A chiral selectivity relaxed paralog of DTD for proofreading tRNA mischarging in Animalia

ABSTRACT D-aminoacyl-tRNA deacylase (DTD), a trans -editing factor found in bacteria and eukaryotes, removes D-amino acids mischarged on tRNAs as well as achiral glycine mischarged on tRNA Ala . An invariant cross-subunit Gly- cis Pro motif forms the mechanistic basis of strict L-amino acid rejection from the catalytic site. Here, we present the identification of a DTD variant, named ATD ( A nimalia-specific t RNA d eacylase), that harbors a Gly- trans Pro motif. The cis -to- trans switch causes a “gain of function” through L-chiral selectivity in ATD resulting in the clearing of L-alanine mischarged on tRNA Thr (G4•U69) by eukaryotic AlaRS. The biochemical proofreading activity of ATD is conserved across diverse classes of phylum Chordata. Animalia genomes enriched in tRNA Thr (G4•U69) genes are in strict association with the presence of ATD, underlining the mandatory requirement of a dedicated factor to proofread tRNA misaminoacylation. The study highlights the emergence of ATD during genome expansion as a key event associated with the evolution of Animalia.