Mechanisms of myosin II force generation. Insights from novel experimental techniques and approaches.

Myosin II is a molecular motor that converts chemical energy derived from ATP hydrolysis into mechanical work. Myosin II isoforms are responsible for muscle contraction and a range of cell functions relying on the development of force and motion. When the motor attaches to actin, ATP is hydrolyzed, and inorganic phosphate (Pi) and ADP are released from its active site. These reactions are coordinated with changes in the structure of myosin, promoting the so called "power-stroke" that causes sliding of actin filaments. The general features of the myosin-actin interactions are well accepted, but there are critical issues that remain poorly understood, mostly due to technological limitations. In recent years, there has been a significant advance in structural, biochemical, and mechanical methods that have advanced the field considerably. New modeling approaches have also allowed researchers to understand actomyosin interactions at different levels of analysis. This paper reviews recent studies looking into the interaction between myosin II and actin filaments, which leads to the power stroke and force generation. It reviews studies conducted with single myosin molecules, myosins working in filaments, muscle sarcomeres, myofibrils and fibers. It also reviews the mathematical models that have been used to understand the mechanics of myosin II, in approaches focusing on single molecules to ensembles. Finally, it includes brief sections on translational aspects, and how changes in the myosin motor by mutations and/or posttranslational modifications may cause detrimental effects in diseases and aging, among other conditions, and how myosin II has become an emerging drug target.

Twitch potentiation and myosin light chain phosphorylation in skeletal muscle

Potenciação muscular é o aumento da força ativa produzida durante um abalo muscular resultante da atividade prévia, e pode ser descrita como efeito de escada ("staircase") e potenciação pós-tetânica (PPT). O efeito de escada é o aumento na força ativa observado durante estimulação muscular de baixa frequência. PPT é o aumento da força ativa observado após uma contração tetânca. Embora sob investigação, existem evidências que o mecanismo responsável pela potenciação muscular é a fosforilação das cadeias moleculares regulatórias de peso molecular leve (CMR) da miosina, que depende das concentrações intracelulares de Ca2+. Estudos têm proposto que as CRM movem as pontes cruzadas, afastando-as do filamento grosso de miosina quando elas são fosforiladas. Este processo aproximaria as pontes cruzadas da actina, aumentando a probabilidade da interação dos filamentos, o que aumentaria a sensibilidade do Ca2+ e a produção de força. Este artigo revisa as evidências deste mecanismo, investigando estudos que lidam com células intactas e sem membrana do músculo esquelético, e com o músculo esquelético intacto. Sensibilidade ao Ca2+, cadeias moleculares leves de miosina, fosforilação, pontes cruzadas