title: Retention of the yeast Sac1p phosphatase in the endoplasmic reticulum causes distinct changes in cellular phosphoinositide levels and stimulates microsomal ATP transport.
abstract: The yeast phosphoinositide phosphatase Sac1p localizes to endoplasmic reticulum (ER) and Golgi membranes and has compartment-specific functions in these organelles. In this study we analyzed in detail the topology of Sac1p. Our data show that Sac1p is a type II transmembrane protein with a large N-terminal cytosolic domain, which is anchored in the membrane by the two potential transmembrane helices near the C terminus. Based on this topology, we created a mutation that caused retention of Sac1p in the ER and as a consequence showed specific alterations in cellular phosphoinositide levels. Our results suggest that Sac1p controls a pool of phosphatidylinositol 3-phosphate and phosphatidylinositol 4-phosphate in the ER. Retention of Sac1p in the ER also stimulates ATP transport into the ER lumen but causes the same Golgi-specific defects that are seen in a sac1 null mutant. Taken together this study provides evidence that Sac1p is an important 4-phosphatase in the ER controlling different aspects of ER-based protein processing and secretion.
authors.affiliation: Zentrum für Molekulare Biologie der Universität Heidelberg (ZMBH), Im Neuenheimer Feld 282, D-69120 Heidelberg, Germany.
authors.forename: Gerlinde
authors.initials: G
authors.lastname: Konrad
authors.forename: Tanja
authors.initials: T
authors.lastname: Schlecker
authors.forename: Frank
authors.initials: F
authors.lastname: Faulhammer
authors.forename: Peter
authors.initials: P
authors.lastname: Mayinger
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism*; D020816:Amino Acid Motifs; D001426:Bacterial Proteins / Q000378:metabolism*; D001692:Biological Transport; D002462:Cell Membrane / Q000378:metabolism; D002473:Cell Wall / Q000378:metabolism; D003600:Cytosol / Q000378:metabolism; D004247:DNA / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D017353:Gene Deletion; D005816:Genetic Complementation Test; D006056:Golgi Apparatus / Q000378:metabolism*; D050356:Lipid Metabolism; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; D008856:Microscopy, Fluorescence; D008861:Microsomes / Q000378:metabolism*; D009154:Mutation; D018129:Phosphatidylinositol Phosphates / Q000378:metabolism; D010716:Phosphatidylinositols / Q000378:metabolism*; D010957:Plasmids / Q000378:metabolism; D017434:Protein Structure, Tertiary; D013997:Time Factors
chemical_list: D001426:Bacterial Proteins; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; D018129:Phosphatidylinositol Phosphates; D010716:Phosphatidylinositols; C099636:Sac1 protein, Chlamydomonas reinhardtii; C055525:phosphatidylinositol 3-phosphate; C037178:phosphatidylinositol 4-phosphate; D000255:Adenosine Triphosphate; D004247:DNA