Fig. 4.

The structures of SadAK3, SadAK3b-V1 (V1), and SadAK3b-V2 (V2) are depicted together with their sequences and plots of their coiled-coil parameters. Structures, sequences, and plots are in scale to each other and aligned on their inserts. The colors in the plots correspond to the colors of the structures; the sequences for SadAK3 and SadAK3b are black and red, respectively. The discontinuities in the SadAK3b structures are highlighted by vertical shades throughout the figure, colored light red for V1, and additionally light blue for V2. The red box indicates the 3₁₀ helix within the stammer (see also Fig. S3D). In the plots for periodicity, supercoil angle, and coiled-coil radius, the SadAK3b structures locally deviate from the SadAK3 structure, whereas the deviations at the stammer are more pronounced and localized than at the stutter. This is in line with the plot of the Crick angle shift, showing the deviation of the observed from the expected Crick angle for heptad repeat. These curves were calculated under the assumption that all structures have a continuous heptad repeat. Therefore the Crick angles for V1 and V2 start to depart from the expected value at the beginning of the stammer and reach their maximum deviation at its end. For the length of the N@d layers, which are again in heptad repeat, this deviation stays constant, until the stutter mediates the transition back to the heptad register of the C-terminal GCN4 adaptor. Because the alignment is based on the inserts, the Crick angle deviation for SadAK3 is constantly at the maximum deviation of the SadAK3b structures.