title: Synaptotagmin activates membrane fusion through a Ca2+-dependent trans interaction with phospholipids.
abstract: Synaptotagmin-1 is the calcium sensor for neuronal exocytosis, but the mechanism by which it triggers membrane fusion is not fully understood. Here we show that synaptotagmin accelerates SNARE-dependent fusion of liposomes by interacting with neuronal Q-SNARES in a Ca2+-independent manner. Ca2+-dependent binding of synaptotagmin to its own membrane impedes the activation. Preventing this cis interaction allows Ca2+ to trigger synaptotagmin binding in trans, accelerating fusion. However, when an activated SNARE acceptor complex is used, synaptotagmin has no effect on fusion kinetics, suggesting that synaptotagmin operates upstream of SNARE assembly in this system. Our results resolve major discrepancies concerning the effects of full-length synaptotagmin and its C2AB fragment on liposome fusion and shed new light on the interactions of synaptotagmin with SNAREs and membranes. However, our findings also show that the action of synaptotagmin on the fusion-arrested state of docked vesicles in vivo is not fully reproduced in vitro.
authors: Department of Neurobiology, Max Planck Institute for Biophysical Chemistry, Am Fassberg 11, D-37077 Göttingen, Germany.
authors: Alexander
authors: A
authors: Stein
authors: Anand
authors: A
authors: Radhakrishnan
authors: Dietmar
authors: D
authors: Riedel
authors: Dirk
authors: D
authors: Fasshauer
authors: Reinhard
authors: R
authors: Jahn
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D008081:Liposomes / Q000378:metabolism; D008561:Membrane Fusion / Q000502:physiology*; D046912:Multiprotein Complexes; D009474:Neurons / Q000378:metabolism; D010446:Peptide Fragments / Q000235:genetics / Q000378:metabolism*; D010743:Phospholipids / Q000378:metabolism*; D051381:Rats; D050600:SNARE Proteins / Q000378:metabolism; D050863:Synaptotagmin I / Q000235:genetics / Q000378:metabolism*
chemical_list: D008081:Liposomes; D046912:Multiprotein Complexes; D010446:Peptide Fragments; D010743:Phospholipids; D050600:SNARE Proteins; D050863:Synaptotagmin I; D002118:Calcium