Novel Ca super(2+)/calmodulin-dependent protein kinase II gamma -subunit variants expressed in vascular smooth muscle, brain, and cardiomyocytes

Ca super(2+)/calmodulin-dependent protein kinase II (CaM kinase II) gamma -subunits were cloned from a porcine aortic smooth muscle cDNA library resulting in identification of alternatively spliced CaM kinase II gamma sub(B) and gamma sub(C)-subunits and a novel gamma -subunit variant predicted to encode a 60.2-kDa polypeptide, which was designated the gamma sub(G)-subunit. A clone predicted to encode a 62.2-kDa gamma -subunit, designated as gamma sub(E), was isolated with a variable domain structure similar to a gamma sub(B)-subunit but with a 114-nucleotide insertion in the conserved "association" domain of CaM kinase II subunits. A full-length gamma sub(E)-subunit construct expressed in COS cells resulted in multimeric CaM kinase II holoenzymes (470 kDa) with activation and autoregulatory properties similar to expressed holoenzymes composed of gamma sub(B)-, gamma sub(C)-, or gamma sub(G)-subunits. Expression of gamma sub(E) and related gamma -subunit mRNAs containing the 114-base insertion was documented in porcine tissues by reverse transcriptase-polymerase chain reaction. CaM kinase II subunits containing the 38-amino acid insert were identified by Western analysis of partially purified CaM kinase II from carotid arterial smooth muscle and brain using a sequence-specific anti-peptide antibody. Immunoprecipitations of tissue homogenates indicated a comparatively high level of expression of subunits containing the insert in brain and provided evidence for their co-assembly with other more abundant subunits into CaM kinase II heteromultimers. Our analyses indicate the following patterns of gamma -subunit expression: vascular smooth muscle, gamma sub(B) > gamma sub(C) > gamma sub(E,G); heart, gamma sub(B) > gamma sub(E,C); brain, gamma sub(E) and related subunits >> gamma sub(A,B,C,G).