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Abstract：
Spinal muscular atrophy (SMA) is a neurodegenerative disease caused by the absence of a functional copy of the Survival of Motor Neuron 1 gene (SMN1). The nearly identical paralog, SMN2, cannot compensate for the loss of SMN1 because exon 7 is aberrantly skipped from most SMN2 transcripts, a process mediated by synergistic activities of Src-associated during mitosis, 68 kDa (Sam68/KHDRBS1) and heterogeneous nuclear ribonucleoprotein (hnRNP) A1. This results in the production of a truncated, nonfunctional protein that is rapidly degraded. Here, we present several crystal structures of Sam68 RNA-binding domain (RBD). Sam68-RBD forms stable symmetric homodimers by antiparallel association of helices α3 from two monomers. However, the details of domain organization and the dimerization interface differ significantly from previously characterized homologs. We demonstrate that Sam68 and hnRNP A1 can simultaneously bind proximal motifs within the central region of SMN2 (ex7). Furthermore, we show that the RNA-binding pockets of the two proteins are close to each other in their heterodimeric complex and identify contact residues using crosslinking-mass spectrometry. We present a model of the ternary Sam68·SMN2 (ex7)·hnRNP A1 complex that reconciles all available information on SMN1/2 splicing. Our findings have important implications for the etiology of SMA and open new avenues for the design of novel therapeutics to treat splicing diseases.
摘要：
脊髓性肌萎缩症（SMA）是一种神经退行性疾病，由运动神经元存活1基因（SMN1）的功能拷贝缺失引起。几乎相同的模拟，SMN2，不能补偿SMN1的损失，因为外显子7被从大多数SMN2转录物中异常跳过，一个由Sam68/KHDRBS1和hnRNPA1协同活性介导的过程。这导致产生一个截断的，快速降解的非功能性蛋白质。在这里，我们介绍了Sam68RNA结合域（RBD）的几种晶体结构。Sam68-RBD通过来自两个单体的螺旋α3的反平行缔合形成稳定的对称同型二聚体。然而,域组织和二聚化界面的细节与先前表征的同源物显著不同。我们证明Sam68和hnRNPA1可以同时结合SMN2（ex7）中心区域内的近端基序。Further,我们表明，两种蛋白质的RNA结合口袋在它们的异源二聚体复合物中彼此接近，并使用交联-质谱鉴定接触残基。我们提出了三元Sam68·SMN2（ex7）·hnRNPA1复合物的模型，该模型调和了有关SMN1/2剪接的所有可用信息。我们的发现对SMA的病因具有重要意义，并为设计治疗剪接疾病的新疗法开辟了新途径。本文受版权保护。保留所有权利。
