Structure Of Biological Membranes Research Articles

Comparison of Unsaturated Phospholipids Effect on Phase Separation in Cholesterol Free and Cholesterol Containing Bilayers

In model membranes phospholipids (PLs) with high and low transition melting temperatures (Tm) may segregate laterally, especially in the presence of cholesterol. Cholesterol prefers interacting with PLs with saturated acyl chains over those with monounsaturated and especially polyunsaturated acyl chains. In addition to unsaturation, the headgroup and the phospholipid backbone (glycerol versus sphingosine) will also affect how cholesterol interacts with the PLs. Likely these interactions between cholesterol and different phospholipids plays a role in the formation of lateral membrane structure. In this project we study how cholesterol promotes the segregation of low and high Tm lipids into ordered and disordered domains.We have determined the formation of liquid-ordered phase with time-resolved fluorescence spectroscopy of trans-parinaric acid (tPA) in ternary bilayers containing cholesterol, palmitoyl-sphingomyelin (PSM) and different unsaturated PLs. The results were compared to results from cholesterol-free bilayers.The results showed that cholesterol lowered the amount of PSM needed to form liquid-ordered phase (Lo) compared to gel phase formation in cholesterol free bilayers. When the number of double bonds increased in the low Tm lipid, even lower amounts of PSM was needed to form Lo. We will further investigate if cholesterol have the same effect on formation of ordered phases when the high Tm lipid is varied and determine how the domain properties changes as a consequence.In conclusion, cholesterol enhances phase separation of low and high Tm lipids. The aversion of cholesterol for polyunsaturated PLs further enchases the phase separation. Altogether, this supports an important role of cholesterol to maintain and regulate lateral structure in biological membranes.

High Resolution Imaging Atomic Force Microscope Study of Interactions at the Membrane-Fluid Interface

The cell membrane is essential for all living systems, serving as a barrier between cells and their environment. It is typically composed of a lipid bilayer, containing embedded and/or anchored proteins that mediate different biological function such as energy conversion, signal transduction and solute transport [1]. To elucidate the basic structure of biological membranes it is necessary to make direct experimental observations of the molecular organization of the protein and lipid bilayer under physiologically relevant conditions. Using a bespoke high resolution Atomic Force Microscopy (AFM) it is possible to characterize the structure and function of both native and model lipid membranes with embedded proteins [2].During this study we focus our attention on transmembrane MvP voltage-gated potassium channels embedded in a lipid bilayer, which are activated by changes in transmembrane potential [3]. High resolution AFM images of the membrane channel reveal the predicted tetrameric channel structure of the ion channel. Interestingly, we observed the formation of an asymmetric depression in the supporting lipid membrane surrounding the channel. This may be due to an alteration in the lipid bilayer structure to accommodate the ion channel. Using AFM is possible to investigate the interactions between proteins and membrane- liquid interface [4], [5] aiding our understanding and leading to future therapeutic application.[1] D. J. Muller et al., Nature protocols, vol. 2, no. 9, pp. 2191--2197, 2007.[2] A. Sumino et al., Scientific reports, vol. 3, 2013.[3] A. M. Randich et al., Biochemistry, vol. 53, pp. 1627--1636, 2014.[4] K. H. Sheikh and S. P. Jarvis, Journal of the American Chemical Society, vol. 133, pp. 18296--18303, 2011.[5] U. M. Feber et al., Eur Biophys, vol. 40, pp. 329-338, 2011.

Fracture faces of frozen membranes: 50th anniversary.

In 1961, the development of an improved freeze-etching (FE) procedure to prepare rapidly frozen biological cells or tissues for electron microscopy raised two important questions. How does a frozen cell membrane fracture? What do the extensive face views of the cell’s membranes exposed by the fracture process of FE tell us about the overall structure of biological membranes? I discovered that all frozen membranes tend to split along weakly bonded lipid bilayers. Consequently, the fracture process exposes internal membrane faces rather than either of the membrane’s two external surfaces. During etching, when ice is allowed to sublime after fracturing, limited regions of the actual membrane surfaces are revealed. Examination of the fractured faces and etched surfaces provided strong evidence that biological membranes are organized as lipid bilayers with some proteins on the surface and other proteins extending through the bilayer. Membrane splitting made it possible for electron microscopy to show the relative proportion of a membrane’s area that exists in either of these two organizational modes.

Effect of the nature of phospholipids on the degree of their interaction with isobornylphenol antioxidants

The parameters of complexation between natural phospholipids (lecithin, sphingomyelin, and cephalin) with antioxidants of a new class, isobornylphenols (IBPs), were determined by UV and IR spectroscopy. The self-organization of phospholipids (PLs) was studied depending on the structure of IBPs by dynamic light scattering. The nature of phospholipids and the structure of IBPs was found to produce a substantial effect both on the degree of complexation and on the size of PL aggregates in a nonpolar solvent. Based on the obtained data it was concluded that the structure of biological membranes mainly depends on the complexation of IBP with sphingomyelin.

Biomimetic modification of large diameter carbon nanotubes and the desalination behavior of its reverse osmosis membrane

Based on the fact that wide diameter carbon nanotube (CNTs) has higher water conductance and lower cost than narrow one, this paper built a set of RO membranes with modified 1.35nm diameter CNTs (10,10) and calculated their desalinating properties by molecular dynamics simulations. Inspired by the structure of biological membrane which has perfect ion selectivity, different charged and polar groups (CONH2, NH3+, COO‐, OH) were added to the interior of CNTs. The potential of mean force (PMF), conductance and axial density distributions of water and ions in CNTs were examined under hydrostatic pressure. Results showed that water flux of 1.35nm diameter (10,10) unmodified CNTs was about 3 times of 1.1nm diameter (8,8) CNTs (Chen S. and Corry B., 2009) [1]. Compared to CNTs with functional groups at entrance, water flux of CNTs with modified groups in the interior decrease slightly, while salt rejection greatly improved. With certain number, type and position of functional groups (CONH2, NH3+, COO−), 100% salt rejection could be achieved without affecting water conductance evidently. Water flux of 100% salt rejection modified CNTs was from 146% to 167% of unmodified (8,8) CNT (Chen S. and Corry B., 2009) [1]. Compared to four functional groups (COO−, CONH2, OH) in the interior, one functional group added at entrance and four functional groups added in the interior could obtain both higher desalination and high water conductance.

Progress in study on the role of exosome-derived microRNA in diagnosis and treatment of diseases

Exosome is a kind of biological membrane structure at nanometer level. It is secreted by various cells in the body and widely distributed in most body fluids, such as saliva, blood, and milk. Biological active substances, including mRNAs, microRNAs, cytokines, and transcription factor, have been identified in the exosomes. MiRNAs are short and non-coding RNAs that modulate gene expression at the posttranscriptional level. MiRNAs extensively involves in henogenesis, cell proliferation and apoptosis. With various biological functions, exosome-derived miRNAs can not only be served as biomarkers to diagnose tumor, neurological diseases and mental disorders, but also possess potential as therapeutic targets.

Cholesterol Modified Self-Assemblies and Their Application to Nanomedicine.

Cholesterol is a ubiquitous molecule in biological systems, and in particular plays various important roles in mammalian cellular processes. The presence of cholesterol is integral to the structure and behavior of biological membranes, and profoundly influences membrane involvement in cellular mechanisms. This review focuses on the incorporation of cholesterol into synthetic nanomaterials and assemblies, focusing on LC phase behavior, morphology/self-organization and hydrophobic interactions, all important factors in the design of nanomedicines. We highlight cholesteryl conjugates, liposomes and polymeric micelles, focusing on self-assembly capabilities, drug encapsulation and intracellular delivery. An area of considerable interest identified in this review is the use of cholesteryl-functional vectors to deliver drugs or nucleic acids. Such applications depend on the ability of the nanoparticle carrier to associate with both the cellular and endosomal membrane.

ChemInform Abstract: Synthesis of Side Chain N,N′‐Diaminoalkylated Derivatives of Basic Amino Acids for Application in Solid‐Phase Peptide Synthesis

AbstractReview: 65 refs.

Lipid domains in model membranes: a brief historical perspective.

All biological membranes consist of a complex composite of macromolecules and macromolecular assemblies, of which the fluid lipid-bilayer component is a core element with regard to cell encapsulation and barrier properties. The fluid lipid bilayer also supports the functional machinery of receptors, channels and pumps that are associated with the membrane. This bilayer is stabilized by weak physical and colloidal forces, and its nature is that of a self-assembled system of amphiphiles in water. Being only approximately 5 nm in thickness and still encapsulating a cell that is three orders of magnitude larger in diameter, the lipid bilayer as a material has very unusual physical properties, both in terms of structure and dynamics. Although the lipid bilayer is a fluid, it has a distinct and structured trans-bilayer profile, and in the plane of the bilayer the various molecular components, viz different lipid species and membrane proteins, have the capacity to organize laterally in terms of differentiated domains on different length and time scales. These elements of small-scale structure and order are crucial for the functioning of the membrane. It has turned out to be difficult to quantitatively study the small-scale structure of biological membranes. A major part of the insight into membrane micro- and nano-domains and the concepts used to describe them have hence come from studies of simple lipid bilayers as models of membranes, by use of a wide range of theoretical, experimental and simulational approaches. Many questions remain to be answered as to which extent the result from model studies can carry over to real biological membranes.

Lipid peroxidation modifies the assembly of biological membranes "The Lipid Whisker Model".

When the Fluid Mosaic Model (FMM) of biological membrane structure was introduced 42 years ago, it was visualized as a basic model for cell membranes that could explain existing data on membrane proteins and lipid structures and their dynamics. According to the (FMM), a membrane was described as a biological fluid of proteins and lipids oriented in two dimensions. The basic structure of all cell and organelle membranes is the lipid bilayer. Protein molecules are distributed in different regions of the bilayer and perform diverse functions. Cell membranes are active, fluid structures, and most of their molecules are able to travel in the plane of the membrane (Singer and Nicolson, 1972). The viscosity of a lipid membrane largely depends on whether the acyl chains attached to glycerophospholipids are grouped into a rigid state or exist in a relatively disordered, fluid state. Long chain saturated fatty acids maximize Van der Waals forces, and increase the viscosity of the membrane (Chapman and Benga, 1984). Fluidity is defined as the ease of movement and represents the reciprocal of the viscosity of the membrane (Lee, 1991). The fluid properties of biological membranes are critical for various cell functions. Still slight changes in membrane fluidity may cause unusual function and pathological processes (Garcia et al., 2005). After more than 40 years, the (FMM), described by Singer and Nicolson is still relevant to recognize the structure, function, and dynamics of biological membranes (Nicolson, 2014). However, several biological processes cannot be explained on the basis of this typical phospholipid orientation and utilize other phospholipid conformations (Catala, 2012) that are described in this article.

Water and Lipid Bilayers.

Water is crucial to the structure and function of biological membranes. In fact, the membrane's basic structural unit, i.e. the lipid bilayer, is self-assembled and stabilized by the so-called hydrophobic effect, whereby lipid molecules unable to hydrogen bond with water aggregate in order to prevent their hydrophobic portions from being exposed to water. However, this is just the beginning of the lipid-bilayer-water relationship. This mutual interaction defines vesicle stability in solution, controls small molecule permeation, and defines the spacing between lamella in multi-lamellar systems, to name a few examples. This chapter will describe the structural and dynamical properties central to these, and other water- lipid bilayer interactions.

How Do Membranes Respond to Pressure?

Bilayers formed by phospholipids are fundamental structures of biological membranes. The mechanical perturbation brought about by pressure significantly affects the membrane states of phospholipid bilayers. In this chapter, we focus our attention on the pressure responsivity for bilayers of some major phospholipids contained in biological membranes. At first, the membrane states and phase transitions of phospholipid bilayers depending on water content, temperature and pressure are explained by using the bilayer phase diagrams of dipalmitoylphosphatidylcholine (DPPC), which is the most familiar phospholipid in model membrane studies. Subsequently, the thermotropic and barotropic bilayer phase behavior of various kinds of phospholipids with different molecular structures is discussed from the comparison of their temperature--pressure phase diagrams to that of the DPPC bilayer. It turns out that a slight change in the molecular structure of the phospholipids produces a significant difference in the bilayer phase behavior. The systematic pressure studies on the phase behavior of the phospholipid bilayers reveal not only the pressure responsivity for the bilayers but also the role and meaning of several important phospholipids existing in real biological membranes.

Solvent-assisted lipid bilayer formation on silicon dioxide and gold.

Planar lipid bilayers on solid supports mimic the fundamental structure of biological membranes and can be investigated using a wide range of surface-sensitive techniques. Despite these advantages, planar bilayer fabrication is challenging, and there are no simple universal methods to form such bilayers on diverse material substrates. One of the novel methods recently proposed and proven to form a planar bilayer on silicon dioxide involves lipid deposition in organic solvent and solvent exchange to influence the phase of adsorbed lipids. To scrutinize the specifics of this solvent-assisted lipid bilayer (SALB) formation method and clarify the limits of its applicability, we have developed a simplified, continuous solvent-exchange version to form planar bilayers on silicon dioxide, gold, and alkanethiol-coated gold (in the latter case, a lipid monolayer is formed to yield a hybrid bilayer) and varied the type of organic solvent and rate of solvent exchange. By tracking the SALB formation process with simultaneous quartz crystal microbalance-dissipation (QCM-D) and ellipsometry, it was determined that the acoustic, optical, and hydration masses along with the acoustic and optical thicknesses, measured at the end of the process, are comparable to those observed by employing conventional fabrication methods (e.g., vesicle fusion). As shown by QCM-D measurements, the obtained planar bilayers are highly resistant to protein adsorption, and several, but not all, water-miscible organic solvents could be successfully used in the SALB procedure, with isopropanol yielding particularly high-quality bilayers. In addition, fluorescence recovery after photobleaching (FRAP) measurements demonstrated that the coefficient of lateral lipid diffusion in the fabricated bilayers corresponds to that measured earlier in the planar bilayers formed by vesicle fusion. With increasing rate of solvent exchange, it was also observed that the bilayer became incomplete and a phenomenological model was developed in order to explain this feature. The results obtained allowed us to clarify and discriminate likely steps of the SALB formation process as well as determine the corresponding influence of organic solvent type and flow conditions on these steps. Taken together, the findings demonstrate that the SALB formation method can be adapted to a continuous solvent-exchange procedure that is technically minimal, quick, and efficient to form planar bilayers on solid supports.

بررسی بیان ژن های طویل ساز گونه Mortirella alpine در شرایط مناسب تولید آراشیدونیک اسید و روغن

بررسی بیان ژن های طویل ساز گونه Mortirella alpine در شرایط مناسب تولید آراشیدونیک اسید و روغن

Ceramide–lipid interactions studied by MD simulations and solid-state NMR

Ceramides play a key modulatory role in many cellular processes, which results from their effect on the structure and dynamics of biological membranes. In this study, we investigate the influence of C16-ceramide (C16) on the biophysical properties of DMPC lipid bilayers using solid-state NMR and atomistic molecular dynamics (MD) simulations. MD simulations and NMR measurements were carried out for a pure DMPC bilayer and for a 20% DMPC–C16 mixture. Calculated key structural properties, namely area per lipid, chain order parameters, and mass density profiles, indicate that C16 has an ordering effect on the DMPC bilayer. Furthermore, the simulations predict that specific hydrogen-bonds form between DMPC and C16 molecules. Multi-nuclear solid-state NMR was used to verify these theoretical predictions. Chain order parameters extracted from 13C1H dipole couplings were measured for both lipid and ceramide and follow the trend suggested by the MD simulations. Furthermore, 1H-MAS NMR experiments showed a direct contact between ceramide and lipids.

Choline Plasmalogens Isolated from Swine Liver Inhibit Hepatoma Cell Proliferation Associated with Caveolin-1/Akt Signaling

Plasmalogens play multiple roles in the structures of biological membranes, cell membrane lipid homeostasis and human diseases. We report the isolation and identification of choline plasmalogens (ChoPlas) from swine liver by high performance thin layer chromatography (HPTLC) and high performance liquid chromatography (HPLC)/MS. The growth and viability of hepatoma cells (CBRH7919, HepG2 and SMMC7721) was determined following ChoPlas treatment comparing with that of human normal immortal cell lines (HL7702). Result indicated that ChoPlas inhibited hepatoma cell proliferation with an optimal concentration and time of 25 μmol/L and 24 h. To better understand the mechanism of the ChoPlas-induced inhibition of hepatoma cell proliferation, Caveolin-1 and PI3K/Akt pathway signals, including total Akt, phospho-Akt(pAkt) and Bcl-2 expression in CBRH7919 cells, were determined by western blot. ChoPlas treatment increased Caveolin-1 expression and reduced the expression of phospho-Akt (pAkt) and Bcl-2, downstream targets of the PI3K/Akt pathway. Further cell cycle analysis showed that ChoPlas treatment induced G1 and G1/S phase transition cell cycle arrest. The expression of essential cell cycle regulatory proteins involved in the G1 and G1/S phase transitions, cyclin D, CDK4, cyclin E and CDK2, were also analyzed by western blot. ChoPlas reduced CDK4, cyclin E and CDK2 expression. Taken together, the results indicate that swine liver-derived natural ChoPlas inhibits hepatoma cell proliferation associated with Caveolin-1 and PI3K/Akt signals.

Identification and Quantitation of Fatty Acid Double Bond Positional Isomers: A Shotgun Lipidomics Approach Using Charge-Switch Derivatization

The specific locations of double bonds in mammalian lipids have profound effects on biological membrane structure, dynamics and lipid second messenger production. Herein, we describe a shotgun lipidomics approach that exploits charge-switch derivatization with N-(4-aminomethylphenyl) pyridinium (AMPP) and tandem mass spectrometry for identification and quantification of fatty acid double bond positional isomers. Through charge-switch derivatization of fatty acids followed by positive-ion mode ionization and fragmentation analysis, a marked increase in analytic sensitivity (low fmol/μL) and the identification of double bond positional isomers can be obtained. Specifically, the locations of proximal double bonds in AMPP-derivatized fatty acids are identified by diagnostic fragment ions resulting from the markedly reduced 1,4-hydrogen elimination from the proximal olefinic carbons. Additional fragmentation patterns resulting from allylic cleavages further substantiated the double bond position assignments. Moreover, quantification of fatty acid double bond positional isomers is achieved by the linear relationship of the normalized intensities of characteristic fragment ions vs the isomeric compositions of discrete fatty acid positional isomers. The application of this approach for the analysis of fatty acids in human serum demonstrated the existence of two double bond isomers of linolenic acid (i.e., Δ(6,9,12) 18:3, γ-linolenic acid (GLA), and Δ(9,12,15) 18:3, α-linolenic acid (ALA)). Remarkably, the isomeric ratio of GLA vs ALA esterified in neutral lipids was 3-fold higher than the ratio of their nonesterified moieties. Through this developed method, previously underestimated or unidentified alterations in fatty acid structural isomers can be determined facilitating the identification of novel biomarkers and maladaptive alterations in lipid metabolism during disease.

Structural studies of biological membranes using ESEEM spectroscopy of spin labels and deuterium substitution

Electron Spin Echo Envelope Modulation (ESEEM) spectroscopy in conjunction with biochemical techniques of site-directed spin labeling and deuterium substitution in molecules or parts of molecules can be used to gain insights into supramolecular structure of biological membranes. The review covers the applications of this approach to study water penetration into the hydrophobic part of model phospholipid membranes and into the ion channels of biological membranes, to determine the localization and orientation of peptide antibiotics in membranes, and to investigate the conformations of enzymes and membrane proteins.

1H NMR-Based Metabolomic Analysis of Sub-Lethal Perfluorooctane Sulfonate Exposure to the Earthworm, Eisenia fetida, in Soil.

1H NMR-based metabolomics was used to measure the response of Eisenia fetida earthworms after exposure to sub-lethal concentrations of perfluorooctane sulfonate (PFOS) in soil. Earthworms were exposed to a range of PFOS concentrations (five, 10, 25, 50, 100 or 150 mg/kg) for two, seven and fourteen days. Earthworm tissues were extracted and analyzed by 1H NMR. Multivariate statistical analysis of the metabolic response of E. fetida to PFOS exposure identified time-dependent responses that were comprised of two separate modes of action: a non-polar narcosis type mechanism after two days of exposure and increased fatty acid oxidation after seven and fourteen days of exposure. Univariate statistical analysis revealed that 2-hexyl-5-ethyl-3-furansulfonate (HEFS), betaine, leucine, arginine, glutamate, maltose and ATP are potential indicators of PFOS exposure, as the concentrations of these metabolites fluctuated significantly. Overall, NMR-based metabolomic analysis suggests elevated fatty acid oxidation, disruption in energy metabolism and biological membrane structure and a possible interruption of ATP synthesis. These conclusions obtained from analysis of the metabolic profile in response to sub-lethal PFOS exposure indicates that NMR-based metabolomics is an excellent discovery tool when the mode of action (MOA) of contaminants is not clearly defined.

Effects of high hydrostatic pressure on the dynamic structure of living Escherichia coli membrane: a study using high pressure time-resolved fluorescence anisotropy measurement

High hydrostatic pressure has a significant impact on the structure of biological membranes. Here, we elucidated the effects of hydrostatic pressure on a model palmitoyl-oleylphosphatidylcholine (POPC) membrane and a natural membrane of mesophilic Escherichia coli by means of time-resolved fluorescence anisotropy measurement using 1-[4-(trimethylamino)phenyl]-6-phenyl-1,3,5-hexatriene (TMA-DPH). Hydrostatic pressure of 50 MPa increased the order parameter S of the E. coli cell membrane from 0.782 to 0.815 at 37°C and it markedly reduced the rotational diffusion coefficient D w of TMA-DPH to 69.4% of that observed at 0.1 MPa. High pressure exerted similar effects on the living E. coli cell membrane to those obtained with POPC in terms of the changes in S and D w . Therefore, the dynamic behavior of the natural membrane in response to high pressure could in part be deduced from studies of the model membrane as long as the membrane is in the liquid-crystalline phase.