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 prote ins into the host erythrocyte. Parasite proteins exported into the host cel l not only have to cross the parasite plasma membrane but also must travers e the parasitophorous vacuolar membrane (PVM) that surrounds the parasite. The PVM of Plasmodium chabaudi-infected erythrocytes was analyzed by immuno fluorescence using an antibody against a known PVM protein: a fluorescent l ipid probe, and electron microscopy. These analyses reveal qualitatively di fferent membranous projections from the PVM. Some PVM projections are unifo rmly labeled with the antibody and with lipid probes and probably correspon d to the Maurer's clefts. In contrast to this uniform labeling of the PVM a nd projections, a 93-kDa P. chabaudi erythrocyte membrane-associated protei n is occasionally detected in vesicle-like structures adjacent to the paras ite. These vesicle-like structures are found only coincident with protein s ynthesis and are located at discrete sites on the PVM. These observations s uggest that the 93-kDa protein does not move along the membranous projectio ns of the PVM toward the erythrocyte membrane. It is proposed that the 93-k Da protein is secreted directly into the erythrocyte cytoplasm at discrete PVM domains and then binds to the cytoplasmic face of the erythrocyte membr ane.