Max-Delbrück-Center for Molecular Medicine in the Helmholtz Association, Berlin-Buch, Germany.
Institute of Biophysical Chemistry and Center for Biomolecular Magnetic Resonance, Goethe University, Frankfurt am Main, Germany.
EMBO J. 2021 Mar 15;40(6):e106094. doi: 10.15252/embj.2020106094. Epub 2021 Feb 12.
The assembly of a specific polymeric ubiquitin chain on a target protein is a key event in the regulation of numerous cellular processes. Yet, the mechanisms that govern the selective synthesis of particular polyubiquitin signals remain enigmatic. The homologous ubiquitin-conjugating (E2) enzymes Ubc1 (budding yeast) and Ube2K (mammals) exclusively generate polyubiquitin linked through lysine 48 (K48). Uniquely among E2 enzymes, Ubc1 and Ube2K harbor a ubiquitin-binding UBA domain with unknown function. We found that this UBA domain preferentially interacts with ubiquitin chains linked through lysine 63 (K63). Based on structural modeling, in vitro ubiquitination experiments, and NMR studies, we propose that the UBA domain aligns Ubc1 with K63-linked polyubiquitin and facilitates the selective assembly of K48/K63-branched ubiquitin conjugates. Genetic and proteomics experiments link the activity of the UBA domain, and hence the formation of this unusual ubiquitin chain topology, to the maintenance of cellular proteostasis.
特定聚合泛素链在靶蛋白上的组装是调节许多细胞过程的关键事件。然而，控制特定多泛素信号选择性合成的机制仍然是个谜。同源泛素连接酶 (E2) 酶 Ubc1（酵母）和 Ube2K（哺乳动物）专门通过赖氨酸 48（K48）生成聚合泛素。在 E2 酶中，Ubc1 和 Ube2K 独有的具有未知功能的泛素结合 UBA 结构域。我们发现这个 UBA 结构域优先与通过赖氨酸 63（K63）连接的泛素链相互作用。基于结构建模、体外泛素化实验和 NMR 研究，我们提出 UBA 结构域将 Ubc1 与 K63 连接的多泛素对齐，并促进 K48/K63 分支泛素缀合物的选择性组装。遗传和蛋白质组学实验将 UBA 结构域的活性，以及这种异常泛素链拓扑结构的形成，与细胞蛋白质稳态的维持联系起来。
