title: On the three-finger protein domain fold and CD59-like proteins in Schistosoma mansoni.
abstract: It is believed that schistosomes evade complement-mediated killing by expressing regulatory proteins on their surface. Recently, six homologues of human CD59, an important inhibitor of the complement system membrane attack complex, were identified in the schistosome genome. Therefore, it is important to investigate whether these molecules could act as CD59-like complement inhibitors in schistosomes as part of an immune evasion strategy.
  
  
  
  Herein, we describe the molecular characterization of seven putative SmCD59-like genes and attempt to address the putative biological function of two isoforms. Superimposition analysis of the 3D structure of hCD59 and schistosome sequences revealed that they contain the three-fingered protein domain (TFPD). However, the conserved amino acid residues involved in complement recognition in mammals could not be identified. Real-time RT-PCR and Western blot analysis determined that most of these genes are up-regulated in the transition from free-living cercaria to adult worm stage. Immunolocalization experiments and tegument preparations confirm that at least some of the SmCD59-like proteins are surface-localized; however, significant expression was also detected in internal tissues of adult worms. Finally, the involvement of two SmCD59 proteins in complement inhibition was evaluated by three different approaches: (i) a hemolytic assay using recombinant soluble forms expressed in Pichia pastoris and E. coli; (ii) complement-resistance of CHO cells expressing the respective membrane-anchored proteins; and (iii) the complement killing of schistosomula after gene suppression by RNAi. Our data indicated that these proteins are not involved in the regulation of complement activation.
  
  
  
  Our results suggest that this group of proteins belongs to the TFPD superfamily. Their expression is associated to intra-host stages, present in the tegument surface, and also in intra-parasite tissues. Three distinct approaches using SmCD59 proteins to inhibit complement strongly suggested that these proteins are not complement inhibitors and their function in schistosomes remains to be determined.
authors.affiliation: Centro de Biotecnologia, Instituto Butantan, São Paulo, Brazil.
authors.forename: Leonardo P
authors.initials: LP
authors.lastname: Farias
authors.forename: Greice
authors.initials: G
authors.lastname: Krautz-Peterson
authors.forename: Cibele A
authors.initials: CA
authors.lastname: Tararam
authors.forename: Bogar O
authors.initials: BO
authors.lastname: Araujo-Montoya
authors.forename: Tatiana R
authors.initials: TR
authors.lastname: Fraga
authors.forename: Henrique K
authors.initials: HK
authors.lastname: Rofatto
authors.forename: Floriano P
authors.initials: FP
authors.lastname: Silva
authors.forename: Lourdes
authors.initials: L
authors.lastname: Isaac
authors.forename: Akram A
authors.initials: AA
authors.lastname: Da'dara
authors.forename: R Alan
authors.initials: RA
authors.lastname: Wilson
authors.forename: Charles B
authors.initials: CB
authors.lastname: Shoemaker
authors.forename: Luciana C C
authors.initials: LC
authors.lastname: Leite
mesh_terms: D000818:Animals; D003165:Complement System Proteins / Q000378:metabolism*; D006224:Cricetinae; D005260:Female; D015801:Helminth Proteins / Q000737:chemistry* / Q000276:immunology*; D054884:Host-Pathogen Interactions; D006801:Humans; D057131:Immune Evasion; D008297:Male; D008565:Membrane Proteins / Q000737:chemistry / Q000276:immunology; D008958:Models, Molecular; D011487:Protein Conformation; D012550:Schistosoma mansoni / Q000737:chemistry* / Q000276:immunology*
chemical_list: D015801:Helminth Proteins; D008565:Membrane Proteins; D003165:Complement System Proteins