title: Calcium uptake and proton transport by acidocalcisomes of Toxoplasma gondii.
abstract: Acidocalcisomes are acidic calcium stores found in diverse organisms, being conserved from bacteria to humans. They possess an acidic matrix that contains several cations bound to phosphates, which are mainly present in the form of short and long polyphosphate chains. Their matrix is acidified through the action of proton pumps such as a vacuolar proton ATPase and a vacuolar proton pyrophosphatase. Calcium uptake occurs through a Ca(2+)/H(+) countertransporting ATPase located in the membrane of the organelle. Acidocalcisomes have been identified in a variety of microorganisms, including Apicomplexan parasites such as Plasmodium and Eimeria species, and in Toxoplasma gondii. We report the purification and characterization of an acidocalcisome fraction from T. gondii tachyzoites after subcellular fractionation and further discontinuous iodixanol gradient purification. Proton and calcium transport activities in the fraction were characterized by fluorescence microscopy and spectrophotometric methods using acridine orange and arsenazo III, respectively. This work will facilitate the understanding of the function of acidocalcisomes in Apicomplexan parasites, as we can now isolate highly purified fractions that could be used for proteomic analysis to find proteins that may clarify the biogenesis of these organelles.
authors.affiliation: Department of Cellular Biology and Center for Tropical and Emerging Global Diseases, University of Georgia, Athens, Georgia, United States of America.
authors.forename: Peter
authors.initials: P
authors.lastname: Rohloff
authors.forename: Kildare
authors.initials: K
authors.lastname: Miranda
authors.forename: Juliany C F
authors.initials: JC
authors.lastname: Rodrigues
authors.forename: Jianmin
authors.initials: J
authors.lastname: Fang
authors.forename: Melina
authors.initials: M
authors.lastname: Galizzi
authors.forename: Helmut
authors.initials: H
authors.lastname: Plattner
authors.forename: Joachim
authors.initials: J
authors.lastname: Hentschel
authors.forename: Silvia N J
authors.initials: SN
authors.lastname: Moreno
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D015415:Biomarkers / Q000378:metabolism; D002118:Calcium / Q000378:metabolism*; D002122:Calcium Chloride / Q000494:pharmacology; D002463:Cell Membrane Permeability / Q000187:drug effects; D017136:Ion Transport / Q000187:drug effects; D015388:Organelles / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D011122:Polyphosphates / Q000378:metabolism; D017494:Proton Pumps / Q000378:metabolism; D011522:Protons; D012965:Sodium Chloride / Q000494:pharmacology; D013347:Subcellular Fractions / Q000187:drug effects / Q000378:metabolism; D014122:Toxoplasma / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D014283:Triiodobenzoic Acids / Q000494:pharmacology
chemical_list: D015415:Biomarkers; D011122:Polyphosphates; D017494:Proton Pumps; D011522:Protons; D014283:Triiodobenzoic Acids; D012965:Sodium Chloride; D000255:Adenosine Triphosphate; C044834:iodixanol; D002122:Calcium Chloride; D002118:Calcium