Figure 6. Ubc-related domain structures.

Upper panel: UEV domains of Vps23 and Mms2 are shown (blue) in ribbon representation with ubiquitin (yellow) in ribbon and surface representations. Ile⁴⁴, the centre of the hydrophobic recognition patch on the ubiquitin, is shown as green spheres. Ubiquitin molecules are placed in the same orientation as in Figure 1 for comparison. Protein data bank identication codes used are: Vps23 UEV, 1UZX; Mms2 UEV, 1ZGU. Lower panels: Ubc5 (blue) is shown on the left with ubiquitin (yellow). The catalytically important Cys⁸⁵ is depicted as yellow sphere. Yeast Ubc4 is presented in the middle panel for comparison. Again, catalytic Cys⁸⁶ is shown as yellow sphere. On the right, Ubc9 (blue) complexed with SUMO (small ubiquitin-related modifier) (yellow) is shown [109], as there is no equivalent structure of a Ubc–ubiquitin conjugate available. Leu⁶⁵ on SUMO, equivalent to Ile⁴⁴ from sequence alignment, is indicated as green sphere and Cys⁹³ of Ubc9 as yellow sphere. Protein data bank identication codes used are: Ubc5, 2FUH; Ubc4, 1QCQ; Ubc9/SUMO, 1Z5S. The SUMO molecule is also placed in the same orientation as the ubiqutin molecule.