Newey S E, Benson M A, Ponting C P, Davies K E, Blake D J
Department of Human Anatomy and Genetics, University of Oxford, UK.
Curr Biol. 2000 Oct 19;10(20):1295-8. doi: 10.1016/s0960-9822(00)00760-0.
Dystrophin coordinates the assembly of a complex of structural and signalling proteins that is required for normal muscle function. A key component of the dystrophin-associated protein complex (DPC) is alpha-dystrobrevin, a dystrophin-related and -associated protein whose absence results in muscular dystrophy and neuromuscular junction defects [1,2]. The current model of the DPC predicts that dystrophin and dystrobrevin each bind a single syntrophin molecule [3]. The syntrophins are PDZ-domain-containing proteins that facilitate the recruitment of signalling proteins such as nNOS (neuronal nitric oxide synthase) to the DPC [4]. Here we show, using yeast two-hybrid analysis and biochemical binding studies, that alpha-dystrobrevin in fact contains two independent syntrophin-binding sites in tandem. The previously undescribed binding site is situated within an alternatively spliced exon of alpha-dystrobrevin, termed the variable region-3 (vr3) sequence, which is specifically expressed in skeletal and cardiac muscle [5,6]. Analysis of the syntrophin-binding region of dystrobrevin reveals a tandem pair of predicted alpha helices with significant sequence similarity. These alpha helices, each termed a syntrophin-binding motif, are also highly conserved in dystrophin and utrophin. Together these data show that there are four potential syntrophin-binding sites per dystrophin complex in skeletal muscle: two on dystrobrevin and two on dystrophin or utrophin. Furthermore, alternative splicing of dystrobrevin provides a mechanism for regulating the stoichiometry of syntrophin association with the DPC. This is likely to have important consequences for the recruitment of specific signalling molecules to the DPC and ultimately for its function.
肌营养不良蛋白协调结构和信号蛋白复合物的组装，而这种复合物是正常肌肉功能所必需的。肌营养不良蛋白相关蛋白复合物（DPC）的一个关键成分是α-肌营养不良素结合蛋白，它是一种与肌营养不良蛋白相关且相互关联的蛋白，其缺失会导致肌肉萎缩症和神经肌肉接头缺陷[1,2]。目前关于DPC的模型预测，肌营养不良蛋白和α-肌营养不良素结合蛋白各自结合一个肌萎缩蛋白分子[3]。肌萎缩蛋白是含有PDZ结构域的蛋白，有助于将诸如神经元型一氧化氮合酶（nNOS）等信号蛋白招募到DPC[4]。在此，我们通过酵母双杂交分析和生化结合研究表明，α-肌营养不良素结合蛋白实际上串联包含两个独立的肌萎缩蛋白结合位点。先前未描述的结合位点位于α-肌营养不良素结合蛋白的一个可变剪接外显子内，称为可变区-3（vr3）序列，该序列在骨骼肌和心肌中特异性表达[5,6]。对肌营养不良素结合蛋白的肌萎缩蛋白结合区域的分析揭示了一对串联的预测α螺旋，它们具有显著的序列相似性。这些α螺旋，每个都称为肌萎缩蛋白结合基序，在肌营养不良蛋白和抗肌萎缩蛋白中也高度保守。这些数据共同表明，在骨骼肌中每个肌营养不良蛋白复合物有四个潜在的肌萎缩蛋白结合位点：两个在α-肌营养不良素结合蛋白上，两个在肌营养不良蛋白或抗肌萎缩蛋白上。此外，α-肌营养不良素结合蛋白的可变剪接提供了一种调节肌萎缩蛋白与DPC结合化学计量的机制。这可能对将特定信号分子招募到DPC并最终对其功能产生重要影响。
