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Elife. 2017 Mar 27;6. pii: e22964. doi: 10.7554/eLife.22964.

Dilation of fusion pores by crowding of SNARE proteins.

Author information

1
Department of Cellular and Molecular Physiology, School of Medicine, Yale University, New Haven, United States.
2
Nanobiology Institute, Yale University, West Haven, United States.
3
Department of Cell Biology, School of Medicine, Yale University, New Haven, United States.
4
Department of Physics, Columbia University, New York, United States.
5
Department of Chemical Engineering, Columbia University, New York, United States.
6
Molecular Biophysics and Biochemistry, Yale University, New Haven, United States.
7
Laboratoire de Neurophotonique, Université Paris Descartes, Faculté des Sciences Fondamentales et Biomédicales, Centre National de la Recherche Scientifique, Paris, France.

Abstract

Hormones and neurotransmitters are released through fluctuating exocytotic fusion pores that can flicker open and shut multiple times. Cargo release and vesicle recycling depend on the fate of the pore, which may reseal or dilate irreversibly. Pore nucleation requires zippering between vesicle-associated v-SNAREs and target membrane t-SNAREs, but the mechanisms governing the subsequent pore dilation are not understood. Here, we probed the dilation of single fusion pores using v-SNARE-reconstituted ~23-nm-diameter discoidal nanolipoprotein particles (vNLPs) as fusion partners with cells ectopically expressing cognate, 'flipped' t-SNAREs. Pore nucleation required a minimum of two v-SNAREs per NLP face, and further increases in v-SNARE copy numbers did not affect nucleation rate. By contrast, the probability of pore dilation increased with increasing v-SNARE copies and was far from saturating at 15 v-SNARE copies per face, the NLP capacity. Our experimental and computational results suggest that SNARE availability may be pivotal in determining whether neurotransmitters or hormones are released through a transient ('kiss and run') or an irreversibly dilating pore (full fusion).

KEYWORDS:

E. coli; SNARE proteins; biophysics; cell biology; exocytosis; fusion pore; membrane fusion; protein crowding; structural biology

PMID:
28346138
DOI:
10.7554/eLife.22964
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