title: Disruption of the Rickettsia rickettsii Sca2 autotransporter inhibits actin-based motility.
abstract: Rickettsii rickettsii, the etiologic agent of Rocky Mountain spotted fever, replicates within the cytosol of infected cells and uses actin-based motility to spread inter- and intracellularly. Although the ultrastructure of the actin tail and host proteins associated with it are distinct from those of Listeria or Shigella, comparatively little is known regarding the rickettsial proteins involved in its organization. Here, we have used random transposon mutagenesis of R. rickettsii to generate a small-plaque mutant that is defective in actin-based motility and does not spread directly from cell to cell as is characteristic of spotted fever group rickettsiae. The transposon insertion site of this mutant strain was within Sca2, a member of a family of large autotransporter proteins. Sca2 exhibits several features suggestive of its apparent role in actin-based motility. It displays an N-terminal secretory signal peptide, a C-terminal predicted autotransporter domain, up to four predicted Wasp homology 2 (WH2) domains, and two proline-rich domains, one with similarity to eukaryotic formins. In a guinea pig model of infection, the Sca2 mutant did not elicit fever, suggesting that Sca2 and actin-based motility are virulence factors of spotted fever group rickettsiae.
authors.affiliation: Laboratory of Intracellular Parasites, Rocky Mountain Laboratories, 903 South 4th Street, Hamilton, MT 59840, USA.
authors.forename: Betsy
authors.initials: B
authors.lastname: Kleba
authors.forename: Tina R
authors.initials: TR
authors.lastname: Clark
authors.forename: Erika I
authors.initials: EI
authors.lastname: Lutter
authors.forename: Damon W
authors.initials: DW
authors.lastname: Ellison
authors.forename: Ted
authors.initials: T
authors.lastname: Hackstadt
mesh_terms: D000199:Actins / Q000378:metabolism*; D000595:Amino Acid Sequence; D000818:Animals; D001426:Bacterial Proteins / Q000235:genetics / Q000502:physiology*; D004251:DNA Transposable Elements; D004195:Disease Models, Animal; D005260:Female; D055786:Gene Knockout Techniques; D006168:Guinea Pigs; D008124:Locomotion; D026901:Membrane Transport Proteins / Q000235:genetics / Q000502:physiology*; D008969:Molecular Sequence Data; D016254:Mutagenesis, Insertional; D021382:Protein Sorting Signals; D017434:Protein Structure, Tertiary; D012284:Rickettsia rickettsii / Q000235:genetics / Q000472:pathogenicity / Q000502:physiology*; D012373:Rocky Mountain Spotted Fever / Q000382:microbiology; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D037521:Virulence Factors / Q000235:genetics / Q000502:physiology*
chemical_list: D000199:Actins; D001426:Bacterial Proteins; D004251:DNA Transposable Elements; D026901:Membrane Transport Proteins; D021382:Protein Sorting Signals; D037521:Virulence Factors