A plasma membrane‐type Ca 2+ ‐ATPase co‐localizes with a vacuolar H + ‐pyrophosphatase to acidocalcisomes of Toxoplasma gondii

Ca 2+ ‐ATPases are likely to play critical roles in the biochemistry of Toxoplasma gondii , since these protozoa are obligate intracellular parasites and the Ca 2+ concentration in their intracellular location is three orders of magnitude lower than in the extracellular medium. Here, we report the cloning and sequencing of a gene encoding a plasma membrane‐type Ca 2+ ‐ATPase (PMCA) of T.gondii ( TgA1 ). The predicted protein (TgA1) exhibits 32–36% identity to vacuolar Ca 2+ ‐ATPases of Trypanosoma cruzi, Saccharomyces cerevisiae, Entamoeba histolytica and Dictyostelium discoideum . Sequencing of both cDNA and genomic DNA from T.gondii indicated that TgA1 contains two introns near the C‐terminus. A hydropathy profile of the protein suggests 10 transmembrane domains. TgA1 suppresses the Ca 2+ hypersensitivity of a mutant of S.cerevisiae that has a defect in vacuolar Ca 2+ accumulation. Indirect immunofluorescence and immunoelectron microscopy analysis indicate that TgA1 localizes to the plasma membrane and co‐localizes with the vacuolar H + ‐pyrophosphatase to intracellular vacuoles identified morphologically and by X‐ray microanalysis as the acidocalcisomes. This vacuolar‐type Ca 2+ ‐ATPase could play an important role in Ca 2+ homeostasis in T.gondii .