Structure of the NAT10 acetyltransferase and mechanism of tRNA acetylation

NAT10 is the sole eukaryotic acetyltransferase that catalyzes N4-acetylcytidine (ac⁴C) modification of RNA. While dysregulation of NAT10 is associated with cancer and premature aging syndromes, the requirement for its acetyltransferase activity and how NAT10 coordinates catalysis and RNA binding remain poorly understood. Here, we report single particle cryo-electron microscopy structures of eukaryotic (Chaetomium thermophilum) NAT10 in complex with a designer cytidine-CoA cofactor-based ligand in the presence and absence of ADP. NAT10 forms a symmetrical heart-shaped dimer where a Gcn5-related N-acetyltransferase (GNAT) domain with an atypically opened active site is flanked by conserved helicase and RNA-binding domains. Biochemical reconstitution of NAT10 in the presence of the adapter protein THUMPD1 reveals that tRNA acetylation is enabled by two conserved active site residues (His548 and Tyr549 in CtNAT10) and two basic patches: one proximal and one distal from the active site, and suggests that binding orientation rather than affinity drives catalysis. Finally, we harness structure-guided mutations in cellular studies to demonstrate the necessity for NAT10 catalytic acetyltransferase activity in fungal thermoadaptation and mammalian etoposide-induced cellular senescence, respectively. Our findings provide a structural foundation for understanding NAT10-catalyzed cytidine acetylation, with implications for regulation and therapeutic targeting of its distinct RNA acetyltransferase activity.