Myosin II is a biomolecular machine that is responsible for muscle contraction. Myosin II motors act cooperatively: during muscle contraction, multiple motors bind to a single actin filament and pull it against an external load, like people pulling on a rope in a tug-of-war. We model the dynamics of actomyosin filaments in order to study the evolution of motor–motor cooperativity. We find that filament backsliding—the distance an actin slides backward when a motor at the end of its cycle releases—is central to the speed and efficiency of muscle contraction. Our model predicts that this backsliding has been reduced through evolutionary adaptations to the motor’s binding propensity, the strength of the motor’s power stroke, and the force dependence of the motor’s release from actin. These properties optimize the collective action of myosin II motors, which is not a simple sum of individual motor actions. The model also shows that these evolutionary variables can explain the speed–efficiency trade-off observed across different muscle tissues. This is an example of how evolution can tune the microscopic properties of individual proteins in order to optimize complex biological functions.

肌球蛋白 II 是一种负责肌肉收缩的生物分子机器。肌球蛋白 II 马达协同作用：在肌肉收缩期间，多个马达与单个肌动蛋白丝结合并拉动它以抵抗外部负载，就像人们在拔河比赛中拉绳子一样。我们模拟肌动球蛋白丝的动力学，以研究运动 - 运动协同性的演变。我们发现细丝后滑——当运动结束时肌动蛋白向后滑动的距离——是肌肉收缩速度和效率的核心。我们的模型预测，通过对电机的结合倾向、电机动力冲程的强度以及电机从肌动蛋白释放的力依赖性的进化适应，这种后退已经减少。这些特性优化了肌球蛋白 II 马达的集体作用，这不是单个运动动作的简单总和。该模型还表明，这些进化变量可以解释在不同肌肉组织中观察到的速度-效率权衡。这是进化如何调整单个蛋白质的微观特性以优化复杂生物功能的一个例子。