Kj. Glover et al., Structural evaluation of phospholipid bicelles for solution-state studies of membrane-associated biomolecules, BIOPHYS J, 81(4), 2001, pp. 2163-2171
Several complementary physical techniques have been used to characterize th
e aggregate structures formed in solutions containing dimyristoylphosphatid
ylcholine (DMPC)/dihexanoylphosphatidylcholine (DHPC) at ratios of less tha
n or equal to0.5 and to establish their morphology and lipid organization a
s that of bicelles. P-31 NMR studies showed that the DMPC and DHPC componen
ts were highly segregated over a wide range of DMPC/DHPC ratios (q = 0.05-0
.5) and temperatures (15 degreesC and 37 degreesC). Only at phospholipid co
ncentrations below 130 mM did the bicelles appear to undergo a change in mo
rphology. These results were corroborated by fluorescence data, which demon
strated the inverse dependence of bicelle size on phospholipid concentratio
n as well as a distinctive change in phospholipid arrangement at low concen
trations. In addition, dynamic light scattering and electron microscopy stu
dies supported the hypothesis that the bicellar phospholipid aggregates are
disk-shaped. The radius of the planar domain of the disk was found to be d
irectly proportional to the ratio of DMPC/DHPC and inversely proportional t
o the total phospholipid concentration when the DMPC/DHPC ratio was held co
nstant at 0.5. Taken together, these results suggest that bicelles with low
q retain the morphology and bilayer organization typical of their liquid-c
rystalline counterparts, making them useful membrane mimetics.