Expression of a catalytically active polypeptide of calmodulin-dependent protein kinase II alpha subunit in Escherichia coli.

Two cDNAs, one containing the entire coding region of alpha subunit of Ca2+/calmodulin-dependent protein kinase II (CaM kinase II) and the other containing only its protein kinase domain, were separately ligated into the bacterial expression vector pET3a and expressed in Escherichia coli. The activity of the recombinant alpha subunit protein was dependent on Ca2+/calmodulin, whereas the activity of the recombinant protein containing only the protein kinase domain (recombinant alpha-I protein) was absolutely independent of Ca2+/calmodulin. These proteins showed similar enzymatic properties to brain CaM kinase II with some minor differences. These results directly demonstrated that the protein kinase domain alone without the rest of the subunit was sufficient to exhibit its activity.