title: Characterization of rickettsial adhesin Adr2 belonging to a new group of adhesins in α-proteobacteria.
abstract: BACKGROUND
  Rickettsia prowazekii is the etiological agent of epidemic typhus and is an obligate intracellular bacterium that grows as a parasite freely within the cytoplasm of a eukaryotic host cell. Previous studies have shown that rOmpA and rOmpB which belong to the family of rickettsial cell surface antigens are involved in vitro in the adhesion of Rickettsiae to epithelial cells. Recently, two putative rickettsial adhesins have been identified using high resolution 2D-PAGE coupled with mass spectrometry. In this study, we further characterize and describe the adhesin Adr2 from R. prowazekii.
  
  
  RESULTS
  Using an overlay assay coupled with mass spectrometry two adhesins, Adr1 (RP827) and Adr2 (RP828), were identified from the R. prowazekii proteome Recombinant R. prowazekii Adr2 was expressed through fusion with Dsbc in Escherichia coli, purified and concentrated, thus allowing production of specific monoclonal antibodies, as confirmed by western blot assays. Finally, inhibition of rickettsiae-induced cytotoxicity with monoclonal anti-Adr2 antibody has showed a greatest impact on bacterial cell entry at 8 h post-infection (ca50%) and then decreased progressively to attempt 18% of inhibition at day 7. These, correlated to the inhibition of rickettsiae-induced cytotoxicity with monoclonal anti-rOmpB antibody. Thus, Adr2 is sufficient to mediate R. prowazekii entry into the cell at early stage of mammalian cell infection.
  
  
  CONCLUSIONS
  Our results suggest that R. prowazekii Adr2 could be the main actor promoting the entry of rickettsiae into the host cells. The present study opens the framework for future investigations for better understanding of the Adr2 -mediated mechanisms involved in adhesion/invasion or intracellular survival of R. prowazekii.
authors.affiliation: Université de la Méditerranée, Unité des Rickettsies, URMITE CNRS-IRD, Faculté de Médecine, 27 Bd Jean Moulin, 13385 Marseille cedex 05, France.
authors.forename: Manohari
authors.initials: M
authors.lastname: Vellaiswamy
authors.forename: Malgorzata
authors.initials: M
authors.lastname: Kowalczewska
authors.forename: Vicky
authors.initials: V
authors.lastname: Merhej
authors.forename: Claude
authors.initials: C
authors.lastname: Nappez
authors.forename: Renaud
authors.initials: R
authors.lastname: Vincentelli
authors.forename: Patricia
authors.initials: P
authors.lastname: Renesto
authors.forename: Didier
authors.initials: D
authors.lastname: Raoult
mesh_terms: D018829:Adhesins, Bacterial / Q000302:isolation & purification / Q000378:metabolism*; D000818:Animals; D000907:Antibodies, Bacterial / Q000276:immunology; D001422:Bacterial Adhesion; D002478:Cells, Cultured; D003001:Cloning, Molecular; D015180:Electrophoresis, Gel, Two-Dimensional; D004926:Escherichia coli / Q000235:genetics; D005347:Fibroblasts / Q000382:microbiology*; D015870:Gene Expression; D013058:Mass Spectrometry; D051379:Mice; D011994:Recombinant Proteins / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism; D012283:Rickettsia prowazekii / Q000235:genetics* / Q000472:pathogenicity*
chemical_list: D018829:Adhesins, Bacterial; D000907:Antibodies, Bacterial; D011994:Recombinant Proteins