Department of Electrical and Computer Engineering, University of Minnesota - Twin Cities, Minneapolis, MN, 55455, USA.
Department of Biochemistry, Molecular Biology, and Biophysics, University of Minnesota - Twin Cities, Minneapolis, MN, 55455, USA.
Sci Rep. 2019 Mar 26;9(1):5210. doi: 10.1038/s41598-019-41569-4.
Patients with Duchenne muscular dystrophy (DMD) lack the protein dystrophin, which is a critical molecular component of the dystrophin-glycoprotein complex (DGC). Dystrophin is hypothesized to function as a molecular shock absorber that mechanically stabilizes the sarcolemma of striated muscle through interaction with the cortical actin cytoskeleton via its N-terminal half and with the transmembrane protein β-dystroglycan via its C-terminal region. Utrophin is a fetal homologue of dystrophin that can subserve many dystrophin functions and is therefore under active investigation as a dystrophin replacement therapy for DMD. Here, we report the first mechanical characterization of utrophin using atomic force microscopy (AFM). Our data indicate that the mechanical properties of spectrin-like repeats in utrophin are more in line with the PEVK and Ig-like repeats of titin rather than those reported for repeats in spectrin or dystrophin. Moreover, we measured markedly different unfolding characteristics for spectrin repeats within the N-terminal actin-binding half of utrophin compared to those in the C-terminal dystroglycan-binding half, even though they exhibit identical thermal denaturation profiles. Our results demonstrate dramatic differences in the mechanical properties of structurally homologous utrophin constructs and suggest that utrophin may function as a stiff elastic element in series with titin at the myotendinous junction.
患有杜氏肌营养不良症（DMD）的患者缺乏肌营养不良蛋白，该蛋白是肌营养不良蛋白聚糖复合物（DGC）的关键分子成分。肌营养不良蛋白被认为是一种分子减震器，通过其 N 端半部分与皮质肌动蛋白细胞骨架相互作用，并通过其 C 端区域与跨膜蛋白β-肌营养不良蛋白相互作用，从而机械稳定横纹肌的肌膜。utrophin 是肌营养不良蛋白的一种胎儿同源物，可发挥许多肌营养不良蛋白的功能，因此被积极研究作为 DMD 的肌营养不良蛋白替代疗法。在这里，我们使用原子力显微镜（AFM）首次对 utrophin 进行了机械特性表征。我们的数据表明，utrophin 中的 spectrin 样重复的机械性能与 titin 的 PEVK 和 Ig 样重复更吻合，而不是与 spectrin 或 dystrophin 中的重复报告的那样。此外，我们测量了 utrophin N 端肌动蛋白结合半部分中 spectrin 重复的明显不同的展开特性，与 C 端肌球蛋白结合半部分中的展开特性不同，尽管它们表现出相同的热变性曲线。我们的结果表明，结构同源的 utrophin 构建体的机械性能存在显著差异，并表明 utrophin 可能在肌腱连接处以串联的方式作为刚性弹性元件发挥作用。
