The Jinek lab in collaboration with the Martinez lab and the Leitner group elucidated the mechanism how the human tRNA ligase complex is protected from oxidation which inactivates this essential complex for tRNA biogenesis and the unfolded protein response. The inactivating oxidation occurs on a Cysteine in the active-site of the catalytic subunit RTCB of the ligase complex. The oxidoreductase PYROXD1 protects the complex from oxidation and the researchers could now show that its carboxy-terminal tail directly interacts with the catalytic center of RTCB. Futhermore, they could show that PYROXD1 does not interact with the guanylylated form of RTCB, which is by itself protected from oxidation. Their findings have been published in the article " Mechanistic basis for PYROXD1-mediated protection of the human tRNA ligase complex against oxidative inactivation" in the journal Nature Structural Molecular Biology.
Abstract
The metazoan tRNA ligase complex (tRNA-LC) has essential roles in tRNA biogenesis and unfolded protein response. Its catalytic subunit RTCB contains a conserved active-site cysteine that is susceptible to metal ion-induced oxidative inactivation. The flavin-containing oxidoreductase PYROXD1 preserves the activity of human tRNA-LC in a NAD(P)H-dependent manner, but its protective mechanism remains elusive. Here, we report a cryogenic electron microscopic structure of the human RTCB-PYROXD1 complex, revealing that PYROXD1 directly interacts with the catalytic center of RTCB through its carboxy-terminal tail. NAD(P)H binding and FAD reduction allosterically control PYROXD1 activity and RTCB recruitment, while reoxidation of PYROXD1 enables timed release of RTCB. PYROXD1 interaction is mutually exclusive with Archease-mediated RTCB guanylylation, and guanylylated RTCB is intrinsically protected from oxidative inactivation. Together, these findings provide a mechanistic framework for the protective function of PYROXD1 that maintains the activity of the tRNA-LC under aerobic conditions.
Read the Publication in Nature Structural Molecular Biology (Open Access)
Abstract, figure and title from Loeff et al (2025) Nat Struct Mol Biol published under a CC BY 4.0 license.