Structure Analysis of a Collagen Model Polypeptide, (Pro–Pro–Gly)10

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Abstract
A detailed conformation study of the polypeptide (Pro–Pro–Gly)10, synthesized as a collagen model, has been done using X-ray diffraction. Several structures having the observed helical parameters (unit height=8.61 Å, unit twist=51.4°) together with standard bond lengths and angles were generated and tested in terms of an existence of intermolecular van der Waals contacts and least squares calculations using 49 equatorial reflections. It was found from these studies that three polypeptide chains make a three-stranded rope of which the helical parameters are similar to but significantly different from those of the collagen models proposed so far. There exist two possible models for (Pro–Pro–GIy)10 according to the type of hydrogen bonding. One is the model having a hydrogen bond so-called ‘standard’ structure type, and the other has a hydrogen bond of collagen 11 type. The two-dimensional electron density map, synthesized with the observed structure factors, agrees well with these models. In the least squares calculations, atomic scattering factors were modified by taking into account of effects of amorphous water between the three-stranded ropes.