title: Coupled synthesis and translocation restrains polyphosphate to acidocalcisome-like vacuoles and prevents its toxicity.
abstract: Eukaryotes contain inorganic polyphosphate (polyP) and acidocalcisomes, which sequester polyP and store amino acids and divalent cations. Why polyP is sequestered in dedicated organelles is not known. We show that polyP produced in the cytosol of yeast becomes toxic. Reconstitution of polyP translocation with purified vacuoles, the acidocalcisomes of yeast, shows that cytosolic polyP cannot be imported, whereas polyP produced by the vacuolar transporter chaperone (VTC) complex, an endogenous vacuolar polyP polymerase, is efficiently imported and does not interfere with growth. PolyP synthesis and import require an electrochemical gradient, probably as a driving force for polyP translocation. VTC exposes its catalytic domain to the cytosol and carries nine vacuolar transmembrane domains. Mutations in the VTC transmembrane regions, which are likely to constitute the translocation channel, block not only polyP translocation but also synthesis. Given that they are far from the cytosolic catalytic domain of VTC, this suggests that the VTC complex obligatorily couples synthesis of polyP to its import in order to avoid toxic intermediates in the cytosol. Sequestration of otherwise toxic polyP might be one reason for the existence of acidocalcisomes in eukaryotes.
authors.affiliation: Department of Biochemistry, University of Lausanne, Ch. des Boveresses 155, 1066 Epalinges, Switzerland.
authors.forename: Rūta
authors.initials: R
authors.lastname: Gerasimaitė
authors.affiliation: Department of Biochemistry, University of Lausanne, Ch. des Boveresses 155, 1066 Epalinges, Switzerland.
authors.forename: Shruti
authors.initials: S
authors.lastname: Sharma
authors.affiliation: Department of Biochemistry, University of Lausanne, Ch. des Boveresses 155, 1066 Epalinges, Switzerland.
authors.forename: Yann
authors.initials: Y
authors.lastname: Desfougères
authors.affiliation: Department of Biochemistry, University of Lausanne, Ch. des Boveresses 155, 1066 Epalinges, Switzerland.
authors.forename: Andrea
authors.initials: A
authors.lastname: Schmidt
authors.affiliation: Department of Biochemistry, University of Lausanne, Ch. des Boveresses 155, 1066 Epalinges, Switzerland andreas.mayer@unil.ch.
authors.forename: Andreas
authors.initials: A
authors.lastname: Mayer
mesh_terms: D017766:Acid Anhydride Hydrolases / Q000235:genetics / Q000378:metabolism; D001692:Biological Transport; D020134:Catalytic Domain; D003600:Cytosol / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D008564:Membrane Potentials; D018832:Molecular Chaperones / Q000235:genetics / Q000378:metabolism*; D009154:Mutation; D011122:Polyphosphates / Q000378:metabolism* / Q000633:toxicity; D017434:Protein Structure, Tertiary; D012441:Saccharomyces cerevisiae / Q000201:enzymology / Q000235:genetics / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism*; D013997:Time Factors; D014617:Vacuoles / Q000201:enzymology / Q000378:metabolism*; D033921:Vesicular Transport Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: D018832:Molecular Chaperones; D011122:Polyphosphates; D029701:Saccharomyces cerevisiae Proteins; C499587:VTC1 protein, S cerevisiae; D033921:Vesicular Transport Proteins; D017766:Acid Anhydride Hydrolases; C020137:exopolyphosphatase
keywords: Acidocalcisome; Inorganic polyphosphate; VTC complex; Yeast vacuole