STRUCTURAL BASES OF REGULATION OF SKELETAL MUSCLE

Muscle contraction is regulated by both Ca2+ dependent thin filament activation and mechanosensing-based thick filament activation that switches ON the motors in relation to the load. Evidence is growing for the involvement in thick filament regulation of the cytoskeleton protein titin, which runs from the midpoint of the thick filament to the end of the sarcomere, and the myosin binding protein C (MyBP-C), which is bound to the backbone of the thick filament in its central one-third and bridges thin and thick filaments. We use X-ray diffraction to investigate MyBP-C role in inter-filament communication and titin role in thick filament mechanosensing. The experiments, conducted in intact frog skeletal muscle fibres, exploit the finding that X-ray fine structure of myosin based reflections reports the footprints of both MyBP-C and titin and represent a testbed for future investigation on skinned fibres and whole muscles of rodent models with mutations in specific proteins.

肌肉收缩受Ca2+依赖的细肌丝（thin filament）激活和基于机械感知（mechanosensing）的粗肌丝（thick filament）激活双重调控，后者根据负荷开启马达。越来越多的证据表明，细胞骨架蛋白肌联蛋白（Titin）和肌球蛋白结合蛋白C（MyBP-C）参与粗肌丝的调控——肌联蛋白从粗肌丝中点延伸至肌节（sarcomere）末端，而MyBP-C结合于粗肌丝中央三分之一区域的主链上，并在细肌丝与粗肌丝之间架起桥梁。我们利用X射线衍射（X-ray diffraction）技术研究MyBP-C在肌丝间通讯（inter-filament communication）中的作用，以及肌联蛋白在粗肌丝机械感知中的功能。这些实验在完整的蛙骨骼肌纤维中进行，利用了以下发现：基于肌球蛋白的反射的X射线精细结构可反映MyBP-C和肌联蛋白的痕迹，且该实验体系为未来研究特定蛋白突变的啮齿动物模型的去膜纤维（skinned fibres）及完整肌肉提供了试验平台。