title: Steady-state free Ca(2+) in the yeast endoplasmic reticulum reaches only 10 microM and is mainly controlled by the secretory pathway pump pmr1.
abstract: Over recent decades, diverse intracellular organelles have been recognized as key determinants of Ca(2+) signaling in eukaryotes. In yeast however, information on intra-organellar Ca(2+) concentrations is scarce, despite the demonstrated importance of Ca(2+) signals for this microorganism. Here, we directly monitored free Ca(2+) in the lumen of the endoplasmic reticulum (ER) of yeast cells, using a specifically targeted version of the Ca(2+)-sensitive photoprotein aequorin. Ca(2+) uptake into the yeast ER displayed characteristics distinctly different from the mammalian ER. At steady-state, the free Ca(2+) concentration in the ER lumen was limited to approximately 10 microM, and ER Ca(2+) sequestration was insensitive to thapsigargin, an inhibitor specific for mammalian ER Ca(2+) pumps. In pmr1 null mutants, free Ca(2+) in the ER was reduced by 50%. Our findings identify the secretory pathway pump Pmr1, predominantly localized in the Golgi, as a major component of ER Ca(2+) uptake activity in yeast.
authors.affiliation: Institut für Biochemie der Universität Stuttgart, Pfaffenwaldring 55, D-70569 Stuttgart, Germany.
authors.forename: J
authors.initials: J
authors.lastname: Strayle
authors.forename: T
authors.initials: T
authors.lastname: Pozzan
authors.forename: H K
authors.initials: HK
authors.lastname: Rudolph
mesh_terms: D018528:ATP-Binding Cassette Transporters / Q000378:metabolism*; D000331:Aequorin / Q000378:metabolism; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism* / Q000493:pharmacokinetics; D000252:Calcium-Transporting ATPases; D003513:Cycloheximide / Q000494:pharmacology; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006056:Golgi Apparatus / Q000378:metabolism; D006706:Homeostasis; D007476:Ionophores / Q000494:pharmacology; D008954:Models, Biological; D018832:Molecular Chaperones; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins; D012519:Sarcoplasmic Reticulum / Q000378:metabolism*; D013696:Temperature; D019284:Thapsigargin / Q000494:pharmacology; D014638:Vanadates / Q000494:pharmacology
chemical_list: D018528:ATP-Binding Cassette Transporters; D004791:Enzyme Inhibitors; D007476:Ionophores; D018832:Molecular Chaperones; D011500:Protein Synthesis Inhibitors; D011993:Recombinant Fusion Proteins; C101767:SSC1 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D000001:Calcimycin; D014638:Vanadates; D000331:Aequorin; D019284:Thapsigargin; D003513:Cycloheximide; D000252:Calcium-Transporting ATPases; D002118:Calcium