Gasdermin D pore structure reveals preferential release of mature interleukin-1

As organelles of the innate immune system, inflammasomes activate caspase-1 and other inflammatory caspases that cleave gasdermin D (GSDMD). Caspase-1 also cleaves inactive precursors of the interleukin (IL)-1 family to generate mature cytokines such as IL-1 beta and IL-18. Cleaved GSDMD formstransmembrane pores to enable the release of IL-1 and to drive cell lysisthrough pyroptosis(1-9). Here we report cryo-electron microscopy structures of the pore and the prepore of GSDMD. These structures reveal the different conformations ofthe two states, as well as extensive membrane-binding elements including a hydrophobic anchor and three positively charged patches. The GSDMD pore conduit is predominantly negatively charged. By contrast, IL-1 precursors have an acidic domain that is proteolytically removed by caspase-1(10). When permeabilized by GSDMD pores, unlysed liposomes release positively charged and neutral cargoes faster than negatively charged cargoes of similar sizes, and the pores favour the passage of IL-1 beta and IL-18 over that of their precursors. Consistent with these findings, living-but not pyroptotic-macrophages preferentially release mature IL-1 beta upon perforation by GSDMD. Mutation of the acidic residues of GSDMD compromises this preference, hindering intracellular retention ofthe precursor and secretion ofthe mature cytokine. The GSDMD pore therefore mediates IL-1 release by electrostatic filtering, which suggests the importance of charge in addition to size in the transport of cargoes across this large channel.

Automated summary

Inflammasomes activate caspase-1 to cleave GSDMD and generate mature cytokines like IL-1 beta and IL-18, which are released through pores formed by GSDMD. The GSDMD pore mediates IL-1 release by electrostatic filtering, favoring the passage of mature cytokines over their precursors.