A novel protein antigen of the malaria parasite Plasmodium falciparum, located on the surface of gametes and sporozoites.
A Plasmodium falciparum cDNA clone was isolated of which the insert is transcribed at high rates as a 1.4-kb mRNA in the sexual stages of the malaria parasite. The cDNA clone contains a copy of a non-interrupted gene which codes for a protein of 157 amino acids (Mr = 16607). This 16-kDa protein does not contain repetitive sequences and is characterised by a putative N-terminal signal sequence, a hydrophobic membrane anchor sequence and a highly hydrophilic C-terminal region suggesting that it is an integral membrane protein. Rabbit antisera raised against a synthetic peptide covering amino acids 31-47 of the 16-kDa protein and against recombinant fusion proteins recognised the 16-kDa antigen in protein extracts of gametocytes, macrogamete/zygotes and sporozoites by Western blot analysis. The rabbit antisera also reacted with gametes, gametocytes and sporozoites in a standard immunofluorescence assay. By immunoelectron microscopy using the protein A-gold method the 16-kDa protein could be clearly visualised on the surface of macrogametes and sporozoites, whereas the antigen was not detectable in the asexual erythrocytic stages of the parasite. The 16-kDa antigen of P. falciparum therefore might have the potential to elicit a dual protective immune response against the sporozoite and sexual stage parasites.
Moelans
I I
II
Department of Molecular Biology, Faculty of Science, University of Nijmegen, The Netherlands.
Meis
J F
JF
Kocken
C
C
Konings
R N
RN
Schoenmakers
J G
JG
D000595:Amino Acid Sequence; D000818:Animals; D000953:Antigens, Protozoan / Q000032:analysis* / Q000737:chemistry / Q000235:genetics / Q000276:immunology*; D000954:Antigens, Surface / Q000032:analysis / Q000737:chemistry / Q000235:genetics / Q000276:immunology; D001483:Base Sequence; D015153:Blotting, Western; D003001:Cloning, Molecular; D008565:Membrane Proteins / Q000032:analysis / Q000737:chemistry / Q000235:genetics / Q000276:immunology*; D016253:Microscopy, Immunoelectron; D008969:Molecular Sequence Data; D009710:Nucleotide Mapping; D010963:Plasmodium falciparum / Q000254:growth & development / Q000276:immunology*; D011487:Protein Conformation; D015800:Protozoan Proteins / Q000032:analysis / Q000737:chemistry / Q000235:genetics / Q000276:immunology*; D011993:Recombinant Fusion Proteins / Q000276:immunology
D000953:Antigens, Protozoan; D000954:Antigens, Surface; D008565:Membrane Proteins; D015800:Protozoan Proteins; D011993:Recombinant Fusion Proteins; C068959:Pfs16 protein, Plasmodium falciparum