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J Biol Chem. 2018 Dec 7;293(49):19101-19112. doi: 10.1074/jbc.RA118.005884. Epub 2018 Oct 12.

5-Diphosphoinositol pentakisphosphate (5-IP7) regulates phosphate release from acidocalcisomes and yeast vacuoles.

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From the Center for Tropical and Emerging Global Diseases and.
the Departments of Cellular Biology and.
the Department of Chemistry and Pharmacy, University of Freiburg, 79098 Freiburg, Germany.
Microbiology and Infectious Diseases, University of Georgia, Athens, Georgia 30602 and.
From the Center for Tropical and Emerging Global Diseases and


Acidocalcisomes of Trypanosoma brucei and the acidocalcisome-like vacuoles of Saccharomyces cerevisiae are acidic calcium compartments that store polyphosphate (polyP). Both organelles possess a phosphate-sodium symporter (TbPho91 and Pho91p in T. brucei and yeast, respectively), but the roles of these transporters in growth and orthophosphate (Pi) transport are unclear. We found here that Tbpho91 -/- trypanosomes have a lower growth rate under phosphate starvation and contain larger acidocalcisomes that have increased Pi content. Heterologous expression of TbPHO91 in Xenopus oocytes followed by two-electrode voltage clamp recordings disclosed that myo-inositol polyphosphates stimulate both sodium-dependent depolarization of the oocyte membrane potential and Pi conductance. Deletion of the SPX domain in TbPho91 abolished this stimulation. Inositol pyrophosphates such as 5-diphosphoinositol pentakisphosphate generated outward currents in Na+/Pi-loaded giant vacuoles prepared from WT or from TbPHO91-expressing pho91Δ strains but not from the pho91Δ yeast strains or from the pho91Δ strains expressing PHO91 or TbPHO91 with mutated SPX domains. Our results indicate that TbPho91 and Pho91p are responsible for vacuolar Pi and Na+ efflux and that myo-inositol polyphosphates stimulate the Na+/Pi symporter activities through their SPX domains.


SPX domain; Saccharomyces cerevisiae; Trypanosoma brucei; Xenopus; acidocalcisome; inositol phosphate; inositol pyrophosphate; phosphate/sodium symporter; vacuole

[Available on 2019-12-07]
[Indexed for MEDLINE]

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