Structural characterization of the beta-bend ribbon spiral: crystallographic analysis of two long (L-Pro-Aib)n sequential peptides

The molecular and crystal structures of two terminally blocked (L-Pro-Aib)n (n = 3, 4) sequential peptides were determined by X-ray diffraction. In both crystals two molecules in the asymmetric unit are found. Either molecule in the asymmetric unit of each structure shows a right-handed beta-bend ribbon spiral, stabilized by the maximum possible number of intramolecular N-H...O=C H-bonds. Thus, for the first time it was possible to characterize at atomic resolution this polypeptide conformation.