsia project. Listeria monocytogenes, Shigella flexneri, and Rickettisia conorii are three bacterial pathogens that are able to polymerize actin into ’comet tail’ structures and move within the cytosol of infected cells. The actin-based motilities of L. monocytogenes and S. flexneri are known to require the bacterial proteins ActA and IscA, respectively, and several mammalian cytoskeleton proteins including Arp2/3 complex and VASP (vasodilator-stimulated phosphoprotein) for L. monotyogenes and vinculin and N-WASP (the neural Wiskott-Aldrich syndrome protein) for S. flexneri.
We have previously reported that the actin tails of Rickettsia conorii, another intracellular bacterium, unlike those of Listeria of Shigella are composed of long unbranched actin filaments apparently devoid of Arp2/3 complex (J. Cell. Science, 1999).
Then, we identified a R. conorii surface protein, RickA, as a novel type of Arp2/3 activator. In vitro, RickA activates, albeit far less efficiently than ActA, the nucleating activity of Arp2/3 and its capacity to induce branch formation. In infected cells, Arp2/3 is detected on the bacterial surface but not in the Rickettsia tails, as it is the case for Listeria and Shigella tails. When expressed in mammalian cells, and targeted to the membrane, RickA induces filopodia. Thus RickA-induced actin polymerisation, which results in the generation of the long actin filaments reminiscent of those present in filopodia, appears as a powerful tool for the study of filopodia formation.
|The Rickettsia actin tails consist of long filaments. Electron microscopy of myosin S1 decorated actin tails of R. conorii and L. monocytogenes.|