Dosemeci A, Choi C
Laboratory of Neurobiology, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland 20892, USA.
Neurochem Res. 1997 Sep;22(9):1151-7. doi: 10.1023/a:1027373404145.
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.
突触后致密物组分中的一种主要蛋白质是α-CAM激酶II，即Ca2+/钙调蛋白依赖性蛋白激酶的α亚基。与突触后致密物相关的CaM激酶II的自身磷酸化可能是诱导活性依赖性突触修饰的关键事件。本研究聚焦于该酶非Ca(2+)依赖性自身磷酸化的调控及其后果。在分离的突触后致密物中，在Ca2+存在下亚化学计量水平的自身磷酸化足以触发α-CaM激酶II的最大非Ca(2+)依赖性自身磷酸化。在无Ca2+时磷酸化的大部分位点可被制剂中的内源性磷酸酶活性去磷酸化。非Ca(2+)依赖性自身磷酸化与钙调蛋白与突触后致密物结合的急剧减少相关。这可能代表一种生理机制，该机制降低了细胞器对钙调蛋白的捕获能力，从而增加了钙调蛋白对棘突内其他成分的可用性。
