Basu Sushmita, Rajendra K C, Alagar Suresh, Bahadur Ranjit Prasad
Computational Structural Biology Lab, Department of Biotechnology, Indian Institute of Technology Kharagpur, Kharagpur 721302, India.
Computational Structural Biology Lab, Department of Biotechnology, Indian Institute of Technology Kharagpur, Kharagpur 721302, India.
Biochim Biophys Acta Proteins Proteom. 2022 Apr 1;1870(4):140766. doi: 10.1016/j.bbapap.2022.140766. Epub 2022 Feb 5.
Amyotrophic lateral sclerosis (ALS) and fronto-temporal lobar degeneration (FTLD) are progressive neurological disorders affecting motor neurons. Cellular aggregates of fused in sarcoma (FUS) protein are found in cytoplasm of ALS and FTLD patients. Nuclear localisation signal (NLS) domain of FUS binds to Karyopherin β2 (Kapβ2), which drives nuclear transport of FUS from cytoplasm. Several pathogenic mutations are reported in FUS NLS, which are associated with its impaired nuclear transport and cytoplasmic mis-localisation. P525L mutation in NLS is most commonly found in cases of juvenile ALS (jALS), which affects individuals below 25 years of age. jALS progresses aggressively causing death within a year of its onset. This study elucidates the molecular mechanism behind jALS-causing P525L mutation hindering nuclear transport of FUS. We perform multiple molecular dynamics simulations in aqueous and hydrophobic solvent to understand the effect of the mutation at molecular level. Dynamics of Kapβ2-FUS complex is better captured in hydrophobic solvent compared to aqueous solvent. P525 and Y526 (PY-motif) of NLS exhibit fine-tuned stereochemical arrangement, which is essential for optimum Kapβ2 binding. P525L causes loss of several native contacts at interface leading to weaker binding, which promotes self-aggregation of FUS in cytoplasm. Native complex samples closed conformation, while mutant complex exhibits open conformation exposing hydrophilic residues of Kapβ2 to hydrophobic solvent. Mutant complex also fails to exhibit spring-like motion essential for its transport through nuclear pore complex. This study provides a mechanistic insight of binding affinity between NLS and Kapβ2 that inhibits self-aggregation of FUS preventing the disease condition.
肌萎缩侧索硬化症（ALS）和额颞叶变性（FTLD）是影响运动神经元的进行性神经疾病。在ALS和FTLD患者的细胞质中发现了融合肉瘤（FUS）蛋白的细胞聚集体。FUS的核定位信号（NLS）结构域与核转运蛋白β2（Kapβ2）结合，后者驱动FUS从细胞质向细胞核的转运。据报道，FUS NLS中存在几种致病突变，这些突变与其核转运受损和细胞质错误定位有关。NLS中的P525L突变最常见于青少年肌萎缩侧索硬化症（jALS）病例中，该病影响25岁以下的个体。jALS进展迅速，发病后一年内导致死亡。本研究阐明了导致jALS的P525L突变阻碍FUS核转运背后的分子机制。我们在水性和疏水性溶剂中进行了多次分子动力学模拟，以在分子水平上了解该突变的影响。与水性溶剂相比，在疏水性溶剂中能更好地捕捉到Kapβ2-FUS复合物的动力学。NLS的P525和Y526（PY基序）表现出微调的立体化学排列，这对于最佳的Kapβ2结合至关重要。P525L导致界面处几个天然接触的丧失，从而导致结合减弱，这促进了FUS在细胞质中的自我聚集。天然复合物呈现封闭构象，而突变复合物呈现开放构象，使Kapβ2的亲水残基暴露于疏水性溶剂中。突变复合物也未能表现出其通过核孔复合物转运所必需的弹簧状运动。本研究提供了NLS与Kapβ2之间结合亲和力的机制性见解，该亲和力抑制了FUS的自我聚集，从而预防了疾病状态。
