Fig. 3 C9 structure in the monomeric and assembled forms. a The cryo EM structure of polyC9 with 22 subunits (different colours) in a circular assembly, two orientations shown, oblique-view and top-down. The resolved strands in the β-barrel conform to the S = n/2 architecture19. The model excludes the membrane spanning region due to the lower resolution (Supplementary Fig. 5a). b Cartoon representation of C9 monomer (colour) docked to a previously unfurled assembled C9 dimer (grey, left). The position of TMH1 as well as the HTH blocks the elongation face. c Relative positions of the HTH of polyC9 (dark blue) and monomeric C9 (light blue). The central β-sheet of the MACPF domain is also shown (red). In polyC9, the HTH partially occupies the region vacated by the TMH2 α-helices (yellow). d Zoom in view of the HTH domain in the polyC9 EM map, key residues found in the interface between HTH and β-barrel are shown in sticks and labelled. e Cartoon representation of two HTH regions, plus key residues in the interface, from neighbouring C9 molecules in the polyC9 structure