The bacterial tRNA adenosine deaminase (TadA) generates inosine by deaminating the adenosine residue at the wobble position of tRNAArg-2. This modification is essential for the decoding system. In this study, we determined the crystal structure ofAquifex aeolicusTadA at a 1.8-Å resolution. This is the first structure of a deaminase acting on tRNA.A. aeolicusTadA has an α/β/α three-layered fold and forms a homodimer. TheA. aeolicusTadA dimeric structure is completely different from the tetrameric structure of yeast CDD1, which deaminates mRNA and cytidine, but is similar to the dimeric structure of yeast cytosine deaminase. However, in theA. aeolicusTadA structure, the shapes of the C-terminal helix and the regions between the β4 and β5 strands are quite distinct from those of yeast cytosine deaminase and a large cavity is produced. This cavity contains many conserved amino acid residues that are likely to be involved in either catalysis or tRNA binding. We made a docking model of TadA with the tRNA anticodon stem loop.
Crystal Structure of Yeast Cytosine Deaminase
