Structure of a HOIP/E2~ubiquitin complex reveals RBR E3 ligase mechanism and regulation.
Structure of a HOIP/E2~ubiquitin complex reveals RBR E3 ligase mechanism and regulation.
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DOI：
10.1038/nature16511
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发表时间：
2016-01-28
期刊：
影响因子：
64.8
通讯作者：
Riedl SJ
中科院分区：
文献类型：
--
作者：
Lechtenberg BC;Rajput A;Sanishvili R;Dobaczewska MK;Ware CF;Mace PD;Riedl SJ
泛素化是影响细胞信号传导和功能各个方面的核心过程。泛素化的一个关键步骤是泛素从E2泛素结合酶转移到底物或生长的泛素链，这是由E3泛素连接酶介导的。环型E3连接酶通常促进泛素从E2直接转移到底物。然而，RBR家族的ring型E3连接酶打破了这一范式，与泛素形成共价中间体，类似于hect型E3连接酶。RBR家族包括Parkin和HOIP， HOIP是线性泛素链组装复合物（LUBAC）的中心催化因子。虽然对RBR E3连接酶Parkin和hari整体自抑制形式的结构了解是可用的，但没有完整的完全活性RBR E3连接酶或其任何复合物的结构存在。因此，RBR的作用机制在很大程度上仍然是一个谜。在这里，我们提出了具有E2~泛素缀合物的完全活性的hop -RBR转移复合物的第一个结构，这阐明了RBR E3连接酶的复杂性。活跃的hop - rbr采用与自抑制rbr明显不同的构象。HOIP-RBR以细长的方式结合E2~泛素缀合物，E2和E3催化中心理想地对准泛素转移，这在结构上需要并实现了类似hect的机制。此外，令人惊讶的是，RBRs固有的三个不同的螺旋- ibr折叠基序形成泛素结合区，这些泛素结合区与E2~Ub缀合物的活化泛素以及一个额外的调控泛素分子结合。发现的特征揭示了HOIP-RBR E3连接酶周期的关键状态，并与Parkin和hari进行比较，提示了RBR E3连接酶的一般机制。
Ubiquitination is a central process affecting all facets of cellular signaling and function. A critical step in ubiquitination is the transfer of ubiquitin from an E2 ubiquitin-conjugating enzyme to a substrate or a growing ubiquitin chain, which is mediated by E3 ubiquitin ligases. RING-type E3 ligases typically facilitate the transfer of ubiquitin from the E2 directly to the substrate. The RBR family of RING-type E3 ligases, however, breaks this paradigm by forming a covalent intermediate with ubiquitin similarly to HECT-type E3 ligases. The RBR family includes Parkin and HOIP, the central catalytic factor of the linear ubiquitin chain assembly complex (LUBAC). While structural insights into the RBR E3 ligases Parkin and HHARI in their overall autoinhibited forms are available, no structures exist of intact fully active RBR E3 ligases or any of their complexes. Thus, the RBR mechanism of action has remained largely enigmatic. Here we present the first structure of the fully active HOIP-RBR in its transfer complex with an E2~ubiquitin conjugate, which elucidates the intricate nature of RBR E3 ligases. The active HOIP-RBR adopts a conformation markedly different from that of autoinhibited RBRs. HOIP-RBR binds the E2~ubiquitin conjugate in an elongated fashion, with the E2 and E3 catalytic centers ideally aligned for ubiquitin transfer, which structurally both requires and enables a HECT-like mechanism. In addition, surprisingly, three distinct helix–IBR-fold motifs inherent to RBRs form ubiquitin-binding regions that engage the activated ubiquitin of the E2~Ub conjugate as well as an additional regulatory ubiquitin molecule. The features uncovered reveal critical states of the HOIP-RBR E3 ligase cycle, and comparison with Parkin and HHARI suggests a general mechanism for RBR E3 ligases.