Extended Data Fig. 4: Structural analyses of caspase-4–pro-IL-18 complex.

a, Structural comparison of the caspase-4–pro-IL-18 complex with the caspase-4–GSDMD-C binary complex (PDB code: 6KMZ). b, Superimposition of OspC3^ARD–caspase-4-p20/p10 structure in the ternary complex with the reported OspC3^ARD–caspase-4-p30 structure (PDB code: 7WR1). c, Superimposition of caspase-4-p20/p10 structure in the ternary complex with caspase-4-p20/p10 in the GSDMD-C complex (PDB code: 6KMZ). d, Sigma-A weighted 2F_o − F_c electron density map (contoured at 1.0 σ) of caspase-4-bound pro-IL-18 overlapped with the cartoon-loop model. e, Cartoon model of pro-IL-18 in the ternary complex. The caspase-4 cleavage-site D36 is shown as a magenta sphere, and the propeptide is in lemon. Residues involved in the interaction between the propeptide and the post-cleavage-site region are labelled and shown as sticks. f, Purified pro-IL-18 protein was treated with a Cys-Lys-specific crosslinker sulfo-GMBS (7.3 Å) under an optimized reaction condition and the samples were analysed by mass spectrometry. The table lists the identified crosslinked Cys-Lys pairs and the corresponding residues are mapped onto the pro-IL-18 structure on the left (cartoon model). C74 is located in a long flexible loop region, and thus showed highly efficient crosslinking with multiple distant residues. K103 and C112 are also located in relatively flexible regions, and a weak K103-C112 crosslinking signal appeared. The pro-IL-18 structure predicts two specific crosslinking pairs (C10-K148 and C10-K44), the latter of which did not appear due to a strong hydrogen bond between K44 and D8. g, Close-up view of the N terminus of caspase-4 p10 around the pro-IL-18-binding exosite interface. The pro-IL-18 structure is shown in surface scheme. The deduced extension from the N terminus of caspase-4 p10 is shown as dotted arrow and has clashes with the C-terminus of pro-IL-18.