Crystal and molecular structure of a collagen-like polypeptide (Pro-Pro-Gly)10

(Pro-Pro-Gly)₁₀ forms single crystals, providing X-ray diffraction data to 0.22 nm resolution. In the crystals, the polypeptides form triplexes that aggregate end-to-end in quasi-infinite helices with axial translation per tripeptide h = 0.287 nm and the corresponding rotation t = ?102.9 °. The structure, which may be an allomorph of collagen, has been refined by the linked-atom least-squares procedure. In addition, three water molecules per tripeptide have been detected by Fourier difference syntheses. One of them forms an intrachain hydrogen-bonded bridge O(Pro₂) - - - W - - - O(Gly). There are also interchain hydrogen bonds (Gly)NH - - - O(Pro₁) within the triplex.