Combined influence of cholesterol and synthetic amphiphillic peptides upon bilayer thickness in model membranes

Abstract

Deuterium (2H) NMR was used to study bilayer hydrophobic thickness and mechanical properties when cholesterol and/or synthetic amphiphillic polypeptides were added to deuterated POPC lipid bilayer membranes in the liquid-crystalline (fluid) phase. Smoothed acyl chain orientational order profiles were used to calculate bilayer hydrophobic thickness. Addition of 30 mol% cholesterol to POPC at 25 degrees C increased the bilayer thickness from 2.58 to 2.99 nm. The peptides were chosen to span the bilayers with more or less mismatch between the hydrophobic peptide length and membrane hydrophobic thickness. The average thickness of the pure lipid bilayers was significantly perturbed upon addition of peptide only in cases of large mismatch, being increased (decreased) when the peptide hydrophobic length was greater (less) than that of the pure bilayer, consistent with the "mattress" model of protein lipid interactions (Mouritsen, O.G., and M. Bloom. 1984. Biophys. J. 46:141-153). The experimental results were also used to examine the combined influence of the polypeptides and cholesterol on the orientational order profile and thickness expansivity of the membranes. A detailed model for the spatial distribution of POPC and cholesterol molecules in the bilayers was proposed to reconcile the general features of these measurements with micromechanical measurements of area expansivity in closely related systems. Experiments to test the model were proposed.

Aggregation and Dynamics of Oligocholate Transporters in Phospholipid Bilayers Revealed by Solid-State NMR Spectroscopy

“…The lipid− chain cross peaks rose similarly rapidly as in the DLPC bilayer, with an average distance of 2 Å to the lipid CH 2 . Hence, as the hydrophobic thickness of POPC membranes increased from 2.6 to 3.0 nm, 41 the macrocycle actually became closer to the lipid tails. This result provides the strongest evidence for the TM stacking model for the cyclic oligocholates.…”

“…41 POPG was added to increase the colloidal stability of the liposomes in our leakage assays. 21 Inclusion of cholesterol into the POPC/POPG membrane is known to increase its hydrophobicity and hydrophobic thickness 41 but, counterintuitively, enhanced the transmembrane movement of glucose induced by 1 and 2. 21 Since hydrophobic interactions are hypothesized to drive the stacking of the oligocholate macrocycles, DLPC was chosen for its lower hydrophobicity.…”

Methods for studying transmembrane peptides in bicelles: consequences of hydrophobic mismatch and peptide sequence

“…Previous studies of model transmembrane peptides comprised of polyleucine or Ala-Leu repeats of varying lengths in model membrane systems have shown they form stable a-helices [11,[16][17][18][19][20][21][22][23][24]. These peptides commonly contain flanking tryptophans or lysines which are thought to act as anchoring residues that stabilize the helix within the bilayer and discourage peptide aggregation [18,19,22,25]. The N-and C-termini are capped (acetylated and amidated, respectively) in order to stabilize the helix dipole and to mimic continuation of the membrane-spanning segment to other regions of a membrane incorporated protein.…”

Modulation of the bilayer thickness of exocytic pathway membranes by membrane proteins rather than cholesterol

“…Additionally, cholesterol has also been shown to affect the thickness of artificial bilayer systems in vitro. Extensive experimental and computational data for pure phospholipid͞cholesterol systems have demonstrated that, under certain circumstances, cholesterol increases bilayer thickness (18)(19)(20), presumably due to the ordering of the acyl chains of phospholipids. Because cholesterol is ubiquitous in eukaryotic cell membranes, it has been suggested that cholesterol is a principal modulator of bilayer thickness in these cells.…”