title: Crystal structure of (Gly-Pro-Hyp)(9) : implications for the collagen molecular model.
abstract: Collagens have long been believed to adopt a triple-stranded molecular structure with a 10/3 symmetry (ten triplet units in three turns) and an axial repeat of 29 Å. This belief even persisted after an alternative structure with a 7/2 symmetry (seven triplet units in two turns) with an axial repeat of 20 Å had been proposed. The uncertainty regarding the helical symmetry of collagens is attributed to inadequate X-ray fiber diffraction data. Therefore, for better understanding of the collagen helix, single-crystal analyses of peptides with simplified characteristic amino acid sequences and similar compositions to collagens have long been awaited. Here we report the crystal structure of (Gly-Pro-Hyp)(9) peptide at a resolution of 1.45 Å. The repeating unit of this peptide, Gly-Pro-Hyp, is the most typical sequence present in collagens, and it has been used as a basic repeating unit in fiber diffraction analyses of collagen. The (Gly-Pro-Hyp)(9) peptide adopts a triple-stranded structure with an average helical symmetry close to the ideal 7/2 helical model for collagen. This observation strongly suggests that the average molecular structure of collagen is not the accepted Rich and Crick 10/3 helical model but is a 7/2 helical conformation.
authors.affiliation: Department of Macromolecular Science, Osaka University, Toyonaka, Osaka, Japan. okuyamak@chem.sci.osaka-u.ac.jp
authors.forename: Kenji
authors.initials: K
authors.lastname: Okuyama
authors.forename: Keita
authors.initials: K
authors.lastname: Miyama
authors.forename: Kazunori
authors.initials: K
authors.lastname: Mizuno
authors.forename: Hans Peter
authors.initials: HP
authors.lastname: Bächinger
mesh_terms: D003094:Collagen / Q000737:chemistry*; D018360:Crystallography, X-Ray; D006860:Hydrogen Bonding; D008958:Models, Molecular; D009842:Oligopeptides / Q000138:chemical synthesis / Q000737:chemistry*; D011392:Proline / Q000737:chemistry; D017510:Protein Folding; D017433:Protein Structure, Secondary; D013329:Structure-Activity Relationship; D014867:Water / Q000737:chemistry
chemical_list: D009842:Oligopeptides; C088188:glycyl-prolyl-hydroxyproline; D014867:Water; D003094:Collagen; D011392:Proline