Magnetically Aligned Phospholipid Bilayers with LargeqRatios Stabilize Magnetic Alignment with High Order in the Gel and L_αPhases

Abstract

The magnetic alignment behavior ofbicelles (magnetically alignable phospholipid bilayered membranes) as a function of the q ratio (1,2-dihexanoyl-sn-glycerol phosphatidylcholine/1,2-dimyristoyl-sn-glycerol phosphatidylcholine mole ratio) and temperature was studied by spin-labeled X-band electron paramagnetic resonance (EPR) spectroscopy and solid-state 2H and 31P NMR spectroscopy. Well-aligned bicelle samples were obtained at 45 degrees C for q ratios between 2.5 and 9.5 in both the EPR and NMR spectroscopic studies. The molecular order of the system, S(mol), increased as the q ratio increased and as the temperature decreased. For higher q ratios (> or = 5.5), bicelles maintained magnetic alignment when cooled below the main phase transition temperature (approximately 30 degrees C when in the presence of lanthanide cations), which is the first time, to our knowledge, that bicelles were magnetically aligned in the gel phase. For the 9.5 q ratio sample at 25 degrees C, S(mol) was calculated to be 0.83 (from 2H NMR spectra, utilizing the isotopic label perdeuterated 1,2-dimyristoyl-sn-glycerol phosphatidylcholine) and 0.911 (from EPR spectra utilizing the spin probe 3beta-doxyl-5alpha-cholestane). The molecular ordering of the high q ratio bicelles is comparable to literature values of S(mol) for both multilamellar vesicles and macroscopically aligned phospholipid bilayers on glass plates. The order parameter S(bicelle) revealed that the greatest degree of bicelle alignment was found at higher temperatures and larger q ratios (S(bicelle) = -0.92 for q ratio 8.5 at 50 degrees C).

Comprehensive Analysis of Lipid Dynamics Variation with Lipid Composition and Hydration of Bicelles Using Nuclear Magnetic Resonance (NMR) Spectroscopy

“…In these samples, a broad powder pattern, such as 31 P line shape, was observed, indicating the presence of unaligned lipids. Under these conditions, bicelles most likely exhibit an ellipsoidal morphology with a dispersion of 31 P chemical shifts, which is commonly observed for bicelles at high q ratios 21,33. The lack of alignment at these hydration levels can be attributed to numerous factors; however, the most likely factor under these circumstances is the sample viscosity.…”

“…As such, increasing the q ratio as a mean to exemplify dipolar couplings is a reasonable approach to improve spectral resolutions of a SLF spectrum. Unfortunately, this approach may compromise the alignment of bicelles; however, bicelles have been shown to exhibit macroscopic alignment over a wide range of q ratios from 2.5 to 5.5 33. Therefore, there must exist a q ratio where experimental conditions, bicelles alignment, and spectral resolutions can be satisfied for a specific membrane protein.…”

When detergent meets bilayer: Birth and coming of age of lipid bicelles

“…At these higher magnetic field strengths of 1.25 T and 3.4 T, respectively, reduced concentrations of lanthanide ions were needed to achieve magneticalignment of bicelles. The magnetic-alignment of bicelles at high q was investigated by EPR and NMR spectroscopy [124]. …”

Time-resolved EPR immersion depth studies of a transmembrane peptide incorporated into bicelles

“…Bicelles are in the form of bicelle discs or perforated lamellar sheets in the gel or L α -phases, respectively [25, 26]. The reduction decay curves and rate constants reveal that the bicelle system in the L α -phase possesses higher reducing ability than in the gel-phase.…”