Plasmodium vivax merozoite surface protein-3 contains coiled-coil motifs in an alanine-rich central domain.
Plasmodium merozoites are covered with a palisade layer of proteins that are arranged as organized bundles or appear as protruding spikes by electron microscopy. Here we present a third Plasmodium vivax merozoite surface protein, PvMSP-3, which is associated with but not anchored in the merozoite membrane. Serum from a P. vivax immune squirrel monkey was used to screen a lambdagt11 P. vivax genomic DNA (gDNA) library. Plaque-selected antibodies from clone no. 6.1, and rabbit antisera against its encoded protein, produced a pattern in immunofluorescence assays (IFAs) that is consistent with a localization at the surface of mature schizonts and free merozoites. Specific antisera also agglutinated merozoites and recognized a protein of 150 000 Da by SDS-PAGE. The complete msp-3 gene and flanking sequences were cloned from a P. vivax lambda Dash II gDNA library and also partly characterized by RACE (rapid amplification of cDNA ends). The immediate upstream sequence contains non-coding repeats and a putative protein encoding open reading frame (ORF), which are also present on the msp-3 5'RACE gene product. Pvmsp-3 encodes a protein with a calculated mass of 89 573 Da, which has a potential signal peptide and a major central alanine-rich domain (31%) that exhibits largely alpha-helical secondary structure and is flanked by charged regions. The protein does not have a putative transmembrane domain or a consensus sequence for a glycosylphosphatidylinositol (GPI) anchor modification. However, the alanine-rich domain has heptad repeats that are predicted to form coiled-coil tertiary structures, which mediate protein-protein interactions. PvMSP-3 is structurally related to P. falciparum MSP-3 and the 140000 Da MSP of P. knowlesi. Characterization of PvMSP-3, thus, also begins to define a new interspecies family of evolutionarily related Plasmodium merozoite proteins.
Department of Medical and Molecular Parasitology, New York University School of Medicine, NY 10010, USA. Mary.Galinski@malaria.org
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Galinski
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Corredor-Medina
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Povoa
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Crosby
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Ingravallo
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Barnwell
D000409:Alanine / Q000737:chemistry; D000595:Amino Acid Sequence; D000818:Animals; D000953:Antigens, Protozoan / Q000737:chemistry* / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D001483:Base Sequence; D015153:Blotting, Western; D003001:Cloning, Molecular; D005455:Fluorescent Antibody Technique; D017125:Genes, Protozoan; D006801:Humans; D008969:Molecular Sequence Data; D010966:Plasmodium vivax / Q000737:chemistry* / Q000235:genetics; D017433:Protein Structure, Secondary; D015800:Protozoan Proteins / Q000737:chemistry* / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D011817:Rabbits; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000378:metabolism; D015183:Restriction Mapping; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012453:Saimiri
D000953:Antigens, Protozoan; D015800:Protozoan Proteins; D011993:Recombinant Fusion Proteins; C089133:merozoite surface protein 3, Plasmodium; D000409:Alanine