Examining the in vivo role of the amino terminus of the essential myosin light chain.
The functional significance of the actin binding region at the amino terminus of the cardiac essential myosin light chain (ELC) remains obscure. Previous experiments carried out in vitro indicated that modulation of residues 5-14 could induce an inotropic effect, increasing maximal ATPase activity at submaximal Ca(2+) concentrations (Rarick, H. M., Opgenorth, T. J., von Geldern, T. W., Wu-Wong, J. R., and Solaro, R. J. (1996) J. Biol. Chem. 271, 27039-27043). Using transgenesis, we effected a cardiac-specific replacement of ELC with a protein containing a 10-amino acid deletion at positions 5-14. Both the ventricular (ELC1vDelta5-14) and atrial (ELC1aDelta5-14) isoforms lacking this peptide were stably incorporated into the sarcomere at high efficiencies. Surprisingly when the kinetics of skinned fibers isolated from the ELC1vDelta5-14 or ELC1aDelta5-14 mice were examined, no alterations in either unloaded shortening or maximum shortening velocities were apparent. Myofibrillar Mg(2+)-ATPase activity was also unchanged in these preparations. No significant changes in the fiber kinetics in the cognate compartments were observed when either deletion-containing protein replaced endogenous ELC1v or ELC1a. The data indicate that the previously postulated importance of this region in mediating critical protein interactions between the cardiac ELCs and the carboxyl-terminal residues of actin in vivo should be reassessed.
Sanbe
A
A
Department of Pediatrics, Division of Molecular Cardiovascular Biology, The Children's Hospital Research Foundation, Cincinnati, Ohio 45229-3039, USA.
Gulick
J
J
Fewell
J
J
Robbins
J
J
D000595:Amino Acid Sequence; D000818:Animals; D016275:Atrial Function; D002118:Calcium / Q000502:physiology; D006321:Heart / Q000502:physiology*; D066298:In Vitro Techniques; D007700:Kinetics; D051379:Mice; D008822:Mice, Transgenic; D008969:Molecular Sequence Data; D009200:Myocardial Contraction / Q000235:genetics / Q000502:physiology*; D009206:Myocardium / Q000378:metabolism*; D018994:Myosin Light Chains / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D010446:Peptide Fragments / Q000737:chemistry / Q000378:metabolism; D016415:Sequence Alignment; D017384:Sequence Deletion; D017386:Sequence Homology, Amino Acid; D016276:Ventricular Function
D018994:Myosin Light Chains; D010446:Peptide Fragments; D002118:Calcium