title: Augmenting neurotransmitter release by enhancing the apparent Ca2+ affinity of synaptotagmin 1.
abstract: Synaptotagmin 1 likely acts as a Ca2+ sensor in neurotransmitter release by Ca2+-binding to its two C2 domains. This notion was strongly supported by the observation that a mutation in the C2A domain causes parallel decreases in the apparent Ca2+ affinity of synaptotagmin 1 and in the Ca2+ sensitivity of release. However, this study was based on a single loss-of-function mutation. We now show that tryptophan substitutions in the synaptotagmin 1 C2 domains act as gain-of-function mutations to increase the apparent Ca2+ affinity of synaptotagmin 1. The same substitutions, when introduced into synaptotagmin 1 expressed in neurons, enhance the Ca2+ sensitivity of release. Mutations in the two C2 domains lead to comparable and additive effects in release. Our results thus show that the apparent Ca2+ sensitivity of release is dictated by the apparent Ca2+ affinity of synaptotagmin 1 in both directions, and that Ca2+ binding to both C2 domains contributes to Ca2+ triggering of release.
authors.affiliation: Department of Neuroscience, Baylor College of Medicine, One Baylor Plaza, Houston, TX 7703, USA.
authors.forename: J-S
authors.initials: JS
authors.lastname: Rhee
authors.forename: L Y
authors.initials: LY
authors.lastname: Li
authors.forename: O-H
authors.initials: OH
authors.lastname: Shin
authors.forename: J-C
authors.initials: JC
authors.lastname: Rah
authors.forename: J
authors.initials: J
authors.lastname: Rizo
authors.forename: T C
authors.initials: TC
authors.lastname: Südhof
authors.forename: C
authors.initials: C
authors.lastname: Rosenmund
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D002413:Cations, Divalent / Q000378:metabolism / Q000494:pharmacology; D002478:Cells, Cultured; D018698:Glutamic Acid / Q000378:metabolism*; D051379:Mice; D018345:Mice, Knockout; D008958:Models, Molecular; D009154:Mutation / Q000235:genetics; D017434:Protein Structure, Tertiary; D050863:Synaptotagmin I / Q000737:chemistry / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D013997:Time Factors; D014364:Tryptophan / Q000235:genetics / Q000378:metabolism
chemical_list: D002413:Cations, Divalent; D050863:Synaptotagmin I; D018698:Glutamic Acid; D014364:Tryptophan; D002118:Calcium