Purification and characterization of Ca2+/calmodulin-dependent protein kinase IV kinase from rat brain

Calmodulin-dependent protein kinase IV (CaM-kinase IV) kinase was recently discovered in the rat brain by its activity to activate the inactive recombinant CaM-kinase IV expressed in Escherichia coli [Okuno, S. and Fujisawa, H. (1993) J. Biochem. 114, 167-170]. In the present study, CaM-kinase IV kinase was purified approximately 2,000-fold from rat cerebral cortex by purification procedures including calmodulin affinity chromatography, and its properties were examined. The highly purified CaM-kinase IV kinase gave one major protein band corresponding to a molecular weight of about 66,000 upon SDS-PAGE. The purified CaM-kinase IV kinase phosphorylated and concomitantly activated CaM-kinase IV purified from rat brain as well as the recombinant kinase expressed in Escherichia coli in a Ca2+/calmodulin-dependent manner. The phosphorylation of CaM-kinase IV by CaM-kinase IV kinase occurred on only serine residue(s). Among a number of proteins, including several known to be phosphorylated by the various protein kinases tested, CaM-kinase IV was the best substrate for CaM-kinase IV kinase. Since syntide-2, a synthetic peptide known to be a good peptide substrate for calmodulin-dependent protein kinase II (CaM-kinase II), was a fairly good substrate for CaM-kinase IV kinase, some kinetic properties of CaM-kinase IV kinase were examined using syntide-2 as a substrate. The Km value for the peptide substrate in the presence of Ca2+/calmodulin was almost two orders of magnitude lower than that in its absence, although the Vmax value was almost the same in the presence and absence of Ca2+/calmodulin.