Solid supported lipid bilayers from artificial and natural lipid mixtures - long-term stable, homogeneous and reproducible.

Supported lipid bilayers (SLBs) are increasingly accepted as experimental models to study the behaviour of membrane active proteins like α-synuclein, as they can easily be investigated by surface sensitive analytical methods. In this study we show the assembly and long-term stability of SLBs on glass substrates by vesicle deposition from various lipid mixtures. For the investigation of the SLBs we use supercritical angle fluorescence microscopy and spectroscopy. We concentrate on the important factors for reproducible bilayer assembly like the purification of the substrate and the handling of the lipid vesicle suspension. By using a new combined steady-state/flow approach we were able to create homogeneous SLBs with a long-term stability over seven days, which to our knowledge have not been reported in the literature so far, including SLBs containing up to 70% negatively charged lipids, SLBs from artificial lipid mixtures containing cholesterol as well as SLBs from natural lipid extracts.

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. In this study, we focus on the changes in the lipid bilayer caused by this intrusion. In situ X-ray reflectivity was applied to determine the vertical density structure of the bilayer before and after exposure to α-synuclein. It was found that the α-synuclein insertion, wild type and E57K variant, caused a reduction in bilayer thickness. This effect may be one factor in the membrane pore formation ability of α-synuclein.

Atmospheric pressure chemical ionization Fourier transform ion cyclotron resonance mass spectrometry for complex thiophenic mixture analysis.

RATIONALE: Polycyclic aromatic sulfur heterocycles (PASHs) are detrimental species for refining processes in petroleum industry. Current mass spectrometric methods that determine their composition are often preceded by derivatization and dopant addition approaches. Different ionization methods have different impact on the molecular assignment of complex PASHs. The analysis of such species under atmospheric pressure chemical ionization (APCI) is still considered limited due to uncontrolled ion generation with low- and high-mass PASHs. METHODS: The ionization behavior of a model mixture of five selected PASH standards was investigated using an APCI source with nitrogen as the reagent gas. A complex thiophenic fraction was separated from a vacuum gas oil (VGO) and injected using the same method. The samples were analyzed using Fourier transform ion cyclotron resonance mass spectrometry (FTICR MS). RESULTS: PASH model analytes were successfully ionized and mainly [M + H](+) ions were produced. The same ionization pattern was observed for the real thiophenic sample. It was found that S1 class species were the major sulfur-containing species found in the VGO sample. These species indicated the presence of alkylated benzothiophenic (BT), dibenzothiophenic (DBT) and benzonaphthothiophenic (BNT) series that were detected by APCI-FTICR MS. CONCLUSIONS: This study provides an established APCI-FTICR MS method for the analysis of complex PASHs. PASHs were detected without using any derivatization and without fragmentation. The method can be used for the analysis of S-containing crude oil samples.