In this work, two end-charged cyclic
peptide nanotubes (CPNTs)
embedded in 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine
(POPE) were designed to simulate transmembrane ion channels. Density
functional theory (DFT) computations at the level of M06-2X/6-31G
give different assembling modes of the negatively charged ELWL–CPNT
and positively charged RLWL–CPNT as (L–L)(D–L)(D–D)(L–L)(D–D)(L–L)(D–D)
and (D–D)(L–L)(D–D)(L–L)(D–D)(L–L)(D–D),
respectively. Molecular dynamics (MD) simulations indicate that a
charge at a CPNT end obviously affects the structure of the channel
water chain and the diffusion behavior of K+. The regions
with the highest probability of H-bond defects in the channel water
chains are gap5 and gap2 in ELWL/POPE–CPNT and RLWL/POPE–CPNT,
respectively. K+ can easily enter either CPNT by desolvation,
and behaves more actively in RLWL/POPE–CPNT, shuttling rapidly
and frequently between an α-plane zone and an adjacent midplane
region. Results of this work reveal that a charge at the end of an
ionic channel may significantly alter the transport characteristics
of the channel.