Superhelical TIF2 structure and packing in the C2 unit cell. (a) The C2 unit cell is shown in cross-eyed stereo as a grey box with the origin at the bottom right and its four asymmetric units. One asymmetric unit consists of 13 short helices of the TIF2 peptide (coloured cylinders) that are arranged around the NCS axis, which is shown as a red line. Another asymmetric unit centred on the NCS axis is shown in grey with space-filling models (green) of the cholic acid molecules that wedge between the helices. The asymmetric units combine to form a continuous left-handed superhelix that traverses the crystal, which is well visible through a surface representation of three individually coloured asymmetric units. The fourth asymmetric unit is coloured blue and the N-termini of the helices are marked by a sphere, showing that the arrangement of TIF2 helices is not all parallel as assumed in the models in Figs. 4(a) and 4(b). The SHELXE-derived electron density is contoured at 1 r.m.s.d. for the whole unit cell. (b) View of the asymmetric unit projected along the NCS axis with the individual chains labelled. The 14th helix A′ shown in dark blue serves to highlight the repeating pattern in the superhelix. The N-termini are marked by spheres and point to the outside of the superhelix. Leucine side chains that construct the hydrophobic core are drawn as grey stick models. (c) View 90° rotated relative to (b).