Extended Data Figure 6. Detailed analysis of the 2CARD-Ub interface.
Electron density map (2Fo-Fc) was contoured at σ = 0.9. Surface types were defined in the 2D representation on the left (as in Fig. 3b). a, Proximal Ub occupies surfaces IV and V on 2CARD. Surface IV interacts with the hydrophobic patch (L8/I44/V70) of proximal Ub, whereas V interacts with a combination of hydrophilic (N60/Q62) and hydrophobic (F45/A46) residues of proximal Ub. b, The distal Ub bound to 2CARD(D) simultaneously occupies both surfaces VI and V, whereas distal Ub’s bound to 2CARD(B) and (C) occupy surface VI alone (due to the lack of adjacent V). The interaction between distal Ub and VI is identical no matter whether the same Ub forms an additional interaction with V. Thus, only the distal Ub–2CARD(D) interaction is shown. Surface VI forms a combination of hydrophilic and hydrophobic interactions with Q49/R42 and L8/I44/V70 on distal Ub, respectively. Surface V interacts with distal Ub in the same manner as with proximal Ub, forming contacts with F45/A46/N60/N62 of Ub. Additional interactions involving surface V were seen with F4/T66/H68 of both distal and proximal Ubs (not shown in a), but they appear less intimate than those involving F45/A46/N60/N62.