Ca(2+)-independent autophosphorylation of postsynaptic density-associated Ca2+/calmodulin-dependent protein kinase.
A major protein in the postsynaptic density fraction is alpha-CAM kinase II, the alpha-subunit of the Ca2+/calmodulin-dependent protein kinase. Autophosphorylation of the postsynaptic density-associated CaM kinase II is likely to be a crucial event in the induction of activity-dependent synaptic modification. This study focuses on the regulation and consequences of Ca(2+)-independent autophosphorylation of the enzyme. In isolated postsynaptic densities, a sub-stochiometric level of autophosphorylation in the presence of Ca2+ is sufficient to trigger maximal Ca(2+)-independent autophosphorylation of alpha-CaM Kinase II. A major fraction of the sites phosphorylated in the absence of Ca2+ can be dephosphorylated by the endogenous phosphatase activity in the preparation. Ca(2+)-independent autophosphorylation is correlated with a drastic decrease in calmodulin binding to postsynaptic densities. This may represent a physiological mechanism that lower the calmodulin trapping capacity of the organelle, thus increasing the availability of calmodulin to other elements within a spine.
Dosemeci
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Laboratory of Neurobiology, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland 20892, USA. ayse@codon.nih.gov
Choi
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D000818:Animals; D001481:Basal Metabolism; D002118:Calcium / Q000502:physiology*; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism*; D010766:Phosphorylation; D051381:Rats; D013569:Synapses / Q000378:metabolism*
D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D002118:Calcium