Structural comparison between heptameric states consisting of different lengths of β-barrel. (A) Cryo-EM map of the prepore state II, density corresponds to one protomer shown in golden rod color, and the rest of the protomers in gray color. (B) Fitted atomic model of one protomer. (C) Cryo-EM map of the prepore state III, one protomer is shown in blue. (D) Fitted atomic model of one protomer of the prepore state III. (E) Cryo-EM map of the prepore state IV, where density corresponding to one protomer is shown in deep pink color and the remaining six protomers in gray. (F) Fitted atomic model. (G) Population distribution of different oligomeric states. (H) Population distribution of different heptameric states in the prehemolytic condition. (I) Population distribution of different arc-like states. (J) Comparison between the prepore state II (golden) vs state IV (deep pink). The D108, T109, K110, Y148, V149, and Q150 residues are shown in deep green color. The minor upward shift on some loops is highlighted using a black arrow. (K) Comparison between the prepore state III (blue) vs state IV (deep pink). (L) Comparison between the prepore state IV (deep pink) and pore state (green).