Reconstitution of ventricular myosin with atrial light chains 1 improves its functional properties

Atrial light chain 1 (ALC-1) is expressed in embryonic and hypertrophied human ventricles but not in normal adult human ventricles. We investigated the effects of recombinant human atrial light chains (hALC-1) on the structure and enzymatic activity of synthetic filaments of ventricular myosin. The endogenous ventricular myosin light chain 1 (VLC-1) was partially replaced by recombinant hALC-1 yielding hALC-1 levels of 12%, 24% and 42%. This reconstitution of ventricular myosin with hALC-1 did not change the length of synthetic myosin filaments but led to more rounded myosin heads in comparison with those of control filaments. Actin-activated ATPase activity of myosin, a parameter of functional activity of molecular motor, amounted to 79.5 nmol Pi/mg per min in control myosin filaments. Reconstitution with hALC-1 caused a profound increase of the actin-activated myosin ATPase activity in a dose dependent manner, for example, synthetic myosin filaments formed with 12%, 24% and 42% hALC-1 reconstituted myosin revealed the actin-activated ATPase activity increased by 18%, 26% and 36%, respectively, as compared to control. These results strongly suggest that in vivo expression of ALC-1 enhances ventricular myosin function, thereby contributing to cardiac compensation.