Amphioxus adenosine-to-inosine tRNA-editing enzyme that can perform C-to-U and A-to-I deamination of DNA

An adenosine-to-inosine tRNA-editing deaminase ADAT2 from amphioxus (Branchiostoma japonicum) in complex with ADAT3 can perform A-to-I editing of tRNA and convert C-to-U and A-to-I deamination of DNA. Adenosine-to-inosine tRNA-editing enzyme has been identified for more than two decades, but the study on its DNA editing activity is rather scarce. We show that amphioxus (Branchiostoma japonicum) ADAT2 (BjADAT2) contains the active site 'HxE-PCxxC' and the key residues for target-base-binding, and amphioxus ADAT3 (BjADAT3) harbors both the N-terminal positively charged region and the C-terminal pseudo-catalytic domain important for recognition of substrates. The sequencing of BjADAT2-transformed Escherichia coli genome suggests that BjADAT2 has the potential to target E. coli DNA and can deaminate at TCG and GAA sites in the E. coli genome. Biochemical analyses further demonstrate that BjADAT2, in complex with BjADAT3, can perform A-to-I editing of tRNA and convert C-to-U and A-to-I deamination of DNA. We also show that BjADAT2 preferentially deaminates adenosines and cytidines in the loop of DNA hairpin structures of substrates, and BjADAT3 also affects the type of DNA substrate targeted by BjADAT2. Finally, we find that C89, N113, C148 and Y156 play critical roles in the DNA editing activity of BjADAT2. Collectively, our study indicates that BjADAT2/3 is the sole naturally occurring deaminase with both tRNA and DNA editing capacity identified so far in Metazoa.

Automated summary

A study has identified an adenosine-to-inosine tRNA-editing deaminase, ADAT2, from amphioxus that can perform A-to-I editing of tRNA and convert C-to-U and A-to-I deamination of DNA when in complex with ADAT3. The study also reveals the key residues and binding sites involved in these activities. Furthermore, it suggests that ADAT2/3 is the only enzyme with both tRNA and DNA editing capabilities found in Metazoa.