UIS2 function in establishing transport mechanisms at the malaria parasite-host cell interface

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Project Summary Malaria disease remains a serious public health problem. Progress in Malaria control has slowed in recent years while resistance to frontline antimalarials is emerging in the most afflicted regions, underscoring a pressing need to decipher the fundamental biology of the parasite to provide novel therapeutic options. During the pathogenic blood stage, malaria parasites develop within a protective vacuole inside host erythrocytes. Export of effector proteins out of the vacuole remodels the host cell to create a niche for replication while transport of nutrients across this barrier fuels rapid parasite growth. Both of these processes depend on a vacuole membrane pore formed by the parasite protein EXP2, which allows small molecule exchange between the host cytosol and vacuole and is also assembled into the PTEX complex to mediate translocation of effector proteins into the host cell. While these mechanisms are critical to parasite survival and disease pathogenesis, it is unknown how EXP2/PTEX function is specifically established in the vacuole membrane. We recently identified an interaction between EXP2/PTEX and UIS2, a secreted parasite protein that also localizes to the vacuole. Preliminary observations suggest UIS2 is an integral protein of the vacuolar membrane and conditional knockdown of UIS2 in Plasmodium falciparum revealed an essential function in protein export. We hypothesize that UIS2 is required to establish EXP2 function in the PVM, critically enabling both protein export and nutrient uptake. UIS2 contains a purple acid phosphatase domain but is unlikely to be catalytically active as it appears to be missing several key metal coordinating residues. Aim 1 will study the membrane association and topology of UIS2 and evaluate the catalytic activity of the phosphatase domain in vitro and its importance to UIS2 function in vivo. Aim 2 will investigate the function of UIS2 in transport across the vacuolar membrane by determining its precise impact on EXP2 and formation of the nutrient pore. These studies will define the role of UIS2 in PVM transport processes critical to parasite survival and Malaria pathology. Intriguingly, UIS2 is broadly conserved among vacuole-dwelling apicomplexans and the Toxoplasma ortholog of UIS2, known as GRA44, is also critical to an analogous but mechanistically distinct protein export pathway. Thus UIS2/GRA44 may represent a unifying feature of the vacuolar export machinery in these diverse apicomplexans that could suggest novel, widely applicable control strategies for this important group of pathogens.