Retention of the yeast Sac1p phosphatase in the endoplasmic reticulum causes distinct changes in cellular phosphoinositide levels and stimulates microsomal ATP transport.
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.
Konrad
Gerlinde
G
Zentrum für Molekulare Biologie der Universität Heidelberg (ZMBH), Im Neuenheimer Feld 282, D-69120 Heidelberg, Germany.
Schlecker
Tanja
T
Faulhammer
Frank
F
Mayinger
Peter
P
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
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