Structural studies on human adenosine-to-inosine tRNA editing

Abstract

Adenosine deaminase acting on tRNAs (ADAT) is a eukaryotic heterodimer, composed by ADAT2 and ADAT3, that catalyses the deamination of adenosine-to-inosine in the anticodon loop of tRNAs. ADAT proteins are essential for the cell, as the adenosine-to-inosine modification enables the proper recognition of all the codons during translation. Indeed, a single point mutation in one of the subunits of the heterodimer is causing mental retardation in some patients. However, there is no structural information of any eukaryotic deaminase, thus hampering the development of any kind of treatment. In this work, we have studied the human ADAT2-ADAT3-tRNA complex using cryo-EM and SAXS, proposing a model of the ternary complex which sheds light on the molecular insights of the deamination and paves the way for further structural studies.

Also, the emergence of ADAT proteins in eukaryotes entails the enrichment of potential ADAT-substrates within tRNA pools. The only exception to this evolutionary trend is the tRNAGlyACC, which is not transcribed in humans. In this thesis, we have determined the atomic structure of the tRNAGlyACC by X-ray crystallography, which presents a typical L-shape conformation but with a cleaved anticodon loop, probably digested by a RNase. This finding supports the hypothesis of a disordered structure in the tRNAGlyACC anticodon loop nucleotides, and it may explain its absence in the human transcriptome.