Gramicidin conformational studies with mixed-chain unsaturated phospholipid bilayer systems

Abstract

The transition of gramicidin from a nonchannel to a channel form was investigated using mixed-chain phosphatidylcholine lipid bilayers. Gramicidin and phospholipids were codispersed, after removal of the solvents chloroform/methanol or trifluoroethanol which resulted in nonchannel and channel conformations, respectively, as confirmed using circular dichroism (CD). The fluorescence emission maxima of the nonchannel form were shifted toward shorter wavelengths by heating at 60 degrees C (for 0-12 h), which converted it to a channel form, again as confirmed by CD. The channel form did not respond to heat treatment. Heat treatment also increased the fluorescence anisotropy of the nonchannel gramicidin tryptophans. The rate of transition from the nonchannel to channel conformation was found to be faster if phosphatidylethanolamine was present in combination with phosphatidylcholine compared to phosphatidylcholine alone. Also, gramicidin in bilayers of the polyunsaturated 1-palmitoyl-2-docosahexaenoyl-phosphatidylcholine converted more rapidly compared to 1-palmitoyl-2-oleoylphosphatidylcholine. Using the fluorescence anisotropy of the membrane lipid probe 1,6-diphenyl-1,3,5-hexatriene, it was also shown that the motional properties of the surrounding lipid acyl chains differed for the channel and nonchannel gramicidin conformations. The possibility that lipids tending to favor the hexagonal phase (HII) would enhance the rate of the nonchannel to channel transition was supported by 31P NMR which revealed the presence of some HII lipids in the channel preparations. The results of this study suggest that gramicidin may serve as a useful model for similar conformational transitions in other more complex membrane proteins.

Energy‐transducing properties of primary proton pumps reconstituted into archaeal bipolar lipid vesicles

“…In both lipid preparations gramicidin is more effective when added to the liposomes from a solution in dimethylsulfoxide than from a solution in ethanol. This observation agrees with the conclusion that addition to lipid bilayers of gramicidin dissolved in dimethylsulfoxide or ethanol resulted in channel and non-channel conformations, respectively [23].…”

The effect of temperature and lipid on the conformational transition of gramicidin A in lipid vesicles

“…These spectra changes are caused by the changes of the tryptophan microenvironment, particularly indole side chains, during the conformational transitions in gramicidin A as it gradually converts from a double-stranded helix to a singlestranded helical dimer. 20 This result is in agreement with the previous study of monitoring the gramicidin A conformation in lipids, in which the fluorescence wavelength at 335 nm also was shown to shift to longer wavelengths. 28 Figure 2 shows representative plots of the fluorescence intensity at 335 nm against incubation time at 808C for four different molar ratios of DMPC/gramicidin A.…”

“…18 The rate of transition from the double-stranded helix to the single-stranded helical dimer depends on the lipid head group, acyl chain length, and unsaturated content. [19][20][21][22][23] Two models of this conformational change have been proposed. In the ''zipper'' mechanism, the intertwined chains unscrew in opposite directions by progressively shifting the antiparallel chains past each other.…”

Effect of pyrrolidinium based ionic liquid on the channel form of gramicidin in lipid vesicles

“…2. The emission maximum of channel formation was in agreement with the previously reported literature [15,37]. From the results it was observed that the emission maximum wavelength of channel form of gramicidin b 6.3 -helical conformation remains almost constant, i.e.…”

“…In channel conformation, the gramicidin exists as characteristic single-stranded b 6.3 helical conformation having typical peaks of positive ellipticity around 218 and 235 nm, with a valley around 230 nm and negative ellipticity below 208 nm [12,37,38]. Fig.…”