title: Characterization of the Trichomonas vaginalis surface-associated AP65 and binding domain interacting with trichomonads and host cells.
abstract: BACKGROUND
  AP65 is a prominent adhesin of Trichomonas vaginalis that mediates binding of parasites to host vaginal epithelial cells (VECs). AP65 with no secretion signal sequence, membrane targeting peptide, and anchoring motif was recently found to be secreted.
  
  
  RESULTS
  We first wanted to demonstrate surface association of AP65 to the parasite followed by the identification of the binding epitope interacting with both organisms and VECs. AP65 was found to bind to trichomonads, but not to trypsin-treated parasites, in an auto-ligand assay, suggesting the existence of a surface protein associating with AP65. Since rabbit antiserum IgG antibodies reactive with epitopes localized to the N-terminal region of AP65 inhibit the attachment of live parasites to VECs, we hypothesized that the binding domain was localized to this region. We subcloned five overlapping fragments of AP65 called c1 through c5, and expression of recombinant clones was confirmed with antibodies to AP65. Each purified recombinant protein was then tested for binding activity using an established ligand assay, and fragment c1 with the first twenty-five amino acids in the N-terminal domain was required for binding to VECs and, surprisingly, also to parasites. Importantly, c1 competed with the binding of AP65 to both cells types.
  
  
  CONCLUSIONS
  T. vaginalis AP65 is a secreted, surface-associated protein and a model is proposed to explain how this secreted protein functions as an adhesin.
authors.affiliation: Department of Microbiology, University of Texas Health Science Center, 7703 Floyd Curl Drive, San Antonio, TX 78229-3900, USA. anafgarcia01@yahoo.com
authors.forename: Ana F
authors.initials: AF
authors.lastname: Garcia
authors.forename: Jf
authors.initials: J
authors.lastname: Alderete
mesh_terms: D000818:Animals; D002448:Cell Adhesion; D015815:Cell Adhesion Molecules / Q000737:chemistry / Q000378:metabolism*; D004847:Epithelial Cells / Q000378:metabolism*; D000939:Epitopes / Q000378:metabolism; D005260:Female; D006801:Humans; D008565:Membrane Proteins / Q000737:chemistry / Q000378:metabolism*; D017434:Protein Structure, Tertiary / Q000502:physiology; D015800:Protozoan Proteins / Q000737:chemistry / Q000378:metabolism*; D011994:Recombinant Proteins / Q000378:metabolism; D014246:Trichomonas vaginalis / Q000737:chemistry* / Q000187:drug effects / Q000502:physiology; D014357:Trypsin / Q000494:pharmacology; D014621:Vagina
chemical_list: D015815:Cell Adhesion Molecules; D000939:Epitopes; D008565:Membrane Proteins; D015800:Protozoan Proteins; D011994:Recombinant Proteins; D014357:Trypsin