Structure of PML mutant Dieselzyme 4. (A) Cartoon representation of Dieselzyme 4. The locations of clustered mutations described in the text, designated Region 1 and Region 2, are highlighted with a red and orange box respectively. Mutations in Dieselzyme 4 are labeled and shown as sticks. Lid helices α5 and α8 are shown for clarity and colored green. The catalytic triad is shown as orange ball and stick. (B) 90° rotation of (A). (C) Zoom in of Region 1 as seen in the wild-type PML structure. (D) Zoom in of Region 1 as seen in the Dieselzyme 4 structure. Mutations are highlighted as magenta sticks. New H-bonds present in Dieselzyme 4 are shown as dashed black lines. (E) Zoom in of Region 2 as seen in the wild-type PML structure. The “helical loop” between residues 202 and 207 is highlighted orange. Potential H-bonds between residues R220 and H216 from helix α8, the loop region, and crystallographic waters are shown as orange dashes. The bound calcium is shown as a cyan sphere. (F) Zoom in of Region 2 as seen in the Dieselzyme 4 structure. The remodeled “helical loop” between residues 202 and 207 is highlighted in orange. Residues G202E and E207 that form potential new salt-bridges with R220 and/or H216 from helix α8 are highlighted with a star. Other H-bonds are shown as red dashes. The bound calcium is shown as a cyan sphere.