Ca2+ regulates the interaction between synaptotagmin and syntaxin 1.
While there is compelling evidence that the synaptic vesicle protein synaptotagmin serves as the major Ca2+ sensor for regulated exocytosis, it is not known how Ca2+ binding initiates membrane fusion. Here we report that Ca2+ increases the affinity, by approximately 2 orders of magnitude, between synaptotagmin and syntaxin 1, a component of the synaptic fusion apparatus. This effect is specific for divalent cations which can stimulate exocytosis of synaptic vesicles (Ca2+ > Ba2+, Sr2+ >> Mg2+). The Ca(2+)-dependence of the interaction was composed of two components with EC50 values of 0.7 and 180 microM Ca2+. The interaction is mediated by the carboxyl-terminal region of syntaxin 1 (residues 194-288) and is regulated by a novel Ca(2+)-binding site(s) which does not require phospholipids and is not disrupted by mutations that abolish Ca(2+)-dependent phospholipid binding to synaptotagmin. We propose that this interaction constitutes an essential step in excitation-secretion coupling.
Chapman
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Howard Hughes Medical Institute, Boyer Center for Molecular Medicine, Yale University School of Medicine, New Haven, Connecticut 06510, USA.
Hanson
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Jahn
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D000595:Amino Acid Sequence; D000818:Animals; D000954:Antigens, Surface / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D001665:Binding Sites; D001921:Brain / Q000378:metabolism; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D002135:Calcium-Binding Proteins; D005089:Exocytosis; D066298:In Vitro Techniques; D008562:Membrane Glycoproteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D015394:Molecular Structure; D009419:Nerve Tissue Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011485:Protein Binding / Q000187:drug effects; D011487:Protein Conformation / Q000187:drug effects; D051381:Rats; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D017384:Sequence Deletion; D013572:Synaptic Vesicles / Q000378:metabolism; D050857:Synaptotagmins; D050827:Syntaxin 1
D000954:Antigens, Surface; D002135:Calcium-Binding Proteins; D008562:Membrane Glycoproteins; D009419:Nerve Tissue Proteins; D011994:Recombinant Proteins; C494213:Stx1a protein, rat; D050827:Syntaxin 1; D050857:Synaptotagmins; D002118:Calcium