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Conformational analysis of polytripeptides (Gly-Pro-Ala)n, (Gly-Ala-Hyp)n, and (Gly-Ala-Ala)n in connection with the problem of collagen structure

✍ Scribed by V. G. Tumanyan; R. A. Abagyan; N. G. Esipova

Publisher
Wiley (John Wiley & Sons)
Year
1984
Tongue
English
Weight
665 KB
Volume
23
Category
Article
ISSN
0006-3525

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✦ Synopsis

Synopsis

Conformational analysis of triple helices of a type of collagen was performed with typical collagen tripeptide sequences based on Gly-Pro-Ala, Gly-Ala-Hyp, and Gly-Ala-Ala. During energy minimization, the possibility of continual deformation of the pyrrolidine cycle was taken into account in order to achieve better accuracy in the resulting structure. The (Gly-Pro-Ala), structure is almost isomorphic to the (Gly-Pro-Hyp), structure obtained in the previous work [Tumanyan, V.G. & Esipova, N.G. ( 1982) Biopolymers 21, 475-4971, For a collagen-type structure, the optimal conformation of (Gly-Ala-Hyp), tends to have a decreased unit twist ( t = 15"), although the energy advantage with respect to the conformation with t = 45" is not so significant. A similar situation is observed for (Gly-Ala-Ala),. In this case, the energy decrease during unwinding to t = 15" from t = 45" is quite small. The conformations of (Gly-Ala-Hyp),, and (Gly-Ala-Ala), with t = 15" exhibit a similarity with a triple complex of polyproline I1 helices-a noncoiled coil such as (Gly-Pro-Hyp), and (Gly-Pro-Ala),. A similar structure may be postulated for subcomponent cql of the first component of a human complement containing substantial Gly-X-Pro and Gly-X-Y tripeptide derivatives in the primary structure (X, Y = any amino acid). The results suggest that the observed helical symmetry of collagen ( t = 36") is a consequence of superposition of diffraction patterns (for sufficiently long segments) from various helices ( t varies from -15" for Gly-X-Hyp and Gly-X-Y to -56" for Gly-Pro-Ala). For short alternating segments, some unification of different helical structures is possible.

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