Structural insights into tRNA recognition of the human FTSJ1-THADA complex.

tRNA undergoes various post-transcriptional modifications in the anticodon loop. FTSJ1, a protein conserved among most eukaryotes, mediates 2'-O-methylations at position 32 (Nm32) or position 34 (Nm34), complexed with THADA or WDR6, respectively. These methylations are crucial for accurate translation and cellular growth. FTSJ1 mutations are associated with non-syndromic X-linked intellectual disability. Although the structure of the FTSJ1-WDR6 complex in yeast has been solved, the structural details of the FTSJ1-THADA complex formation and substrate recognition remain unclear. Herein, using cryo-electron microscopy, we solve the high-resolution structure of FTSJ1-THADA with or without a tRNA substrate. FTSJ1 binds to THADA via its C-terminal region, with a unique interaction mode distinct from the FTSJ1-WDR6 complex. The tRNA substrate is anchored inside THADA, and key THADA residues for THADA-tRNA interaction are identified via structural and biochemical analyses. These findings demonstrate how FTSJ1 and THADA form a complex to mediate Nm32 modification in various tRNAs.