MRC Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge, CB2 0QH, UK.
Max Planck Institute of Biochemistry, Am Klopferspitz 18, 82152, Martinsried, Germany.
Nat Commun. 2023 Apr 15;14(1):2160. doi: 10.1038/s41467-023-37504-x.
TRIM proteins are the largest family of E3 ligases in mammals. They include the intracellular antibody receptor TRIM21, which is responsible for mediating targeted protein degradation during Trim-Away. Despite their importance, the ubiquitination mechanism of TRIM ligases has remained elusive. Here we show that while Trim-Away activation results in ubiquitination of both ligase and substrate, ligase ubiquitination is not required for substrate degradation. N-terminal TRIM21 RING ubiquitination by the E2 Ube2W can be inhibited by N-terminal acetylation, but this doesn't prevent substrate ubiquitination nor degradation. Instead, uncoupling ligase and substrate degradation prevents ligase recycling and extends functional persistence in cells. Further, Trim-Away degrades substrates irrespective of whether they contain lysines or are N-terminally acetylated, which may explain the ability of TRIM21 to counteract fast-evolving pathogens and degrade diverse substrates.
TRIM 蛋白是哺乳动物中最大的 E3 连接酶家族。它们包括细胞内抗体受体 TRIM21，它负责在 Trim-Away 期间介导靶向蛋白质降解。尽管它们很重要，但 TRIM 连接酶的泛素化机制仍然难以捉摸。在这里，我们表明，虽然 Trim-Away 的激活导致连接酶和底物的泛素化，但连接酶的泛素化对于底物降解并不是必需的。E2 Ube2W 对 TRIM21 N 端 RING 的泛素化可以被 N 端乙酰化抑制，但这并不能阻止底物的泛素化或降解。相反，将连接酶和底物降解解偶联可以防止连接酶的回收，并延长细胞内的功能持久性。此外，Trim-Away 降解底物，无论它们是否含有赖氨酸或是否被 N 端乙酰化，这可能解释了 TRIM21 能够对抗快速进化的病原体并降解多种底物的能力。
