Key result
hALC-1 bound more strongly to myosin than hVLC-1 (>3-fold lower KD), leading to preferential sarcomeric sorting and increased contractility without changing the systolic Ca2+ signal.
Effect estimate: greater than three-fold lower KD
Intense myosin binding of hALC-1 provides a molecular mechanism for preferential sarcomeric sorting and Ca2+-independent positive inotropic activity in cardiomyocytes.
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. 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-MYH664–915IQala4) 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 Ca2+ (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 KD) to rβ-MYH664–915 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 Ca2+ signal remained unchanged. Intense myosin binding of hALC-1 provides a mechanism for preferential sarcomeric sorting and Ca2+-independent positive inotropic activity.
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Petzhold et al. (2011) studied this question. hALC-1 (human atrial light chain 1) vs. hVLC-1 (human ventricular light chain 1) or beta-galactosidase was evaluated on Binding affinity, sarcomeric sorting, and contractility (greater than three-fold lower KD). hALC-1 bound more strongly to myosin than hVLC-1 (>3-fold lower KD), leading to preferential sarcomeric sorting and increased contractility without changing the systolic Ca2+ signal.
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