The mammalian tRNA ligase complex (tRNA-LC) catalyzes the splicing of intron-containing pre-tRNAs in the nucleus and the splicing of XBP1 mRNA during the unfolded protein response (UPR) in the cytoplasm. We recently reported that the tRNA-LC coevolved with PYROXD1, an essential oxidoreductase that protects the catalytic cysteine of RTCB, the catalytic subunit of the tRNA-LC, against aerobic oxidation. In this study, we show that the oxidoreductase Thioredoxin (TRX) preserves the enzymatic activity of RTCB under otherwise inhibiting concentrations of oxidants. TRX physically interacts with oxidized RTCB, and reduces and reactivates RTCB through the action of its redox-active cysteine pair. We further show that TRX interacts with RTCB at late stages of UPR. Since the interaction requires oxidative conditions, our findings suggest that prolonged UPR generates reactive oxygen species. Thus, our results support a functional role for TRX in securing and repairing the active site of the tRNA-LC, thereby allowing pre-tRNA splicing and UPR to occur when cells encounter mild, but still inhibitory levels of reactive oxygen species.

中文翻译：

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硫氧还蛋白调节氧化还原状态和人 tRNA 连接酶复合物的活性

哺乳动物 tRNA 连接酶复合物 (tRNA-LC) 催化细胞核中含有内含子的前 tRNA 的剪接以及细胞质中未折叠蛋白反应 (UPR) 过程中XBP1 mRNA的剪接。我们最近报道，tRNA-LC 与 PYROXD1 共同进化，PYROXD1 是一种重要的氧化还原酶，可保护 RT​​CB（tRNA-LC 的催化亚基）的催化半胱氨酸免受有氧氧化。在这项研究中，我们证明氧化还原酶硫氧还蛋白 (TRX) 在氧化剂浓度受到抑制的情况下保留了 RTCB 的酶活性。TRX 与氧化的 RTCB 发生物理相互作用，并通过其氧化还原活性半胱氨酸对的作用还原并重新激活 RTCB。我们进一步表明 TRX 在 UPR 的后期阶段与 RTCB 相互作用。由于相互作用需要氧化条件，我们的研究结果表明延长的 UPR 会产生活性氧。因此，我们的结果支持 TRX 在保护和修复 tRNA-LC 活性位点方面的功能作用，从而在细胞遇到温和但仍处于抑制水平的活性氧时允许前 tRNA 剪接和 UPR 发生。