A. Dosemeci et C. Choi, CA2-INDEPENDENT AUTOPHOSPHORYLATION OF POSTSYNAPTIC DENSITY-ASSOCIATED CA2+()CALMODULIN-DEPENDENT PROTEIN-KINASE/, Neurochemical research, 22(9), 1997, pp. 1151-1157
A major protein in the postsynaptic density fraction is alpha-CAM kina
se II, the alpha-subunit of the Ca2+/calmodulin-dependent protein kina
se. Autophosphorylation of the postsynaptic density-associated CaM kin
ase II is likely to be a crucial event in the induction of activity-de
pendent synaptic modification. This study focuses on the regulation an
d consequences of Ca2+-independent autophosphorylation of the enzyme.
In isolated postsynaptic densities, a sub-stochiometric level of autop
hosphorylation in the presence of Ca2+ is sufficient to trigger maxima
l Ca2+-independent autophosphorylation of alpha-CaM Kinase II. A major
fraction of the sites phosphorylated in the absence of Ca2+ can be de
phosphorylated by the endogenous phosphatase activity in the preparati
on. Ca2+-independent autophosphorylation is correlated with a drastic
decrease in calmodulin binding to postsynaptic densities. This may rep
resent a physiological mechanism that lowers the calmodulin trapping c
apacity of the organelle, thus increasing the availability of calmodul
in to other elements within a spine.