title: Phosphatidylinositol 4,5-bisphosphate regulates SNARE-dependent membrane fusion.
abstract: Phosphatidylinositol 4,5-bisphosphate (PI 4,5-P(2)) on the plasma membrane is essential for vesicle exocytosis but its role in membrane fusion has not been determined. Here, we quantify the concentration of PI 4,5-P(2) as approximately 6 mol% in the cytoplasmic leaflet of plasma membrane microdomains at sites of docked vesicles. At this concentration of PI 4,5-P(2) soluble NSF attachment protein receptor (SNARE)-dependent liposome fusion is inhibited. Inhibition by PI 4,5-P(2) likely results from its intrinsic positive curvature-promoting properties that inhibit formation of high negative curvature membrane fusion intermediates. Mutation of juxtamembrane basic residues in the plasma membrane SNARE syntaxin-1 increase inhibition by PI 4,5-P(2), suggesting that syntaxin sequesters PI 4,5-P(2) to alleviate inhibition. To define an essential rather than inhibitory role for PI 4,5-P(2), we test a PI 4,5-P(2)-binding priming factor required for vesicle exocytosis. Ca(2+)-dependent activator protein for secretion promotes increased rates of SNARE-dependent fusion that are PI 4,5-P(2) dependent. These results indicate that PI 4,5-P(2) regulates fusion both as a fusion restraint that syntaxin-1 alleviates and as an essential cofactor that recruits protein priming factors to facilitate SNARE-dependent fusion.
authors.affiliation: Department of Biochemistry, University of Wisconsin, Madison, WI 53706, USA.
authors.forename: Declan J
authors.initials: DJ
authors.lastname: James
authors.forename: Chuenchanok
authors.initials: C
authors.lastname: Khodthong
authors.forename: Judith A
authors.initials: JA
authors.lastname: Kowalchyk
authors.forename: Thomas F J
authors.initials: TF
authors.lastname: Martin
mesh_terms: D000818:Animals; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D004305:Dose-Response Relationship, Drug; D005089:Exocytosis / Q000187:drug effects / Q000502:physiology*; D008081:Liposomes / Q000378:metabolism; D008561:Membrane Fusion / Q000187:drug effects / Q000502:physiology*; D021962:Membrane Microdomains / Q000187:drug effects / Q000378:metabolism / Q000648:ultrastructure; D016716:PC12 Cells; D019269:Phosphatidylinositol 4,5-Diphosphate / Q000378:metabolism* / Q000494:pharmacology; D051381:Rats; D050600:SNARE Proteins / Q000378:metabolism*; D050827:Syntaxin 1 / Q000187:drug effects / Q000378:metabolism; D022161:Transport Vesicles / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure
chemical_list: D008081:Liposomes; D019269:Phosphatidylinositol 4,5-Diphosphate; D050600:SNARE Proteins; D050827:Syntaxin 1