Jiang Wentong, Wang Wei, Kong Yinfei, Zheng Sanduo
Graduate School of Peking Union Medical College, Beijing 100730, China.
National Institute of Biological Sciences, Beijing 102206, China.
Sci Adv. 2023 Jul 14;9(28):eadg8369. doi: 10.1126/sciadv.adg8369.
G protein-coupled receptor (GPCR) signaling is precisely controlled to avoid overstimulation that results in detrimental consequences. Gβγ signaling is negatively regulated by a Cullin3 (Cul3)-dependent E3 ligase, KCTD5, which triggers ubiquitination and degradation of free Gβγ. Here, we report the cryo-electron microscopy structures of the KCTD5-Gβγ fusion complex and the KCTD7-Cul3 complex. KCTD5 in pentameric form engages symmetrically with five copies of Gβγ through its C-terminal domain. The unique pentameric assembly of the KCTD5/Cul3 E3 ligase places the ubiquitin-conjugating enzyme (E2) and the modification sites of Gβγ in close proximity and allows simultaneous transfer of ubiquitin from E2 to five Gβγ subunits. Moreover, we show that ubiquitination of Gβγ by KCTD5 is important for fine-tuning cyclic adenosine 3´,5´-monophosphate signaling of GPCRs. Our studies provide unprecedented insights into mechanisms of substrate recognition by unusual pentameric E3 ligases and highlight the KCTD family as emerging regulators of GPCR signaling.
G蛋白偶联受体（GPCR）信号传导受到精确控制，以避免过度刺激导致有害后果。Gβγ信号传导受到一种依赖Cullin3（Cul3）的E3连接酶KCTD5的负调控，KCTD5会触发游离Gβγ的泛素化和降解。在此，我们报告了KCTD5-Gβγ融合复合物和KCTD7-Cul3复合物的冷冻电子显微镜结构。五聚体形式的KCTD5通过其C末端结构域与五个拷贝的Gβγ对称结合。KCTD5/Cul3 E3连接酶独特的五聚体组装使泛素结合酶（E2）和Gβγ的修饰位点紧密相邻，并允许泛素从E2同时转移到五个Gβγ亚基上。此外，我们表明KCTD5对Gβγ的泛素化对于微调GPCR的环磷酸腺苷信号传导很重要。我们的研究为不寻常的五聚体E3连接酶识别底物的机制提供了前所未有的见解，并突出了KCTD家族作为GPCR信号传导的新兴调节因子。
