Calcium‐Dependent Dissociation of Synaptotagmin from Synaptic SNARE Complexes

• Published in: Journal of neurochemistry Vol. 74; no. 1; pp. 367 - 374
• Main Authors: Leveque, Christian, Boudier, Jeanne‐Andree, Takahashi, Masami, Seagar, Michael
• Format: Journal Article
• Language: English
• Published: Oxford UK Blackwell Science Ltd 01.01.2000; Blackwell
• Subjects: Adenosine Triphosphate - analogs & derivatives; Adenosine Triphosphate - pharmacology; Animals; Biological and medical sciences; Brain - drug effects; Brain - metabolism; Calcium - physiology; Calcium-Binding Proteins; Carrier Proteins - antagonists & inhibitors; Cell Membrane - metabolism; Cell physiology; Drug Resistance; Endocytosis; Ethylmaleimide - pharmacology; Exocytosis; Exocytosis - physiology; Fundamental and applied biological sciences. Psychology; Membrane Glycoproteins - metabolism; Membrane Proteins - metabolism; Molecular and cellular biology; N-Ethylmaleimide-Sensitive Proteins; Nerve Tissue Proteins - metabolism; N‐Ethylmaleimide‐sensitive fusion protein; Rats; SNARE complex; SNARE Proteins; Sodium Dodecyl Sulfate - pharmacology; Synapses - metabolism; Synaptic vesicle; Synaptic Vesicles - metabolism; Synaptosomal‐associated protein of 25 kDa; Synaptotagmin I; Synaptotagmins; Syntaxin; Vesicle‐associated membrane protein; Vesicular Transport Proteins; Vertebrata; Synaptosome; Mammalia; Calcium; Rat; Synaptic transmission; Rodentia; Synaptic vesicle; Molecular complex; Synaptotagmin; Exocytosis; In vitro
• ISSN: 0022-3042; 1471-4159
• DOI: 10.1046/j.1471-4159.2000.0740367.x

: The formation of the synaptic core (SNARE) complex constitutes a crucial step in synaptic vesicle fusion at the nerve terminal. The interaction of synaptotagmin I with this complex potentially provides a means of conferring Ca2+‐dependent regulation of exocytosis. However, the subcellular compartments in which interactions occur and their modulation by Ca2+ influx remain obscure. Sodium dodecyl sulfate (SDS)‐resistant core complexes, associated with synaptotagmin I, were enriched in rat brain fractions containing plasma membranes and docked synaptic vesicles. Depolarization of synaptosomes triggered [3H]GABA release and Ca2+‐dependent dissociation of synaptotagmin from the core complex. In perforated synaptosomes, synaptotagmin dissociation was induced by Ca2+ (30‐300 μM) but not Sr2+ (1 mM); it apparently required intact membrane bilayers but did not result in disassembly of trimeric SNARE complexes. Synaptotagmin was not associated with unstable v‐SNARE/t‐SNARE complexes, present in fractions containing synaptic vesicles and cytoplasm. These complexes acquired SDS resistance when N‐ethylmaleimide‐sensitive fusion protein (NSF) was inhibited with N‐ethylmaleimide or adenosine 5′‐O‐(3‐thiotriphosphate), suggesting that constitutive SNARE complex disassembly occurs in undocked synaptic vesicles. Our findings are consistent with models in which the Ca2+‐triggered release of synaptotagmin precedes vesicle fusion. NSF may then dissociate ternary core complexes captured by endocytosis and recycle/prime individual SNARE proteins.