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. Here 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. Cryo-electron microscopy (cryo-EM) structure illustrates assembly mechanism for the 44-mer Tricho GSDM pore. Second, RCD-1-1/RCD-1-2, encoded by polymorphic rcd-1 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 . Cryo-EM structure reveals a pore of 11 RCD-1-1/RCD-1-2 heterodimers and heterodimerization-triggered pore assembly mechanism. This study shows mechanistic diversities in GSDM activation and indicates versatile functions of GSDMs.