Stevenson S, Rothery S, Cullen M J, Severs N J
National Heart and Lung Institute, Imperial College School of Medicine, London, England.
Circ Res. 1998;82(1):82-93. doi: 10.1161/01.res.82.1.82.
Dystrophin and beta-dystroglycan are components of a complex of at least nine proteins (the dystrophin-glycoprotein complex) that physically link the membrane cytoskeleton in skeletal and cardiac muscle, through the plasma membrane, to the extracellular matrix. Mutations in the dystrophin gene, which result in an absence or a quantitative or qualitative alteration of dystrophin, cause a subset of familial dilated cardiomyopathies as well as Duchenne and Becker muscular dystrophy. Biochemical studies on isolated skeletal muscle molecules indicate that dystrophin is bound to the glycoprotein complex via beta-dystroglycan, with the C-terminus of beta-dystroglycan binding to the cysteine-rich domain and first half of the C-terminal domain of dystrophin. Ultrastructural labeling has demonstrated a close spatial relationship between dystrophin and beta-dystroglycan in intact skeletal muscle, but no previous ultrastructural labeling studies have examined the dystrophin/beta-dystroglycan interaction in cardiac muscle. In the present study, we have applied complementary immunoconfocal microscopy and double immunogold fracture-label, a freeze-fracture cytochemical technique that allows high-resolution visualization of labeled membrane components in thin section and in platinum-carbon replicas, to investigate the spatial relationship between dystrophin and beta-dystroglycan in rat cardiac muscle. When immunogold probes of two different sizes for the two proteins were used, "doublets" representing side-by-side antibody labeling were demonstrated in en face views at the level of the plasma membrane. The results support the conclusions that dystrophin and beta-dystroglycan directly interact at the cytoplasmic face of the rat cardiac muscle plasma membrane.
肌营养不良蛋白和β-肌聚糖是一个至少由九种蛋白质组成的复合体（肌营养不良蛋白-糖蛋白复合体）的组成成分，该复合体通过质膜将骨骼肌和心肌中的膜细胞骨架与细胞外基质物理连接起来。肌营养不良蛋白基因的突变会导致肌营养不良蛋白缺失或数量或质量上的改变，从而引发一部分家族性扩张型心肌病以及杜氏和贝克型肌营养不良症。对分离出的骨骼肌分子进行的生化研究表明，肌营养不良蛋白通过β-肌聚糖与糖蛋白复合体结合，β-肌聚糖的C末端与肌营养不良蛋白富含半胱氨酸的结构域以及C末端结构域的前半部分结合。超微结构标记已证明在完整的骨骼肌中肌营养不良蛋白和β-肌聚糖之间存在紧密的空间关系，但此前尚无超微结构标记研究检测过心肌中肌营养不良蛋白/β-肌聚糖的相互作用。在本研究中，我们应用了互补的免疫共聚焦显微镜和双重免疫金断裂标记法（一种冷冻断裂细胞化学技术，可在薄切片和铂-碳复制品中对标记的膜成分进行高分辨率可视化）来研究大鼠心肌中肌营养不良蛋白和β-肌聚糖之间的空间关系。当使用针对这两种蛋白质的两种不同大小的免疫金探针时，在质膜水平的正面视图中显示出代表并排抗体标记的“双峰”。结果支持了肌营养不良蛋白和β-肌聚糖在大鼠心肌质膜的细胞质面直接相互作用的结论。
