Artificial Gramicidins

Abstract

Gramicidin A, gA is a natural protein channel with a well-established, simple structure, and function: cations and water are transported together along the channel. Importantly, the dipolar orientation of water molecules within the pore can influence the ionic translocation. The need for simple artificial systems biomimicking the gA functions has been desired and they were until last decade unknown. Several interesting papers highlighted in this minireview have been published and supramolecular systems described here can be considered as primitive gA mimics. The dynamics of ions/water and protons confined within gA channels is difficult to structurally analyze and simpler artificial systems designed at the atomic level would have a crucial relevance for understanding such translocation scenarios at the molecular level. The directional ordering of confined water-wires or ions, as observed inside primitive gA channels is reminiscent with specific interactions between water and the natural gA. This dipolar orientation may induce specific dielectric properties which most probably influence the biological recognition at bio-interfaces or translocation of charge species along artificial channel pathways.

Keywords: biomimetic; gramicidin A; hydrophilic; hydrophobic; ion channels.

Graphical Abstract

X-ray crystal structures of gA (left) and the hydrophilic T-channel of triazole 3 (right) at the same dimensional scale.

Figure 1

Artificial Gramicidin A ion channel forming compounds: aromatic foldameric polyamide 1, aromatic foldameric hydrazides 2a–2e. bola-amphiphile triazole 3 and arylene-ethynylene macrocycle 4.

Figure 2

(a) Single crystal structure of 1 and the accompanying water wires; (b) X-ray crystal structures of gA (top) and the hydrophilic T-channel of triazole 3 (bottom) at the same dimensional scale, (c) Probability plots describing the average distribution of water molecules confined within the T-channels (d) simulated hydrophobic tubular pores from macrocycle 4. Schematic representation on reconstitution of (e) 2b and 2c and (f) 3 in bilayer membrane models.