Top and side views of a model of the AChM2 funnel-like pentameric bundle. The channel architecture was calculated using the three-dimensional coordinates of the M2 helix in the lipid bilayer based on restraints from solid-state NMR experiments, and by imposing a symmetric pentameric organization. The top view has the C-terminal synaptic side in front. The wide mouth of the funnel is on the N-terminal, intracellular side of the pore. Middle view shows the side chains from the pore lining residues of Glu1, Ser8, Val15, Leu18, and Gln22. Bottom view contour depicts the pore profile. From Opella et al (1999).