Figure 4.

Helical wheel diagram of the coiled-coil interactions between HX1 and HX2. In an antiparallel coiled-coil, the a and d positions of each helix intercalate to form the hydrophobic core. Compared with most coiled-coils, the P-CR has an uncommonly high proportion of aromatic residues in the a and d positions, which are typically occupied by aliphatic residues. The e and g positions typically form salt bridges between helices, but in the P-CR only the solvent-exposed face appears to form these (Supplemental Fig S4). This figure was illustrated with DrawCoil 1.0 (Grigoryan and Keating, 2008). Circled residue abbreviations are filled with color based on R group properties: hydrophobic (gray), polar neutral (orange), charged acidic (red), and charged basic (blue).