In muscle, titin proteins connect myofilaments together and are thought to be critical for contraction, especially during residual force enhancement (RFE) when steady-state force is elevated after an active stretch. We investigated titin’s function during contraction using small-angle X-ray diffraction to track structural changes before and after 50% titin cleavage and in the RFE-deficient, mdm titin mutant. We report that the RFE state is structurally distinct from pure isometric contractions, with increased thick filament strain and decreased lattice spacing, most likely caused by elevated titin-based forces. Furthermore, no RFE structural state was detected in mdm muscle. We posit that decreased lattice spacing, increased thick filament stiffness, and increased non-cross-bridge forces are the major contributors to RFE. We conclude that titin directly contributes to RFE.

中文翻译：

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肌纤维残余力增强的独特机械和结构特征


在肌肉中，肌苷蛋白将肌丝连接在一起，被认为对收缩至关重要，尤其是在残余力增强 （RFE） 期间，当主动拉伸后稳态力升高时。我们使用小角 X 射线衍射来跟踪 50% 肌苷切割前后的结构变化以及 RFE 缺陷的 mdm 肌苷突变体，研究了肌皮蛋白在收缩过程中的功能。我们报告说，RFE 状态在结构上与纯等长收缩不同，粗丝应变增加，晶格间距减小，很可能是由基于蒂蛋白的力增加引起的。此外，在 mdm 肌肉中未检测到 RFE 结构状态。我们认为晶格间距减小、粗丝刚度增加和非交叉桥力增加是 RFE 的主要贡献者。我们得出结论，titin 直接导致 RFE。