The coiled coil is a biologically important structural pattern of helix-helix oligomerization in proteins . The heptad repeat motif is a frequent driver of coiled coils; in it, residues in two or more α-helices interlock in a repeating hpphppp pattern, with hydrophobic residues (h) typically in the first and fourth positions and polar residues (p) in-between (charged residues are often found at the fifth and seventh positions) . The heptad repeat is not a mere polarity matching motif: it leverages the spatial fitting of each helix's side-chains into inter-residue gaps in the other helices, in what Crick termed a 'knobs' into 'holes' pattern . This structural matching further requires helices to become supercoiled, at 3.5 residues per turn, by slightly bending their axes in a left-handed fashion .