Identification, expression, and functional characterization of MAEBL, a sporozoite and asexual blood stage chimeric erythrocyte-binding protein of Plasmodium falciparum.
MAEBL is a chimeric erythrocyte binding protein reported in rodent malaria parasites Plasmodium yoelii and Plasmodium berghei, that has the gene structure similar to erythrocyte binding proteins, but N-terminal homology to subdomains I and II of Apical membrane antigen-1. We report here the sequence analysis and gene structure of the Plasmodium falciparum maebl gene. We have cloned and expressed a putative red cell binding domain, M2, of this gene in Escherichia coli, purified the recombinant protein (r-PfM2) and studied its in vitro binding specificity to human red cells. Binding of r-PfM2 protein to red cells was abolished by pretreatment with papain, while increased binding was observed to neuraminidase-treated red cells. Polyclonal antibodies to r-PfM2 recognized native MAEBL protein in blood stage schizont extracts of the parasite on Western blots and within the apical complex of free merozoites, by indirect immunofluorescent assay (IFA). MAEBL expression in P. falciparum sporozoites was also detected by reverse transcriptase polymerase chain reaction (RT-PCR) and IFA. High titer antibodies to r-PfM2 were observed in human sera obtained from a malaria endemic region some of which inhibited r-PfM2 binding to red cells. Individuals immunized with irradiated sporozoites tested positive for anti-MAEBL antibodies by ELISA. The dual stage expression of MAEBL makes it an excellent pre-erythrocytic and erythrocytic stage vaccine target antigen.
Ghai
Mala
M
Department of Immunology, Walter Reed Army Institute of Research, Silver Spring, MD 20910, USA.
Dutta
Sheetij
S
Hall
Ted
T
Freilich
Daniel
D
Ockenhouse
Christian F
CF
D000595:Amino Acid Sequence; D000818:Animals; D000913:Antibodies, Protozoan / Q000097:blood / Q000276:immunology; D000953:Antigens, Protozoan; D002352:Carrier Proteins / Q000737:chemistry / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D003001:Cloning, Molecular; D004912:Erythrocytes / Q000378:metabolism* / Q000469:parasitology; D006801:Humans; D008565:Membrane Proteins / Q000737:chemistry / Q000235:genetics; D008969:Molecular Sequence Data; D010963:Plasmodium falciparum / Q000254:growth & development* / Q000378:metabolism; D015800:Protozoan Proteins / Q000737:chemistry / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D011956:Receptors, Cell Surface / Q000737:chemistry / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000378:metabolism*; D017422:Sequence Analysis, DNA
D000913:Antibodies, Protozoan; D000953:Antigens, Protozoan; D002352:Carrier Proteins; C066001:Duffy antigen binding protein, Plasmodium; C468522:MAEBL protein, Plasmodium falciparum; D008565:Membrane Proteins; D015800:Protozoan Proteins; D011956:Receptors, Cell Surface; D011993:Recombinant Fusion Proteins; C090077:apical membrane antigen I, Plasmodium; C065668:erythrocyte-binding antigen 175, Plasmodium