Figure 3.

Experimentally resolved structure of a lattice edge in a hexagonal barrel viewed (A) from the top, (B) from the side, and (C) in cross section. The two antiparallel proximal leg-segments (red and green) are in the front of the top view and on top in the side view and cross section, the two antiparallel distal leg-segments (blue and amber) are in the back of the top view and at the bottom of the side view and cross section. Proximal and distal legs are similar in structure and are clearly asymmetric, with two faces made of α-helices and two faces made of connecting loops. A gradual right-handed twist along the leg has rotated the elliptic cross sections of the distal legs by ∼90° relative to those of the proximal legs. The cartoons in Figs. 4 and 7 are based on this structure. (Reproduced with permission from the authors and Macmillan Publishers from the supplementary material to Fotin et al. (8).)