Ca(2+)-ATPases of Saccharomyces cerevisiae: diversity and possible role in protein sorting.
The PMR1 gene of Saccharomyces cerevisiae is thought to encode a putative Ca(2+)-ATPase [1]. Membranes isolated from wild-type cells and from pmr1 null mutant of S. cerevisiae were fractionated on sucrose density gradients. In the pmr1 mutant we found a decrease in activity of the P-type ATPase and of ATP-dependent, protonophore-insensitive Ca2+ transport in light membranes, that comigrate with the Golgi marker GDPase. We conclude that the product of the PMR1 gene (Pmr1p) is indeed a Ca(2+)-ATPase of the Golgi and Golgi-like membranes. Surprisingly, the pmr1 null mutation abolished Ca(2+)-ATPase activity in Golgi and/or Golgi-like membranes only to 50% under conditions where they are separated from vacuolar membranes. This indicates that an additional Ca(2+)-ATPase is localized in Golgi and/or Golgi-like membranes. Moreover, a third Ca(2+)-ATPase is found in the ER and ER-like membranes. The data are consistent with the assumption that these Ca(2+)-ATPases are encoded by gene(s) different from PMR1. Disruption of PMR1 Ca(2+)-ATPase causes significant redistribution of enzyme activities and of total protein in compartments of the secretory pathway. A decrease in activity is observed for three integral membrane proteins: NADPH cytochrome c reductase, dolichyl phosphate mannose synthase, and Ca(2+)-ATPase, and also for total protein in Golgi, Golgi-like compartments and in vacuoles, whereas a corresponding increase of these activities is observed in endoplasmic reticulum and endoplasmic reticulum-like membranes. We assume that Ca(2+)-ATPases and sufficient Ca2+ gradients across the organellar membranes are important for the correct sorting of proteins to the various compartments of the secretory apparatus.
Okorokov
L A
LA
Lehrstuhl für Zellbiologie und Pflanzenphysiologie, Universitat Regensburg, Germany. Okorokov@uenf.br
Lehle
L
L
D001692:Biological Transport; D002118:Calcium / Q000378:metabolism; D000252:Calcium-Transporting ATPases / Q000235:genetics / Q000378:metabolism*; D002458:Cell Fractionation; D002462:Cell Membrane / Q000201:enzymology; D004721:Endoplasmic Reticulum / Q000201:enzymology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005656:Fungal Proteins / Q000378:metabolism*; D006056:Golgi Apparatus / Q000201:enzymology*; D017136:Ion Transport; D008364:Mannosyltransferases / Q000378:metabolism; D009154:Mutation; D009251:NADPH-Ferrihemoprotein Reductase / Q000378:metabolism; D006180:Proton-Translocating ATPases / Q000378:metabolism; D011755:Pyrophosphatases / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000201:enzymology*; D014617:Vacuoles / Q000201:enzymology; D014638:Vanadates / Q000494:pharmacology
D004791:Enzyme Inhibitors; D005656:Fungal Proteins; D014638:Vanadates; D009251:NADPH-Ferrihemoprotein Reductase; D008364:Mannosyltransferases; C022755:dolichyl-phosphate beta-D-mannosyltransferase; D011755:Pyrophosphatases; C010357:guanosine-diphosphatase; D006180:Proton-Translocating ATPases; D000252:Calcium-Transporting ATPases; D002118:Calcium