近日，美国纪念斯隆-凯特琳癌症中心Christopher D. Lima等研究人员合作揭示泛素途径中转硫醇作用中间体的结构基础。2024年8月14日，国际知名学术期刊《自然》在线发表了这一成果。

研究人员表示，转硫醇作用（也称为硫酯交换反应）反应用于乙酰辅酶A、脂肪酸和聚酮的生物合成，以及泛素（Ub）和类泛素（Ubl）蛋白的翻译后修饰。在泛素途径中，E1酶催化泛素从E1Ub硫酯向E2Ub硫酯的转移。转硫醇作用还用于将泛素从E2Ub硫酯转移到HECT（同源于E6AP C端）和RBR（环间环）E3连接酶，形成E3Ub硫酯。关于泛素途径中的酶如何推动硫酯键的等能转移，目前尚不清楚。

研究人员通过化学策略，利用接近天然酶和近乎天然泛素，分离出E1–Ub(T)–E2和E2–Ub(T)–E3HECT复合物（T表示处于硫酯中的泛素或正在进行硫酯化的泛素）的瞬态中间体模拟物，并通过单颗粒冷冻电镜捕获并可视化了一系列结构。这些结构及相关的生化实验揭示了泛素、E1、E2和E3在构象上的变化，这些变化与化学反应协调，以促进泛素从每个酶向下一个酶的方向性转移。

Title: Structural basis for transthiolation intermediates in the ubiquitin pathway

Author: Kochaczyk, Tomasz, Hann, Zachary S., Lux, Michaelyn C., Delos Reyes, Avelyn Mae V., Ji, Cheng, Tan, Derek S., Lima, Christopher D.

Issue&Volume: 2024-08-14

Abstract: Transthiolation (also known as transthioesterification) reactions are used in the biosynthesis of acetyl coenzyme A, fatty acids and polyketides, and for post-translational modification by ubiquitin (Ub) and ubiquitin-like (Ubl) proteins1,2,3. For the Ub pathway, E1 enzymes catalyse transthiolation from an E1~Ub thioester to an E2~Ub thioester. Transthiolation is also required for transfer of Ub from an E2~Ub thioester to HECT (homologous to E6AP C terminus) and RBR (ring-between-ring) E3 ligases to form E3~Ub thioesters4,5,6. How isoenergetic transfer of thioester bonds is driven forward by enzymes in the Ub pathway remains unclear. Here we isolate mimics of transient transthiolation intermediates for E1–Ub(T)–E2 and E2–Ub(T)–E3HECT complexes (where T denotes Ub in a thioester or Ub undergoing transthiolation) using a chemical strategy with native enzymes and near-native Ub to capture and visualize a continuum of structures determined by single-particle cryo-electron microscopy. These structures and accompanying biochemical experiments illuminate conformational changes in Ub, E1, E2 and E3 that are coordinated with the chemical reactions to facilitate directional transfer of Ub from each enzyme to the next.

DOI: 10.1038/s41586-024-07828-9

Source: https://www.nature.com/articles/s41586-024-07828-9