Article

Saturation with cholesterol increases vertical order and smoothes the surface of the phosphatidylcholine bilayer: A molecular simulation study

Department of Computational Biophysics and Bioinformatics, Jagiellonian University, Krakow, Poland.
Biochimica et Biophysica Acta (Impact Factor: 4.66). 10/2011; 1818(3):520-9. DOI: 10.1016/j.bbamem.2011.10.023
Source: PubMed

ABSTRACT Molecular dynamics (MD) simulations of a mono-cis-unsaturated 1-palmitoyl-2-oleoyl-phosphatidylcholine (POPC) bilayer and a POPC bilayer containing 50mol% cholesterol (POPC-Chol50) were carried out for 200ns to compare the spatial organizations of the pure POPC bilayer and the POPC bilayer saturated with Chol. The results presented here indicate that saturation with Chol significantly narrows the distribution of vertical positions of the center-of-mass of POPC molecules and POPC atoms in the bilayer. In the POPC-Chol50 bilayer, the same moieties of the lipid molecules are better aligned at a given bilayer depth, forming the following clearly separated membrane regions: the polar headgroup, the rigid core consisting of steroid rings and upper fragments of the acyl chains, and the fluid hydrocarbon core consisting of Chol chains and the lower fragments of POPC chains. The membrane surface of the POPC-Chol50 bilayer is smooth. The results have biological significance because the POPC-Chol50 bilayer models the bulk phospholipid portion of the fiber-cell membrane in the eye lens. It is hypothesized that in the eye lens cholesterol-induced smoothing of the membrane surface decreases light-scattering and helps to maintain lens transparency.

Full-text

Available from: Marta Pasenkiewicz-Gierula, Jun 02, 2015
2 Followers
 · 
85 Views
  • [Show abstract] [Hide abstract]
    ABSTRACT: Lipids rafts are considered to be functional nanoscale membrane domains enriched in cholesterol and sphingolipids, characteristic in particular of the external leaflet of cell membranes. Lipids, together with membrane-associated proteins, are therefore considered to form nanoscale units with potential specific functions. Although the understanding of the structure of rafts in living cells is quite limited, the possible functions of rafts are widely discussed in the literature, highlighting their importance in cellular functions. In this review, we discuss the understanding of rafts that has emerged based on recent atomistic and coarse-grained molecular dynamics simulation studies on the key lipid raft components, which include cholesterol, sphingolipids, glycolipids, and the proteins interacting with these classes of lipids. The simulation results are compared to experiments when possible.
    Chemistry and Physics of Lipids 11/2014; 184. DOI:10.1016/j.chemphyslip.2014.10.004 · 2.59 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Human lens-lipid membranes prepared from the total lipids extracted from clear and cataractous lens cortexes and nuclei of 61–70-year-old donors by use of a rapid solvent-exchange method were investigated. The measured cholesterol-to-phospholipid (Chol/PL) molar ratio in these membranes was 1.8 and 4.4 for cortex and nucleus of clear lenses, respectively, and 1.14 and 1.45 for cataractous lenses. Properties and organization of the lipid bilayer were investigated by use of electron paramagnetic resonance spin-labeling methods. Formation of Chol crystals was confirmed by use of differential scanning calorimetry. Pure cholesterol bilayer domains (CBDs) were formed in all the membranes investigated. It was shown that in clear lens membranes of the nucleus, Chol exists in three different environments: (1) dispersed in phospholipid bilayers (PCDs), (2) in CBDs, and (3) in Chol crystals. In clear lens membranes of the cortex, and in cortical and nuclear cataractous lens membranes, Chol crystals were not detected, because of the lower Chol content. Profiles of membrane properties (alkyl-chain order, fluidity, oxygen transport, and hydrophobicity) across the PCD were very similar for clear and cataractous membranes. Profiles of the oxygen transport parameter across the CBD were, however, different for cortical clear and cataractous membranes—the amount and size of CBDs was less in cataractous membranes. These results suggest that high Chol content, formation of CBDs, and formation of Chol crystals should not be regarded as major predispositions for the development of age-related cataracts.
    European Biophysics Journal 12/2014; 44(1-2). DOI:10.1007/s00249-014-1004-7 · 2.47 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The mica supported binary monolayers containing phospholipids: 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC), 2-oleoyl-1-palmitoyl-sn-glycero-3-phosphocholine (POPC), 1,2-dipalmitoyl-sn-glycero-3-phospho-rac-(1-glycerol) (DPPG), and cholesterol (Chol), mixed at different molar fractions, were investigated by measurements of the contact angles of water, formamide and diiodomethane. This allowed calculation of apparent surface Gibbs energy (further in the paper termed as 'surface free energy') of the monolayers according to the theoretical approach developed by Chibowski (Contact Angle Hysteresis Model, CAH). Then, based on the surface free energy values, the molar interaction Gibbs energy of the lipid molecules with the given probe liquid was evaluated. These values correlate with the values of excess area, interpreted as an indicator of the condensing effect of cholesterol on phospholipid monolayers at the air-water interface. The results indicate that the thermodynamic parameters of interactions depend on the monolayer composition and the probe liquid used to their determination. Changes of the parameters are discussed in relation to the monolayer packing, ordering, tilting of the molecules, and properties of the probe liquids as well.
    Chemistry and Physics of Lipids 05/2014; DOI:10.1016/j.chemphyslip.2014.05.007 · 2.59 Impact Factor