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Calcium-dependent serine phosphorylation of synaptophysin
J L Rubenstein1, P Greengard, A J Czernik
1Laboratory of Molecular and Cellular Neuroscience, Rockefeller University, New York, New York 10021-6399.
Synapse (New York, N.Y.)
|February 1, 1993
Summary
Calcium-dependent phosphorylation of synaptophysin, a key synaptic vesicle protein, is regulated by Ca(2+)/calmodulin-dependent protein kinase II (CaM kinase II) under physiological conditions, impacting neuronal function.
Area of Science:
- Neuroscience
- Molecular Biology
- Cell Biology
Background:
- Synaptophysin is a major integral membrane protein of small synaptic vesicles.
- Synaptic vesicle protein phosphorylation plays a critical role in regulating neurotransmission.
Purpose of the Study:
- To investigate the role of calcium (Ca2+) in the regulation of synaptophysin phosphorylation.
- To identify the specific kinase involved in synaptophysin phosphorylation.
Main Methods:
- Phosphorylation assays using 32P-orthophosphate labeling in rat cerebrocortical slices and synaptosomes.
- Biochemical analysis of purified synaptic vesicles and CaM kinase II.
- In vitro phosphorylation experiments with purified synaptophysin and CaM kinase II.
Main Results:
- K(+)-induced depolarization increased serine phosphorylation of synaptophysin in a Ca(2+)-dependent manner.
- Ca2+ and calmodulin stimulated synaptophysin phosphorylation in purified synaptic vesicles.
- CaM kinase II directly phosphorylated synaptophysin, producing similar phosphopeptide maps to in vivo phosphorylation.
Conclusions:
- Ca(2+)-dependent phosphorylation of synaptophysin is mediated by CaM kinase II.
- This phosphorylation mechanism is active under physiological conditions, suggesting a role in synaptic function.