Examining synaptotagmin 1 function in dense core vesicle exocytosis under direct control of Ca2+ |
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Authors: | Sørensen Jakob B Fernández-Chacón Rafael Südhof Thomas C Neher Erwin |
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Affiliation: | Max-Planck-Institut für Biophysikalische Chemie, Abteilung Membranbiophysik, Am Fassberg 11, D-37077 G?ttingen, Germany. jsoeren@gwdg.de |
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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. |
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