Characterization of mouse neuronal Ca2+/calmodulin kinase II inhibitor alpha.

We have overexpressed an 8.5-kDa mouse Ca(2+)/calmodulin kinase II inhibitor alpha protein (mCaMKIINalpha) in Escherichia coli and demonstrate that the recombinant protein is a potent inhibitor of Ca(2+)/calmodulin kinase II (CaMKII) in vitro. However, antibodies raised against recombinant mCaMKIINalpha react with an approximately 37-kDa protein present in mouse brain. The pattern of expression of the approximately 37-kDa protein is similar to that of mCaMKIINalpha mRNA as both are expressed in normal but not Japanese encephalitis virus (JEV)-infected mouse brain. Subcellular localization studies indicate that the approximately 37-kDa protein is present in the post-synaptic density (PSD) where mCaMKIIalpha is known to perform key regulatory functions. We conclude that the approximately 37-kDa protein identified in this study is mCaMKIINalpha and its localization in the PSD indicates a novel role for this protein in the regulation of neuronal CaMKIIalpha.