Characterization of the parasitophorous vacuole membrane from Plasmodium chabaudi and implications about its role in the export of parasite proteins.

Little is known about how the malaria parasite transports and targets proteins into the host erythrocyte. Parasite proteins exported into the host cell not only have to cross the parasite plasma membrane but also must traverse the parasitophorous vacuolar membrane (PVM) that surrounds the parasite. The PVM of Plasmodium chabaudi-infected erythrocytes was analyzed by immunofluorescence using an antibody against a known PVM protein, a fluorescent lipid probe, and electron microscopy. These analyses reveal qualitatively different membranous projections from the PVM. Some PVM projections are uniformly labeled with the antibody and with lipid probes and probably correspond to the Maurer's clefts. In contrast to this uniform labeling of the PVM and projections, a 93-kDa P. chabaudi erythrocyte membrane-associated protein is occasionally detected in vesicle-like structures adjacent to the parasite. These vesicle-like structures are found only coincident with protein synthesis and are located at discrete sites on the PVM. These observations suggest that the 93-kDa protein does not move along the membranous projections of the PVM toward the erythrocyte membrane. It is proposed that the 93-kDa protein is secreted directly into the erythrocyte cytoplasm at discrete PVM domains and then binds to the cytoplasmic face of the erythrocyte membrane.