POLYMERS OF TRIPEPTIDES AS COLLAGEN MODELS .4. STRUCTURE ANALYSIS OF POLY(L-PROLYL-GLYCYL-L-PROLINE)

Poly(l-prolyl-glycyl-l-proline) closely resembles collagen in its X-ray diffraction pattern, which indicates that it has a triple-helical structure with the same helical parameters as the protein. A detailed conformational analysis has been made of the polytripeptide. A computer was used systematically to generate structures having the observed helical parameters, as well as standard bond lengths and angles, and to test these structures in terms of acceptable intramolecular and intermolecular van der Waals distances and agreement between calculated and observed intensities. These computations narrowed down the possibilities to a unique conformation which resembles the collagen II model in its mode of interchain hydrogen bonding. Conformations of the collagen I type were found to make short intermolecular contacts, and those in which the glycyl NH is hydrogen bonded in the manner of the two-bonded model proved incompatible with the observed intensities of the equatorial reflections. It is suggested that the conformation found for the polytripeptide may be representative of the structure of collagen as a whole. © 1969.