Department of Biochemistry, School of Biomedical Sciences, University of Otago, Dunedin, 9054, New Zealand.
Nat Commun. 2017 Nov 27;8(1):1788. doi: 10.1038/s41467-017-01665-3.
Ubiquitin chains linked through lysine63 (K63) play a critical role in inflammatory signalling. Following ligand engagement of immune receptors, the RING E3 ligase TRAF6 builds K63-linked chains together with the heterodimeric E2 enzyme Ubc13-Uev1A. Dimerisation of the TRAF6 RING domain is essential for the assembly of K63-linked ubiquitin chains. Here, we show that TRAF6 RING dimers form a catalytic complex where one RING interacts with a Ubc13~Ubiquitin conjugate, while the zinc finger 1 (ZF1) domain and linker-helix of the opposing monomer contact ubiquitin. The RING dimer interface is conserved across TRAFs and we also show that TRAF5-TRAF6 heterodimers form. Importantly, TRAF5 can provide ZF1, enabling ubiquitin transfer from a TRAF6-bound Ubc13 conjugate. Our study explains the dependence of activity on TRAF RING dimers, and suggests that both homo- and heterodimers mediated by TRAF RING domains have the capacity to synthesise ubiquitin chains.
泛素链通过赖氨酸 63（K63）连接在炎症信号中起着关键作用。在免疫受体与配体结合后，RING E3 连接酶 TRAF6 与异二聚体 E2 酶 Ubc13-Uev1A 一起构建 K63 连接的链。TRAF6 RING 结构域的二聚化对于 K63 连接的泛素链的组装是必不可少的。在这里，我们表明 TRAF6 RING 二聚体形成一个催化复合物，其中一个 RING 与 Ubc13~泛素缀合物相互作用，而锌指 1（ZF1）结构域和相反单体的连接螺旋与泛素接触。RING 二聚体界面在 TRAFs 中是保守的，我们还表明 TRAF5-TRAF6 异二聚体形成。重要的是，TRAF5 可以提供 ZF1，从而能够从 TRAF6 结合的 Ubc13 缀合物中转移泛素。我们的研究解释了对 TRAF RING 二聚体活性的依赖性，并表明由 TRAF RING 结构域介导的同二聚体和异二聚体都具有合成泛素链的能力。
