Effects of the deep-sea osmolyte TMAO on the temperature and pressure dependent structure and phase behavior of lipid membranes.

We studied the interaction of lipid membranes with the deep-sea osmolyte trimethalamine-N-oxide (TMAO), which is known to stabilize proteins most efficiently against various environmental stress factors, including high hydrostatic pressure (HHP). Small-angle X-ray-scattering was applied in combination with fluorescence and infrared spectroscopy, calorimetric and AFM measurements to yield insights into the influence of TMAO on the supramolecular structure, hydration level, lipid order as well as the phase behavior of one- and three-component model biomembranes, covering a large region of the temperature-pressure phase space. Our results show that TMAO has not only a marked effect on the conformational dynamics and stability of proteins and nucleic acids, but also on lipid bilayer systems.

Exploring the effects of cosolutes and crowding on the volumetric and kinetic profile of the conformational dynamics of a poly dA loop DNA hairpin: a single-molecule FRET study.

We investigated the volumetric and kinetic profile of the conformational landscape of a poly dA loop DNA hairpin (Hp) in the presence of salts, osmolytes and crowding media, mimicking the intracellular milieu, using single-molecule FRET methodology. Pressure modulation was applied to explore the volumetric and hydrational characteristics of the free-energy landscape of the DNA Hp, but also because pressure is a stress factor many organisms have to cope with, e.g.

Adsorption Behavior of Lysozyme at Titanium Oxide-Water Interfaces.

We present an in situ X-ray reflectivity study of the adsorption behavior of the protein lysozyme on titanium oxide layers under variation of different thermodynamic parameters, such as temperature, hydrostatic pressure, and pH value. Moreover, by varying the layer thickness of the titanium oxide layer on a silicon wafer, changes in the adsorption behavior of lysozyme were studied. In total, we determined less adsorption on titanium oxide compared with silicon dioxide, while increasing the titanium oxide layer thickness causes stronger adsorption.

Human Apolipoprotein A1 at Solid/Liquid and Liquid/Gas Interfaces.

An X-ray reflectivity study on the adsorption behavior of human apolipoprotein A1 (apoA1) at hydrophilic and hydrophobic interfaces is presented. It is shown that the protein interacts via electrostatic and hydrophobic interactions with the interfaces, resulting in the absorption of the protein. pH dependent measurements at the solid/liquid interface between silicon dioxide and aqueous protein solution show that in a small pH range between pH 4 and 6, adsorption is increased due to electrostatic attraction.

Neutron Reflectometry Elucidates Protein Adsorption from Human Blood Serum onto PEG Brushes.

Poly(ethylene glycol) (PEG) brushes are reputed for their ability to prevent undesired protein adsorption to material surfaces exposed to biological fluids. Here, protein adsorption out of human blood serum onto PEG brushes anchored to solid-supported lipid monolayers was characterized by neutron reflectometry, yielding volume fraction profiles of lipid headgroups, PEG, and adsorbed proteins at subnanometer resolution. For both PEGylated and non-PEGylated lipid surfaces, serum proteins adsorb as a thin layer of approximately 10 Å, overlapping with the headgroup region.

Membrane Permeation versus Amyloidogenicity: A Multitechnique Study of Islet Amyloid Polypeptide Interaction with Model Membranes.

Islet amyloid polypeptide (IAPP) is responsible for cell depletion in the pancreatic islets of Langherans, and for multiple pathological consequences encountered by patients suffering from type 2 Diabetes Mellitus. We have examined the amyloidogenicity and cytotoxic mechanisms of this peptide by investigating model-membrane permeation and structural effects of fragments of the human IAPP and several rat IAPP mutants. In vitro experiments and molecular dynamics simulations reveal distinct physical segregation, membrane permeation, and amyloid aggregation processes that are mediated by two separate regions of the peptide.

α-Synuclein insertion into supported lipid bilayers as seen by in situ X-ray reflectivity.

Large aggregates of misfolded α-synuclein inside neuronal cells are the hallmarks of Parkinson's disease. The protein's natural function and its supposed toxicity, however, are believed to be closely related to its interaction with cell and vesicle membranes. Upon this interaction, the protein folds into an α-helical structure and intercalates into the membrane.

Temperature-driven adsorption and desorption of proteins at solid-liquid interfaces.

The heat-induced desorption and adsorption of the proteins lysozyme, ribonuclease A, bovine serum albumin, and fibronectin at protein layers was investigated in two different environments: pure buffer and protein solution. Using two different environments allows us to distinguish between thermodynamic and kinetic mechanisms in the adsorption process. We observed a desorption in buffer and an adsorption in protein solution, depending upon protein properties, such as size, stability, and charge.