Biocenter, Institute of Molecular Physiology, Johannes Gutenberg-Universität (JGU), Mainz, Germany.
Graduate School of Systemic Neurosciences (GSN), Planegg-Martinsried, Germany.
EMBO J. 2022 Apr 19;41(8):e108443. doi: 10.15252/embj.2021108443. Epub 2022 Feb 3.
Post-translational modifications (PTMs) have emerged as key modulators of protein phase separation and have been linked to protein aggregation in neurodegenerative disorders. The major aggregating protein in amyotrophic lateral sclerosis and frontotemporal dementia, the RNA-binding protein TAR DNA-binding protein (TDP-43), is hyperphosphorylated in disease on several C-terminal serine residues, a process generally believed to promote TDP-43 aggregation. Here, we however find that Casein kinase 1δ-mediated TDP-43 hyperphosphorylation or C-terminal phosphomimetic mutations reduce TDP-43 phase separation and aggregation, and instead render TDP-43 condensates more liquid-like and dynamic. Multi-scale molecular dynamics simulations reveal reduced homotypic interactions of TDP-43 low-complexity domains through enhanced solvation of phosphomimetic residues. Cellular experiments show that phosphomimetic substitutions do not affect nuclear import or RNA regulatory functions of TDP-43, but suppress accumulation of TDP-43 in membrane-less organelles and promote its solubility in neurons. We speculate that TDP-43 hyperphosphorylation may be a protective cellular response to counteract TDP-43 aggregation.
翻译后修饰（PTMs）已成为蛋白质相分离的关键调节因子，并与神经退行性疾病中的蛋白质聚集有关。肌萎缩侧索硬化症和额颞叶痴呆中的主要聚集蛋白，即RNA结合蛋白TAR DNA结合蛋白（TDP-43），在疾病状态下其C端的几个丝氨酸残基会发生过度磷酸化，这一过程通常被认为会促进TDP-43的聚集。然而，我们在此发现，酪蛋白激酶1δ介导的TDP-43过度磷酸化或C端磷酸模拟突变会减少TDP-43的相分离和聚集，反而使TDP-43凝聚物更具液体样和动态性。多尺度分子动力学模拟显示，通过增强磷酸模拟残基的溶剂化作用，TDP-43低复杂性结构域的同型相互作用减少。细胞实验表明，磷酸模拟取代并不影响TDP-43的核输入或RNA调节功能，但会抑制TDP-43在无膜细胞器中的积累，并促进其在神经元中的溶解性。我们推测，TDP-43过度磷酸化可能是一种保护性的细胞反应，以对抗TDP-43的聚集。
