Biochemical and Physiological Regulation of Cardiac Myocyte Contraction by Cardiac-Specific Myosin Light Chain Kinase.
ABSTRACT 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.
- SourceAvailable from: Morihiko Takeda[Show abstract] [Hide abstract]
ABSTRACT: Two myosin light chain (MLC) kinase (MLCK) proteins, smooth muscle (encoded by mylk1 gene) and skeletal (encoded by mylk2 gene) MLCK, have been shown to be expressed in mammals. Even though phosphorylation of its putative substrate, MLC2, is recognized as a key regulator of cardiac contraction, a MLCK that is preferentially expressed in cardiac muscle has not yet been identified. In this study, we characterized a new kinase encoded by a gene homologous to mylk1 and -2, named cardiac MLCK, which is specifically expressed in the heart in both atrium and ventricle. In fact, expression of cardiac MLCK is highly regulated by the cardiac homeobox protein Nkx2-5 in neonatal cardiomyocytes. The overall structure of cardiac MLCK protein is conserved with skeletal and smooth muscle MLCK; however, the amino terminus is quite unique, without significant homology to other known proteins, and its catalytic activity does not appear to be regulated by Ca(2+)/calmodulin in vitro. Cardiac MLCK is phosphorylated and the level of phosphorylation is increased by phenylephrine stimulation accompanied by increased level of MLC2v phosphorylation. Both overexpression and knockdown of cardiac MLCK in cultured cardiomyocytes revealed that cardiac MLCK is likely a new regulator of MLC2 phosphorylation, sarcomere organization, and cardiomyocyte contraction.Circulation Research 04/2008; 102(5):571-80. · 11.09 Impact Factor
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ABSTRACT: On-line bioinformatics tools were used to identify and characterize all paralogs (intragenomic homologs) of muscle myosin regulatory light chains in the human genome. The initial search yielded 22 possible paralogs, but careful examination of supporting data eliminated most of these. Five paralogs were clearly identified with the tissue types (skeletal and cardiac muscles, smooth muscle, non-muscle cytoplasm) in which they are expressed. Sequence comparisons and phylogenetic analysis showed early divergence of a common ancestor of smooth muscle and non-muscle paralogs from a common ancestor of skeletal and cardiac muscle paralogs. An unusual sixth human paralog was very similar to the regulatory light chain of "superfast" myosin, which to date has been found only in cat. Finally, a unique and questionable "precursor lymphocyte" paralog was tentatively identified. Three-dimensional structural models of all seven human paralogs were constructed using the known structure of chicken fast skeletal muscle regulatory light chain as a template.Journal of Muscle Research and Cell Motility 02/2006; 27(1):69-74. · 1.93 Impact Factor
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ABSTRACT: Zipper-interacting protein kinase (ZIPK) is a member of the death-associated protein kinase family associated with apoptosis in nonmuscle cells where it phosphorylates myosin regulatory light chain (RLC) to promote membrane blebbing. ZIPK mRNA and protein are abundant in heart tissue and isolated ventricular neonatal rat cardiac myocytes. An unbiased substrate search performed with purified ZIPK on heart homogenates led to the discovery of a prominent 20-kDa protein substrate identified as RLC of ventricular myosin. Biochemical analyses showed ZIPK phosphorylated cardiac RLC at Ser-15 with a V(max) value 2-fold greater than the value for smooth/nonmuscle RLC; cardiac RLC is a favorable biochemical substrate. Knockdown of ZIPK in cardiac myocytes by small interfering RNA significantly decreased the extent of RLC Ser-15 phosphorylation. Thus, ZIPK may act as a cardiac RLC kinase and thereby affect contractility.Journal of Biological Chemistry 02/2010; 285(8):5122-6. · 4.60 Impact Factor