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A small GTP-binding protein dissociates from synaptic vesicles during exocytosis
G Fischer von Mollard1, T C Südhof, R Jahn
1Department of Neurochemistry, Max-Planck Institute for Psychiatry, Martinsried, Germany.
Nature
|January 3, 1991
Summary
Small GTP-binding proteins regulate membrane traffic. In nerve terminals, rab3A protein dissociates from synaptic vesicles after calcium-dependent exocytosis, providing direct evidence for a regulatory cycle.
Area of Science:
- Cell Biology
- Neuroscience
- Molecular Biology
Background:
- Low-molecular-weight GTP-binding proteins are implicated as regulators of membrane traffic.
- Mutations in yeast sec4 or ypt1 genes affect membrane flow, suggesting a role for these proteins.
- A proposed model involves GTP-binding proteins cycling between soluble and membrane-bound states, but direct evidence is lacking.
Purpose of the Study:
- To investigate the dynamic association of the small GTP-binding protein rab3A with synaptic vesicles during exocytosis.
- To provide direct evidence for the proposed association-dissociation cycle of GTP-binding proteins in membrane traffic.
Main Methods:
- Utilized isolated rat brain nerve terminals to study synaptic vesicle exocytosis.
- Monitored the association state of rab3A with vesicle membranes before, during, and after stimulation.
Main Results:
- Rab3A was found to quantitatively dissociate from synaptic vesicle membranes following calcium-dependent exocytosis.
- The dissociation of rab3A was partially reversible upon recovery after stimulation.
- These findings provide direct evidence for an association-dissociation cycle of rab3A.
Conclusions:
- Rab3A undergoes an association-dissociation cycle linked to synaptic vesicle exocytosis.
- This cycle supports the hypothesis that small GTP-binding proteins regulate membrane traffic through dynamic membrane association and dissociation.