Figure 19. Concentric β-barrel models for Type 1A trimer. (a) Wedge schematic of a cross-section of the barrels. (b & c) Flattened representations of the inner and outer barrels of the trimer. The dashed line indicates the location where Sy5 and Ct1 of the outer barrels link to Sy6 and Sy8 of the inner barrel. Green and red backgrounds as in Fig. 5. (d) Ribbon representation of an atomic-scale model as viewed from the side. Ribbons are colored by the rainbow spectrum beginning with red at the N-termini and ending with magenta at the C-termini.
We suggest that if and/or when either of these structures interact with the membrane, the NAC domains traverses the alkyl phase as a β-barrel with K80 of the β-turn region interacting with negatively charged lipid head-groups of the trans bilayer while the Nt domains remain on the surface of the cis bilayer as partially-occupied amphipathic α-helices. These types of trimers may serve as precursors for larger transmembrane channels.