Innovative Self-Assembly of 15-Mer Chimeric α-Peptide-Oligourea Foldamers toward Cl^--Selective Ion Channels

Constructing artificial ion channels is a challenging task. Herein, the de novo design of transmembrane ion channels made up of amphiphilic peptide-oligourea chimeric helices is described. They consist of an oligourea segment (7-mer) attached to the C-terminus of a short peptide (8-mer). Mass spectrometry (MS) and transmission electron microscopy (TEM) analyses show that in an aqueous solution, two of these chimeras (HPU-E and HPU-N) independently form defined oligomeric structures. TEM also shows that they form fiber bundles. The third related chimera HPU-F does not oligomerize (MS) but forms spherical nanostructures (TEM). HPU-E and HPU-N exhibit anion transport activity across lipid bilayers via antiport mechanism (HPU-N > HPU-E). The anion selectivity of HPU-N is Cl^->NO₃ ^- > Br^->SCN^- > I^- > AcO^->F^-, which can be due to anion binding within the channels rather than size exclusion. Patch-clamp data support HPU-N's Cl^- selectivity (PCl^-/PI^- = 3.26). X-ray crystal structure (1.77 Å) of HPU-N reveals well-packed α-helices, and cryo-electron microscopy data shows the formation of nanotubes (13.7 Å diameter pores) and transmembrane channels. The study shows that α-peptide-oligourea-based de novo design can yield unique bioactive molecules with defined structures and functions.