Collagen triple helix puckers

In the context of the collagen triple helix it can be concluded that the Cf-exo pucker of the proline in Yaa position is favored by stereoelectronic effects of a (4R)-OH substituent which also stabilizes the traus-Xaa-(4R)-Hyp peptide bond, thus preorganizing this residue in a conformation that best befits a triple helix. Conversely, in the Xaa position the Pro residue is preferred in the Cy-endo pucker the related dihedral angles are reported in Table 11.3. 

Figure 3 Ring puckers of proline derivatives and their effect on the conformational stability of the collagen triple helix. The C -exo conformation corresponds to a trans (Z) orientation of the peptide bond, that native collagen helices prefer. The equilibrium ratio X trans/cis was measured by NMR in model compounds.

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