Fig. 1

Structure of D4. a. Overall structure of D4. Cartoon diagram shows the three dimensional structure of D4. The A and B subunits from the free-D4 structure (4dof) are displayed and labeled. C-terminal strand of the central β-sheet is colored green. Additional β sheets seen in D4 structures are colored magenta; amino acid residues forming the strands are labeled. Structural elements that are involved in homodimer interactions in different D4 structures are painted in blue, violet and green. b. Comparison with human UNG (hUNG). Cartoon drawing shows superimposition of the structure of substrate-free hUNG (1akz) in wheat color and D4 (4dof subunit a) in cyan. Overall structural fold is very similar for both proteins. The N and C-terminal additional β sheets in D4 are colored dark. N and C-terminal ends of D4 are labeled. c. A20 binding on D4. Cartoon drawing shows the A20 binding site on D4 structure. Structure of D4 (4dof, subunit A, cyan) was superimposed on the D4 chain A of D4:A20 complex (4od8, yellow). A20 segment from 4od8 is shown in wheat color. Amino acid residues Arg167 and Pro173 of D4 and Trp43 and Lys44 of A20 play important role in the binding. These residues are shown as stick models. N and C-terminus of A20 are labeled