Temasek Life Sciences Laboratory and Department of Biological Sciences, The National University of Singapore, Singapore 117604, Singapore.
Department of Biomedical Engineering and Center for Science & Engineering of Living Systems (CSELS), Washington University in St. Louis, St. Louis, MO 63130, USA.
Mol Cell. 2020 Mar 19;77(6):1237-1250.e4. doi: 10.1016/j.molcel.2020.01.025. Epub 2020 Feb 11.
Low-complexity protein domains promote the formation of various biomolecular condensates. However, in many cases, the precise sequence features governing condensate formation and identity remain unclear. Here, we investigate the role of intrinsically disordered mixed-charge domains (MCDs) in nuclear speckle condensation. Proteins composed exclusively of arginine-aspartic acid dipeptide repeats undergo length-dependent condensation and speckle incorporation. Substituting arginine with lysine in synthetic and natural speckle-associated MCDs abolishes these activities, identifying a key role for multivalent contacts through arginine's guanidinium ion. MCDs can synergize with a speckle-associated RNA recognition motif to promote speckle specificity and residence. MCD behavior is tunable through net-charge: increasing negative charge abolishes condensation and speckle incorporation. Contrastingly, increasing positive charge through arginine leads to enhanced condensation, speckle enlargement, decreased splicing factor mobility, and defective mRNA export. Together, these results identify key sequence determinants of MCD-promoted speckle condensation and link the dynamic material properties of speckles with function in mRNA processing.
低复杂度蛋白结构域可促进多种生物分子凝聚物的形成。然而，在许多情况下，对于控制凝聚物形成和身份的精确序列特征仍不清楚。在这里，我们研究了固有无序混合电荷结构域（MCD）在核斑点凝聚中的作用。由精氨酸-天冬氨酸二肽重复组成的蛋白质会发生长度依赖性凝聚和斑点掺入。在合成和天然斑点相关 MCD 中用赖氨酸取代精氨酸会破坏这些活性，这表明多价接触通过精氨酸的胍离子发挥关键作用。MCD 可以与斑点相关的 RNA 识别基序协同作用，以促进斑点的特异性和居留性。通过净电荷可以调节 MCD 的行为：增加负电荷会破坏凝聚和斑点掺入。相反，通过精氨酸增加正电荷会导致凝聚增强、斑点增大、剪接因子迁移率降低以及 mRNA 输出缺陷。总之，这些结果确定了 MCD 促进斑点凝聚的关键序列决定因素，并将斑点的动态物质特性与 mRNA 处理功能联系起来。
