title: Fusion pore formation and expansion induced by Ca2+ and synaptotagmin 1.
abstract: Fusion pore formation and expansion, crucial steps for neurotransmitter release and vesicle recycling in soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE)-dependent vesicle fusion, have not been well studied in vitro due to the lack of a reliable content-mixing fusion assay. Using methods detecting the intervesicular mixing of small and large cargoes at a single-vesicle level, we found that the neuronal SNARE complexes have the capacity to drive membrane hemifusion. However, efficient fusion pore formation and expansion require synaptotagmin 1 and Ca(2+). Real-time measurements show that pore expansion detected by content mixing of large DNA cargoes occurs much slower than initial pore formation that transmits small cargoes. Slow pore expansion perhaps provides a time window for vesicles to escape the full collapse fusion pathway via alternative mechanisms such as kiss-and-run. The results also show that complexin 1 stimulates pore expansion significantly, which could put bias between two pathways of vesicle recycling.
authors.affiliation: Department of Biochemistry, Biophysics, and Molecular Biology, Iowa State University, Ames, IA 50011, USA.
authors.forename: Ying
authors.initials: Y
authors.lastname: Lai
authors.forename: Jiajie
authors.initials: J
authors.lastname: Diao
authors.forename: Yanxin
authors.initials: Y
authors.lastname: Liu
authors.forename: Yuji
authors.initials: Y
authors.lastname: Ishitsuka
authors.forename: Zengliu
authors.initials: Z
authors.lastname: Su
authors.forename: Klaus
authors.initials: K
authors.lastname: Schulten
authors.forename: Taekjip
authors.initials: T
authors.lastname: Ha
authors.forename: Yeon-Kyun
authors.initials: YK
authors.lastname: Shin
mesh_terms: D033942:Adaptor Proteins, Vesicular Transport / Q000378:metabolism; D000818:Animals; D055592:Biophysical Phenomena; D002118:Calcium / Q000378:metabolism*; D015342:DNA Probes; D050356:Lipid Metabolism; D008561:Membrane Fusion / Q000502:physiology*; D008954:Models, Biological; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed; D009419:Nerve Tissue Proteins / Q000378:metabolism; D009474:Neurons / Q000378:metabolism; D051381:Rats; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D050600:SNARE Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D050863:Synaptotagmin I / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
chemical_list: D033942:Adaptor Proteins, Vesicular Transport; D015342:DNA Probes; D009419:Nerve Tissue Proteins; D011993:Recombinant Fusion Proteins; D050600:SNARE Proteins; D050863:Synaptotagmin I; C494312:Syt1 protein, rat; C095992:complexin I; D002118:Calcium