Transmembrane Polyproline Helix.

The third most abundant polypeptide conformation in nature, the polyproline-II helix, is a polar, extended secondary structure with a local organization stabilized by intercarbonyl interactions within the peptide chain. Here we design a hydrophobic polyproline-II helical peptide based on an oligomeric octahydroindole-2-carboxylic acid scaffold and demonstrate its transmembrane alignment in model lipid bilayers by means of solid-state 19F NMR. As result, we provide a first example of a purely artificial transmembrane peptide with a structural organization that is not based on hydrogen-bonding.