Structure of Galectin-3 bound to a model membrane containing ganglioside GM1.

Galectin-3 (Gal-3) is a β-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.

Unusually High Concentration of Alkyl Ammonium Hydroxide in the Cation-Hydroxide-Water Coadsorbed Layer on Pt.

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.

Shiga Toxin Induces Lipid Compression: A Mechanism for Generating Membrane Curvature.

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.

Fibrillar and Nonfibrillar Amyloid Beta Structures Drive Two Modes of Membrane-Mediated Toxicity.

In Alzheimer's disease, the amyloid-beta peptide (Aβ) is implicated in neuronal toxicity via interactions with the cell membrane. Monomeric Aβ (Aβ) 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 Aβ.

Enhanced Ordering in Monolayers Containing Glycosphingolipids: Impact of Carbohydrate Structure.

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.

Functional Characterization of Cell-Free Expressed OprF Porin from Pseudomonas aeruginosa Stably Incorporated in Tethered Lipid Bilayers.

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.

Structural Variations in Hybrid All-Nanoparticle Gibbsite Nanoplatelet/Cellulose Nanocrystal Multilayered Films.

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.

Coupling neutron reflectivity with cell-free protein synthesis to probe membrane protein structure in supported bilayers.

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).

Protein-Containing Lipid Bilayers Intercalated with Size-Matched Mesoporous Silica Thin Films.

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.

Nanostructural determination of a lipid bilayer tethered to a gold substrate.

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.

Influence of the Human and Rat Islet Amyloid Polypeptides on Structure of Phospholipid Bilayers: Neutron Reflectometry and Fluorescence Microscopy Studies.

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 β-cells.

Neutron study of phospholipids 1-palmitoyl-2-oleoyl-sn-glycero-3-phospho-ethanolamine spray coating on titanium implants.

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.

Analysis of biosurfaces by neutron reflectometry: from simple to complex interfaces.

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.

Interactions of small dendrimers with sodium dodecyl sulfate at the air-water interface.

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.

Carbohydrate conformation and lipid condensation in monolayers containing glycosphingolipid Gb3: influence of acyl chain structure.

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).

Thickness and refractive index of DPPC and DPPE monolayers by multiple-beam interferometry.

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.

X-ray and neutron investigation of self-assembled lipid layers on a titanium surface.

Titanium is the most widely preferred metal material for bone reconstruction in orthopedics and dentistry. To improve its biological performance, various coatings can be applied. In this investigation, a biomimetic coating on a model implant surface was studied in X-ray and neutron reflectivity experiments to probe the quality of this coating, which is only few nanometers thick.

Equilibrium or quenched: fundamental differences between lipid monolayers, supported bilayers, and membranes.

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.

Structure and thermodynamics of lipid bilayers on polyethylene glycol cushions: fact and fiction of PEG cushioned membranes.

In developing well hydrated polymer cushioned membranes, structural studies are often neglected. In this work, neutron and X-ray reflectivity studies reveal that hybrid bilayer/polyethylene glycol (PEG) systems created from mixtures of phospholipids and PEG conjugated lipopolymers do not yield a hydrated cushion beneath the bilayer unless the terminal ends of the lipopolymers are functionalized with reactive end groups and can covalently bind (tether) to the underlying support surface. While reactive PEG tethered systems yielded bilayers with near complete surface coverage, a bimodal distribution of heights with sub-micrometer lateral dimensions was observed consisting of cushioned membrane domains and uncushioned regions in close proximity to the support.

pH responsive polymer cushions for probing membrane environment interactions.

A robust and straightforward method for the preparation of lipid membranes upon dynamically responsive polymer cushions is reported. Structural characterization demonstrates that complete, well-packed membranes with tunable mobility can be constructed on the polymeric cushion. With this system, membrane conformational changes induced by cellular cytoskeleton interactions can be modeled.

Investigating the interface of superhydrophobic surfaces in contact with water.

Neutron reflectivity (NR) is used to probe the solid, liquid, vapor interface of a porous superhydrophobic (SH) surface submerged in water. A low-temperature, low-pressure technique was used to prepare a rough, highly porous organosilica aerogel-like film. UV/ozone treatments were used to control the surface coverage of hydrophobic organic ligands on the silica framework, allowing the contact angle with water to be continuously varied over the range of 160 degrees (superhydrophobic) to <10 degrees (hydrophilic).