Fig. 1: Multiple-mode screening strategy to identify the XIAP:CASP7 PPI inhibitor.

A The cartoon binding model of a small-molecule inhibitor (gray) targeting multiple modes to block the interaction of linker-BIR2 of XIAP (yellow) with CASP7 (blue and light blue) and cause cell apoptosis. B The allosteric binding site, including the exposed Cys246 for I-Lys binding, can be found in both XIAP-bound and XIAP-free form CASP7 structures (PDB codes 1I51 and 1K86). The inhibitor, 643943, binds into modes 1 and 2 to disrupt interactions between CASP7 and XIAP though inducing XIAP-bound to unbound structure and directly stabilizes active-form CASP7. C Multiple-mode strategy increases the chance of 643943 (orange) fitting to the binding site in CASP7. The common site-moiety map was identified by superimposing site-moiety-maps of mode 1 and mode 2 and consists of four core anchors (H1, H2, V1 and V2). D The docked conformation of 643943 at allosteric inhibition site of CASP7. 643943 (orange) interacts with two residues, D93 (anchor H1) and Q243 (anchor H2), through hydrogen bonds (green dashed lines).