title: Phosphatidylinositol 4,5-bisphosphate clusters act as molecular beacons for vesicle recruitment.
abstract: Synaptic-vesicle exocytosis is mediated by the vesicular Ca(2+) sensor synaptotagmin-1. Synaptotagmin-1 interacts with the SNARE protein syntaxin-1A and acidic phospholipids such as phosphatidylinositol 4,5-bisphosphate (PIP2). However, it is unclear how these interactions contribute to triggering membrane fusion. Using PC12 cells from Rattus norvegicus and artificial supported bilayers, we show that synaptotagmin-1 interacts with the polybasic linker region of syntaxin-1A independent of Ca(2+) through PIP2. This interaction allows both Ca(2+)-binding sites of synaptotagmin-1 to bind to phosphatidylserine in the vesicle membrane upon Ca(2+) triggering. We determined the crystal structure of the C2B domain of synaptotagmin-1 bound to phosphoserine, allowing development of a high-resolution model of synaptotagmin bridging two different membranes. Our results suggest that PIP2 clusters organized by syntaxin-1 act as molecular beacons for vesicle docking, with the subsequent Ca(2+) influx bringing the vesicle membrane close enough for membrane fusion.
authors.affiliation: Department of Nanobiophotonics, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany.
authors.forename: Alf
authors.initials: A
authors.lastname: Honigmann
authors.forename: Geert
authors.initials: G
authors.lastname: van den Bogaart
authors.forename: Emilio
authors.initials: E
authors.lastname: Iraheta
authors.forename: H Jelger
authors.initials: HJ
authors.lastname: Risselada
authors.forename: Dragomir
authors.initials: D
authors.lastname: Milovanovic
authors.forename: Veronika
authors.initials: V
authors.lastname: Mueller
authors.forename: Stefan
authors.initials: S
authors.lastname: Müllar
authors.forename: Ulf
authors.initials: U
authors.lastname: Diederichsen
authors.forename: Dirk
authors.initials: D
authors.lastname: Fasshauer
authors.forename: Helmut
authors.initials: H
authors.lastname: Grubmüller
authors.forename: Stefan W
authors.initials: SW
authors.lastname: Hell
authors.forename: Christian
authors.initials: C
authors.lastname: Eggeling
authors.forename: Karin
authors.initials: K
authors.lastname: Kühnel
authors.forename: Reinhard
authors.initials: R
authors.lastname: Jahn
mesh_terms: D000818:Animals; D018360:Crystallography, X-Ray; D005089:Exocytosis; D008954:Models, Biological; D008958:Models, Molecular; D016716:PC12 Cells; D019269:Phosphatidylinositol 4,5-Diphosphate / Q000378:metabolism*; D011485:Protein Binding; D011487:Protein Conformation; D051381:Rats; D013572:Synaptic Vesicles / Q000378:metabolism*; D050863:Synaptotagmin I / Q000737:chemistry / Q000378:metabolism*; D050827:Syntaxin 1 / Q000378:metabolism*
chemical_list: D019269:Phosphatidylinositol 4,5-Diphosphate; D050863:Synaptotagmin I; D050827:Syntaxin 1; C494312:Syt1 protein, rat