title: Examining synaptotagmin 1 function in dense core vesicle exocytosis under direct control of Ca2+.
abstract: We tested the long-standing hypothesis that synaptotagmin 1 is the Ca2+ sensor for fast neurosecretion by analyzing the intracellular Ca2+ dependence of large dense-core vesicle exocytosis in a mouse strain carrying a mutated synaptotagmin C2A domain. The mutation (R233Q) causes a twofold increase in the KD of Ca2+-dependent phospholipid binding to the double C2A-C2B domain of synaptotagmin. Using photolysis of caged calcium and capacitance measurements we found that secretion from mutant cells had lower secretory rates, longer secretory delays, and a higher intracellular Ca2+-threshold for secretion due to a twofold increase in the apparent KD of the Ca2+ sensor for fast exocytosis. Single amperometric fusion events were unchanged. We conclude that Ca2+-dependent phospholipid binding to synaptotagmin 1 mirrors the intracellular Ca2+ dependence of exocytosis.
authors.affiliation: Max-Planck-Institut für Biophysikalische Chemie, Abteilung Membranbiophysik, Am Fassberg 11, D-37077 Göttingen, Germany. jsoeren@gwdg.de
authors.forename: Jakob B
authors.initials: JB
authors.lastname: Sørensen
authors.forename: Rafael
authors.initials: R
authors.lastname: Fernández-Chacón
authors.forename: Thomas C
authors.initials: TC
authors.lastname: Südhof
authors.forename: Erwin
authors.initials: E
authors.lastname: Neher
mesh_terms: D000818:Animals; D001120:Arginine / Q000235:genetics; D002118:Calcium / Q000502:physiology*; D002135:Calcium-Binding Proteins; D019439:Chromaffin Cells / Q000378:metabolism; D004056:Differential Threshold; D025802:Electric Capacitance; D005089:Exocytosis / Q000502:physiology*; D005973:Glutamine / Q000235:genetics; D007425:Intracellular Membranes / Q000378:metabolism; D008562:Membrane Glycoproteins / Q000235:genetics / Q000502:physiology*; D051379:Mice; D008817:Mice, Mutant Strains; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000502:physiology*; D010743:Phospholipids / Q000378:metabolism; D017354:Point Mutation / Q000235:genetics; D022142:Secretory Vesicles / Q000502:physiology*; D050863:Synaptotagmin I; D050857:Synaptotagmins; D013997:Time Factors
chemical_list: D002135:Calcium-Binding Proteins; D008562:Membrane Glycoproteins; D009419:Nerve Tissue Proteins; D010743:Phospholipids; D050863:Synaptotagmin I; C494311:Syt1 protein, mouse; D005973:Glutamine; D050857:Synaptotagmins; D001120:Arginine; D002118:Calcium