Synaptotagmin-1 docks secretory vesicles to syntaxin-1/SNAP-25 acceptor complexes.
Docking, the initial association of secretory vesicles with the plasma membrane, precedes formation of the SNARE complex, which drives membrane fusion. For many years, the molecular identity of the docked state, and especially the vesicular docking protein, has been unknown, as has the link to SNARE complex assembly. Here, using adrenal chromaffin cells, we identify the vesicular docking partner as synaptotagmin-1, the calcium sensor for exocytosis, and SNAP-25 as an essential plasma membrane docking factor, which, together with the previously known docking factors Munc18-1 and syntaxin, form the minimal docking machinery. Moreover, we show that the requirement for Munc18-1 in docking, but not fusion, can be overcome by stabilizing syntaxin/SNAP-25 acceptor complexes. These findings, together with cross-rescue, double-knockout, and electrophysiological data, lead us to propose that vesicles dock when synaptotagmin-1 binds to syntaxin/SNAP-25 acceptor complexes, whereas Munc18-1 is required for the downstream association of synaptobrevin to form fusogenic SNARE complexes.
de Wit
Heidi
H
Department of Functional Genomics, Center for Neurogenomics and Cognitive Research, Neuroscience Campus Amsterdam, Vrije Universiteit Amsterdam and VU Medical Center, 1081 HV Amsterdam, the Netherlands.
Walter
Alexander M
AM
Milosevic
Ira
I
Gulyás-Kovács
Attila
A
Riedel
Dietmar
D
Sørensen
Jakob B
JB
Verhage
Matthijs
M
D000818:Animals; D002462:Cell Membrane / Q000378:metabolism*; D019439:Chromaffin Cells / Q000378:metabolism*; D055786:Gene Knockout Techniques; D051379:Mice; D051938:Munc18 Proteins / Q000378:metabolism; D022142:Secretory Vesicles / Q000378:metabolism*; D050863:Synaptotagmin I / Q000378:metabolism*; D050827:Syntaxin 1 / Q000235:genetics / Q000378:metabolism*
D051938:Munc18 Proteins; C497938:Stxbp1 protein, mouse; D050863:Synaptotagmin I; D050827:Syntaxin 1