Calmodulin-Dependent Protein Phosphorylation in Synaptic Junctions
- 1 November 1985
- journal article
- research article
- Published by Wiley in Journal of Neurochemistry
- Vol. 45 (5), 1620-1634
- https://doi.org/10.1111/j.1471-4159.1985.tb07235.x
Abstract
Synaptic junctions (SJs) from rat forebrain were examined for Ca2+/calmodulin (CaM)-dependent kinase activity and compared to synaptic plasma membrane (SPM) and postsynaptic density (PSD) fractions. The kinase activity in synaptic fractions was examined for its capacity to phosphorylate endogenous proteins or exogenous synapsin I, in the presence or absence of Ca2+ plus CaM. When assayed for endogenous protein phosphorylation, SJs contained approximately 25-fold greater amounts of Ca2+/CAM-dependent kinase activity than SPMs, and fivefold more activity than PSDs. When kinase activities were measured by phosphorylation of exogenous synapsin I, SJs contained fourfold more activity than SPMs, and 10-fold more than PSDs. The phosphorylation of SJ proteins of 60- and 50-kilodalton (major PSD protein) polypeptides were greatly stimulated by Ca2+/CaM; levels of phosphorylation for these proteins were 23- and 17-fold greater than basal levels, respectively. Six additional proteins whose phosphorylation was stimulated 6-15-fold by Ca2+/CAM were identified in SJs. These proteins include synapsin I, and proteins of 240, 207, 170, 140, and 54 kilodaltons. The 54-kilodalton protein is a highly phosphorylated form of the major PSD protein and the 170-kilodalton component is a cell-surface glycoprotein of the postsynaptic membrane that binds concanavalin A. The CaM-dependent kinase in SJ fractions phosphorylated endogenous phosphoproteins at serine and/or threonine residues. Ca2+-dependent phosphorylation in SJ fractions was strictly dependent on exogenous CaM, even though SJs contained substantial amounts of endogenous CaM (15 .mu.g CaM/mg SJ protein). Exogenous CaM, after being functionally incorporated into SJs, was rapidly removed by sequential washings. These observations suggest that the SJ-associated CaM involved in regulating Ca2+-dependent protein phosphorylation may be in dynamic equilibrium with the cytoplasm. These findings indicate that a brain CaM-dependent kinase(s) and substrate proteins are concentrated at SJs and that CaM-dependent protein phosphorylation may play an important role in mechanisms that underlie synaptic communication.Keywords
This publication has 49 references indexed in Scilit:
- Identification of the Major Postsynaptic Density Protein as Homologous with the Major Calmodulin‐Binding Subunit of a Calmodulin‐Dependent Protein KinaseJournal of Neurochemistry, 1984
- Synapsin I (Protein I), a nerve terminal-specific phosphoprotein. II. Its specific association with synaptic vesicles demonstrated by immunocytochemistry in agarose-embedded synaptosomes.The Journal of cell biology, 1983
- Purification and Characterization of a Ca2+‐ and Calmodulin‐Dependent Protein Kinase from Rat BrainJournal of Neurochemistry, 1982
- Ca2+ and Calmodulin‐Dependent Phosphorylation of Endogenous Synaptic Vesicle Tubulin by a Vesicle‐Bound Calmodulin Kinase SystemJournal of Neurochemistry, 1982
- Identification of myosin in isolated synaptic junctionsBrain Research, 1981
- Function of a calmodulin in postsynaptic densities. III. Calmodulin-binding proteins of the postsynaptic density.The Journal of cell biology, 1981
- Function of calmodulin in postsynaptic densities. II. Presence of a calmodulin- activatable protein kinase activityThe Journal of cell biology, 1981
- ROLE OF CALMODULIN IN NEUROTRANSMITTER RELEASE AND SYNAPTIC FUNCTION*Annals of the New York Academy of Sciences, 1980
- Calmodulin Plays a Pivotal Role in Cellular RegulationScience, 1980
- ISOLATION OF POSTSYNAPTIC DENSITIES FROM RAT BRAINThe Journal of cell biology, 1974