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Fine Tuning of Microscopic Properties in Two-Component Zwitterionic- Anionic Lipid Bilayers: Determinant Role of H-Bonding
Structure, dynamics, and functioning of hydrated lipid bilayers - model cell
membranes - are governed by a thin balance of intermolecular interactions between
constituents of these systems. Besides the hydrophobic effect, which determines
the overall bilayer skeleton, important contribution is made by Hbonds
between lipids, water, and ions. This determines crucial phenomena in
cell membranes: dynamic clustering, hydration, fine tuning of microscopic
physico-chemical properties, which permit fast adaptation of membranes to
external agents (e.g., proteins). Characteristics of H-bonds (strength, spatial
location, etc.) dramatically depend on local polarity properties of water-lipid
environment. Here, we calculated free energies of H-bonded complexes between
lipids and water in explicit solvents of different polarity (water, methanol,
chloroform) mimicking membrane environment at different depth. The
strongest H-bonds were observed in nonpolar environment, although the overall
bilayer organization imposes serious limitations on the distribution of
various types of H-bonds over hydrophobic/hydrophilic regions (corresponding
to dielectric media with low and high permeability). This creates a delicate balance,
which determines a unique H-bonding pattern for each particular lipid
bilayer. This was confirmed via atomistic molecular dynamics (MD) of several
hydrated lipid bilayers. Understanding of the factors regulating H-bonding propensities
in such systems is indispensable for rational design of new membranelike
materials with predefined properties. One example - an artificial lipid with
engineered hydroxyl group - is studied via MD simulations. It is shown that
such lipids can induce significant changes of key characteristics of model membranes.
This opens new avenues in goal-oriented design of artificial membranes
with engineered properties.