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Science 330 (6003): 502-505

Copyright © 2010 by the American Association for the Advancement of Science

Fast Vesicle Fusion in Living Cells Requires at Least Three SNARE Complexes

Ralf Mohrmann,1,2,* Heidi de Wit,3 Matthijs Verhage,3 Erwin Neher,1 Jakob B. Sørensen1,4,5,*

Abstract: Exocytosis requires formation of SNARE [soluble N-ethylmaleimide–sensitive factor attachment protein (SNAP) receptor] complexes between vesicle and target membranes. Recent assessments in reduced model systems have produced divergent estimates of the number of SNARE complexes needed for fusion. Here, we used a titration approach to answer this question in intact, cultured chromaffin cells. Simultaneous expression of wild-type SNAP-25 and a mutant unable to support exocytosis progressively altered fusion kinetics and fusion-pore opening, indicating that both proteins assemble into heteromeric fusion complexes. Expressing different wild-type:mutant ratios revealed a third-power relation for fast (synchronous) fusion and a near-linear relation for overall release. Thus, fast fusion typically observed in synapses and neurosecretory cells requires at least three functional SNARE complexes, whereas slower release might occur with fewer complexes. Heterogeneity in SNARE-complex number may explain heterogeneity in vesicular release probability.

1 Department of Membrane Biophysics, Max-Planck Institute for Biophysical Chemistry, Göttingen, Germany.
2 Department of Physiology, University of Saarland, Homburg, Germany.
3 Center for Neurogenomics and Cognitive Research, Department of Functional Genomics, Vrije Universiteit (VU) Amsterdam and VU Medical Center, Amsterdam, Netherlands.
4 Department of Neuroscience and Pharmacology, Faculty of Health Sciences, University of Copenhagen, Copenhagen, Denmark.
5 Lundbeck Foundation Center for Biomembranes in Nanomedicine, University of Copenhagen, Copenhagen, Denmark.

* To whom correspondence should be addressed. E-mail: Ralf.Mohrmann{at}uks.eu (R.M.); jakobbs{at}sund.ku.dk (J.B.S.)

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