MD Studies On The Influences Of An Electric Field On Water Movement In A Transmembrane Peptide Nanotube

In this work, MD simulations have been performed to explore how a gradient oruniform electric field influences the water behaviors through a transmembrane octa-or hexa-PNT.MD simulations show that a transmembrane8×cyclo-(WL)4-PNT can withstanda gradient electric (GE) field with Eano more than0.9V/nm. Here, the ratio of aconstant (Ea) and the z-directional length (Lz) of the simulation box was used toindicate the gradient of a GE field. Under a GE filed with Ea≤0.3V/nm, nosignificant changes of the number and array of channel water and H-bonds betweenthem are observed. As Eaincreases from0.3to0.9V/nm, the number of channel waterand H-bonds increases with the augment of Ea. Nevertheless, the1-2-1-2water chainstill dominates in the channel. When Eareaches0.9V nm-1, a water molecule in anα-plane zone may be dragged by its neighboring water molecules in a midplane region,resulting in its significant deviation from the channel axis. Channel water moleculessimultaneously suffer the opposite orientation affects from the ambient (the barecarbonyl groups at two mouths of the tube and phospholipid heads) and the introducedgradient electric field. With the augment of the gradient, the dipoles of channel waterare gradually oriented along the tube axis in the sequence from gap1to7. Besides,under a GE field, the rightward and leftward hopping rates of channel water are nolonger equal to each other. Namely, channel water performs an asymmetric transportation.MD simulations show that a uniform electric (UE) field with an intensity (E) nogreater than0.5V/nm doesn’t have significant influences on the position in POPE andthe structural stability of a transmembrane8×cyclo-(WL)3-PNT. When E reaches0.7V/nm, the structral instability of the tube begins to appear although the PNTframework still remains. Under a UE field with E≤0.5V/nm, the numbers of channelwater and H-bonds between them increase with the augment of E, and channel waterchanges to have a certain distribution probability in α-plane zones from its inital onlyoccurring in midplane regions. Nevertheless, when E reaches0.7V/nm, the numbersof channel water and H-bonds significantly decrease, showing that the filling state ofchannel water in a tube is simultaneously affected by the introduced UE field andthe structural stability of the tube. The introduction of a UE enlarges the hopping ratesof water molecules across the tube mouths (kinand kout), but cuts down the hoppingrates of channel water inside the tube (krand kl).