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Credit: [Coiled Coils]. Source: Wellcome Collection.
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![Introduction; ——- It has recently ]? een suggested «ässss-t simultaneously by Pauling & Corey (1953) and^Crick (1952) that the structure of qC -feeratin may be based on a coiled-coilj } toséis^., on a helix with a small repeat whose axis has been slightly deformed so that it follows a larger more gradual helix . The small helix proposed is the d -helix of Pauling, Corey & Bransom (1951). It is therefore of interest to calculate the Fourier transform (or continuous structure factor) of structures of this sort. Those considered here are the continuous coiled-coil and the t \ discontinuous coiled-coil. The former is an infinitely thin *wire M of electron density, and the latter is a set of scattering points (atoms) placed at regular intervals on a coiled-coil locus. It will be shown that the two results are very closely related. To obtain the s trucare factors for a structure of this type made up of real atoms, one follows a similar procedure to that described by clochran Crick & Yand (1952) in calculating the transform of the simple d -helixj S^at-4-s-, one considers the atoms as being in sets, each set consisting of one atom from each residue. Thus all the nitrogen atoms of the polypeptide backbone will be in one set, all the oxygen atoms of the backbone in another^ and so on. One then uses the formula derived in this paper to calculate the contribution of each set separately, allowance being made for the finite size of the atom by multiplying the result for a set of points by the appropriate atomic scattering factor in the usual way. The results are then added together, with proper allowance for phase, to give the structure factor for the complete structure.](https://iiif.wellcomecollection.org/image/b18172039_PP_CRI_H_1_9_0002.jp2/full/800%2C/0/default.jpg)
