A protective glycosylphosphatidylinositol-anchored membrane protein of Plasmodium yoelii trophozoites and merozoites contains two epidermal growth factor-like domains.
Using sera from mice immunized and protected against Plasmodium yoelii malaria, we identified a novel blood-stage antigen gene, pypag-2. The 2.1-kb pypag-2 cDNA contains a single open reading frame that encodes a 409-amino-acid protein with a predicted molecular mass of 46.8 kDa. Unlike many characterized plasmodial antigens, blocks of tandemly repeated amino acids are lacking in the pypAg-2 protein sequence. Recombinant pypAg-2, comprising the full-length protein minus the predicted N-terminal signal and C-terminal anchor sequences, was produced and used to raise a high-titer polyclonal rabbit antiserum. This antiserum was used to identify and characterize the native protein through immunoblotting, immunoprecipitation and immunofluorescence assays. Consistent with the presence of a glycosylphosphatidylinositol anchor, pypAg-2 fractionated with the detergent phase of Triton X-114-solubilized proteins and could be metabolically labeled with [(3)H]palmitic acid. By immunofluorescence, pypAg-2 expression was localized to both the trophozoite and merozoite membranes. Similar to Plasmodium falciparum merozoite surface protein 1, pypAg-2 contains two C-terminal epidermal growth factor (EGF)-like domains. Most importantly, immunization with recombinant pypAg-2 protected mice against lethal P. yoelii malaria. Thus, pypAg-2 is a target of protective immune responses and represents a novel addition to the family of merozoite surface proteins that contain one or more EGF-like domains.
Burns
J M
JM
Department of Microbiology, Meharry Medical College, Nashville, Tennessee 37208, USA. jburns@mail.mmc.edu
Belk
C C
CC
Dunn
P D
PD
D000595:Amino Acid Sequence; D000818:Animals; D000954:Antigens, Surface / Q000032:analysis; D001483:Base Sequence; D004815:Epidermal Growth Factor / Q000032:analysis*; D017261:Glycosylphosphatidylinositols / Q000032:analysis*; D007114:Immunization; D008288:Malaria / Q000517:prevention & control; D008297:Male; D051379:Mice; D008969:Molecular Sequence Data; D010967:Plasmodium yoelii / Q000737:chemistry*; D015800:Protozoan Proteins / Q000032:analysis* / Q000276:immunology; D011817:Rabbits
D000954:Antigens, Surface; D017261:Glycosylphosphatidylinositols; D015800:Protozoan Proteins; D004815:Epidermal Growth Factor