Figure 4.

ssDNA adenosine deaminases and their design and application in genomic DNA base editing. (Top) These enzymes can hydrolytically deaminate adenines in ssDNA and ssRNA to yield an inosine, which is then processed into guanine via DNA replication and/or repair processes. Overall, this reaction gives rise to A·T→G·C base pair conversion. (Middle) Representative ABE architectures are shown, with the essential and non-essential components indicated with solid and dashed outlines, respectively. (Bottom) The secondary structure of the TadA enzyme is shown, with an emphasis on the core CDA fold. Locations of the substrate-binding loops and active site residues are indicated, and key mutations discovered using either rational design or directed evolution approaches to enhance certain properties of the corresponding ABE are shown in dark and light green, respectively.