Department of Neurology, Senator Paul D Wellstone Muscular Dystrophy Cooperative Research Center, University of Washington, Seattle, Washington, United States of America.
PLoS Genet. 2010 May 20;6(5):e1000958. doi: 10.1371/journal.pgen.1000958.
Mutations in dystrophin can lead to Duchenne muscular dystrophy or the more mild form of the disease, Becker muscular dystrophy. The hinge 3 region in the rod domain of dystrophin is particularly prone to deletion mutations. In-frame deletions of hinge 3 are predicted to lead to BMD, however the severity of disease can vary considerably. Here we performed extensive structure-function analyses of truncated dystrophins with modified hinges and spectrin-like repeats in mdx mice. We found that the polyproline site in hinge 2 profoundly influences the functional capacity of a microdystrophin(DeltaR4-R23/DeltaCT) with a large deletion in the hinge 3 region. Inclusion of polyproline in microdystrophin(DeltaR4-R23/DeltaCT) led to small myofibers (12% smaller than wild-type), Achilles myotendinous disruption, ringed fibers, and aberrant neuromuscular junctions in the mdx gastrocnemius muscles. Replacing hinge 2 of microdystrophin(DeltaR4-R23/DeltaCT) with hinge 3 significantly improved the functional capacity to prevent muscle degeneration, increase muscle fiber area, and maintain the junctions. We conclude that the rigid alpha-helical structure of the polyproline site significantly impairs the functional capacity of truncated dystrophins to maintain appropriate connections between the cytoskeleton and extracellular matrix.
肌营养不良蛋白基因突变可导致杜氏肌营养不良症或更为轻微的贝克肌营养不良症。肌营养不良蛋白杆状结构域中的铰链 3 区域特别容易发生缺失突变。铰链 3 的框内缺失预计会导致 BMD，但疾病的严重程度可能有很大差异。在这里，我们在 mdx 小鼠中对具有修饰铰链和类似血影蛋白重复的截断肌营养不良蛋白进行了广泛的结构功能分析。我们发现，铰链 2 中的多脯氨酸位点极大地影响了具有铰链 3 区域大缺失的微肌营养不良蛋白（DeltaR4-R23/DeltaCT）的功能能力。多脯氨酸包含在微肌营养不良蛋白（DeltaR4-R23/DeltaCT）中会导致小肌纤维（比野生型小 12%）、跟腱肌纤维和节段性纤维以及 mdx 比目鱼肌中的异常神经肌肉接头。用铰链 3 替代微肌营养不良蛋白（DeltaR4-R23/DeltaCT）的铰链 2 可显著提高功能能力，以防止肌肉退化、增加肌纤维面积并维持连接。我们得出结论，多脯氨酸位点的刚性α-螺旋结构显著损害了截断肌营养不良蛋白的功能能力，无法维持细胞骨架和细胞外基质之间的适当连接。
