The Role of the N-Terminus of the Myosin Essential Light Chain in Cardiac Muscle Contraction

To study the regulation of cardiac muscle contraction by the myosin essential light chain (ELC) and the physiological significance of its N-terminal extension, we generated transegenic (Tg) mice by partially replacing the endogenous mouse ventricular ELC with either the human ventricular ELC wild type (Tg-WT) or its 43-anubi-acid N-terminal truncation mutant (Tg-Delta 43) in the murine hearts. The mutant protein is similar in sequence to the short ELC variant present in skeletal muscle, and ELC protein distributed in Tg-Delta 43 ventricles resembles that of fast skeletal muscle. Cardiac muscle preparations from Tg-Delta 43 mice demonstrate reduced force per cross-sectional area of muscle, which is likely caused by reduced number of force-generating myosin cross-bridges and/or by decreased force per cross-bridge. As the mice grow older, the contractile force per cross-sectional area further decreases in Tg-Delta 43 mice and the mutant hearts develop a phenotype of nonpathologic hypertrophy while still maintaining normal cardiac performance. The myocardium of older Tg-Delta 43 mice also exhibits reduced myosin content. Our results suggest that the role of the N-terminal ELC extension is to maintain the integrity of myosin and to modulate force generation by decreasing myosin neck region compliance and promoting strong cross-bridge formation and / or by enhancing myosin attachment to actin. (c) 2009 Elsevier Ltd. All rights reserved.