AI Article Synopsis
- The study tests the hypothesis that the C-terminus of human cardiac myosin light chain isoforms influences their binding affinity to the myosin lever arm, affecting their sorting and contractility.
- Circular dichroism and spectroscopy were used to analyze protein interactions, revealing that the hALC-1 isoform binds significantly stronger to myosin heavy chain fragments than the hVLC-1 isoform.
- The results indicate that stronger binding of hALC-1 leads to its preferential localization in the sarcomere and enhances contractility in cardiomyocytes without altering Ca(2+) levels.
Article Abstract
Aims: In this paper, we tested the hypothesis that different binding affinities of the C-terminus of human cardiac alkali (essential) myosin light chain (A1) isoforms to the IQ1 motif of the myosin lever arm provide a molecular basis for distinct sarcomeric sorting and inotropic activity.
Methods And Results: We employed circular dichroism and surface plasmon resonance spectroscopy to investigate structural properties, secondary structures, and protein-protein interactions of a recombinant head-rod fragments of rat cardiac β-myosin heavy chain aa664-915 with alanine-mutated IQ2 domain (rβ-MYH(664-915)IQ(ala4)) and A1 isoforms [human atrial (hALC1) and human ventricular (hVLC-1) light chains]. Double epitope-tagging competition was used to monitor the intracellular localization of exogenously introduced hALC-1 and hVLC-1 constructs in neonatal rat cardiomyocytes. Contractile functions of A1 isoforms were investigated by monitoring shortening and intracellular-free Ca(2+) (Fura-2) of adult rat cardiomyocytes infected with adenoviral (Ad) vectors using hALC-1 or β-galactosidase as expression cassettes. hALC-1 bound more strongly (greater than three-fold lower K(D)) to rβ-MYH(664-915) than did hVLC-1. Sorting specificity of A1 isoforms to sarcomeres of cardiomyocytes rose in the order hVLC-1 to hALC-1. Replacement of endogenous VLC-1 by hALC-1 in adult rat cardiomyocytes increased contractility while the systolic Ca(2+) signal remained unchanged.
Conclusion: Intense myosin binding of hALC-1 provides a mechanism for preferential sarcomeric sorting and Ca(2+)-independent positive inotropic activity.
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| http://dx.doi.org/10.1093/cvr/cvr026 | DOI Listing |
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