title: Synaptotagmin mutants Y311N and K326/327A alter the calcium dependence of neurotransmission.
abstract: Synaptotagmin I, a calcium-binding synaptic vesicle protein, is thought to act as the calcium sensor for fast neurotransmission, but what synaptotagmin I does, upon binding calcium, to trigger exocytosis is still unknown. To begin to examine the role of synaptotagmin I's interactions with calcium-dependent binding partners, three mutant versions of synaptotagmin I reported to affect calcium-dependent self-oligomerization (Y311N, K327A, and K326/327A) were expressed in cultured mouse hippocampal neurons lacking endogenous synaptotagmin I, and effects on neurotransmission were evaluated by comparison with transmission rescued by wild-type synaptotagmin I. All three mutants reduced transmitter release. To separate effects on calcium binding from effects on calcium-dependent oligomerization, we measured the calcium dependence of exocytosis for two of the mutants. Both showed apparent calcium affinity much lower than wild-type, a reduction sufficient to account for the neurotransmission defects. We conclude that self-oligomerization is unlikely to play any significant role in triggering synaptic vesicle exocytosis.
authors.affiliation: Molecular Neurobiology Laboratory, Salk Institute for Biological Studies, La Jolla, CA 92037, USA.
authors.forename: Catherine R
authors.initials: CR
authors.lastname: Borden
authors.forename: Charles F
authors.initials: CF
authors.lastname: Stevens
authors.forename: Jane M
authors.initials: JM
authors.lastname: Sullivan
authors.forename: Yongling
authors.initials: Y
authors.lastname: Zhu
mesh_terms: D019943:Amino Acid Substitution; D000818:Animals; D002118:Calcium / Q000378:metabolism; D020013:Calcium Signaling / Q000235:genetics*; D002135:Calcium-Binding Proteins / Q000235:genetics* / Q000378:metabolism; D002478:Cells, Cultured; D015536:Down-Regulation / Q000235:genetics; D019706:Excitatory Postsynaptic Potentials / Q000235:genetics; D005089:Exocytosis / Q000235:genetics; D006624:Hippocampus / Q000378:metabolism*; D008562:Membrane Glycoproteins / Q000235:genetics*; D051379:Mice; D018345:Mice, Knockout; D009154:Mutation / Q000235:genetics*; D009419:Nerve Tissue Proteins / Q000235:genetics*; D011108:Polymers / Q000378:metabolism; D017729:Presynaptic Terminals / Q000378:metabolism*; D009435:Synaptic Transmission / Q000235:genetics*; D013572:Synaptic Vesicles / Q000378:metabolism; D050863:Synaptotagmin I; D050857:Synaptotagmins
chemical_list: D002135:Calcium-Binding Proteins; D008562:Membrane Glycoproteins; D009419:Nerve Tissue Proteins; D011108:Polymers; D050863:Synaptotagmin I; C494311:Syt1 protein, mouse; D050857:Synaptotagmins; D002118:Calcium