Driving Force for Water Permeation Across Lipid Membranes

The permeation of water across lipid
membranes is of paramount
importance in biological and technological processes. The driving
force for such energetically unfavorable processes is explored here.
To determine the effect of the lipid membrane conformation, water
transport in both liquid-crystalline and ordered gel phases is studied
in zwitterionic dipalmitoyl phosphatidylcholine (DPPC) bilayers and
anionic 1,2-dilauroyl-sn-glycero-3-phosphol-l-serine (DLPS) bilayers via atomistic molecular dynamics simulations.
These phases are accessed by changing the temperature in DPPC membranes
and by additionally changing the valency of counterions (i.e., Na+ and Zn2+) in DLPS membranes. The membrane conformation
is found to play a critical function in water permeation, regardless
of the type of lipid. The fluctuations in the potential energy are
found to have a significant, if not the exclusive, role in the transportation
of water across lipid membranes.