Three-dimensional structure of APOBEC2 . α Helices 2 and 3, which hold the histidine and the cysteines forming the catalytic pocket, are indicated in blue. The zinc atom is indicated as a yellow sphere, the residues coordinating the zinc atom are colored in red, and the glutamate acting as proton donor in purple (beneath the zinc atom). The β strands providing the molecule's scaffold are indicated in bright green. The loops that might play a role in substrate recognition are indicated: the loop conserved in TadA  is in orange and the SSS loop is in pink. PDB: 2NYT.