title: Identification, expression, and functional characterization of MAEBL, a sporozoite and asexual blood stage chimeric erythrocyte-binding protein of Plasmodium falciparum.
abstract: 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.
authors.affiliation: Department of Immunology, Walter Reed Army Institute of Research, Silver Spring, MD 20910, USA.
authors.forename: Mala
authors.initials: M
authors.lastname: Ghai
authors.forename: Sheetij
authors.initials: S
authors.lastname: Dutta
authors.forename: Ted
authors.initials: T
authors.lastname: Hall
authors.forename: Daniel
authors.initials: D
authors.lastname: Freilich
authors.forename: Christian F
authors.initials: CF
authors.lastname: Ockenhouse
mesh_terms: 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
chemical_list: 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