Alternative splicing generates a CaM kinase IIbeta isoform in myocardium that targets the sarcoplasmic reticulum through a putative alphaKAP and regulates GAPDH.

We report the isolation of a full length cDNA from cardiac muscle that encodes a approximately 73 kDa calcium/calmodulin (CaM) dependent kinase IIbeta isoform (CaMKIIbeta(C)) that was generated by alternative splicing of the CaMKIIbeta gene. Antipeptide antibodies raised to specific regions of the kinase identified a 73 kDa kinase polypeptide in cardiac SR. Anti-alpha kinase anchoring protein (alphaKAP) antibodies identified a 25 kDa polypeptide in cardiac SR and RT-PCR followed by sequence analysis confirmed the presence of a full length alphaKAP encoding transcript in myocardium. Protein interaction assays revealed that the 73 kDa CaMKIIbeta(C) binds GAPDH to modulate the production of NADH in a Ca2+/CaM dependent reaction. The presence of a CaMKIIbeta isoform that can target the SR presumably via its membrane anchor alphaKAP defines a previously unrecognized Ca2+/CaM regulatory system in myocardium.