Ca
Regulates the Interaction between Synaptotagmin and Syntaxin 1 (*)
- From the Howard Hughes Medical Institute and Departments of Pharmacology and Cell Biology, Boyer Center for Molecular Medicine, Yale University School of Medicine, New Haven, Connecticut 06510
- § To whom correspondence should be addressed. Tel.: 203-737-4454; Fax: 203-737-1763.
Abstract
While there is compelling evidence that the synaptic vesicle protein synaptotagmin serves as the major Ca
sensor for regulated exocytosis, it is not known how Ca
binding initiates membrane fusion. Here we report that Ca
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
(Ca
> Ba
, Sr
Mg
). The Ca
-dependence of the interaction was composed of two components with EC
values of 0.7 and 180 μM Ca
. The interaction is mediated by the carboxyl-terminal region of syntaxin 1 (residues 194-288) and is regulated by a novel
Ca
-binding site(s) which does not require phospholipids and is not disrupted by mutations that abolish Ca
-dependent phospholipid binding to synaptotagmin. We propose that this interaction constitutes an essential step in excitation-secretion
coupling.
Footnotes
-
↵¶ Supported by the Helen Hay Whitney Foundation.
-
↵* The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore by hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
-
↵1 The abbreviations used are:
- NSF
-
N-ethlymaleimide-sensitive fusion factor
- GST
-
glutathione S-transferase
- PAGE
-
polyacrylamide gel electrophoresis
- SNAP
-
soluble NSF attachment protein
- SNARE
-
SNAP receptor.
-
- Received May 22, 1995.
- Revision received June 29, 1995.
- © 1995 by The American Society for Biochemistry and Molecular Biology, Inc.
