Structural Evaluation of Phospholipid Bicelles for Solution-State Studies of Membrane-Associated Biomolecules

Abstract

Several complementary physical techniques have been used to characterize the aggregate structures formed in solutions containing dimyristoylphosphatidylcholine (DMPC)/dihexanoylphosphatidylcholine (DHPC) at ratios of < or =0.5 and to establish their morphology and lipid organization as that of bicelles. (31)P NMR studies showed that the DMPC and DHPC components were highly segregated over a wide range of DMPC/DHPC ratios (q = 0.05-0.5) and temperatures (15 degrees C and 37 degrees C). Only at phospholipid concentrations below 130 mM did the bicelles appear to undergo a change in morphology. These results were corroborated by fluorescence data, which demonstrated the inverse dependence of bicelle size on phospholipid concentration as well as a distinctive change in phospholipid arrangement at low concentrations. In addition, dynamic light scattering and electron microscopy studies supported the hypothesis that the bicellar phospholipid aggregates are disk-shaped. The radius of the planar domain of the disk was found to be directly proportional to the ratio of DMPC/DHPC and inversely proportional to the total phospholipid concentration when the DMPC/DHPC ratio was held constant at 0.5. Taken together, these results suggest that bicelles with low q retain the morphology and bilayer organization typical of their liquid-crystalline counterparts, making them useful membrane mimetics.

Solid‐state NMR analysis of the orientation and dynamics of epigallocatechin gallate, a green tea polyphenol, incorporated into lipid bilayers

“…[23,24] Thus, mixtures of DHPC and DMPC in water would be expected to form discoidal aggregates in which a flat DMPC bilayer is stabilized by the DHPC rim. [25] Using solid-state 31 P NMR spectrometry, we confirmed that the surfaces of bicelles orient parallel to the magnetic field (data not shown). Below T c , an isotropic peak was observed at approximately 0 ppm.…”

Three-way Interaction between 14-3-3 Proteins, the N-terminal Region of Tyrosine Hydroxylase, and Negatively Charged Membranes

“…The sample was then transferred to room temperature, vortexed, and subsequently warmed to 38°C on a water bath for 30 min and transferred back to 4°C for 15 min of equilibration. This cold vortex/warm vortex cycle was repeated several times until a clear, viscous solution with a blue tint occurred at 38°C (44) SPR Measurements-The SPR analyses were carried out using the Biacore 3000 biosensor (Biacore AB), normally at 25°C. The interaction of TH-(1-43) and THp-(1-43) with 14-3-3 proteins was studied with the sensor chip CM5.…”

“…Two model systems where used: spherical bilayer vesicles and disc-like bicelles with a circular bilayer plane encircled by DHPC lipids in a micelle arrangement (44). The quality of far-UV CD spectra in the presence of bicelles was better than in the presence of vesicles, the latter causing decreased signal-to-noise in peptide spectra due to increased light scattering at shorter wavelengths.…”

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

“…This alignment is confirmed by well- Tables S1, S2 and S3, with properties such as the melting temperature (T m ) of the phospholipids and the CMC of the detergents. Static mosaicities fall below 5° for the best oriented systems; the quality of the orientation of MAPCHO bicelles is therefore as good as the one of classical bicelles 41 . The best dynamic mosaicities are also very good, for example 6° with the D14PC/14PC system at 77°C.…”

“…Indeed, the presence of a significant amount of free surfactant can be a drawback in particular when samples need to be diluted 42 . By studying the effect of dilution on 31 P NMR spectra, the concentration of free detergent (or critical bicellar concentration, CBC) can be determined 41,42 . Examples of such spectra are shown in the supporting information ( Figure S6), and CBC values are listed in Table 1, calculated as described by Beaugrand et al 42 .…”