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1.
Biophys J ; 122(11): 1926-1937, 2023 06 06.
Artículo en Inglés | MEDLINE | ID: mdl-35986516

RESUMEN

Galectin-3 (Gal-3) is a ß-galactosidase-binding protein involved in various biological processes, including neuronal growth and adhesion. The pairing of Gal-3 with ganglioside GM1's pentasaccharide chain at the outer leaflet of the plasma membrane, which triggers downstream cell-signaling cascades, seems to be involved in these processes. A crucial feature of Gal-3 is its ability to form oligomers and supramolecular assemblies that connect various carbohydrate-decorated molecules. Although we know the atomistic structure of Gal-3 bound to small carbohydrate ligands, it remains unclear how Gal-3 binds GM1 in a membrane. Furthermore, the influence of this interaction on Gal-3's structure and oligomeric assembly has to be elucidated. In this study, we used X-ray reflectivity (XR) from a model membrane to determine the structure and surface coverage of Gal-3 bound to a membrane containing GM1. We observed that the carbohydrate recognition domain interacts with GM1's pentasaccharide, while the N-terminal domain is pointed away from the membrane, likely to facilitate protein-protein interactions. In a membrane containing 20 mol % GM1, Gal-3 covered ∼50% of the membrane surface with one Gal-3 molecule bound per 2130 Å2. We used molecular dynamics simulations and Voronoi tessellation algorithms to build an atomistic model of membrane-bound Gal-3, which is supported by the XR results. Overall, this work provides structural information describing how Gal-3 can bind GM1's pentasaccharide chain, a prerequisite for triggering regulatory processes in neuronal growth and adhesion.


Asunto(s)
Gangliósido G(M1) , Galectina 3 , Gangliósido G(M1)/química , Galectina 3/metabolismo , Gangliósidos , Membrana Celular/metabolismo , Simulación de Dinámica Molecular
2.
Langmuir ; 38(22): 6959-6966, 2022 06 07.
Artículo en Inglés | MEDLINE | ID: mdl-35604017

RESUMEN

We report neutron reflectometry (NR) studies of polyethylene glycol (PEG)-tethered model lipid membranes at the solid-liquid interface and of cholera toxin's B-subunit (CTxB) binding to tethered membranes containing ganglioside GM1 receptors. First, tethered polymer brushes were formed by grafting silane-functionalized PEG lipopolymers to quartz from solution. Subsequent deposition of lipids by Langmuir-Blodgett/Langmuir-Schaefer (LB/LS) resulted in a tethered bilayer structure separated from the solid support by a hydrated PEG layer. NR revealed that the tethers formed a highly hydrated polymer brush, uniformly separating the bilayer from the underlying solid substrate. Further, the lipid bilayer did not significantly perturb the brush's conformation relative to a free brush. Biological functionality of the tethered bilayers was verified by interacting CTxB, with ganglioside GM1 receptors incorporated into the bilayer. The surface coverage of CTxB bound to the lipid membrane, θCTB= 0.58 ± 0.08, was consistent with the coverage predicted for random sequential absorption, and toxin binding did not impact the membrane conformation.


Asunto(s)
Toxina del Cólera , Gangliósido G(M1) , Toxina del Cólera/metabolismo , Gangliósido G(M1)/metabolismo , Membrana Dobles de Lípidos/química , Polietilenglicoles/química , Polímeros/química
3.
ACS Appl Mater Interfaces ; 12(1): 1825-1831, 2020 Jan 08.
Artículo en Inglés | MEDLINE | ID: mdl-31820621

RESUMEN

Interactions between a catalyst and electrolyte have paramount importance for the performance of electrochemical devices. Here, we present the cation-hydroxide-water coadsorption on the Pt surface by a rotating disk electrode and neutron reflectometry. The rotating disk electrode experiments show that the current density of Pt rapidly dropped at hydrogen oxidation potentials due to tetramethylammonium hydroxide (TMAOH)-water coadsorption. Subsequent neutron reflectometry in 0.1 M TMAOD/D2O reveals that the thickness of the coadsorbed layer increased to 18 Å after 10.5 h exposure at 0.1 V vs reverse hydrogen electrode (RHE). The scattering length density analysis revealed that the TMAOD to water ratio in the coadsorbed layer was 4.5, which was significantly higher than the reportedly highest TMAOH concentration in aqueous solution. Finally, we discuss the potential impact of the coadsorbed layer on the performance and durability of alkaline membrane fuel cells, which sheds light on the material design of high-performance alkaline electrochemical devices.

4.
Langmuir ; 35(48): 16024-16036, 2019 12 03.
Artículo en Inglés | MEDLINE | ID: mdl-31509701

RESUMEN

In Alzheimer's disease, the amyloid-beta peptide (Aß) is implicated in neuronal toxicity via interactions with the cell membrane. Monomeric Aß (Aßm) is intrinsically disordered, but it can adopt a range of aggregated conformations with varying toxicities from short fibrillar oligomers (FO), to globular nonfibrillar oligomers (NFO), and full-length amyloid fibrils. NFO is considered to be the most toxic, followed by fibrils, and finally Aßm. To elucidate molecular-level membrane interactions that contribute to their different toxicities, we used liquid surface X-ray scattering and Langmuir trough insertion assays to compare Aßm, FO, and NFO surface activities and interactions with anionic DMPG lipid monolayers at the air/water interface. All Aß species were highly surface active and rapidly adopted ß-sheet rich structures upon adsorption to the air/water interface. Likewise, all Aß species had affinity for the anionic membrane. Aßm rapidly converted to ß-sheet rich assemblies upon binding the membrane, and these aggregated structures of Aßm and FO disrupted hexagonally packed lipid domains and resulted in membrane thinning and instability. In contrast, NFO perturbed membrane structure by extracting lipids from the air/water interface and causing macroscale membrane deformations. Altogether, our results support two models for membrane-mediated Aß toxicity: fibril-induced reorganization of lipid packing and NFO-induced membrane destabilization and lipid extraction. This work provides a structural understanding of Aß neurotoxicity via membrane interactions and aids the effort in understanding early events in Alzheimer's disease and other neurodegenerative diseases.


Asunto(s)
Péptidos beta-Amiloides/química , Adsorción , Aniones , Membranas Artificiales , Fosfolípidos/química , Conformación Proteica
5.
Nano Lett ; 19(10): 7365-7369, 2019 10 09.
Artículo en Inglés | MEDLINE | ID: mdl-31538793

RESUMEN

Biomembranes are hard to compress laterally, and membrane area compressibility has not been associated with biological processes. Using X-ray surface scattering, we observed that bacterial Shiga toxin compresses lipid packing in a gel phase monolayer upon binding to its cellular receptor, the glycolipid Gb3. This toxin-induced reorganization of lipid packing reached beyond the immediate membrane patch that the protein was bound to, and linkers separating the Gb3 carbohydrate and ceramide moieties modulated the toxin's capacity to compress the membrane. Within a natural membrane, asymmetric compression of the toxin-bound leaflet could provide a mechanism to initiate narrow membrane bending, as observed upon toxin entry into cells. Such lipid compression and long-range membrane reorganization by glycolipid-binding proteins represent novel concepts in membrane biology that have direct implications for the construction of endocytic pits in clathrin-independent endocytosis.


Asunto(s)
Membrana Celular/metabolismo , Fosfatidiletanolaminas/metabolismo , Toxina Shiga/metabolismo , Shigella dysenteriae/metabolismo , Trihexosilceramidas/metabolismo , Disentería Bacilar/metabolismo , Endocitosis , Humanos , Modelos Moleculares
6.
Biophys J ; 114(5): 1103-1115, 2018 03 13.
Artículo en Inglés | MEDLINE | ID: mdl-29539397

RESUMEN

The influence of carbohydrate structure on the ordering of glycosphingolipids (GSLs) and surrounding phospholipids was investigated in monolayers at the air-water interface. Binary mixtures composed of GSLs, chosen to span a range of carbohydrate complexity, and zwitterionic dipalmitoylphosphatidylcholine phospholipid, were studied. X-ray reflectivity was used to measure the out-of-plane structure of the monolayers and characterize the extension and conformation of the GSL carbohydrates. Using synchrotron grazing incidence x-ray diffraction, the in-plane packing of the lipid acyl chains and the area per molecule within ordered domains were characterized at different mole ratios of the two components. Our findings indicate that GSL-containing mixtures, regardless of the carbohydrate size, enhance the ordering of the surrounding lipids, resulting in a larger fraction of ordered phase of the monolayer and greater dimensions of the ordered domains. Reduction of the averaged area per molecule within the ordered domains was also observed but only in the cases where there was a size mismatch between the phospholipid headgroups and GSL components, suggesting that the condensation mechanism involves the relief of steric interactions between headgroups in mixtures.


Asunto(s)
Carbohidratos/química , Glicoesfingolípidos/química , Difracción de Rayos X
7.
Langmuir ; 33(38): 9988-9996, 2017 09 26.
Artículo en Inglés | MEDLINE | ID: mdl-28845995

RESUMEN

OprF has a central role in Pseudomonas aeruginosa virulence and thus provides a putative target for either vaccines or antibiotic cofactors that could overcome the bacterium's natural resistance to antibiotics. Here we describe a procedure to optimize the production of highly pure and functional OprF porins that are then incorporated into a tethered lipid bilayer. This is a stable biomimetic system that provides the capability to investigate structural aspects and function of OprF using and neutron reflectometry and electrical impedance spectroscopy. The recombinant OprF produced using the optimized cell-free procedure yielded a quantity of between 0.5 to 1.0 mg/mL with a purity ranging from 85 to 91% in the proteoliposomes. The recombinant OprF is capable of binding IFN-γ and is correctly folded in the proteoliposomes. Because OprF proteins form pores the biomimetic system allowed the measurement of OprF conductance using impedance spectroscopy. The neutron reflectometry measurements showed that the OprF protein is incorporated into the lipid bilayer but with parts of the protein in both the regions above and below the lipid bilayer. Those structural aspects are coherent with the current assumed structure of a transmembrane N-terminal domain composed by eight stranded beta-barrels and a globular C-terminal domain located in the periplasm. Currently there are no crystal structures available for OprF. The experimental model system that we describe provides a basis for further fundamental studies of OprF and particularly for the ongoing biotechnological development of OprF as a target for antibacterial drugs.


Asunto(s)
Pseudomonas aeruginosa , Fenómenos Biofísicos , Membrana Dobles de Lípidos , Porinas , Conformación Proteica
8.
Langmuir ; 33(32): 7896-7907, 2017 08 15.
Artículo en Inglés | MEDLINE | ID: mdl-28715198

RESUMEN

Cellulose nanocrystals (CNCs) are promising biosourced building blocks for the production of high performance materials. In the last ten years, CNCs have been used in conjunction with polymers for the design of multilayered thin films via the layer-by-layer assembly technique. Herein, polymer chains have been replaced with positively charged inorganic gibbsite nanoplatelets (GN) to form hybrid "nanoparticle-only" composite films. A combination of atomic force microscopy and neutron reflectivity experiments was exploited to investigate the growth and structure of the films. Data show that the growth and density of GN/CNC films can be tuned over a wide range during preparation by varying the ionic strength in the CNC suspension and the film drying protocol. Specifically, thin and dense multilayered films or very thick, more porous mixed slabs, as well as intermediate internal structures, could be obtained in a predictable manner. The influence of key physicochemical parameters on the multilayer film buildup was elucidated and the film architecture was linked to the dominating interaction forces between the components. The degree of structural control over these hybrid nanoparticle-only films is much higher than that reported for CNC/polymer films, which offers new properties and potential applications as separation membranes or flame retardant coatings.

9.
Sci Rep ; 7(1): 3399, 2017 06 13.
Artículo en Inglés | MEDLINE | ID: mdl-28611396

RESUMEN

The structure of the p7 viroporin, an oligomeric membrane protein ion channel involved in the assembly and release of the hepatitis C virus, was determined from proteins expressed and inserted directly into supported model lipid membranes using cell-free protein expression. Cell-free protein expression allowed (i ) high protein concentration in the membrane, (ii ) control of the protein's isotopic constitution, and (iii ) control over the lipid environment available to the protein. Here, we used cell-free protein synthesis to directly incorporate the hepatitis C virus (HCV) p7 protein into supported lipid bilayers formed from physiologically relevant lipids (POPC or asolectin) for both direct structural measurements using neutron reflectivity (NR) and conductance measurements using electrical impedance spectroscopy (EIS). We report that HCV p7 from genotype 1a strain H77 adopts a conical shape within lipid bilayers and forms a viroporin upon oligomerization, confirmed by EIS conductance measurements. This combination of techniques represents a novel approach to the study of membrane proteins and, through the use of selective deuteration of particular amino acids to enhance neutron scattering contrast, has the promise to become a powerful tool for characterizing the protein conformation in physiologically relevant environments and for the development of biosensor applications.


Asunto(s)
Membrana Celular/química , Membrana Dobles de Lípidos/química , Lípidos de la Membrana/química , Neutrones , Biosíntesis de Proteínas , Proteínas Virales/química , Membrana Celular/metabolismo , Membrana Dobles de Lípidos/metabolismo , Lípidos de la Membrana/metabolismo , Modelos Moleculares , Conformación Proteica , Proteínas Virales/metabolismo
10.
Nano Lett ; 17(1): 476-485, 2017 01 11.
Artículo en Inglés | MEDLINE | ID: mdl-28073257

RESUMEN

Proteins are key components in a multitude of biological processes, of which the functions carried out by transmembrane (membrane-spanning) proteins are especially demanding for investigations. This is because this class of protein needs to be incorporated into a lipid bilayer representing its native environment, and in addition, many experimental conditions also require a solid support for stabilization and analytical purposes. The solid support substrate may, however, limit the protein functionality due to protein-material interactions and a lack of physical space. We have in this work tailored the pore size and pore ordering of a mesoporous silica thin film to match the native cell-membrane arrangement of the transmembrane protein human aquaporin 4 (hAQP4). Using neutron reflectivity (NR), we provide evidence of how substrate pores host the bulky water-soluble domain of hAQP4, which is shown to extend 7.2 nm into the pores of the substrate. Complementary surface analytical tools, including quartz crystal microbalance with dissipation monitoring (QCM-D) and fluorescence microscopy, revealed successful protein-containing supported lipid bilayer (pSLB) formation on mesoporous silica substrates, whereas pSLB formation was hampered on nonporous silica. Additionally, electron microscopy (TEM and SEM), light scattering (DLS and stopped-flow), and small-angle X-ray scattering (SAXS) were employed to provide a comprehensive characterization of this novel hybrid organic-inorganic interface, the tailoring of which is likely to be generally applicable to improve the function and stability of a broad range of membrane proteins containing water-soluble domains.


Asunto(s)
Acuaporina 4/química , Membrana Dobles de Lípidos/química , Nanoestructuras/química , Dióxido de Silicio/química , Humanos , Tamaño de la Partícula , Porosidad
11.
Eur Phys J E Soft Matter ; 39(12): 123, 2016 Dec.
Artículo en Inglés | MEDLINE | ID: mdl-27966072

RESUMEN

Tethered lipid bilayer membranes (tBLM) are planar membranes composed of free lipids and molecules tethered to a solid planar substrate providing a useful model of biological membranes for a wide range of biophysical studies and biotechnological applications. The properties of the tBLM depend on the free lipids and on the chemistry of the tethering molecules. We present a nanoscale characterization of a tBLM composed of deuterated 1,2-dimyristoyl-sn-glycero-3-phosphocholine (d-DMPC) free lipids, benzyl disulfide undecaethylene glycol phytanol (DLP) tethering molecules, and benzyl disulfiide tetraethylene glycol polar spacer molecules (PSM) used to control the areal density of tethering molecules through coadsorption. The use of selected isotopic substitution provides a way to distinguish the conformation and location of the tethered lipids from the free lipids and to elucidate how the two components influence the structure of the tBLM. These findings provide useful information to optimise the insertion of transmembrane proteins into the tethered bilayer system.


Asunto(s)
Oro/química , Membrana Dobles de Lípidos/química , Nanoestructuras/química , Materiales Biomiméticos/química , Membrana Celular/química , Dimiristoilfosfatidilcolina/química , Conformación Molecular
12.
Angew Chem Int Ed Engl ; 55(32): 9326-30, 2016 08 01.
Artículo en Inglés | MEDLINE | ID: mdl-27320727

RESUMEN

Knowledge of the (supra)molecular structure of an interface that contains amphiphilic ligand molecules is necessary for a full understanding of ion transfer during solvent extraction. Even if molecular dynamics already yield some insight in the molecular configurations in solution, hardly any experimental data giving access to distributions of both extractant molecules and ions at the liquid-liquid interface exist. Here, the combined application of X-ray and neutron reflectivity measurements represents a key milestone in the deduction of the interfacial structure and potential with respect to two different lipophilic ligands. Indeed, we show for the first time that hard trivalent cations can be repelled or attracted by the extractant-enriched interface according to the nature of the ligand.

13.
Langmuir ; 32(17): 4382-91, 2016 05 03.
Artículo en Inglés | MEDLINE | ID: mdl-27065348

RESUMEN

Neutron reflectivity (NR) and fluorescent microscopy (FM) were used to study the interactions of human (hIAPP) and rat (rIAPP) islet amyloid polypeptides with several formulations of supported model lipid bilayers at the solid-liquid interface. Aggregation and deposition of islet amyloid polypeptide is correlated with the pathology of many diseases, including Alzheimer's, Parkinson, and type II diabetes (T2DM). A central component of T2DM pathology is the deposition of fibrils in the endocrine pancreas, which is toxic to the insulin secreting ß-cells. The molecular mechanism by which the cell death occurs is not yet understood, but existing evidence points toward interactions of IAPP oligomers with cellular membranes in a manner leading to loss of their integrity. Our NR and FM results showed that the human sequence variant, hIAPP, had little or no effect on bilayers composed of saturated-acyl chains like zwitterionic DPPC, anionic DPPG, and mixed 80:20 mol % DPPC:DPPG bilayers. In marked contrast, the bilayer structure and stability of anionic unsaturated DOPG were sensitive to protein interaction, and the bilayer was partly solubilized by hIAPP under the conditions used here. The rIAPP, which is considered less toxic, had no perturbing effects on any of the above membrane formulations. Understanding the conditions that result in membrane disruption by hIAPP can be crucial in developing counter strategies to fight T2DM and also physicochemically similar neurodegenerative diseases such as Alzheimer's.


Asunto(s)
Polipéptido Amiloide de los Islotes Pancreáticos/farmacología , Membrana Dobles de Lípidos/química , Difracción de Neutrones , Animales , Humanos , Polipéptido Amiloide de los Islotes Pancreáticos/química , Microscopía Fluorescente , Modelos Moleculares , Conformación Proteica , Ratas
14.
Biointerphases ; 11(1): 011002, 2015 Mar 29.
Artículo en Inglés | MEDLINE | ID: mdl-26714450

RESUMEN

Permanent implants made from titanium are widely used and successfully implemented in medicine to address problems related to orthopedic and oral disorders. However, implants that interact in all cases optimally and durably with bone tissue have yet to be developed. Here, the authors suggest a phospholipids 1-palmitoyl-2-oleoyl-sn-glycero-3-phospho-ethanolamine (POPE) lipid coating to partially mimic the biological cell membrane. To improve the homogeneity of the POPE distribution on the metal surface, the lipids are applied by spray coating. It is shown that the spray coating leads to two types of multilamellar POPE structures. Our experimental results demonstrate that these coatings are stable in a liquid environment in the range of physiological temperatures due to the unique interbilayer interaction of POPE lipids. Additionally, the interaction of the POPE multilayer structure with human serum albumin is considered. A simultaneous analysis of the specular and off-specular data provides structural information necessary to assess the quality of the coating for future applications.


Asunto(s)
Materiales Biocompatibles Revestidos/química , Difracción de Neutrones/métodos , Fosfatidiletanolaminas/análisis , Propiedades de Superficie , Titanio , Aerosoles , Humanos , Unión Proteica , Albúmina Sérica/metabolismo , Temperatura
15.
Biointerphases ; 10(1): 019014, 2015 Mar 16.
Artículo en Inglés | MEDLINE | ID: mdl-25779088

RESUMEN

Because of its high sensitivity for light elements and the scattering contrast manipulation via isotopic substitutions, neutron reflectometry (NR) is an excellent tool for studying the structure of soft-condensed material. These materials include model biophysical systems as well as in situ living tissue at the solid-liquid interface. The penetrability of neutrons makes NR suitable for probing thin films with thicknesses of 5-5000 Å at various buried, for example, solid-liquid, interfaces [J. Daillant and A. Gibaud, Lect. Notes Phys. 770, 133 (2009); G. Fragneto-Cusani, J. Phys.: Condens. Matter 13, 4973 (2001); J. Penfold, Curr. Opin. Colloid Interface Sci. 7, 139 (2002)]. Over the past two decades, NR has evolved to become a key tool in the characterization of biological and biomimetic thin films. In the current report, the authors would like to highlight some of our recent accomplishments in utilizing NR to study highly complex systems, including in-situ experiments. Such studies will result in a much better understanding of complex biological problems, have significant medical impact by suggesting innovative treatment, and advance the development of highly functionalized biomimetic materials.


Asunto(s)
Técnicas de Química Analítica/métodos , Mezclas Complejas/química , Membranas/química , Neutrones
16.
Biophys J ; 107(5): 1146-1155, 2014 Sep 02.
Artículo en Inglés | MEDLINE | ID: mdl-25185550

RESUMEN

Globotriaosylceramide (Gb3), a glycosphingolipid found in the plasma membrane of animal cells, is the endocytic receptor of the bacterial Shiga toxin. Using x-ray reflectivity (XR) and grazing incidence x-ray diffraction (GIXD), lipid monolayers containing Gb3 were investigated at the air-water interface. XR probed Gb3 carbohydrate conformation normal to the interface, whereas GIXD precisely characterized Gb3's influence on acyl chain in-plane packing and area per molecule (APM). Two phospholipids, 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC) and 1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine (DPPE), were used to study Gb3 packing in different lipid environments. Furthermore, the impact on monolayer structure of a naturally extracted Gb3 mixture was compared to synthetic Gb3 species with uniquely defined acyl chain structures. XR results showed that lipid environment and Gb3 acyl chain structure impact carbohydrate conformation with greater solvent accessibility observed for smaller phospholipid headgroups and long Gb3 acyl chains. In general, GIXD showed that Gb3 condensed phospholipid packing resulting in smaller APM than predicted by ideal mixing. Gb3's capacity to condense APM was larger for DSPC monolayers and exhibited different dependencies on acyl chain structure depending on the lipid environment. The interplay between Gb3-induced changes in lipid packing and the lipid environment's impact on carbohydrate conformation has broad implications for glycosphingolipid macromolecule recognition and ligand binding.


Asunto(s)
Trihexosilceramidas/química , Aire , Animales , Conformación de Carbohidratos , Eritrocitos/química , Fosfatidilcolinas/química , Fosfatidiletanolaminas/química , Presión , Solventes/química , Propiedades de Superficie , Porcinos , Agua , Difracción de Rayos X
17.
J Phys Chem B ; 118(40): 11835-48, 2014 Oct 09.
Artículo en Inglés | MEDLINE | ID: mdl-25203770

RESUMEN

We have determined how the bulk behavior of mixtures of small cationic poly(amidoamine) dendrimers (generation 2, PAMAM-G2) and sodium dodecyl sulfate (SDS) affects the structure and composition of the adsorbed layers at the air-water interface. The aim is to reveal how the size of a well-defined hyperbranched polyelectrolyte affects the interfacial and bulk solution behavior of mixtures with oppositely charged surfactants, when the size of the polyelectrolyte approaches that of the surfactant. A combination of electrophoretic mobility, UV-vis spectroscopy, dynamic light scattering, and small-angle X-ray scattering measurements have been employed to characterize the interactions in the bulk solution. PAMAM-G2 associates strongly with SDS in the bulk, forming large aggregates where the size and the charge depend on the bulk composition. We show that kinetically trapped aggregates can be formed at compositions outside the equilibrium two-phase region, and the positively charged aggregates are larger than the negative ones. Surface tensiometry, neutron reflectometry, and ellipsometry have been used to reveal the properties of the interfacial layers. The interfacial structures formed depend strongly on the bulk composition: structured layers are present for samples inside the two-phase region, whereas intact nanostructured aggregates adsorb for samples just outside the two-phase region. The interfacial behavior of PAMAM-G2/SDS mixtures is compared with that of small amines or multivalent ions and oppositely charged surfactants. The implications of aggregate adsorption, dissociation, and spreading processes are discussed as well as the potential of small dendrimers for applications involving the delivery of functional molecules to interfaces.

18.
Anal Bioanal Chem ; 406(19): 4725-33, 2014 Jul.
Artículo en Inglés | MEDLINE | ID: mdl-24842403

RESUMEN

The thickness and refractive index of 1,2-dipalmitoyl-sn-glycero-3-phosphatidyl choline (DPPC) and 1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine (DPPE) monolayers Langmuir--Blodgett (LB) deposited on mica were measured in dry air and bulk water using multiple-beam interferometry (MBI). Measurements of thickness using atomic force microscopy (AFM) of identical monolayers, and X-ray reflectivity (XRR) of the monolayers on quartz were taken for comparison. The measurement of the properties of solid-supported monolayers in dry air allows lipid optical properties to be determined free from solvent effects. The thickness and refractive index measured by MBI were 25.5 ± 0.6 Å and 1.485 ± 0.007 for DPPE monolayers, and 23.9 ± 0.5 Å and 1.478 ± 0.006 for DPPC monolayers in dry air. These thicknesses are consistent with the other techniques used in this work as well as other measurements in the literature. The refractive indices of solid-supported lipid monolayers have not been previously measured. The values are higher than previous measurements on black lipid films done by reflectometry, which is attributed to increased lipid packing density and the absence of hydrocarbon solvents. Applying water to the monolayers had no measurable effect on their properties, indicating that any change in hydration was below detection.


Asunto(s)
1,2-Dipalmitoilfosfatidilcolina/química , Interferometría/métodos , Membrana Dobles de Lípidos/química , Microscopía de Fuerza Atómica/métodos , Fosfatidiletanolaminas/química , Refractometría/métodos
19.
ACS Nano ; 8(4): 3181-91, 2014 Apr 22.
Artículo en Inglés | MEDLINE | ID: mdl-24601564

RESUMEN

In this work, we establish fundamental differences between the structure and packing of lipids in monolayers, supported bilayers, and multilayer films. High resolution grazing incidence X-ray diffraction reveals that monolayer structure is largely retained upon deposition onto substrates with the area per molecule controlled by deposition pressure. Such structural changes are consistent with a quenched rather than equilibrated supported membrane structure. Supported bilayers formed by vesicle fusion exhibit structural similarity to bilayers deposited at 38 mN/m, whereas packing in lipid multilayers more closely resembled bilayers deposited below 30 mN/m. At the molecular level, coupling between opposing lipid acyl chains is observed for all deposition pressures with the outer leaflet templating on the inner leaflet. Leaflet coupling induces a small condensation in the area per lipid molecule and a surprising increase in acyl chain tilt. Moreover, supported lipid bilayers exhibit preferential acyl chain alignment: the system cannot be modeled with freely rotating acyl chains as in free-standing lipid monolayers. Such acyl chain alignment is consistent with orientational texture of lipid tilt directors at larger length scales. These findings clearly demonstrate that supported, gel-phase bilayer membrane structure can be controlled and maintained by deposition onto solid supports and that increasing surface pressure induces preferential alignment of the acyl chains both within and between membrane leaflets.


Asunto(s)
Membrana Celular/química , Membrana Dobles de Lípidos/química , 1,2-Dipalmitoilfosfatidilcolina/química , Aire , Microdominios de Membrana/química , Modelos Moleculares , Conformación Molecular , Agua/química , Difracción de Rayos X
20.
ACS Macro Lett ; 3(2): 121-125, 2014 Feb 18.
Artículo en Inglés | MEDLINE | ID: mdl-35590490

RESUMEN

We show that both gravity and electrostatics are key factors regulating interactions between model cell membranes and self-assembled liquid crystalline aggregates of dendrimers and phospholipids. The system is a proxy for the trafficking of reservoirs of therapeutic drugs to cell membranes for slow diffusion and continuous delivery. Neutron reflectometry measurements were carried out on supported lipid bilayers of varying charge and on hydrophilic silica surfaces. Translocation of the macromolecule across the membrane and adsorption of the lamellar aggregates occur only when the membrane (1) is located above the bulk liquid and (2) has sufficient negative charge. The impact of such dramatic directionality effects due to bulk phase separation and gravity is emphasized for future biochemical investigations. Further, the potential to switch on the interaction mechanism through tuning the charge of the aggregates to activate endocytosis pathways on specific cell types is discussed in the context of targeted drug delivery applications.

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