a, b, Model of the additional ring (a) and its cryo-EM density in the double-ring GSDMA3 pore architecture (b). c, Cryo-EM density of an individual subunit superimposed on the model. d, e, Superposition of the subunit structure in the additional ring with that of GSDMA3-NT in the auto-inhibited conformation (pink)1 (d) and the pore conformation (cyan) (e). f, A hypothetical model for GSDM pore formation. Upon cleavage by an activating enzyme, GSDM-NT monomers may first bind to membrane lipids and then oligomerize to form a soluble pre-pore before membrane insertion.