A plasma membrane-type Ca2+-ATPase co-localizes with a vacuolar H+-pyrophosphatase to acidocalcisomes of Toxoplasma gondii

Ca2+-ATPases are likely to play critical roles in the biochemistry of Toxop lasma gondii, since these protozoa are obligate intracellular parasites and the Ca2+ concentration in their intracellular location is three orders of magnitude lower than in the extracellular medium. Here, we report the cloni ng and sequencing of a gene encoding a plasma membrane-type Ca2+ ATPase (PM CA) of T.gondii (TgA1), The predicted protein (TgA1) exhibits 32-36% identi ty to vacuolar Ca2+-ATPases of Trypanosoma cruzi, Saccharomyces cerevisiae, Entamoeba histolytica and Dictyostelium discoideum, Sequencing of both cDN A and genomic DNA from T.gondii indicated that TgA1 contains two introns ne ar the C-terminus, A hydropathy profile of the protein suggests 10 transmem brane domains. TgA1 suppresses the Ca2+ hypersensitivity of a mutant of S.c erevisiae that has a defect in vacuolar Ca2+ accumulation. Indirect immunof luorescence and immunoelectron microscopy analysis indicate that TgA1 local izes to the plasma membrane and co-localizes with the vacuolar H+-pyrophosp hatase to intracellular vacuoles identified morphologically and by X-ray mi croanalysis as the acidocalcisomes. This vacuolar-type Ca2+-ATPase could pl ay an important role in Ca2+ homeostasis in T.gondii.