The molecular structure of collagen has long been believed to be that of a triple-stranded 10/3 helix (the Rich and Crick model). The meager X-ray diffraction data from native collagen can, however, also be explained in terms of a triple-stranded 7/2 helical model. The recent single-crystal study of the (Gly-Pro-Hyp)9 peptide confirmed that this peptide, which contains the Gly-Pro-Hyp sequence that is used as a basic repeating unit of the Rich and Crick model, does not adopt a 10/3 helix structure, but does adopt a 7/2 helix. The resulting structure will be useful for understanding molecular interactions involving collagen.
