Fig. 4. Improved orthogonality between CC-Tri and CC-Tet*. (A) Helical-wheel representations of the heptad-repeat sequences of CC-Tet and CC-Tet*. In CC-Tet, residues that promote interhelical salt-bridge interactions (lysine and glutamic acid) are positioned at the e and g positions, whereas in CC-Tet* these are at b and c. (B) Slices through the X-ray crystal structures of CC-Tet and CC-Tet* show the structural consequences of the different placements of lysine and glutamic acid residues. Except for these, side chains are omitted for clarity. (C) Normalised fluorescence date for exchange between CC-Tri and CC-Tet*. After annealing, values for the hetero-mixtures (off diagonal) are lower than those for the homomers, indicating orthogonality over the CC-Tri/CC-Tet combination (Fig. 3C).