Effect of Gramicidin A on Structure and Dynamics of Lipid Vesicle Bilayers. A Time-Resolved Fluorescence Depolarization Study

Muller, Johan M.; Ginkel, G. van; Faassen, Ernst E. van

doi:10.1021/bi00009a041

Cited by 13 publications

(9 citation statements)

References 33 publications

(54 reference statements)

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“…It can be inferred that the bilayer surface between gA aggregates is no longer flat, which is consistent with a previous theoretical study (Huang, 1986), where the surface curvature was predicted to change due to the presence of gA. This observation is also consistent with the suggestion that the state of lipids could be different depending on whether they are in contact with the peptide (Muller et al, 1995;Rice & Oldfield, 1979;Pink et al, 1981). At about 5 mol %, almost all of the lipids appeared to associate with gA clusters, and the entire bilayer was transformed into a single molecular complex, the same as that in gA rich domains at lower gA fractions.…”

Section: Discussionsupporting

confidence: 91%

Gramicidin A Aggregation in Supported Gel State Phosphatidylcholine Bilayers

1996

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Using an atomic force microscope, supported bilayers of saturated phosphatidylcholine (in the gel state) containing various amounts of gramicidin A (gA) were imaged in aqueous solutions and at room temperature. gA clusters were directly observed for the first time under these conditions. It was found that, at a lower gA concentration, gA aggregated into domains, composed of small clusters along with a considerable amount of lipids. This basic aggregation unit, most likely a hexamer, remained the same for acyl chain lengths from 14 to 18 carbons. These small clusters were observed to form elongated aggregates (line type) but never into extended pure gA domains. When gA concentrations were increased, for bilayers with 16 carbons or less, gA aggregated into larger domains but the basic unit remained separated by lipid molecules. At about 5 mol % gA, a percolation-like transition occurred at which the line type aggregates were connected to each other. However, for bilayers with more than 16 carbons, multiple lamellar structures were formed at higher gA fractions and the top layer had a ripple-like surface morphology. The molecular mechanism for the formation of these peculiar structures remains to be elucidated.

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Section: Discussionsupporting

confidence: 91%

Gramicidin A Aggregation in Supported Gel State Phosphatidylcholine Bilayers

1996

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“…Third, in high concentrations it can promote the inverted hexagonal H II lipid phase. Fourth, in DOPC the effect of gA on membrane structure has been seen to vary with the depth in the bilayer (Muller et al, 1995). These results are extended here by using DPH to monitor the effects of gA on the hydrocarbon core of DOPC vesicle bilayers.…”

mentioning

confidence: 64%

Effect of Lipid Molecular Structure and Gramicidin A on the Core of Lipid Vesicle Bilayers. A Time-Resolved Fluorescence Depolarization Study

1996

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We have investigated the molecular orientational order and reorientational dynamics of the fluorescent probe 1,6-diphenyl-1,3,5-hexatriene (DPH) in the core of the membrane bilayer. Vesicles of lipids of varying unsaturation and headgroup (POPC, DOPC, DLPC, DLLPC, EGGPG, DOPG, DGDG, and SQDG) were studied using the time-resolved fluorescence anisotropy of DPH. Generally, values of the second order parameter for DPH are found to be very small. However, this should not be interpreted as DPH having low orientational order as witnessed by large values of the next relevant order parameter . This implies considerable transverse populations of DPH molecules within the bilayer. In phosphatidylcholines with an acyl chain of 18 carbon atoms, the value of for DPH decreases with increasing lipid unsaturation and even attains negative values. No effect of the lipid headgroup on the order and dynamics of DPH is detected. Furthermore, we study the peptide-lipid interaction of the hydrophobic antibiotic gramicidin A (gA) in DOPC vesicles using DPH. The nonchannel conformation has an ordering effect on DPH in the bilayer core, which the channel confirmation lacks. This can be understood in terms of the geometrical shape of the gA dimer, as shown previously with the probes TMA-DPH and DPHPC [Muller, J. M., et al. (1995) Biochemistry 34, 3092]. We find that for DPH data the conventional Brownian rotational diffusion (BRD) model and the compound motion model (CMM) give equivalent fits. In this respect, DPH differs from TMA-DPH and DPHPC, for which probes only the CMM allowed a consistent interpretation of the molecular orientation.

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“…This behavior is frequently monitored with fluorescent probes incorporated in the lipid structures at low concentrations. Commonly, probes such as 1,6-diphenyl-1,3,5-hexatriene (DPH), its polar analogue 1-(4-trimethylammonio)-DPH (TMA-DPH), and perylene − are used. The information about the static (structural microheterogeneity, polarity, orientation) and the dynamic (especially nanosecond reorientations) properties of the surrounding lipids can be obtained from observables such as the fluorescence lifetime and fluorescence anisotropy …”

Section: Introductionmentioning

confidence: 99%

Distribution of Hydrophobic Probe Molecules in Lipid Bilayers. 2. Time-Resolved Fluorescence Anisotropy Study of Perylene in Vesicles

et al. 1997

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The orientational distribution and rotational dynamics of planar perylene molecules incorporated into spherical vesicles of palmitoyl-δ-9-oleoyl(16:0,18:1)phophatidylcholine (POPC) was studied using time-resolved fluorescence anisotropy. The experimental anisotropy decay curves were analyzed using a global target approach. Here, anisotropy curves obtained at six temperatures above the gel-lamellar phase transition of the vesicles as well as the two combinations of excitation and emission wavelengths, (256, 470 nm) and (410, 470 nm), were fitted simultaneously. We have utilized two sets of orientational distributions of perylene in the bilayer. One set contains various one-population orientational distributions, while the other consists of models in which the probes are distributed over two distinct orientational populations. We find that in general the models yield statistically equivalant solutions, though the two-population models need a substantially smaller number of fit parameters. The existence of two distinct orientational populations of perylene in the lipid vesicle bilayer is in agreement with the results of Monte Carlo dynamics simulations in the preceding paper, but we argue that additional independent information is needed in order to remove the remaining ambiguities. We conclude that time-resolved anisotropy experiments on macroscopically unoriented samples do not provide sufficient information in order to fully characterize the orientational distribution of probe molecules in the bilayers.

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Effect of Gramicidin A on Structure and Dynamics of Lipid Vesicle Bilayers. A Time-Resolved Fluorescence Depolarization Study

Cited by 13 publications

References 33 publications

Gramicidin A Aggregation in Supported Gel State Phosphatidylcholine Bilayers

Gramicidin A Aggregation in Supported Gel State Phosphatidylcholine Bilayers

Effect of Lipid Molecular Structure and Gramicidin A on the Core of Lipid Vesicle Bilayers. A Time-Resolved Fluorescence Depolarization Study

Distribution of Hydrophobic Probe Molecules in Lipid Bilayers. 2. Time-Resolved Fluorescence Anisotropy Study of Perylene in Vesicles

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