Modularly tunable monopeptidic scaffold enables rapid and combinatorial evolution of a halogen bond-mediated highly active chloride channel, exhibiting an excellent anticancer activity toward human breast cancer.

We describe here a unique family of pore-forming anion-transporting peptides possessing a single-amino-acid-derived peptidic backbone that is the shortest among natural and synthetic pore-forming peptides. These monopeptides with built-in H-bonding capacity self-assemble into an H-bonded 1D columnar structure, presenting three types of exteriorly arranged hydrophobic side chains that closely mimic the overall topology of an α-helix. Dynamic interactions among these side chains and membrane lipids proceed in a way likely similar to how α-helix bundle is formed. This subsequently enables oligomerization of these rod-like structures to form ring-shaped ensembles of varying sizes with a pore size of smaller than 1.0 nm in diameter but sufficiently large for transporting anions across the membrane. The intrinsic high modularity in the backbone further allows rapid tuning in side chains for combinatorial optimization of channel's ion-transport activity, culminating in the discovery of an exceptionally active anion-transporting monopeptide 6L10 with an EC of 0.10 μM for nitrate anions.

Compared to the most active anion-transporting channel that requires a channel:lipid molar ratio of 1:330 (0.3 mol % relative to lipid) to achieve 50% activity, a structurally simple pore-forming tripeptide 6L 3 10 was found to exhibit an extraordinarily strong ability to self-assemble into stable possibly barrel-shaped exceptionally active channels, with record-low EC 50 values of 4.0, 3.0, 1.6, 2.6, and 2.6 nM (e.g., 0.005−0.013 mol % relative to lipid) for Cl − , Br − , I − , NO 3 −