Figure 8. A. Helical wheel projection of S²¹68 TMD2.

Orange and dark blue colored residues are in predicted helical-helical interaction faces A and B, respectively (Pang et al., 2009). The green-colored residue (V41) is in both A and B interfaces. Red asterisks represent the position of non-lethal S²¹68 mutants, which are all in interface A.

B. Model for the S²¹ pinhole formation pathway. Same scheme as in Fig. 1C. S²¹ molecules are first inserted as monomers. ID1, ID2: the inactive dimers 1 and 2; AD, the activated dimer, with the homotypic helical-helical interaction of the glycine zipper containing interface A. In the oligomer state, the A:A interaction transits to A:B heterotypic helical interaction before the heptameric pinhole forms. S²¹68 mutants are mapped in the pathway with either accelerating the process (blue arrow), or blocking it (blue stop arrow).