Effect of amphiphilic environment on the solution structure of mouse TSPO translocator protein.

The translocator protein (TSPO) is a ubiquitous transmembrane protein of great pharmacological interest thanks to its high affinity to many drug ligands. The only high-resolution 3D-structure known for mammalian TSPO was obtained by NMR for the mouse mTSPO in DPC detergent only in presence of the high-affinity PK 11195 ligand. An atomic structure of free-ligand mTSPO is still missing to better understand the interaction of ligands with mTSPO and their effects on the protein conformation.

Dysmyelination and glycolipid interference caused by phenylalanine in phenylketonuria.

Phenylketonuria (PKU) is a metabolic disorder connected to an excess of phenylalanine (Phe) in the blood and tissues, with neurological consequences. The disease's molecular bases seem to be related to the accumulation of Phe at the cell membrane surface. Radiological outcomes in the brain demonstrate decreased water diffusivity in white matter, involving axon dysmyelination of not yet understood origin.

Order vs. Disorder: Cholesterol and Omega-3 Phospholipids Determine Biomembrane Organization.

Lipid structural diversity strongly affects biomembrane chemico-physical and structural properties in addition to membrane-associated events. At high concentrations, cholesterol increases membrane order and rigidity, while polyunsaturated lipids are reported to increase disorder and flexibility. How these different tendencies balance in composite bilayers is still controversial.

Carbohydrate-carbohydrate interaction drives the preferential insertion of dirhamnolipid into glycosphingolipid enriched membranes.

Rhamnolipids (RLs) are among the most important biosurfactants produced by microorganisms, and have been widely investigated because of their multiple biological activities. Their action appears to depend on their structural interference with lipid membranes, therefore several studies have been performed to investigate this aspect. We studied by X-ray scattering, neutron reflectometry and molecular dynamic simulations the insertion of dirhamnolipid (diRL), the most abundant RL, in model cellular membranes made of phospholipids and glycosphingolipids.

Open-Bundle Structure as the Unfolding Intermediate of Cytochrome ' Revealed by Small Angle Neutron Scattering.

The dynamic structure changes, including the unfolding, dimerization, and transition from the compact to the open-bundle unfolding intermediate structure of Cyt ', were detected by a small-angle neutron scattering experiment (SANS). The structure of Cyt ' was changed into an unstructured random coil at pD = 1.7 (R = 25 Å for the Cyt ' monomer).

: a compact software package for model-based analysis of specular neutron and X-ray reflectometry data sets.

constitutes a set of open-source Python scripts that facilitate a range of specular neutron and X-ray reflectivity calculations, involving the generation of theoretical curves and the comparison/fitting of interfacial model reflectivity against experimental data sets. The primary focus of the software is twofold: on one hand to offer a more natural framework for model definition, requiring minimum coding literacy, and on the other hand to include advanced analysis methods that have been proposed in recent work. Particular attention is given to the ability to co-refine reflectivity data and to the estimation of model-parameter uncertainty and covariance using bootstrap analysis and Markov chain Monte Carlo sampling.

Modulation of plant plasma membrane structure by exogenous fatty acid hydroperoxide is a potential perception mechanism for their eliciting activity.

Oxylipins are lipid-derived molecules that are ubiquitous in eukaryotes and whose functions in plant physiology have been widely reported. They appear to play a major role in plant immunity by orchestrating reactive oxygen species (ROS) and hormone-dependent signalling pathways. The present work focuses on the specific case of fatty acid hydroperoxides (HPOs).

Migration Kinetics of Surface Ions in Oxygen-Deficient Perovskite During Topotactic Transitions.

Oxygen diffusivity and surface exchange kinetics underpin the ionic, electronic, and catalytic functionalities of complex multivalent oxides. Towards understanding and controlling the kinetics of oxygen transport in emerging technologies, it is highly desirable to reveal the underlying lattice dynamics and ionic activities related to oxygen variation. In this study, the evolution of oxygen content is identified in real-time during the progress of a topotactic phase transition in La Sr MnO epitaxial thin films, both at the surface and throughout the bulk.

Mutually Beneficial Combination of Molecular Dynamics Computer Simulations and Scattering Experiments.

We showcase the combination of experimental neutron scattering data and molecular dynamics (MD) simulations for exemplary phospholipid membrane systems. Neutron and X-ray reflectometry and small-angle scattering measurements are determined by the scattering length density profile in real space, but it is not usually possible to retrieve this profile unambiguously from the data alone. MD simulations predict these density profiles, but they require experimental control.

Adhesion Process of Biomimetic Myelin Membranes Triggered by Myelin Basic Protein.

The myelin sheath-a multi-double-bilayer membrane wrapped around axons-is an essential part of the nervous system which enables rapid signal conduction. Damage of this complex membrane system results in demyelinating diseases such as multiple sclerosis (MS). The process in which myelin is generated is called myelination.

Insertion and activation of functional Bacteriorhodopsin in a floating bilayer.

The proton pump transmembrane protein bacteriorhodopsin was successfully incorporated into planar floating lipid bilayers in gel and fluid phases, by applying a detergent-mediated incorporation method. The method was optimized on single supported bilayers by using quartz crystal microbalance, atomic force and fluorescence microscopy techniques. Neutron and X-ray reflectometry were used on both single and floating bilayers with the aim of determining the structure and composition of this membrane-protein system before and after protein reconstitution at sub-nanometer resolution.

Soliton-Mediated Magnetic Reversal in an All-Oxide-Based Synthetic Antiferromagnetic Superlattice.

All-oxide-based synthetic antiferromagnets (SAFs) are attracting intense research interest due to their superior tunability and great potentials for antiferromagnetic spintronic devices. In this work, using the LaCaMnO/CaRuTiO (LCMO/CRTO) superlattice as a model SAF, we investigated the layer-resolved magnetic reversal mechanism by polarized neutron reflectivity. We found that the reversal of LCMO layer moments is mediated by nucleation, expansion, and shrinkage of a magnetic soliton.

Magnetic Particle Self-Assembly at Functionalized Interfaces.

We study the assembly of magnetite nanoparticles in water-based ferrofluids in wetting layers close to silicon substrates with different functionalization without and with an out-of-plane magnetic field. For particles of nominal sizes 5, 15, and 25 nm, we extract density profiles from neutron reflectivity measurements. We show that self-assembly is only promoted by a magnetic field if a seed layer is formed at the silicon substrate.

Membrane stiffness and myelin basic protein binding strength as molecular origin of multiple sclerosis.

Myelin basic protein (MBP) and its interaction with lipids of the myelin sheath plays an important part in the pathology of multiple sclerosis (MS). Previous studies observed that changes in the myelin lipid composition lead to instabilities and enhanced local curvature of MBP-lipid multilayer structures. We investigated the molecular origin of the instability and found that the diseased lipid membrane has a 25% lower bending rigidity, thus destabilizing smooth [Formula: see text]µm curvature radius structures such as in giant unilamellar vesicles.

Mucin Thin Layers: A Model for Mucus-Covered Tissues.

The fate of macromolecules of biological or pharmacological interest that enter the mucus barrier is a current field of investigation. Studies of the interaction between the main constituent of mucus, mucins, and molecules involved in topical transmucoidal drug or gene delivery is a prerequisite for nanomedicine design. We studied the interaction of mucin with the bio-inspired arginine-derived amphoteric polymer d,l-ARGO7 by applying complementary techniques.

Tuning spinterface properties in iron/fullerene thin films.

In ferromagnetic (FM) metal/organic semiconductor (OSC) heterostructures charge transfer can occur which leads to induction of magnetism in the non-magnetic OSC. This phenomenon has been described by the change in the density of states in the OSC which leads to a finite magnetic moment at the OSC interface and it is called the 'spinterface'. One of the main motivations in this field of organic spintronics is how to control the magnetic moment in the spinterface.

Long-range excitations in phospholipid membranes.

We investigated the existence of long-range excitations and correlated structures in phospholipid membranes by means of grazing-incidence neutron spin echo spectroscopy, grazing-incidence small-angle neutron scattering, and corresponding theoretical calculations inspired by smectic-membrane theory. All these methods confirmed the existence of thermal excitations in the plane of the surface of the phospholipid membranes or the corresponding structures, respectively. Also, these measurements revealed a temperature dependence of these excitations.

Model-independent recovery of interfacial structure from multi-contrast neutron reflectivity data.

Neutron specular reflectivity at soft interfaces provides sub-nanometre information concerning the molecular distribution of thin films, while the application of contrast variation can highlight the scattering from different parts of the system and lead to an overall reduction in fitting ambiguity. Traditional modelling approaches involve the construction of a trial scattering length density profile based on initial speculation and the subsequent refinement of its parameters through minimization of the discrepancy between the calculated and measured reflectivity. In practice this might produce an artificial bias towards specific sets of solutions.

Reversible Control of Physical Properties via an Oxygen-Vacancy-Driven Topotactic Transition in Epitaxial La Sr MnO Thin Films.

The vacancy distribution of oxygen and its dynamics directly affect the functional response of complex oxides and their potential applications. Dynamic control of the oxygen composition may provide the possibility to deterministically tune the physical properties and establish a comprehensive understanding of the structure-property relationship in such systems. Here, an oxygen-vacancy-induced topotactic transition from perovskite to brownmillerite and vice versa in epitaxial La Sr MnO thin films is identified by real-time X-ray diffraction.

Probing the Interface Structure of Adhering Cells by Contrast Variation Neutron Reflectometry.

Cellular adhesion is a central element in tissue mechanics, biological cell-cell signaling, and cell motility. In this context, the cell-substrate distance has been investigated in the past by studying natural cells and biomimetic cell models adhering on solid substrates. The amount of water in the membrane substrate gap, however, is difficult to determine.

The high-intensity reflectometer of the Jülich Centre for Neutron Science: MARIA.

MARIA (magnetism reflectometer with high incident angle) is a world class vertical sample reflectometer dedicated to the investigation of thin films in the fields of magnetism, soft matter and biology. The elliptical vertically focusing guide allows one to measure small samples with a typical size of 1 × 1 cm very efficiently. The double-bounce polarizer and the pumped He SEOP (spin-exchange optical pumping) neutron spin filter cell for analysing the polarization of the reflected neutron beam can be moved into the beam in seconds.

Low-Resolution Structure of Detergent-Solubilized Membrane Proteins from Small-Angle Scattering Data.

Despite the ever-increasing usage of small-angle scattering as a valuable complementary method in the field of structural biology, applications concerning membrane proteins remain elusive mainly due to experimental challenges and the relative lack of theoretical tools for the treatment of scattering data. This fact adds up to general difficulties encountered also by other established methods (crystallography, NMR) for the study of membrane proteins. Following the general paradigm of ab initio methods for low-resolution restoration of soluble protein structure from small-angle scattering data, we construct a general multiphase model with a set of physical constraints, which, together with an appropriate minimization procedure, gives direct structural information concerning the different components (protein, detergent molecules) of detergent-solubilized membrane protein complexes.

Time-Resolved Neutron Reflectivity during Supported Membrane Formation by Vesicle Fusion.

The formation of supported lipid bilayers (SLB) on hydrophilic substrates through the method of unilamelar vesicle fusion is used routinely in a wide range of biophysical studies. In an effort to control and better understand the fusion process on the substrate, many experimental studies employing different techniques have been devoted to the elucidation of the fusion mechanism. In the present work, we follow the kinetics of membrane formation using time-resolved (TR) neutron reflectivity, focusing on the structural changes near the solid/liquid interface.