Analysis of functional significance of mutant actin identified in hereditary dilated cardiomyopathy

本研究以心肌肌动蛋白与肌球蛋白轻链的相互作用为重点，探讨了心肌肌动蛋白的功能意义。我们比较了从大鼠心脏中获得的心房和心室类型的心肌肌球蛋白，已知它们仅在轻链结构上不同。虽然肌动蛋白激活的ATP酶活性在两种肌球蛋白之间没有差异，但心房型肌球蛋白在体外显示出更高的肌动蛋白滑动速度。而心室型肌球蛋白的体外发力能力较强。单分子力的测量表明这些肌球蛋白的肌动蛋白-肌球蛋白相互作用的不同动力学。我们的结论是肌球蛋白的重链结构决定了催化活性，轻链是其动力学的修饰剂。为了进一步阐明这种修饰的机制，我们研究了Essentila轻链N端肽段对心肌细胞收缩功能的影响。N-末端肽增强收缩力，支持该肽的拴系效应假说。我们还开发了新的实验装置，用于测量由单个心脏单细胞产生的Fwitch力。

In this study, we evaluated the functional significance of cardiac actin focussing on its interaction with myosin ligh chain. We compared the atrial and ventricular types of cardiac myosin obtained from rat heart which are known to differ only in light chain structure. Although acitn-activated ATPase activity did not differ between the two myosins atrial type myosin showed higher actin sliding velocity in vitro. Force generating ability in vitro, however, was highe for ventricular type myosin. Single molecular measurement of force suggested the distinct kinetics of actin-myosin interaction of these myosins. We concluded that the heavy chain structure of myosin determines the catalytic activity and that the light chains are modifiers of its kinetics. To further elucidate the mechanism of this modification, we studied the effect of N-terminus peptide of essentila light chain on contractile function of cardiac myocyte. N-terminu peptide enhanced the contractility supporting the hypothesis of tethering effect of this peptide. We also developed novel experimental set up for measuring the fwitch force developed by a single cardiac mnyocyle.