Model of 3D structure of APRT protein. (A) Ribbon diagram of the wild type (left) and truncated (right) APRT monomer. Truncated protein lack the C-terminal domain which includes S8 and S9 b-strands and H6 a-helix. (B) Calyx-like structural feature of the active site of wild type (left) and truncated (right) APRT monomer. The truncated form lack Leu159, an essential residue for the active site.