Peters M F, Sadoulet-Puccio H M, Grady M R, Kramarcy N R, Kunkel L M, Sanes J R, Sealock R, Froehner S C
Department of Cell and Molecular Physiology, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-7545, USA.
J Cell Biol. 1998 Sep 7;142(5):1269-78. doi: 10.1083/jcb.142.5.1269.
alpha-Dystrobrevin is both a dystrophin homologue and a component of the dystrophin protein complex. Alternative splicing yields five forms, of which two predominate in skeletal muscle: full-length alpha-dystrobrevin-1 (84 kD), and COOH-terminal truncated alpha-dystrobrevin-2 (65 kD). Using isoform-specific antibodies, we find that alpha-dystrobrevin-2 is localized on the sarcolemma and at the neuromuscular synapse, where, like dystrophin, it is most concentrated in the depths of the postjunctional folds. alpha-Dystrobrevin-2 preferentially copurifies with dystrophin from muscle extracts. In contrast, alpha-dystrobrevin-1 is more highly restricted to the synapse, like the dystrophin homologue utrophin, and preferentially copurifies with utrophin. In yeast two-hybrid experiments and coimmunoprecipitation of in vitro-translated proteins, alpha-dystrobrevin-2 binds dystrophin, whereas alpha-dystrobrevin-1 binds both dystrophin and utrophin. alpha-Dystrobrevin-2 was lost from the nonsynaptic sarcolemma of dystrophin-deficient mdx mice, but was retained on the perisynaptic sarcolemma even in mice lacking both utrophin and dystrophin. In contrast, alpha-dystrobrevin-1 remained synaptically localized in mdx and utrophin-negative muscle, but was absent in double mutants. Thus, the distinct distributions of alpha-dystrobrevin-1 and -2 can be partly explained by specific associations with utrophin and dystrophin, but other factors are also involved. These results show that alternative splicing confers distinct properties of association on the alpha-dystrobrevins.
α-肌营养不良蛋白结合蛋白既是肌营养不良蛋白的同源物，也是肌营养不良蛋白复合物的一个组成部分。选择性剪接产生五种形式，其中两种在骨骼肌中占主导：全长α-肌营养不良蛋白结合蛋白-1（84kD）和羧基末端截短的α-肌营养不良蛋白结合蛋白-2（65kD）。使用亚型特异性抗体，我们发现α-肌营养不良蛋白结合蛋白-2定位于肌膜和神经肌肉突触处，在那里，与肌营养不良蛋白一样，它最集中于突触后褶皱深处。α-肌营养不良蛋白结合蛋白-2优先与来自肌肉提取物的肌营养不良蛋白共纯化。相比之下，α-肌营养不良蛋白结合蛋白-1更高度局限于突触，就像肌营养不良蛋白同源物抗肌萎缩蛋白一样，并且优先与抗肌萎缩蛋白共纯化。在酵母双杂交实验和体外翻译蛋白的共免疫沉淀实验中，α-肌营养不良蛋白结合蛋白-2与肌营养不良蛋白结合，而α-肌营养不良蛋白结合蛋白-1与肌营养不良蛋白和抗肌萎缩蛋白都结合。α-肌营养不良蛋白结合蛋白-2在肌营养不良蛋白缺陷的mdx小鼠的非突触肌膜中缺失，但即使在缺乏抗肌萎缩蛋白和肌营养不良蛋白的小鼠中，它仍保留在突触周围肌膜上。相比之下，α-肌营养不良蛋白结合蛋白-1在mdx和抗肌萎缩蛋白阴性的肌肉中仍定位于突触，但在双突变体中不存在。因此，α-肌营养不良蛋白结合蛋白-1和-2的不同分布部分可以通过与抗肌萎缩蛋白和肌营养不良蛋白的特异性结合来解释，但也涉及其他因素。这些结果表明，选择性剪接赋予了α-肌营养不良蛋白结合蛋白不同的结合特性。
