Crystal Structure of the Zα Domain of the Human Editing Enzyme ADAR1 Bound to Left-Handed Z-DNA

The editing enzyme double-stranded RNA adenosine deaminase includes a DNA binding domain, Zα, which is specific for left-handed Z-DNA. The 2.1 angstrom crystal structure of Zα complexed to DNA reveals that the substrate is in the left-handed Z conformation. The contacts between Zα and Z-DNA are made primarily with the “zigzag” sugar-phosphate backbone, which provides a basis for the specificity for the Z conformation. A single base contact is observed to guanine in the syn conformation, characteristic of Z-DNA. Intriguingly, the helix-turn-helix motif, frequently used to recognize B-DNA, is used by Zα to contact Z-DNA.