Tilt Behavior of an Octa-Peptide Nanotube in POPE and Affects on the Transport Characteristics of Channel Water.

MD simulations have been carried out for studying the tilt behaviors of the 8 X (W (L) under bar)(4)-CPNT embedded in the POPE bilayer in a water environment and under an anhydrous condition, respectively. Besides, the dependences of the transport characteristics of channel water on the extent of the CPNT tilt were explored. The results indicate that the presence of water may exacerbate the CPNT tilt but plays an important role in maintaining the integrity of the CPNT by forming water bridges in the end-gaps. Cation-pi interactions between the indole rings of Trp residues and lipid headgroups are the major factor causing the CPNT tilt under an anhydrous condition, while H-bonded interactions between water molecules and the indole rings are primary in a water environment. The dipole orientations of channel water molecules except those in the last end-gap are gradually oriented and eventually only take "+dipole" states under 20 degrees of the CPNT tilt. The average residence time of channel water gradually increases with the intensifying of the CPNT tilt.