Lipid membranes with a majority of cholesterol: applications to the ocular lens and aquaporin 0

J Phys Chem B. 2011 May 26;115(20):6455-64. doi: 10.1021/jp108650u. Epub 2011 May 3.

Abstract

Using molecular dynamics (MD) simulations, we studied the structure and dynamics of two dimyristoylphosphatidylcholine (DMPC):cholesterol bilayers at concentrations representative of the ocular lens (ratios of 1:1 and 1:2). These MD simulations agree well with experimental deuterium order parameters and bilayer peak-to-peak distances. Although it is known that the average surface area per lipid rapidly decreases from low to moderate levels of cholesterol, our simulations indicate that there is a relatively small change in the average lipid area from 50 to 66.7% cholesterol (40.5 ± 0.2 and 39.5 ± 0.1 Å(2)/lipid, respectively). Radial distribution functions for the hydroxyl group on cholesterol indicate the formation of cholesterol-only nanoscale domains for the membrane with 66.7% cholesterol but a uniform distribution of cholesterol and DMPC for the membrane with 50% cholesterol. These small domains form a single shell of hexagonally packed cholesterols that are interconnected in a web-like structure of cholesterol. Calculations of internal DMPC dynamics show that the relaxation times for carbon-hydrogen reorientation of choline decrease with an increase in cholesterol, but the main body (carbonyl-glycerol to C11) is independent of cholesterol concentration. MD simulations of the aquaporin 0 tetramer show stabilization in its interactions with lipid membranes containing cholesterol by forming ring-ring stacking between surface aromatic residues of the protein and the rings of cholesterol. Moreover, there is an increase in hydrogen bonds with longer lifetimes in a mixed bilayer of DMPC and cholesterol.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Animals
  • Aquaporins / chemistry*
  • Aquaporins / metabolism
  • Cattle
  • Cholesterol / chemistry*
  • Cholesterol / metabolism
  • Dimyristoylphosphatidylcholine / chemistry*
  • Dimyristoylphosphatidylcholine / metabolism
  • Eye Proteins / chemistry*
  • Eye Proteins / metabolism
  • Lens, Crystalline / chemistry*
  • Lens, Crystalline / metabolism
  • Lipid Bilayers / chemistry*
  • Lipid Bilayers / metabolism
  • Molecular Dynamics Simulation
  • Protein Multimerization

Substances

  • Aquaporins
  • Eye Proteins
  • Lipid Bilayers
  • aquaporin 0
  • Cholesterol
  • Dimyristoylphosphatidylcholine