Conserved signaling cascades monitor protein-folding homeostasis to ensure proper cellular function. One of the evolutionary conserved key players is IRE1, which maintains endoplasmic reticulum (ER) homeostasis through the unfolded protein response (UPR). Upon accumulation of misfolded proteins in the ER, IRE1 forms clusters on the ER membrane to initiate UPR signaling. What regulates IRE1 cluster formation is not fully understood. Here, we show that the ER lumenal domain (LD) of human IRE1α forms biomolecular condensates in vitro. IRE1α LD condensates were stabilized both by binding to unfolded polypeptides as well as by tethering to model membranes, suggesting their role in assembling IRE1α into signaling-competent stable clusters. Molecular dynamics simulations indicated that weak multivalent interactions drive IRE1α LD clustering. Mutagenesis experiments identified disordered regions in IRE1α LD to control its clustering in vitro and in cells. Importantly, dysregulated clustering of IRE1α mutants led to defects in IRE1α signaling. Our results revealed that disordered regions in IRE1α LD control its clustering and suggest their role as a common strategy in regulating protein assembly on membranes.

中文翻译：

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IRE1α ER 管腔结构域中的无序区域介导其应力诱导的聚集。


保守的信号级联反应监测蛋白质折叠稳态，以确保正常的细胞功能。IRE1 是进化上保守的关键参与者之一，它通过未折叠蛋白反应 （UPR） 维持内质网 （ER） 稳态。当错误折叠的蛋白质在 ER 中积累时，IRE1 在 ER 膜上形成簇以启动 UPR 信号转导。调节 IRE1 簇形成的因素尚不完全清楚。在这里，我们表明人 IRE1α 的 ER 管腔结构域 （LD） 在体外形成生物分子凝聚物。IRE1α LD 缩合物通过与未折叠的多肽结合以及与模型膜拴系来稳定，表明它们在将 IRE1α 组装成信号转导能力稳定簇中的作用。分子动力学模拟表明，弱多价相互作用驱动 IRE1α LD 聚集。诱变实验确定了 IRE1α LD 中的无序区域，以控制其在体外和细胞中的聚集。重要的是，IRE1α 突变体的失调聚集导致 IRE1α 信号传导缺陷。我们的结果表明，IRE1α LD 中的无序区域控制其聚集，并表明它们作为调节膜上蛋白质组装的常见策略。