Effect of unsaturation on the chain order of phosphatidylcholines in a dioleoylphosphatidylethanolamine matrix

Abstract

The properties of phosphatidylcholines (PCs) having a perdeuterated stearic acid, 18:0d35, in the sn-1 position and the fatty acid 18:0, 18:1 omega 9, 18:2 omega 6, 18:3 omega 3, 20:4 omega 6, 20:5 omega 3, or 22:6 omega 3 at the sn-2 position were investigated in a matrix of dioleoylphosphatidylethanolamine (DOPE) by 2H and 31P NMR spectroscopy. At a mole ratio of DOPE/PC = 5:1, the lipids form liquid crystalline lamellar phases below 40 degrees C and coexisting lamellar, inverse hexagonal (Hll), and cubic phases at higher temperatures. The sn-1 chain of the PCs in a DOPE matrix is appreciably more ordered than in pure PCs, corresponding to an increase in the hydrophobic bilayer thickness of approximately 1 A. Distearoylphosphatidylcholine in the DOPE matrix has a higher sn-1 chain order than the unsaturated PCs. We observed distinct differences in the lipid order of upper and lower sections of the hydrocarbon chains caused by changes of temperature, unsaturation, headgroups, and ethanol. Unsaturation lowers chain order, mostly in the lower third of the hydrocarbon chains. By contrast, the increase in chain order caused by the DOPE matrix and the decrease in order with increasing temperature have a constant magnitude for the upper two-thirds of the chain and are smaller for the lower third. Addition of 2 M ethanol reduced order parameters, in effect reversing the increase in chain order caused by the DOPE matrix.

Orientation and Location of the Cyclotide Kalata B1 in Lipid Bilayers Revealed by Solid-State NMR

“…Similar changes in 2 H-NMR order parameters have been reported in studies of membraneactive peptides and attributed to a membrane thinning effect induced by a peptide near the polar/apolar interface (37)(38)(39)(40). When a peptide is localized in the headgroup region of a bilayer, the bilayer area increases and the necessary conservation of the total volume of the membrane then requires a thinning of the membrane, which is apparent as decreased order in the acyl chains (41,42). The orientation and position of kalata B1 in the membrane also agrees with the inferred alignment of kalata B1 in detergent micelles (16).…”

Biophysical studies of a transmembrane peptide derived from the T cell antigen receptor

“…31p NMR spectra, which give information about the organization and dynamics of the lipid headgroups (Seelig, 1978), are shown in Figure 2 for dispersions of DMPC-d54 (a zwitterionic phospholipid) in the absence and presence of different concentrations of CP. Pure DMPC-d54 gave a spectrum with a low field shoulder at about 30 ppm and a high field peak at roughly -15 ppm typical for the preferred planar bilayer organization of this lipid in the Lc~ phase [13,14]. Also the sample containing CP in a 1:50 peptide/lipid molar ratio gave a spectrum typical of an L,~ phase, indicating that CP at this relatively high concentration does not disrupt the membrane.…”

“…The 31p NMR spectra of DMPG/DMPC-d54 (1:3 molar ratio) dispersions are shown in Figure 4. The spectral lineshape, with a low field shoulder and a high field peak, is characteristic for lipids in the L,~ phase [13,14], with the double high field peak around -10 ppm reflecting the fact that the two different lipids have slightly different chemical shift anisotropies. As can be seen in Figure 4, the spectrum in the presence of 2 mol% of CP was similar to the spectrum without CP, indicating that at this concentration the peptide does not significantly influence membrane structure.…”

The αM1 transmembrane segment of the nicotinic acetylcholine receptor interacts strongly with model membranes

“…27,28 The 2 H NMR spectrum of a dispersion of DMPC-d 54 in the absence of peptide is presented in Fig. 3(A).…”