Characterization of magnetically orientable bilayers in mixtures of dihexanoylphosphatidylcholine and dimyristoylphosphatidylcholine by solid-state NMR

Abstract

Mixtures of long-chain and short-chain phosphatidylcholine (PC) were characterized by multinuclear (13C, 31P, 2H) solid-state nuclear magnetic resonance. This work complements and extends previous characterization of such mixtures by focusing on concentrated mixtures at temperatures above the gel to liquid crystalline phase transition temperature (Tm) of the long-chain PC component. Above Tm it was observed that highly oriented, bilayer-like assemblies could be formed of mixtures of dimyristoylphosphatidylcholine (DMPC) and dihexanoylphosphatidylcholine (DHPC) in molar ratios ranging from approximately 1:3.5 to 1:2 (DHPC:DMPC) over a considerable range of lipid concentrations (at least 3-40% w/v total lipid, for a 1:2.5 sample). Orientation was observed to occur only in an L alpha-like phase. The NMR data can be accounted for by a general model of the DHPC-DMPC aggregates in which DHPC can be found in two distinct populations (one highly ordered, one not). The averaged conformations of the glycerol backbone/headgroup regions of the long- and short-chain PC composing the assemblies were judged by solid-state 13C NMR to be similar to each other. The information gleaned about these mixtures and the quality of the oriented NMR spectra obtained suggest that DHPC-DMPC mixtures may prove to be useful as model membrane media in solid-state NMR studies of biomembranes.

Using O 2 to probe membrane immersion depth by 19 F NMR

“…In this study, all measurements were performed by using DMPC͞DHPC molar ratios of either 0.5 or 1.0. In bicellar dispersions, the long chain lipid, DMPC, is known to organize as a bilayer, whereas DHPC coats the hydrophobic edges of the bilayer to form a disk-shaped aggregate, referred to as a bilayered micelle or bicelle (30)(31)(32)(33)(34). If the molar ratio of DMPC to DHPC is between roughly 2.5 and 5, these bicelles are observed to align in a magnetic field.…”

Crystallization of Membrane Proteins: Merohedral Twinning of Crystals

“…The bicelle sizes at a 1:3 DMPC/DHPC molar ratio are: the bilayer thickness -40 Å and the diameter -400 Å. The lipid detergent ratios present in the bicellar systems are relatively high compared to standard micellar systems [20,21].…”

Magnetically Oriented Bicelles with Monoalkylphosphocholines: Versatile Membrane Mimetics for Nuclear Magnetic Resonance Applications

“…Bilayered micelles, or so-called bicelles, were introduced in the 1990's and quickly gained in popularity due to their similarities with biological membranes 1,2 . They are composed of longchain phospholipids organized in a bilayer stabilized by short-chain lipids or detergents in the high curvature region of discs or perforated vesicles.…”