Biochemical and physiological regulation of cardiac myocyte contraction by cardiac-specific myosin light chain kinase.

Cardiac-specific myosin light chain kinase (cMLCK) is the kinase predominantly responsible for the maintenance of the basal level of phosphorylation of cardiac myosin light chain 2 (MLC2), which it phosphorylates at Ser-15. This phosphorylation repels the myosin heads from the thick myosin filament and moves them toward the thin actin filament. Unlike smooth muscle cells, MLC2 phosphorylation in striated muscle cells appears to be a positive modulator of Ca(2+) sensitivity that shifts the Ca(2+)-force relationship toward the left and increases the maximal force response and thus does not initiate muscle contraction. Recent studies have revealed an increasing number of details of the biochemical, physiological, and pathophysiological characteristics of cMLCK. The combination of recent technological advances and the discovery of a novel class of biologically active nonstandard peptides will hopefully translate into the development of drugs for the treatment of heart diseases.