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SynopsisThe thermal triple helix-coil transition of covalently bridged collagenlike peptides with repeating sequences of (Ala-Gly-Pro),, n = 5-15, was studied optically. The peptides were soluble in water/acetic acid (99:l) and were found to form triple-helical structures in this solvent system beginning with n = 8. The thermodynamic analysis of the transition equilibrium curves for n = 9-13 yielded the parameters AH: = -7.0 kJ per tripeptide unit, AS:= -23.1 J deg-' mol-' per tripeptide unit for the coil-to-helix transition, and the apparent nucleation parameter CJ E 5 X lo-*. It was suggested through double-jump temperature experiments that the rate-limiting step during refolding is not only influenced by the difficulties of nucleation, but also by cis-trans isomerization of the Gly-Pro peptide bond.

SynopsisVariations I-XVIII of a trimerlike cross-linked collagen model peptide were synthesized and used to investigate the cooperation of different neighboring Gly-X-Y tripeptides. The carboxyterminal decapentapeptide of the triple-helical part of collagen type I was chosen as the starting point of sequentially modified elongations. The transition temperatures determined by CD measurements show that the incorporation of the imino acid free tripeptides Gly-Ala-Ala and Gly-Ile-Ala results in a weakening of the triple-helical structure. I t is demonstrated that the desired thermal stability of the collagen triple helix requires the "clustered" arrangement of helix-promoting tripeptides, especially of Gly-Pro-Hyp.

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synopsisThe amino acid sequence of the collagen al(1) chain (cal0 is analyzed. Deviations of random tripeptide distribution leads to the definition of clusters. Inside these regions, collagen-typical tripeptides are located. Besides Gly-Pro-Hyp, Gly-PreAla, and Gly-AlaHyp, the polar sequences Gly-Glu-Hyp, Gly-Ala-Arg, Gly-Glu-Arg, and Gly-Pro-Lys form typical sequences. The neighborhood of each tripeptide is analyzed and classified. The proximity to the collagen-typical tripeptides is registered. Cluster theory: Less-typical sequences also fold as members of the collagen triple helix and they are as reasonable as well as important for the collagen structure as the cluster tripeptides, but only the latter are important for the nucleation of the triplehelical folding.