Cleavage-independent activation of ancient eukaryotic gasdermins and structural mechanisms.

Gasdermins (GSDMs) are pore-forming proteins that execute pyroptosis for immune defense. GSDMs are two-domain proteins activated by proteolytic removal of the inhibitory domain. In this work, we report two types of cleavage-independent GSDM activation. First, Tricho GSDM, a pore-forming domain-only protein from the basal metazoan Trichoplax adhaerens , is a disulfides-linked autoinhibited dimer activated by reduction of the disulfides. The cryo-electron microscopy (cryo-EM) structure illustrates the assembly mechanism for the 44-mer Tricho GSDM pore. Second, RCD-1-1 and RCD-1-2, encoded by the polymorphic regulator of cell death-1 ( rcd-1 ) gene in filamentous fungus Neurospora crassa , are also pore-forming domain-only GSDMs. RCD-1-1 and RCD-1-2, when encountering each other, form pores and cause pyroptosis, underlying allorecognition in Neurospora . The cryo-EM structure reveals a pore of 11 RCD-1-1/RCD-1-2 heterodimers and a heterodimerization-triggered pore assembly mechanism. This study shows mechanistic diversities in GSDM activation and indicates versatile functions of GSDMs.