Chen Bo, Mariano Jennifer, Tsai Yien Che, Chan Anna H, Cohen Mickael, Weissman Allan M
Laboratory of Protein Dynamics and Signaling, Center for Cancer Research, Building 560, Room 22-103, National Cancer Institute, Frederick, MD 21702, USA.
Proc Natl Acad Sci U S A. 2006 Jan 10;103(2):341-6. doi: 10.1073/pnas.0506618103. Epub 2006 Jan 3.
Efficient targeting of proteins for degradation from the secretory pathway is essential to homeostasis. This occurs through endoplasmic reticulum (ER)-associated degradation (ERAD). In this study, we establish that a human ubiquitin ligase (E3), gp78, and a specific E2, Ube2g2, are both critically important for ERAD of multiple substrates. gp78 exhibits a complex domain structure that, in addition to the RING finger, includes a ubiquitin-binding Cue domain and a specific binding site for Ube2g2. Disruption of either of these domains abolishes gp78-mediated ubiquitylation and protein degradation, resulting in accumulation of substrates in their fully glycosylated forms in the ER. This suggests that gp78-mediated ubiquitylation is an early step in ERAD that precedes dislocation of substrates from the ER. The in vivo requirement for both an E2-binding site distinct from the RING finger and a ubiquitin-binding domain intrinsic to an E3 suggests a previously unappreciated level of complexity in ubiquitin ligase function. These results also provide proof of principle that interrupting a specific E2-E3 interaction can selectively inhibit ERAD.
将蛋白质从分泌途径中有效靶向降解对于体内平衡至关重要。这一过程通过内质网（ER）相关降解（ERAD）实现。在本研究中，我们证实人泛素连接酶（E3）gp78和特定的E2 Ube2g2对于多种底物的ERAD都至关重要。gp78呈现出复杂的结构域结构，除了环状结构域外，还包括一个泛素结合Cue结构域和一个Ube2g2的特异性结合位点。这些结构域中的任何一个被破坏都会消除gp78介导的泛素化和蛋白质降解，导致底物以其完全糖基化的形式在内质网中积累。这表明gp78介导的泛素化是ERAD中底物从内质网脱位之前的早期步骤。体内对不同于环状结构域的E2结合位点和E3固有的泛素结合结构域的需求表明泛素连接酶功能存在前所未有的复杂程度。这些结果还提供了原理证明，即中断特定的E2 - E3相互作用可以选择性地抑制ERAD。
