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The Yeast Mutant vps5Δ Affected in the Recycling of Golgi Membrane Proteins Displays an Enhanced Vacuolar Mg2+/H+ Exchange Activity
Gilles Borrelly, Jean-Christophe Boyer, Brigitte Touraine, Wojciech Szponarski, Michèle Rambier and Rémy Gibrat
Proceedings of the National Academy of Sciences of the United States of America
Vol. 98, No. 17 (Aug. 14, 2001), pp. 9660-9665
Published by: National Academy of Sciences
Stable URL: http://www.jstor.org/stable/3056408
Page Count: 6
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Growth of the yeast vacuolar protein-sorting mutant vps5Δ affected in the endosome-to-Golgi retromer complex was more sensitive to Mg2+-limiting conditions than was the growth of the wild-type (WT) strain. This sensitivity was enhanced at acidic pH. The vps5Δ strain was also sensitive to Al3+, known to inhibit Mg2+ uptake in yeast cells. In contrast, it was found to be resistant to Ni2+ and Co2+, two cytotoxic analogs of Mg2+. Resistance to Ni2+ did not seem to result from the alteration of plasma-membrane transport properties because mutant and WT cells displayed similar Ni2+ uptake. After plasma-membrane permeabilization, intracellular Ni2+ uptake in vps5Δ cells was 3-fold higher than in WT cells, which is consistent with the implication of the vacuole in the observed phenotypes. In reconstituted vacuolar vesicles prepared from vps5Δ, the rates of H+ exchange with Ni2+, Co2+, and Mg2+ were increased (relative to WT) by 170%, 130%, and 50%, respectively. The rates of H+ exchange with Ca2+, Cd2+, and K+ were similar in both strains, as were α-mannosidase and H+-ATPase activities, and SDS/PAGE patterns of vacuolar proteins. Among 14 other vacuolar protein-sorting mutants tested, only the 8 mutants affected in the recycling of trans-Golgi network membrane proteins shared the same Ni2+ resistance phenotype as vps5Δ. It is proposed that a trans-Golgi network Mg2+/H+ exchanger, mislocalized to vps5Δ vacuole, could be responsible for the phenotypes observed in vivo and in vitro.
Proceedings of the National Academy of Sciences of the United States of America © 2001 National Academy of Sciences