Mechanisms of Protein Transport in Plasmodium

Haldar, Kasturi

Abstract

The long-term objectives are to understand the functions of specialized membrane organelles of plasmodia and their interactions with the host.
The specific aims are to identify and characterize plasmodial activities which may be responsible for membrane traffic in parasitized erythrocytes and may modify the properties of the host erythrocyte. These aspects of parasite biology are directly relevant to understanding intracellular membrane traffic in eucaryotes and parasite survival in the host. In the asexual blood stages, Plasmodium has a complex relationship with the host, which is poorly understood at the biochemical level. The use of biochemical and molecular biological tools to analyze cellular parasite phenomena should elucidate relevant modes of host-parasite interaction. In general, intracellular pathways of membrane traffic are conserved in cells. There is evidence for directed transport of plasmodial proteins to the cytosol and membrane of the infected erythrocyte which results in modifications in the structure and functions of the host cell. Functional or structural homologies between purified plasmodial poly- peptides (often easily detectable at the nucleotide level) and well defined protein molecules involved in vacuolar export suggest a method of investigating the organization of membrane protein traffic in plasmodia. The in vitro cultivation of Plasmodium falciparum permits these studies in human malaria. Relatively large amounts of parasites can be grown in the laboratory to generate adequate quantities of RNA, DNA and immunopurified radiolabelled proteins, whose structure may then be investigated by chemical and enzymatic methods to determine specific aspects of modification at both the nucleotide and polypeptide level. The use of specific antibodies to protein components in microscopy and kinetics analyses of their biosynthesis and turnover (by immunoprecipitation of the polypeptides in pulse chase studies) enables determining their true location in the cell. Essential to the biochemical analysis of parasite modifications of the host erythrocyte is the characterization of cell-free transport across the intraerythrocytic space, which is currently undefined. These novel protein transport events may be understood by examining conditions regulating the biosynthetic export of relevant marker proteins from within the intraerythrocytic parasite. The project will extend a comprehensive effort to study secretory export in Plasmodium.