Fig. 4: Structural basis for the selective inhibitory effects of HOIPINs on LUBAC.
From: Molecular bases for HOIPINs-mediated inhibition of LUBAC and innate immune responses
a Scheme for the Michael addition of HOIPIN-1 or HOIPIN-8 onto the active Cys885 in HOIP. The catalytic Cys885 and the Michael acceptor are shown in red and green, respectively. The additional aromatic rings of HOIPIN-8 are shown in blue. b, c Structures of the HOIPIN-1- and HOIPIN-8-bound HOIP complexes. Crystal structures of the HOIP RING2-LDD domain complexed with HOIPIN-1 (b) or HOIPIN-8 (c) are indicated. Hydrogen bonds are indicated by dashed lines, and crucial residues for interactions with HOIPINs are shown. The upper panels are overall views. The lower panels are close-up views of the HOIPIN-binding sites. d Multiple amino acid sequence alignment of RING2 and the following region of the RBR family E3s. Conserved residues in RING2 are highlighted, and the residues interacting with HOIPINs are indicated by arrowheads. e Structural bases for the selectivity of HOIPIN-8 to HOIP. The structure of the HOIPIN-8-bound HOIP RING2-LDD is compared with the comparable regions of parkin (PDB 4BM9) and HHARI (PDB 5UDH). f The F905A mutant of HOIP is insensitive to HOIPIN-8. NF-κB luciferase activities induced by wild-type HOIP (LUBAC-WT) or the F905A mutant (LUBAC-F905A) with HOIL-1L and SHARPIN were assessed in the presence of various concentrations of HOIPIN-8. Data are shown as mean ± SEM, n = 3. NS not significant, ****P < 0.0001, one-way ANOVA with Tukey’s post hoc test. g Different interactions of HOIPIN-8 and compound [5] with HOIP. Structural comparisons of HOIPIN-8- or compound [5]-bound HOIP (PDB 6GZY) are indicated.
