Fig. 2

HHARI conformational changes accompany UbcH7-Ub binding. a Comparison of HHARI structures in the apo and UbcH7-Ub-bound states. The RING1 domains of the structures were superimposed. The HHARI/UbcH7-Ub structure is colored as in Fig. 1b and the three available apo HHARI structures are colored the indicated shade of gray. The RING1 Loop2_E3 region of HHARI is boxed and a magnified cartoon representation of this region is presented as an inset to the right. The distance between the Cα atoms of His234 from Loop2_E3 of apo and UbcH7-Ub bound HHARI structures is shown. Disordered regions in the UBA-like domains of apo HHARI that become ordered upon UbcH7-Ub binding are shown as semitransparent gray spheres. b The HHARI/UbcH7-Ub (top) and HHARI^APO (bottom) structures are shown as cartoon representations in the same orientation with selected residues shown as sticks. c Comparison of the HHARI RING1 domain to the RING domains of HOIP, c-Cbl, and RNF25. The Cα atoms of the eight residues involved in coordination of two zinc ions (green spheres) were superimposed and the structures are shown as cartoon representations with selected side chains shown as sticks. A sequence alignment of the Loop2_E3 region of the RING domains is shown at the bottom with the loop insertion of HHARI boxed in red and highly conserved residues colored black. Cysteine residues involved in zinc coordination are indicated with a black star and the ‘linchpin’ arginine residue of canonical RING E3s that is involved in stabilization of the closed E2 ~ Ub conformation is indicated with a black triangle. d Comparison of the apo and E2-Ub bound crystal structures of RNF4 and RNF165. The structures are shown as cartoon representations the RING domains were superimposed to create the image