HYDROGEN-BONDING OF WATER TO PHOSPHATIDYLCHOLINE IN THE MEMBRANE AS STUDIED BY A MOLECULAR-DYNAMICS SIMULATION - LOCATION, GEOMETRY, AND LIPID-LIPID BRIDGING VIA HYDROGEN-BONDED WATER
M. Pasenkiewiczgierula et al., HYDROGEN-BONDING OF WATER TO PHOSPHATIDYLCHOLINE IN THE MEMBRANE AS STUDIED BY A MOLECULAR-DYNAMICS SIMULATION - LOCATION, GEOMETRY, AND LIPID-LIPID BRIDGING VIA HYDROGEN-BONDED WATER, The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory, 101(20), 1997, pp. 3677-3691
Hydrogen (H-) bonding between water and phosphatidylcholine was studie
d using a molecular dynamics simulation of a hydrated phosphatidylchol
ine bilayer membrane in the liquid crystalline phase. A membrane in th
e liquid-crystalline phase composed of 72 L-alpha-dimyristoylphosphati
dylcholine (DMPC) and 1622 water molecules was generated, starting fro
m the crystal structure of DMPC. At the beginning of the equilibration
process, the temperature of the system was raised to 550 K for 20 ps,
which was effective in breaking the initial crystalline structure, Th
e thermodynamic and structural parameters became stable after the equi
libration period of 1100 ps, and the trajectory of the system obtained
during the following 500 ps agreed well with most of the published ex
perimental data. Each DMPC molecule forms 5.3 I-I-bonds with water, wh
ile only 4.5 water molecules are H-bonded to DMPC. The primary targets
of water for the formation of H-bonds are the non-ester phosphate oxy
gens (4.0 H-bonds) and the carbonyl oxygens (similar to 1.0 H-bonds).
Of DMPC's H-bonds, 1.7 are formed with water molecules that are simult
aneously H-bonded to two different DMPC oxygens (bridging water). In e
ffect, approximately 70% of the DMPC molecules are linked by water mol
ecules and form clusters of two to seven DMPC molecules. Approximately
70% of the intermolecular water bridges are formed between non-ester
phosphate oxygens. The rest are formed between non-ester phosphate and
carbonyl oxygens. About half of the intermolecular water bridges are
involved in formation of multiple bridges, where two DMPC molecules ar
e linked by more than one parallel bridge. These results suggest a pos
sibility that water bridges are involved in reducing head group mobili
ty and in stabilizing the membrane structure. Non-ester phosphate oxyg
en of DMPC makes one, two, or three H-bonds with water, but two H-bond
s are formed most often (approximate to 60%). In the case where two H-
bonds are formed on non-ester phosphate or carbonyl oxygens, the avera
ge geometry of H-bonding is planar trigonal (in the case of water oxyg
en with two H-bonds, geometry is steric tetragonal). When oxygen atoms
form three H-bonds, the geometry of H-bonding is steric tetragonal bo
th for non-ester phosphate and water oxygens. On average, H-bonds make
nearly right angles with each other when two or three water molecules
are bound to the same DMPC oxygen, but the distribution of the angle
is broad.