Structural insights into ligand-induced CARD assembly in inflammatory caspases.

Non-canonical inflammatory caspases detect cytosolic lipopolysaccharide (LPS) through its caspase activation and recruitment domain (CARD), yet how ligand binding drives higher-order CARD assembly remains poorly understood. Here, we identify CBM7, a minimal SERPINB1-derived peptide, that induces caspase-4 CARD oligomerization. CBM7 promotes formation of a previously unrecognized flexible filament-like CARD architecture distinct from canonical CARD assemblies. Peptide- and LPS-induced CARD assembly require overlapping structural determinants, suggesting that structurally distinct ligands share common features in promoting higher-order CARD assembly. CBM7 also promotes oligomerization across inflammatory caspase CARDs and induces caspase activation, pyroptosis, and inflammatory responses in cells and mice. Together, these findings provide structural insight into ligand-induced inflammatory caspase CARD assembly and establish CBM7 as a chemically defined probe for dissecting the structural basis of inflammatory caspase activation.