Journal
SCIENCE
Volume 330, Issue 6003, Pages 502-505Publisher
AMER ASSOC ADVANCEMENT SCIENCE
DOI: 10.1126/science.1193134
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Funding
- Lundbeck Foundation
- Lundbeck Foundation Center for Biomembranes in Nanomedicine
- Danish Medical Research Council
- Netherlands Organization for Scientific Research [Pionier/VICI900-01-001, ZonMW 903-42-095, VENI 916-36-043]
- NeuroBsik Mouse Phenomics Consortium [BSIK03053]
- European Union [HEALTH-F2-2009-242167]
- Lundbeck Foundation [R28-2008-1976] Funding Source: researchfish
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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.
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