| Summary: | Summary: Vacuolar-proton ATPases (V-ATPases) are conserved complexes that couple the hydrolysis of ATP to the pumping of protons across membranes. V-ATPases are known to play diverse roles in cellular physiology. We studied the Toxoplasma gondii V-ATPase complex and discovered a dual role of the pump in protecting parasites against ionic stress and in the maturation of secretory proteins in endosomal-like compartments. Toxoplasma V-ATPase subunits localize to the plasma membrane and to acidic vesicles, and characterization of conditional mutants of the a1 subunit highlighted the functionality of the complex at both locations. Microneme and rhoptry proteins are required for invasion and modulation of host cells, and they traffic via endosome-like compartments in which proteolytic maturation occurs. We show that the V-ATPase supports the maturation of rhoptry and microneme proteins, and their maturases, during their traffic to their corresponding organelles. This work underscores a role for V-ATPases in regulating virulence pathways. : Stasic et al. characterize the function of the vacuolar proton ATPase in the life cycle of Toxoplasma gondii, a widespread parasite that infects almost one-third of the world’s population. The work presents molecular evidence of the pump’s role in the synthesis of virulence factors of a highly successful pathogen. Keywords: toxoplasma, vacuolar-H+-ATPase, intracellular pH, proton transport, plant-like vacuole, VAC, rhoptries, micronemes, lytic cycle, lysosome
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