Title
Direct Measurement of the Effect of Cholesterol and 6-Ketocholestanol on Membrane Dipole Field Using Vibrational Stark Effect Spectroscopy Coupled with Molecular Dynamics Simulations
Author
Rebika Shrestha, Cari M Anderson, Alfredo E. Cardenas, Ron Elber, Lauren J. Webb
Year
2017
Journal
The Journal of Physical Chemistry B
Abstract
Biological membranes are heterogeneous structures with complex electrostatic profiles arising from lipids, sterols, membrane proteins, and water molecules. We investigated the effect of cholesterol and its derivative 6-ketocholestanol (6-kc) on membrane electrostatics by directly measuring the dipole electric field (F ) within lipid bilayers containing cholesterol or 6-kc at concentrations of 0-40 mol% through the vibrational Stark effect (VSE). We found that adding low concentrations of cholesterol, up to ~10 mol%, increases F, while adding more cholesterol up to 40 mol% lowers F. In contrast, we measured a monotonic increase in F as 6-kc concentration increased. We propose that this membrane electric field is affected by multiple factors: the polarity of the sterol molecules, the reorientation of the phospholipid dipole due to sterol, and the impact of the sterol on hydrogen bonding with surface water. We used molecular dynamics simulations to examine the distribution of phospholipids, sterol and helix in bilayers containing these sterols. At low concentrations, we observed clustering of sterols near the vibrational probe whereas at high concentration, we observed spatial correlation between the positions of the sterol molecules. This work demonstrates how a one-atom difference in a sterol changes the physicochemical and electric field properties of the bilayer.
Full Article
Instrument
J-815
Keywords
Circular dichroism, Secondary structure, Vesicle interactions, Biochemistry