Synaptotagmin I functions as a calcium sensor to synchronize neurotransmitter release.
To characterize Ca(2+)-mediated synaptic vesicle fusion, we analyzed Drosophila synaptotagmin I mutants deficient in specific interactions mediated by its two Ca(2+) binding C2 domains. In the absence of synaptotagmin I, synchronous release is abolished and a kinetically distinct delayed asynchronous release pathway is uncovered. Synapses containing only the C2A domain of synaptotagmin partially recover synchronous fusion, but have an abolished Ca(2+) cooperativity. Mutants that disrupt Ca(2+) sensing by the C2B domain have synchronous release with normal Ca(2+) cooperativity, but with reduced release probability. Our data suggest the Ca(2+) cooperativity of neurotransmitter release is likely mediated through synaptotagmin-SNARE interactions, while phospholipid binding and oligomerization trigger rapid fusion with increased release probability. These results indicate that synaptotagmin is the major Ca(2+) sensor for evoked release and functions to trigger synchronous fusion in response to Ca(2+), while suppressing asynchronous release.
Yoshihara
Motojiro
M
Picower Center for Learning and Memory, Cambridge, MA, USA. motojiro@mit.edu
Littleton
J Troy
JT
D000818:Animals; D001665:Binding Sites; D002118:Calcium / Q000378:metabolism*; D002135:Calcium-Binding Proteins; D004331:Drosophila melanogaster / Q000502:physiology; D004558:Electric Stimulation; D004625:Embryo, Nonmammalian / Q000502:physiology; D005838:Genotype; D008561:Membrane Fusion / Q000502:physiology*; D008562:Membrane Glycoproteins / Q000235:genetics / Q000378:metabolism*; D008565:Membrane Proteins / Q000378:metabolism; D008954:Models, Biological; D009154:Mutation; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism*; D018377:Neurotransmitter Agents / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D050600:SNARE Proteins; D013569:Synapses / Q000502:physiology; D009435:Synaptic Transmission / Q000502:physiology*; D013572:Synaptic Vesicles / Q000378:metabolism; D050863:Synaptotagmin I; D050857:Synaptotagmins; D013997:Time Factors; D033921:Vesicular Transport Proteins
D002135:Calcium-Binding Proteins; D008562:Membrane Glycoproteins; D008565:Membrane Proteins; D009419:Nerve Tissue Proteins; D018377:Neurotransmitter Agents; D050600:SNARE Proteins; D050863:Synaptotagmin I; D033921:Vesicular Transport Proteins; D050857:Synaptotagmins; D002118:Calcium