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Push-and-pull regulation of the fusion pore by synaptotagmin-7

Margarita Segovia, Eva Alés, María Angeles Montes, Imelda Bonifas, Imane Jemal, Manfred Lindau, Anton Maximov, Thomas C. Südhof and Guillermo Alvarez de Toledo
Proceedings of the National Academy of Sciences of the United States of America
Vol. 107, No. 44 (November 2, 2010), pp. 19032-19037
Stable URL: http://www.jstor.org/stable/25748616
Page Count: 6
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Push-and-pull regulation of the fusion pore by synaptotagmin-7
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Abstract

In chromaffin cells, Ca²⁺ 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 Ca²⁺ 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 Ca²⁺ binding to the two synaptotagmin-7 C2 domains in exocytosis. We show that, surprisingly, Ca²⁺ 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 Ca²⁺ 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.

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