Plasmodium vivax, P. cynomolgi, andP. knowlesi:Identification of Homologue Proteins Associated with the Surface of Merozoites

Abstract

Barnwell, J. W., Galinski, M. R., DeSimone, S. G., Perler, F., and Ingravallo, P. 1999.Plasmodium vivax, P. cynomolgi, andP. knowlesi: Identification of homologue proteins associated with the surface of merozoites.Experimental Parasitology91, 238–249. We have identified aPlasmodium vivaxmerozoite surface protein (MSP) that migrates on SDS-polyacrylamide gels at aMrof about 185 kDa. This protein was recognized by aP. vivaxmonoclonal antibody (mAb) that localizes the protein by immunofluorescence to the surface of merozoites and also immunoprecipitates this protein from NP-40 detergent extracts of [35S]methionine metabolically radiolabeledP. vivaxschizonts. TheP. vivaxMSP does not become biosynthetically radiolabeled with [3H]glucoamine, [3H]myristate, [3H]palmitate, or [3H]mannose, indicating that thisP. vivaxMSP is not posttranslationally modified and bound to the merozoite membrane by a glycosylphosphatidylinositol (GPI) lipid anchor. Thus, in this respect, this protein is different from members of the MSP-1 protein family and from MSP-2 and MSP-4 ofP. falciparum. The mAb cross-reacts with and outlines the surface ofP. cynomolgimerozoites and immunoprecipitates a 150-kDaP. cynomolgihomologue. The mAb was used as an affinity reagent to purify the native homologous MSP from NP-40 extracts ofP. cynomolgimature schizonts in order to develop a specific polyclonal antiserum. The resulting anti-PcyMSP rabbit antiserum cross-reacts strongly with theP. vivax185-kDa MSP and also recognizes an analogous 110-kDa protein fromP. knowlesi. We have determined via an immunodepletion experiment that the 110-kDaP. knowlesiMSP corresponds to the PK 110 protein partially characterized earlier (Perleret al.1987). The potential ofP. vivaxMSP as a vaccine candidate was addressed by conductingin vitroinhibition of erythrocyte invasion assays, and the IgG fraction of both theP. vivaxMSP mAb and theP. cynomolgiMSP rabbit antiserum significantly inhibited entry ofP. vivaxmerozoites. We denote, on a preliminary basis, these antigenically related merozite surface proteins PvMSP-185, PcyMSP-150, and PkMSP-110.