PDF(Pubmed)
Abstract：
Striated muscle thick filaments are composed of myosin II and several non-myosin proteins which define the filament length and modify its function. Myosin II has a globular N-terminal motor domain comprising its catalytic and actin-binding activities and a long α-helical, coiled tail that forms the dense filament backbone. Myosin alone polymerizes into filaments of irregular length, but striated muscle thick filaments have defined lengths that, with thin filaments, define the sarcomere structure. The motor domain structure and function are well understood, but the myosin filament backbone is not. Here we report on the structure of the flight muscle thick filaments from Drosophila melanogaster at 4.7 Å resolution, which eliminates previous ambiguities in non-myosin densities. The full proximal S2 region is resolved, as are the connecting densities between the Ig domains of stretchin-klp. The proteins, flightin, and myofilin are resolved in sufficient detail to build an atomic model based on an AlphaFold prediction. Our results suggest a method by which flightin and myofilin cooperate to define the structure of the thick filament and explains a key myosin mutation that affects flightin incorporation. Drosophila is a genetic model organism for which our results can define strategies for functional testing.
摘要：
横纹肌粗丝由肌球蛋白II和几种非肌球蛋白蛋白组成，这些蛋白定义了细丝的长度并改变了其功能。肌球蛋白II具有球状N末端运动结构域，包括其催化和肌动蛋白结合活性和长α螺旋，盘绕的尾巴，形成致密的细丝骨架。肌球蛋白单独聚合成不规则长度的细丝，但是横纹肌粗丝有确定的长度，用细丝，定义肌节结构。运动域的结构和功能是众所周知的，但肌球蛋白纤丝骨架却没有。在这里，我们报告了果蝇的飞行肌肉粗丝的结构，分辨率为4.7。这消除了以前在非肌球蛋白密度中的歧义。完整的近端S2区域被解析，stretchin-klp的Ig域之间的连接密度也是如此。蛋白质，flightin,和myofilin被足够详细地解析，以建立基于AlphaFold预测的原子模型。我们的结果表明了一种方法，通过该方法，flightin和myofilin合作定义了粗丝的结构，并解释了影响flightin掺入的关键肌球蛋白突变。果蝇是一种遗传模型生物，我们的结果可以为其定义功能测试策略。
