Verification of Okuyama Model for Collagen based on Single Crystal Analyses of Model Peptides at High Resolution

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The Rich and Crick model is widely accepted as the molecular structure of collagen during the last five decades. This model was derived from the fiber diffraction data of native collagen and is made up of a triple helical structure in which each peptide strand forms a right-handed 10/1-helical conformation and a pitch length of 85.8 Å. This triple-helical structure can be considered to be a single left-handed 10/3-helix with 28.6 Å axial repeat.On the other hand, we found a left-handed 7/2-helical conformation with 20 Å axial repeat in the single crystal structure of a collagen-model peptide. Since this structure could explain key features of the diffraction patterns from native collagen, we proposed it as a new structural model for collagen (1977). Unfortunately, however, this model has not been acknowledged as a structural model for collagen, but has instead been regarded only as a structure for a collagen-like peptide. Recently, we demonstrated that the both 10/3-and 7/2-helical models could explain X-ray fiber diffraction data from native collagen quantitatively. The aim of the present research is the verification of our 7/2-helical model based on the single crystal structures of collagen model peptides at high resolution.In this study, we have analyzed a total of 14 model peptides at high resolution by using synchrotron radiation. All of these molecular conformations were found to be very close to that of the ideal 7/2-helical model. More than 20 triple helical conformations of collagen model peptides with various sequences have been analyzed in the several groups in the world including our group. All of them support our 7/2-helical model and there is no such supporting data for the Rich and Crick model, which indicated strongly that an average conformation of native collagen is the 7/2-helical structure rather than the now prevailing 10/3-helical model.