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© The Rockefeller University Press,
0021-9525/2002/7/273 $5.00
The Journal of Cell Biology, Volume 158, Number 2, July 22, 2002 273-282
Article |
Calcium-independent stimulation of membrane fusion and SNAREpin formation by synaptotagmin I
Address correspondence to Thomas H. Söllner, Cellular Biochemistry and Biophysics Program, Memorial Sloan Kettering Cancer Center, 1275 York Ave., Rm. 517D, New York, NY 10021. Tel.: (212) 639-5172. Fax: (212) 717-3604. E-mail: t-sollner{at}ski.mskcc.org
Ñeurotransmitter release requires the direct coupling of the calcium sensor with the machinery for membrane fusion. SNARE proteins comprise the minimal fusion machinery, and synaptotagmin I, a synaptic vesicle protein, is the primary candidate for the main neuronal calcium sensor. To test the effect of synaptotagmin I on membrane fusion, we incorporated it into a SNARE-mediated liposome fusion assay. Synaptotagmin I dramatically stimulated membrane fusion by facilitating SNAREpin zippering. This stimulatory effect was topologically restricted to v-SNARE vesicles (containing VAMP 2) and only occurred in trans to t-SNARE vesicles (containing syntaxin 1A and SNAP-25). Interestingly, calcium did not affect the overall fusion reaction. These results indicate that synaptotagmin I can directly accelerate SNARE-mediated membrane fusion and raise the possibility that additional components might be required to ensure tight calcium coupling.
Key Words: SNARE; fusion; synaptotagmin; calcium; exocytosis
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