Localization, biosynthesis, processing and isolation of a major 126 kDa antigen of the parasitophorous vacuole of Plasmodium falciparum

Monoclonal antibodies prepared against a 50 kDa antigen found in Plasmodium falciparum culture supernatants identify a 126 kDa polypeptide which can be localized by immunofluorescence and immunoelectronmicroscopy at the periphery of the schizonts. This polypeptide is released from the infected erythrocytes by mild saponin lysis and is probably a component of the parasitophorous vacuole. Pulse chase kinetic analysis demonstrated its disappearance from the parasitized red blood cell from 6 to 10 h after being synthesized and the concomitant appearance of the 50 kDa molecule in the culture supernatant. Purification of metabolically labeled, schizont infected cells demonstrated that spontaneous release of merozoites is needed for the processing of the 126 to the 50 kDa whereas reinvasion is not. Polyclonal antibodies were raised in rabbit against affinity purified 126 kDa protein. These antibodies, together with another 126 kDa specific monoclonal antibody have enabled us to characterize two other cleavage products of the 126 kDa antigen in culture supernatants, namely 47 and 18 kDa polypeptides. We believe that the processing of the 126 kDa protein into low molecular weight fragments reflects a proteolytic event which may participate in merozoite release.