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If we define the cross-sections of the superhelix as different layers ( +8~-7) along the pitch gaps, we can find 8-14 degree tilting with respect to the central axis of the superhelix bundle. This conflict with the Crick’s classical coiled-coil model, which suggests that each layer should be perpendicular to the bundle axis (i.e. every layer is planar and symmetric)
Second, it was first assumed that SNARE dimerizes as a leucine-zipper. However, the contact region does not contain uniform Leu, Ile, and Val distribution whereas the methionene cluster in the central region implies the four-helix feature.