A single serine in the carboxyl terminus of cardiac essential myosin light chain-1 controls cardiomyocyte contractility in vivo.
Although it is well known that mutations in the cardiac essential myosin light chain-1 (cmlc-1) gene can cause hypertrophic cardiomyopathy, the precise in vivo structural and functional roles of cMLC-1 in the heart are only poorly understood. We have isolated the zebrafish mutant lazy susan (laz), which displays severely reduced contractility of both heart chambers. By positional cloning, we identified a nonsense mutation within the zebrafish cmlc-1 gene to be responsible for the laz phenotype, leading to expression of a carboxyl-terminally truncated cMLC-1. Whereas complete loss of cMLC-1 leads to cardiac acontractility attributable to impaired cardiac sarcomerogenesis, expression of a carboxyl-terminally truncated cMLC-1 in laz mutant hearts is sufficient for normal cardiac sarcomerogenesis but severely impairs cardiac contractility in a cell-autonomous fashion. Whereas overexpression of wild-type cMLC-1 restores contractility of laz mutant cardiomyocytes, overexpression of phosphorylation site serine 195-deficient cMLC-1 (cMLC-1(S195A)) does not reconstitute cardiac contractility in laz mutant cardiomyocytes. By contrast, introduction of a phosphomimetic amino acid on position 195 (cMLC-1(S195D)) rescues cardiomyocyte contractility, demonstrating for the first time an essential role of the carboxyl terminus and especially of serine 195 of cMLC-1 in the regulation of cardiac contractility.
Pubmed ID: 19168438 RIS Download
Amino Acid Sequence | Animals | Base Sequence | Cloning, Molecular | Codon, Nonsense | Ethylnitrosourea | Gene Expression Regulation, Developmental | Genotype | Heart | Models, Molecular | Molecular Conformation | Molecular Sequence Data | Muscle Strength | Mutagens | Myocardial Contraction | Myocytes, Cardiac | Myosin Light Chains | Phenotype | Phosphorylation | Protein Stability | Protein Structure, Tertiary | Sarcomeres | Sequence Homology, Amino Acid | Serine | Time Factors | Zebrafish | Zebrafish Proteins