a, Individual helix generation: the helical phase (Δɸ1), supercoil radius (R) and offset along the Z-axis (Z offset) were exhaustively sampled; a total of 11 free parameters since there is no z offset for the first helix. b, Top-down view of the parallel twisted backbone. c, Representative hydrogen bond networks identified using HBNet. d, Matches of multiple HBNet containing heptads to a single full length backbone. e, Addition of loops to connect the 4 helices into two helix hairpins. f-i, SEC trace, CD spectra and (inset) temperature melt, native MS spectrum and SAXS (black, experimental SAXS data; red, spectra computed from the designed backbones) profile of the design DHD37_ABXB. Experiments were performed once.