Foldameric β-H18/20P mixed helix stabilized by head-to-tail contacts: A way to higher-order structures

Peptidic foldamers are known to exhibit increased diversity in the periodic secondary-structure space in comparison with their natural counterparts, but their higher-order self-organization has been studied less thoroughly. In theory, large-diameter peptide foldamer helices have the capability of self-recognition through axial helix-helix interactions (e.g., head-to-tail), but this phenomenon has previously been observed in only one instance. In this article we report on the discovery of the largest-diameter β-peptidic mixed helix to date, the H18/20P helix. Its formation is solvent-dependent and its folding occurs cooperatively through head-to-tail self-assembly in solution. These findings suggest that axial helix-helix interactions can serve as a new mode for the formation of tertiary/quaternary structures for peptide foldamers, which also show higher-order structural diversity than natural proteins. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.