Two-H-bonded and one-H-bonded structure alternations in collagen

This paper concerns the conformational variability of collagen as related t o the concrete tripeptides (GXY)(n) constituting its primary structure. The previously elaborated model (V.G.Tumanyan, N.G.Esipova, Biophysics 28, 102 1-1025, 1983) with two nets of hydrogen bonds is useful for tripeptides whe re X is an amino acid. If X is an imino acid, the common one-bonded Rich & Crick model is valid. In this work, compound sequences including tripeptide s of different types are considered. Molecular mechanics is used to assess the conformations of the junction regions when a structure with two nets of hydrogen bonds precedes the structure with one net, and vice versa. Thus, all types of sequences typical for natural collagen are covered. It is show n that the combined model representing an alternation of the two-H-bonded m odel and the one-H-bonded Rich & Crick model is satisfactory stereochemical ly, and provides more favorable energy in comparison with the continuous on e-H-bonded model. Besides, a more favorable hydration of the molecule occur es in this case. Some conclusions are made about interchain and intrachain ionic bonds. Thus, it is deduced for the concrete fibrillar protein how a o ne-dimensional structure determines three-dimensional structure. The macrom olecular structure thus suggested is in accord with the experimental data o n hydrogen exchange.