The yeast mutant vps5Delta affected in the recycling of Golgi membrane proteins displays an enhanced vacuolar Mg2+/H+ exchange activity.
Growth of the yeast vacuolar protein-sorting mutant vps5Delta 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 vps5Delta 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 vps5Delta 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 vps5Delta, 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 alpha-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 vps5Delta. It is proposed that a trans-Golgi network Mg2+/H+ exchanger, mislocalized to vps5Delta vacuole, could be responsible for the phenotypes observed in vivo and in vitro.
Borrelly
G
G
Biochimie et Physiologie Moléculaire des Plantes, Ecole Nationale Supérieure d'Agronomie de Montpellier (Agro-M)/Institut National de la Recherche Agronomique, France.
Boyer
J C
JC
Touraine
B
B
Szponarski
W
W
Rambier
M
M
Gibrat
R
R
D017920:Antiporters / Q000378:metabolism*; D029681:Arabidopsis Proteins; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D002412:Cations / Q000378:metabolism; D004352:Drug Resistance, Microbial; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism*; D006056:Golgi Apparatus / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D017136:Ion Transport; D008274:Magnesium / Q000378:metabolism / Q000494:pharmacology*; D008565:Membrane Proteins / Q000378:metabolism*; D010641:Phenotype; D011522:Protons; D012441:Saccharomyces cerevisiae / Q000235:genetics* / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins; D014617:Vacuoles / Q000378:metabolism*; D033921:Vesicular Transport Proteins
D017920:Antiporters; D029681:Arabidopsis Proteins; C120847:AtMHX protein, Arabidopsis; D002352:Carrier Proteins; D002412:Cations; D005656:Fungal Proteins; D008565:Membrane Proteins; D011522:Protons; D029701:Saccharomyces cerevisiae Proteins; C106932:VPS5 protein, S cerevisiae; D033921:Vesicular Transport Proteins; D008274:Magnesium