Malaria is responsible for immense loss of life, morbidity and poverty in endemic countries and is caused by infection of red blood cells by Plasmodium parasites. Central to the pathogenesis of malaria is the parasite’s ability to hijack and renovate erythrocytes by exporting hundreds of effector proteins into the host red blood cell. Export of effector cargo involves proteolytic cleavage of the Plasmodium export element (PEXEL) motif in exported proteins by the aspartyl protease plasmepsin V prior to translocation. Attempts to genetically disrupt the plasmepsin V gene have failed and development of inhibitors have shown that this enzyme is essential for effector export and parasite development in red blood cells.
Prior to blood stage infection, malaria parasites deposited into the host by a mosquito infect the liver. The parasites co-opt host innate responses to disarm hepatocyte autophagy and apoptosis in order to grow. Successful liver stage development is crucial for establishing subsequent blood stage infection that causes malaria. New antimalarials targeting the liver stage will therefore be an important component of future antimalarial therapy. Here, we conditionally delete the plasmepsin V locus from the Plasmodium genome during passage through mosquitoes. This approach does not affect parasite development in the blood or mosquito stages of the lifecycle. Dissection of ΔPlasmepsin V sporozoites from mosquitoes and injection into mice results in parasite clearance in the liver, no malaria infections and protective immunity against lethal sporozoite challenge. Immunofluorescence microscopy reveals that export of a PEXEL-containing effector protein into the hepatocyte is blocked in cells infected with ΔPlasmepsin V sporozoites. Altogether, this study shows plasmepsin V is essential in blood and liver stages owing to a conserved role in export of different malaria effector proteins that commandeer host cells in different ways. Identification of further hepatocyte effectors involved in liver stage survival is underway. Plasmepsin V thus represents a multi-stage, pan-Plasmodium target for a new class of antimalarial drugs.