title: Synaptotagmin-1 may be a distance regulator acting upstream of SNARE nucleation.
abstract: Synaptotagmin-1 triggers Ca(2+)-sensitive, rapid neurotransmitter release by promoting interactions between SNARE proteins on synaptic vesicles and the plasma membrane. How synaptotagmin-1 promotes this interaction is unclear, and the massive increase in membrane fusion efficiency of Ca(2+)-bound synaptotagmin-1 has not been reproduced in vitro. However, previous experiments have been performed at relatively high salt concentrations, screening potentially important electrostatic interactions. Using functional reconstitution in liposomes, we show here that at low ionic strength SNARE-mediated membrane fusion becomes strictly dependent on both Ca(2+) and synaptotagmin-1. Under these conditions, synaptotagmin-1 functions as a distance regulator that tethers the liposomes too far from the plasma membrane for SNARE nucleation in the absence of Ca(2+), but while bringing the liposomes close enough for membrane fusion in the presence of Ca(2+). These results may explain how the relatively weak electrostatic interactions between synaptotagmin-1 and membranes substantially accelerate fusion.
authors.affiliation: Department of Neurobiology, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany.
authors.forename: Geert
authors.initials: G
authors.lastname: van den Bogaart
authors.forename: Shashi
authors.initials: S
authors.lastname: Thutupalli
authors.forename: Jelger H
authors.initials: JH
authors.lastname: Risselada
authors.forename: Karsten
authors.initials: K
authors.lastname: Meyenberg
authors.forename: Matthew
authors.initials: M
authors.lastname: Holt
authors.forename: Dietmar
authors.initials: D
authors.lastname: Riedel
authors.forename: Ulf
authors.initials: U
authors.lastname: Diederichsen
authors.forename: Stephan
authors.initials: S
authors.lastname: Herminghaus
authors.forename: Helmut
authors.initials: H
authors.lastname: Grubmüller
authors.forename: Reinhard
authors.initials: R
authors.lastname: Jahn
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D008081:Liposomes / Q000378:metabolism; D008561:Membrane Fusion / Q000502:physiology; D008958:Models, Molecular; D009994:Osmolar Concentration; D051381:Rats; D050600:SNARE Proteins / Q000737:chemistry / Q000378:metabolism / Q000502:physiology*; D055672:Static Electricity; D050863:Synaptotagmin I / Q000737:chemistry / Q000378:metabolism / Q000502:physiology*
chemical_list: D008081:Liposomes; D050600:SNARE Proteins; D050863:Synaptotagmin I; D002118:Calcium