FUS-NLS/Transportin 1 Complex Structure Provides Insights into the Nuclear Targeting Mechanism of FUS and the Implications in ALS

The C-terminal nuclear localization sequence of FUsed in Sarcoma (FUS-NLS) is critical for its nuclear import mediated by transportin (Trn1). Familial amyotrophic lateral sclerosis (ALS) related mutations are clustered in FUS-NLS. We report here the structural, biochemical and cell biological characterization of the FUS-NLS and its clinical implications. The crystal structure of the FUS-NLS/Trn1 complex shows extensive contacts between the two proteins and a unique α-helical structure in the FUS-NLS. The binding affinity between Trn1 and FUS-NLS (wide-type and 12 ALS-associated mutants) was determined. As compared to the wide-type FUS-NLS (KD = 1.7 nM), each ALS-associated mutation caused a decreased affinity and the range of this reduction varied widely from 1.4-fold over 700-fold. The affinity of the mutants correlated with the extent of impaired nuclear localization, and more importantly, with the duration of disease progression in ALS patients. This study provides a comprehensive understanding of the nuclear targeting mechanism of FUS and illustrates the significance of FUS-NLS in ALS.

肉瘤融合蛋白（FUsed in Sarcoma, FUS）的C端核定位序列（FUS-NLS）在其依赖转运蛋白1（Transportin, Trn1）介导的核输入过程中至关重要。家族性肌萎缩侧索硬化症（Familial Amyotrophic Lateral Sclerosis, ALS）相关突变在FUS-NLS区域呈聚集分布。本研究报道了FUS-NLS的结构生物学、生物化学与细胞生物学表征及其临床意义。FUS-NLS与Trn1复合物的晶体结构显示，二者之间存在广泛的相互作用界面，且FUS-NLS自身具有独特的α螺旋结构。本研究测定了Trn1与野生型FUS-NLS以及12种ALS相关突变体之间的结合亲和力。相较于野生型FUS-NLS（KD=1.7 nM），每一种ALS相关突变均会降低二者的结合亲和力，且亲和力降幅跨度极大，从1.4倍至700倍不等。突变体的结合亲和力与核定位功能受损程度密切相关，更关键的是，其与ALS患者的疾病进展时长显著相关。本研究全面阐明了FUS的核靶向机制，并证实了FUS-NLS在ALS发病过程中的重要意义。