title: Yeast lipin 1 orthologue pah1p regulates vacuole homeostasis and membrane fusion.
abstract: Vacuole homotypic fusion requires a group of regulatory lipids that includes diacylglycerol, a fusogenic lipid that is produced through multiple metabolic pathways including the dephosphorylation of phosphatidic acid (PA). Here we examined the relationship between membrane fusion and PA phosphatase activity. Pah1p is the single yeast homologue of the Lipin family of PA phosphatases. Deletion of PAH1 was sufficient to cause marked vacuole fragmentation and abolish vacuole fusion. The function of Pah1p solely depended on its phosphatase activity as complementation studies showed that wild type Pah1p restored fusion, whereas the phosphatase dead mutant Pah1p(D398E) had no effect. We discovered that the lack of PA phosphatase activity blocked fusion by inhibiting the binding of SNAREs to Sec18p, an N-ethylmaleimide-sensitive factor homologue responsible for priming inactive cis-SNARE complexes. In addition, pah1Δ vacuoles were devoid of the late endosome/vacuolar Rab Ypt7p, the phosphatidylinositol 3-kinase Vps34p, and Vps39p, a subunit of the HOPS (homotypic fusion and vacuole protein sorting) tethering complex, all of which are required for vacuole fusion. The lack of Vps34p resulted in the absence of phosphatidylinositol 3-phosphate, a lipid required for SNARE activity and vacuole fusion. These findings demonstrate that Pah1p and PA phosphatase activity are critical for vacuole homeostasis and fusion.
authors: Department of Biochemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA.
authors: Terry
authors: T
authors: Sasser
authors: Quan-Sheng
authors: QS
authors: Qiu
authors: Surya
authors: S
authors: Karunakaran
authors: Mark
authors: M
authors: Padolina
authors: Anna
authors: A
authors: Reyes
authors: Blake
authors: B
authors: Flood
authors: Sheena
authors: S
authors: Smith
authors: Chad
authors: C
authors: Gonzales
authors: Rutilio A
authors: RA
authors: Fratti
mesh_terms: D033942:Adaptor Proteins, Vesicular Transport / Q000235:genetics / Q000378:metabolism; D000251:Adenosine Triphosphatases / Q000235:genetics / Q000378:metabolism; D058546:Class III Phosphatidylinositol 3-Kinases / Q000235:genetics / Q000378:metabolism; D006706:Homeostasis / Q000502:physiology*; D007425:Intracellular Membranes / Q000378:metabolism*; D008561:Membrane Fusion / Q000502:physiology*; D010711:Phosphatidate Phosphatase / Q000235:genetics / Q000378:metabolism*; D050600:SNARE Proteins / Q000235:genetics / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000201:enzymology* / Q000235:genetics; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism*; D014617:Vacuoles / Q000235:genetics / Q000378:metabolism*; D033921:Vesicular Transport Proteins / Q000235:genetics / Q000378:metabolism; D020691:rab GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism
chemical_list: D033942:Adaptor Proteins, Vesicular Transport; D050600:SNARE Proteins; D029701:Saccharomyces cerevisiae Proteins; C406817:VAM6 protein, S cerevisiae; D033921:Vesicular Transport Proteins; D058546:Class III Phosphatidylinositol 3-Kinases; C079831:PAH1 protein, S cerevisiae; D010711:Phosphatidate Phosphatase; D000251:Adenosine Triphosphatases; C064404:SEC18 protein, S cerevisiae; C079005:YPT7 protein, S cerevisiae; D020691:rab GTP-Binding Proteins