Three dimensional structure of the DWNN domain. (A) Superposition of the 25 lowest energy conformers. (B) Cartoon representation of the overall fold and secondary structure. The backbone adopts a ubiquitin-like β-grasp fold in which the central α-helix packs against a five-stranded β-sheet comprised of strands β1, β2, β4, β5 and β7. Unlike ubiquitin, DWNN contains an additional double-stranded β-sheet at the N-terminal end of the central α-helix, comprising strands β3 and β6. (C) Superposition of the backbone traces of the DWNN domain (in blue) and ubiquitin (1UBI, in yellow). The RMSD over structurally aligned regions between the two structures is 1.88 Å. (D) Structural alignment of the primary sequences of DWNN and ubiquitin, determined using the Dali server. The structurally equivalent regions comprise the following residues of DWNN: 2–9, 11–20, 22–40, 44–50, 53–57, 59–64, 66–75. Molecular fitting, calculation of RMSD's and generation of figures were performed using MOLMOL .