title: An unusual tryptophan-rich domain characterizes two secreted antigens of Plasmodium yoelii-infected erythrocytes.
abstract: Previously, we reported the characterization of pypAg-1, a novel protective membrane protein of Plasmodium yoelii-infected erythrocytes. Immunization studies indicated that pypAg-1 contained at least two protective epitopes. One of these determinants was associated with the N-terminal portion of pypAg-1, that also included a 220 amino acid domain unusually rich in tryptophan residues. Using sera from mice immunized against P. yoelii, we have identified a second related antigen, pypAg-3. The pypag-3 cDNA encodes a 43 kDa blood-stage protein that is also characterized by the presence of a 220 residue tryptophan-rich domain. Of particular interest, sequence comparisons revealed that 24 tryptophan residues are positionally conserved between pypAg-1 and pypAg-3. Otherwise, the two antigens share limited sequence similarity. Full-length recombinant pypAg-3 was expressed, purified and used to produce a high titer polyclonal rabbit antiserum. As with pypAg-1, immunofluorescence studies showed that pypAg-3 is expressed in the cytoplasm and associated with the membrane of P. yoelii infected erythrocytes. In addition, pypAg-1 and pypAg-3 appear to be secreted proteins, as both were detected in culture supernatants of P. yoelii-infected erythrocytes. Finally, metabolically labeled pypAg-1 and pypAg-3 secreted from parasitized cells bind to the surface of uninfected, normal mouse erythrocytes. As such, the conservation of the unusual tryptophan-rich domain between two blood-stage malarial proteins with similar biological properties suggests that it may be important for protein export and/or function.
authors.affiliation: Department of Microbiology, Meharry Medical College, 1005 D.B. Todd Blvd., Nashville, TN 37208, USA. jburns@mail.mmc.edu
authors.forename: J M
authors.initials: JM
authors.lastname: Burns
authors.forename: E K
authors.initials: EK
authors.lastname: Adeeku
authors.forename: C C
authors.initials: CC
authors.lastname: Belk
authors.forename: P D
authors.initials: PD
authors.lastname: Dunn
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D000953:Antigens, Protozoan / Q000737:chemistry* / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D003001:Cloning, Molecular; D018076:DNA, Complementary; D016054:DNA, Protozoan / Q000235:genetics; D004912:Erythrocytes / Q000378:metabolism / Q000469:parasitology*; D019084:Fluorescent Antibody Technique, Indirect; D008288:Malaria / Q000469:parasitology; D008565:Membrane Proteins / Q000737:chemistry* / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D051379:Mice; D008807:Mice, Inbred BALB C; D008810:Mice, Inbred C57BL; D008969:Molecular Sequence Data; D010967:Plasmodium yoelii / Q000235:genetics / Q000276:immunology* / Q000378:metabolism; D016133:Polymerase Chain Reaction; D017434:Protein Structure, Tertiary; D015800:Protozoan Proteins; D011817:Rabbits; D017422:Sequence Analysis, DNA; D014364:Tryptophan / Q000737:chemistry*
chemical_list: D000953:Antigens, Protozoan; D018076:DNA, Complementary; D016054:DNA, Protozoan; D008565:Membrane Proteins; D015800:Protozoan Proteins; C417084:pag-3 protein, Plasmodium yoelii; C117490:pypag-1 protein, Plasmodium yoelii; D014364:Tryptophan