Calcium-independent stimulation of membrane fusion and SNAREpin formation by synaptotagmin I.
Neurotransmitter 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.
Mahal
Lara K
LK
Cellular Biochemistry and Biophysics Program, Memorial Sloan Kettering Cancer Center, 1275 York Avenue, New York, NY 10021, USA.
Sequeira
Sonia M
SM
Gureasko
Jodi M
JM
Söllner
Thomas H
TH
D002118:Calcium / Q000378:metabolism*; D002135:Calcium-Binding Proteins; D008081:Liposomes / Q000378:metabolism; D008561:Membrane Fusion; D008562:Membrane Glycoproteins / Q000378:metabolism* / Q000502:physiology; D008565:Membrane Proteins / Q000378:metabolism* / Q000502:physiology; D009419:Nerve Tissue Proteins / Q000378:metabolism* / Q000502:physiology; D050600:SNARE Proteins; D009435:Synaptic Transmission; D050863:Synaptotagmin I; D050857:Synaptotagmins; D033921:Vesicular Transport Proteins
D002135:Calcium-Binding Proteins; D008081:Liposomes; D008562:Membrane Glycoproteins; D008565:Membrane Proteins; D009419:Nerve Tissue Proteins; D050600:SNARE Proteins; D050863:Synaptotagmin I; D033921:Vesicular Transport Proteins; D050857:Synaptotagmins; D002118:Calcium