Molecular mechanisms of gasdermin D autoinhibition and recognition by inflammatory caspases

Abstract Pyroptosis is an inflammatory form of programmed cell death that plays important roles in immune protection against infections and in inflammatory disorders. Gasdermin D (GSDMD) is an executor of pyroptosis upon cleavage by caspases-1/4/5/11 following canonical and noncanonical inflammasome activation. GSDMD N-terminal domain assembles membrane pores to induce cytolysis, whereas its C-terminal domain inhibits cell death through intramolecular association with the N domain. The crystal structures of the human and murine GSDMD C-terminal domains differ from those of the full-length murine GSDMA3 and the human GSDMB C-terminal domain. Mutations of GSDMD C-domain residues predicted to locate at its interface with the N-domain enhanced pyroptosis, in agreement with the role of the GSDMD C-terminal domain as an autoinhibition domain. We further demonstrate that the full-length GSDMD and its cleavage site peptide, FLTD, can directly bind the catalytic domains of inflammatory caspases. A GSDMD-derived inhibitor, N-acetyl-Phe-Leu-Thr-Asp-chloromethylketone (Ac-FLTD-CMK), inhibits GSDMD cleavage by caspases-1, -4, -5, and -11 in vitro, as well as suppresses pyroptosis downstream of both canonical and noncanonical inflammasomes. By contrast, the inhibitor does not target caspase-3 or apoptotic cell death, suggesting that Ac-FLTD-CMK is a specific inhibitor for inflammatory caspases. The present study not only contributes to our understanding of the distinct mode of GSDMD autoinhibition and recognition by inflammatory caspases, but also reports a specific inhibitor for these caspases that can serve as a tool for investigating inflammasome signaling.