Push-and-pull regulation of the fusion pore by synaptotagmin-7.
In chromaffin cells, Ca(2+) binding to synaptotagmin-1 and -7 triggers exocytosis by promoting fusion pore opening and fusion pore expansion. Synaptotagmins contain two C2 domains that both bind Ca(2+) and contribute to exocytosis; however, it remains unknown whether the C2 domains act similarly or differentially to promote opening and expansion of fusion pores. Here, we use patch amperometry measurements in WT and synaptotagmin-7-mutant chromaffin cells to analyze the role of Ca(2+) binding to the two synaptotagmin-7 C2 domains in exocytosis. We show that, surprisingly, Ca(2+) binding to the C2A domain suffices to trigger fusion pore opening but that the resulting fusion pores are unstable and collapse, causing a dramatic increase in kiss-and-run fusion events. Thus, synaptotagmin-7 controls fusion pore dynamics during exocytosis via a push-and-pull mechanism in which Ca(2+) binding to both C2 domains promotes fusion pore opening, but the C2B domain is selectively essential for continuous expansion of an otherwise unstable fusion pore.
Departamento de Fisiología Médica y Biofísica, Facultad de Medicina, University of Seville, 41009 Seville, Spain.
Margarita
M
Segovia
Eva
E
Alés
María Angeles
MA
Montes
Imelda
I
Bonifas
Imane
I
Jemal
Manfred
M
Lindau
Anton
A
Maximov
Thomas C
TC
Südhof
Guillermo
G
Alvarez de Toledo
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D019439:Chromaffin Cells / Q000166:cytology / Q000378:metabolism*; D005089:Exocytosis / Q000502:physiology*; D005260:Female; D008297:Male; D008561:Membrane Fusion / Q000502:physiology*; D051379:Mice; D018345:Mice, Knockout / Q000235:genetics / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D050863:Synaptotagmin I / Q000235:genetics / Q000378:metabolism; D050857:Synaptotagmins / Q000235:genetics / Q000378:metabolism*
D050863:Synaptotagmin I; C494311:Syt1 protein, mouse; C494303:Syt7 protein, mouse; D050857:Synaptotagmins; D002118:Calcium