Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT, USA.
Nat Commun. 2022 Oct 12;13(1):6005. doi: 10.1038/s41467-022-33434-2.
Cajal bodies (CBs) are ubiquitous nuclear membraneless organelles (MLOs) that concentrate and promote efficient biogenesis of snRNA-protein complexes involved in splicing (snRNPs). Depletion of the CB scaffolding protein coilin disperses snRNPs, making CBs a model system for studying the structure and function of MLOs. Although it is assumed that CBs form through condensation, the biomolecular interactions responsible remain elusive. Here, we discover the unexpected capacity of coilin's N-terminal domain (NTD) to form extensive fibrils in the cytoplasm and discrete nuclear puncta in vivo. Single amino acid mutational analysis reveals distinct molecular interactions between coilin NTD proteins to form fibrils and additional NTD interactions with the nuclear Nopp140 protein to form puncta. We provide evidence that Nopp140 has condensation capacity and is required for CB assembly. From these observations, we propose a model in which coilin NTD-NTD mediated assemblies make multivalent contacts with Nopp140 to achieve biomolecular condensation in the nucleus.
Cajal 体（CBs）是普遍存在的核无膜细胞器（MLOs），它们浓缩并促进参与剪接的 snRNA-蛋白质复合物的有效生物发生（snRNPs）。CB 支架蛋白 coilin 的耗竭会使 snRNPs 分散，使 CB 成为研究 MLOs 结构和功能的模型系统。尽管假定 CB 通过浓缩形成，但负责的生物分子相互作用仍然难以捉摸。在这里，我们发现 coilin 的 N 端结构域（NTD）出人意料地具有在细胞质中形成广泛纤维和体内离散核斑点的能力。单个氨基酸突变分析揭示了 coilin NTD 蛋白之间形成纤维的独特分子相互作用，以及与核 Nopp140 蛋白形成斑点的额外 NTD 相互作用。我们提供的证据表明，Nopp140 具有浓缩能力，是 CB 组装所必需的。根据这些观察结果，我们提出了一个模型，其中 coilin NTD-NTD 介导的组装与 Nopp140 形成多价接触，以实现核内的生物分子浓缩。
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