Department of Structural Biology, Van Andel Institute, 333 Bostwick Avenue NE, Grand Rapids, MI 49503, USA.
Department of Microbiology & Immunology, Weill Cornell Medicine, 1300 York Avenue, New York, NY 10065, USA.
Structure. 2023 May 4;31(5):541-552.e4. doi: 10.1016/j.str.2023.03.010. Epub 2023 Apr 10.
The human UBR5 is a single polypeptide chain homology to E6AP C terminus (HECT)-type E3 ubiquitin ligase essential for embryonic development in mammals. Dysregulated UBR5 functions like an oncoprotein to promote cancer growth and metastasis. Here, we report that UBR5 assembles into a dimer and a tetramer. Our cryoelectron microscopy (cryo-EM) structures reveal that two crescent-shaped UBR5 monomers assemble head to tail to form the dimer, and two dimers bind face to face to form the cage-like tetramer with all four catalytic HECT domains facing the central cavity. Importantly, the N-terminal region of one subunit and the HECT of the other form an "intermolecular jaw" in the dimer. We show the jaw-lining residues are important for function, suggesting that the intermolecular jaw functions to recruit ubiquitin-loaded E2 to UBR5. Further work is needed to understand how oligomerization regulates UBR5 ligase activity. This work provides a framework for structure-based anticancer drug development and contributes to a growing appreciation of E3 ligase diversity.
人类 UBR5 是一种单多肽链同源物，与 E6AP C 末端（HECT）-型 E3 泛素连接酶在哺乳动物胚胎发育中必不可少。UBR5 功能失调的作用就像一种癌蛋白，促进癌症的生长和转移。在这里，我们报告 UBR5 组装成二聚体和四聚体。我们的冷冻电镜（cryo-EM）结构揭示了两个新月形 UBR5 单体头尾相连形成二聚体，两个二聚体面对面结合形成笼状四聚体，所有四个催化 HECT 结构域都朝向中央腔。重要的是，一个亚基的 N 端区域和另一个亚基的 HECT 形成二聚体中的“分子间颚”。我们表明，颚线残基对于功能很重要，这表明分子间颚的作用是招募带有泛素的 E2 到 UBR5。需要进一步的工作来了解寡聚化如何调节 UBR5 连接酶的活性。这项工作为基于结构的抗癌药物开发提供了一个框架，并有助于人们越来越多地认识到 E3 连接酶的多样性。
