© 2005 The Japanese Biochemical Society
Regular Paper |
Repetitive Interactions Observed in the Crystal Structure of a Collagen-Model Peptide, [(Pro-Pro-Gly)9]3
1 Faculty of Technology, Tokyo University of Agriculture & Technology, Koganei, Tokyo 184-8588; and 2 Faculty of Engineering, Kyushu Institute of Technology, Kitakyushu, Fukuoka 804-8500
3 To whom correspondence should be addressed at the present address. Tel: +81-6-6850-5455, Fax: +81-6-6850-5455, E-mail: okuyamak{at}chem.sci.osaka-u.ac.jp
The crystal structure of a collagen-model peptide [(Pro-Pro-Gly)9]3 has been determined at 1.33 Å resolution. Diffraction data were collected at 100 K using synchrotron radiation, which led to the first structural study of [(Pro-Pro-Gly)n]3 under cryogenic conditions. The crystals belong to the P21 space group with cell parameters of a = 25.95, b = 26.56, c = 80.14 Å and ß = 90.0°. The overall molecular conformation was consistent with the left-handed 7/2-helical model with an axial repeat of 20 Å for native collagen. A total of 332 water molecules were found in an asymmetric unit. Proline residues in adjacent triple-helices exhibited three types of hydrophobic interactions. Furthermore, three types of hydrogen-bonding networks mediated by water molecules were observed between adjacent triple-helices. These hydrophobic interactions and hydrogen-bonding networks occurred at intervals of 20 Å along the c-axis based on the previous sub-cell structures [(Pro-Pro-Gly)n]3 (n = 9, 10), which were also seen in the full-cell structure of [(Pro-Pro-Gly)10]3. Five proline residues at the Y position in the X-Y-Gly triplet were found in a down-puckering conformation, this being inconsistent with the recently proposed propensity-based hypothesis. These proline residues were forced to adopt opposing puckering because of the prevailing hydrophobic interaction between triple-helices compared with the Pro:Pro stacking interaction within a triple-helix.
* Present address: Department of Macromolecular Science, Graduate School of Science, Osaka University, 1-1 Machikaneyama, Toyonaka, Osaka 560-0043.