Helical twists of collagen model peptides.

Average helical twists were calculated by the method of Sugeta and Miyazawa (Biopolymers 1967, 5, 673-679) for all of the collagen model peptides analyzed to date. Calculation of the helical twists of all triplets in each peptide strand provided novel insights for several model peptides. In the (Pro-Pro-Gly)n (n = 9 and 10), the helical twists showed cyclic fluctuations between 40 and 65 degrees with a 20 A period, suggesting that their molecular conformations were close enough to the ideal 7/2-helix to show the helical repeat of 20 A. Rather small helical twists in the guest regions of IBP in complex and T3-785 were attributed to the interaction with Integrin I domain and a relaxed conformation caused by three consecutive triplets lacking imino acid residues, respectively. Although most of the triplets used in this study were imino acid-rich triplets, helical twists were scattered in a wide range from 30 to 70 degrees with an overall average of 52.6 degrees . This distribution of helical twists indicated a strong preference for the 7/2-helical conformation (51.4 degrees ) rather than the 10/3-helical model (36 degrees ).