Biochemical properties of the muscle-specific calcium(2+)/calmodulin-dependent protein kinase II beta isoform.

Abstract

Cytosolic calcium (Ca2+) levels are critical for the control of muscle contraction and are tightly regulated by a variety of Ca 2+ transport systems localized in various membranes. Ca2+ binding proteins such as calmodulin (CaM) and Ca2+/CaM-dependent protein kinases (CaM Kinases) are believed to exert major regulatory control on Ca2+ activity. Previous studies in this lab led to the cloning of a cDNA encoding a CaM Kinase II beta isoform from skeletal muscle that differed from the classical beta isoform by the inclusion of three alternatively spliced exons in the variable domain which were enriched in proline residues. A CaM Kinase, assumed to be localized in the sarcoplasmic reticulum (SR), has been implicated in the regulation of excitation-contraction (E-C) coupling. We hypothesized that this novel CaM Kinase II beta isoform called SOCK (Son Of CaM Kinase) may be the CaM Kinase II isoform that regulates E-C coupling by being targeted to specific regions of the SR, whereby it phosphorylates critical Ca2+ transporting proteins such as the ryanodine (RyR) and dihydropyridine (DHPR) receptors in response to changes in Ca2+ levels. (Abstract shortened by UMI.)