scholarly journals Melatonin alters fluid phase co-existence in POPC/DPPC/cholesterol membranes

2020 ◽  
Author(s):  
Nanqin Mei ◽  
Morgan Robinson ◽  
James H. Davis ◽  
Zoya Leonenko
Keyword(s):  
Phase Separation ◽  
Lipid Membranes ◽  
Hydrocarbon Chain ◽  
Phase Behaviour ◽  
Ternary Mixtures ◽  
Lipid Phase ◽  
Biophysical Properties ◽  
Lipid Mixture ◽  
Model Lipid Membranes ◽  
Chain Order

ABSTRACTThe structure and biophysical properties of lipid biomembranes are important for normal function of plasma and organelle membranes, which is essential for proper functioning of living cells. In Alzheimer’s disease (AD) the structure of neuronal membranes becomes compromised by the toxic effect of amyloid-β (Aβ) protein which accumulates at neuron synapses, resulting in membrane perforation and dysfunction, oxidative stress and cell death. Melatonin is an important pineal gland hormone that has been shown to be protective against Aβ toxicity in cellular and animal studies, but the molecular mechanism of this protection is not well understood. It has been shown that melatonin can interact with model lipid membranes and alter the membrane biophysical properties, such as membrane molecular order and dynamics. This effect of melatonin has been previously studied in simple model bilayers with one or two lipid components, we consider a more complex ternary lipid mixture as our membrane model. In this study, we used 2H-NMR to investigate the effect of melatonin on lipid phase behaviour of a three-component model lipid membranes composed of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) and cholesterol. We used deuterium labelled palmitoyl-d31 in POPC-d31 and DPPC-d62 separately, to probe the changes in hydrocarbon chain order as a function of temperature and varying concentrations of melatonin. We found that melatonin concentration influences phase separation in these ternary mixtures somewhat differently depending on whether POPC-d31 or DPPC-d62was used. At 5 mol% melatonin we observed phase separation in samples with POPC-d31, but not with DPPC-d62. However, at 10 mol% melatonin phase separation was observed in both samples with either POPC-d31 or DPPC-d62. These results indicate that melatonin can have a strong effect on membrane structure and physical properties, which may provide some clues to understanding how melatonin protects against Aβ.SIGNIFICANCEMelatonin has been shown to be protective against Aβ pathology in animal and cellular studies. Although the mechanism of this protection is not well-understood, melatonin’s membrane-active properties may be important in this regard. In this work solid-state deuterium nuclear magnetic resonance was used to study the effect of melatonin on the POPC/DPPC/cholesterol model membranes. Specifically, we showed that melatonin modifies lipid hydrocarbon chain order to promote phase separation. This knowledge helps to explain the role of melatonin in lipid domain formation and may provide a deeper understanding of the mechanism of melatonin neuroprotection in AD.

Fluorescent probe partitioning in giant unilamellar vesicles of ‘lipid raft’ mixtures

2010 ◽  
Vol 430 (3) ◽  
pp. 415-423 ◽  
Author(s):  
Janos Juhasz ◽  
James H. Davis ◽  
Frances J. Sharom
Keyword(s):  
Fluorescent Probe ◽  
Lipid Bilayer ◽  
Fluorescent Probes ◽  
Phase Behaviour ◽  
Model Systems ◽  
Fluorescence Probes ◽  
Lipid Phase ◽  
Giant Unilamellar Vesicles ◽  
Unilamellar Vesicles ◽  
Lipid Mixture

Direct visualization of raft-like lo (liquid-ordered) domains in model systems and cells using microscopic techniques requires fluorescence probes with known partitioning preference for one of the phases present. However, fluorescent probes may display dissimilar partitioning preferences in different lipid sys-tems and can also affect the phase behaviour of the host lipid bilayer. Therefore a detailed understanding of the behaviour of fluorescent probes in defined lipid bilayer systems with known phase behaviour is essential before they can be used for identifying domain phase states. Using giant unilamellar vesicles composed of the ternary lipid mixture DOPC (1,2-dioleoyl-sn-glycero-3-phosphocholine)/DPPC (1,2-dipalmitoyl-sn-glycero-3-phosphocholine)/cholesterol, for which the phase behaviour is known, we examined nine commonly used fluorescent probes using confocal fluorescence microscopy. The partitioning preference of each probe was assigned either on the basis of quantification of the domain area fractions or by using a well-characterized ld (liquid-disordered)-phase marker. Fluorescent probes were examined both individually and using dual or triple labelling approaches. Most of the probes partitioned individually into the ld phase, whereas only NAP (naphtho[2,3-a]pyrene) and NBD-DPPE [1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine-N-(7-nitro-2-1,3-benzoxadiazol-4-yl] preferred the lo phase. We found that Rh-DPPE (Lissamine™ rhodamine B–1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine) increased the miscibility transition temperature, Tmix. Interestingly, the partitioning of DiIC18 (1,1′-dioctadecyl-3,3,3′,3′-tetramethylindocarbocyanine perchlorate) was influenced by Bodipy®-PC [2-(4,4-difluoro-5,7-dimethyl-4-bora-3a,4a-diaza-s-indacene-3-pentanoyl)-1-hexa-decanoyl-sn-glycero-3-phosphocholine]. The specific use of each of the fluorescent probes is determined by its photostability, partitioning preference, ability to detect lipid phase separations and induced change in Tmix. We demonstrate the importance of testing a specific fluorescent probe in a given model membrane system, rather than assuming that it labels a particular lipid phase.

scholarly journals Imaging phase separation in model lipid membranes through the use of BODIPY based molecular rotors

2015 ◽  
Vol 17 (28) ◽  
pp. 18393-18402 ◽  
Author(s):  
Michael R. Dent ◽  
Ismael López-Duarte ◽  
Callum J. Dickson ◽  
Niall D. Geoghegan ◽  
Jonathan M. Cooper ◽  
...  
Keyword(s):  
Molecular Dynamics ◽  
Phase Separation ◽  
Fluorescence Spectroscopy ◽  
Molecular Dynamics Simulations ◽  
Lipid Bilayers ◽  
Lipid Membranes ◽  
Molecular Rotors ◽  
Model Lipid Membranes ◽  
Dynamics Simulations

Viscosity in the phase-separated lipid bilayers is investigated through the use of fluorescence spectroscopy and molecular dynamics simulations.

Monte Carlo Simulation of Lattice Model of Amphiphile and Solvent Mixture on a Transputer Array

1991 ◽  
Vol 02 (01) ◽  
pp. 284-287
Author(s):  
D. BRINDLE ◽  
C.M. CARE
Keyword(s):  
Lattice Model ◽  
Mean Field ◽  
Lattice Models ◽  
Ternary Systems ◽  
Solvent Mixture ◽  
Phase Behaviour ◽  
Ternary Mixtures ◽  
Amphiphilic Molecules ◽  
Chain Order ◽  
Water Lattice

A binary mixture of an amphiphilic material and water exhibits a rich phase behaviour as the concentrations of the components or temperature is changed [1]. Similar behaviour is also observed for ternary mixtures of amphiphile, oil and water. Lattice models of ternary systems have been extensively studied [e.g. 2]. However these models usually represent the amphiphilic molecule as a bond or site within the lattice and hence ignore the internal structure of the amphiphile. In this paper we present results for the lattice model of a binary system in which we represent the amphiphilic molecules by extended chains. This allows the nature of the chain packing and its influence on phase behaviour to be investigated. It also allows comparison with mean field calculations of chain order parameters [e.g. 3].

scholarly journals Giant unilamellar vesicles - a perfect tool to visualize phase separation and lipid rafts in model systems.

2009 ◽  
Vol 56 (1) ◽  
Author(s):  
Olga Wesołowska ◽  
Krystyna Michalak ◽  
Jadwiga Maniewska ◽  
Andrzej B Hendrich
Keyword(s):  
Phase Separation ◽  
Lipid Membranes ◽  
Average Diameter ◽  
Model Systems ◽  
Membrane Properties ◽  
Lipid Phase ◽  
Giant Unilamellar Vesicles ◽  
Unilamellar Vesicles ◽  
Simple Method ◽  
Wide Range

Model systems such as black lipid membranes or conventional uni- or multilamellar liposomes are commonly used to study membrane properties and structure. However, the construction and dimensions of these models excluded their direct optical microscopic observation. Since the introduction of the simple method of liposome electroformation in alternating electric field giant unilamellar vesicles (GUVs) have become an important model imitating biological membranes. Due to the average diameter of GUVs reaching up to 100 microm, they can be easily observed under a fluorescent or confocal microscope provided that the appropriate fluorescent probe was incorporated into the lipid phase during vesicle formation. GUVs can be formed from different lipid mixtures and they are stable in a wide range of physical conditions such as pH, pressure or temperature. This mini-review presents information about the methods of GUV production and their usage. Particularly, the use of GUVs in studying lipid phase separation and the appearance and behavior of lipid domains (rafts) in membranes is discussed but also other examples of GUVs use in membrane research are given. The experience of the authors in setting up the GUV-forming equipment and production of GUVs is also presented.

scholarly journals Influence of Triphenyllead Chloride on Biological and Model Membranes

2000 ◽  
Vol 55 (9-10) ◽  
pp. 764-769
Author(s):  
Halina Kleszczyńska ◽  
Krzysztof Bielecki ◽  
Janusz Sarapuk ◽  
Anna Dziamska ◽  
Stanislaw Przestalski
Keyword(s):  
Lipid Membranes ◽  
Lemna Minor ◽  
Model Membranes ◽  
Lipid Phase ◽  
Experimental Conditions ◽  
Inhibition Of Growth ◽  
Model Lipid Membranes ◽  
Osmotic Stability ◽  
Spirodela Oligorrhiza

Abstract The physiological and hemolytic toxicities of triphenyllead chloride (TPhL) as well as its modyfying influence on model lipid membranes were studied. The experiments allowed the determination of TPhL concentrations causing 50% inhibition of growth of Spirodela oligorrhiza, Lemna minor and Solvinia natans (EC50), 100% hemolysis of pig erythrocytes (C100) and destabilization of planar lipid membranes (CC). Also, fluidity of erythrocyte ghosts was measured by fluorescence technique and osmotic sensitivity of erythrocytes to the presence of TPhL. All parameters studied were found to be dependent on pH, of experimental solutions and the concentration of TPhL. Acidic conditions increased EC50, C100 and CC concentrations of TPhL. Fluorescence and osmotic measurements showed that osmotic stability and fluidity decreased with increasing trimethyllead concentration. A possible mechanism of TPhL toxicity is discussed. It is assumed that TPhL is interacting with the lipid phase of the models used. It is also assumed that there may exist various, ionic and nonionic, forms of TPhL as a result of its speciation under different experimental conditions. These species, due to their differentiated lipophilicity, may exert different effects on the model membranes studied.

scholarly journals Structure–function studies of tryptophan mutants of equinatoxin II, a sea anemone pore-forming protein

2000 ◽  
Vol 346 (1) ◽  
pp. 223-232 ◽  
Author(s):  
Petra MALOVRH ◽  
Ariana BARLIĆ ◽  
Zdravko PODLESEK ◽  
Peter MAĆEK ◽  
Gianfranco MENESTRINA ◽  
...  
Keyword(s):  
Secondary Structure ◽  
Lipid Membranes ◽  
Lipid Membrane ◽  
Expression System ◽  
Random Coil ◽  
Tryptophan Residue ◽  
Lipid Phase ◽  
Wild Type ◽  
Model Lipid Membranes ◽  
Equinatoxin Ii

Equinatoxin II (EqtII) is a eukaryotic cytolytic toxin that avidly creates pores in natural and model lipid membranes. It contains five tryptophan residues in three different regions of the molecule. In order to study its interaction with the lipid membranes, three tryptophan mutants, EqtII Trp45, EqtII Trp116/117 and EqtII Trp149, were prepared in an Escherichia coli expression system [here, the tryptophan mutants are classified according to the position of the remaining tryptophan residue(s) in each mutated protein]. They all possess a single intrinsic fluorescent centre. All mutants were less haemolytically active than the wild-type, although the mechanism of erythrocyte damage was the same. EqtII Trp116/117 resembles the wild-type in terms of its secondary structure content, as determined from Fourier-transform infrared (FTIR) spectra and its fluorescent properties. Tryptophans at these two positions are buried within the hydrophobic interior of the protein, and are transferred to the lipid phase during the interaction with the lipid membrane. The secondary structure of the other two mutants, EqtII Trp45 and EqtII Trp149, was altered to a certain extent. EqtII Trp149 was the most dissimilar from the wild-type, displaying a higher content of random-coil structure. It also retained the lowest number of nitrogen-bound protons after exchange with 2H2O, which might indicate a reduced compactness of the molecule. Tryptophans in EqtII Trp45 and EqtII Trp149 were more exposed to water, and also remained as such in the membrane-bound form.

An effect of antibiotic amphotericin B on ion transport across model lipid membranes and tonoplast membranes

2005 ◽  
Vol 70 (5) ◽  
pp. 668-675 ◽  
Author(s):  
Monika Hereć ◽  
Halina Dziubińska ◽  
Kazimierz Trębacz ◽  
Jacek W. Morzycki ◽  
Wiesław I. Gruszecki
Keyword(s):  
Ion Transport ◽  
Amphotericin B ◽  
Lipid Membranes ◽  
Model Lipid Membranes
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