Screening Glycolipids Against Proteins in Vitro Using Picodiscs and Catch-and-Release Electrospray Ionization-Mass Spectrometry.

This work describes the application of the catch-and-release electrospray ionization-mass spectrometry (CaR-ESI-MS) assay, implemented using picodiscs (complexes comprised of saposin A and lipids, PDs), to screen mixtures of glycolipids (GLs) against water-soluble proteins to detect specific interactions. To demonstrate the reliability of the method, seven gangliosides (GM1, GM2, GM3, GD1a, GD1b, GD2, and GT1b) were incorporated, either individually or as a mixture, into PDs and screened against two lectins: the B subunit homopentamer of cholera toxin (CTB5) and a subfragment of toxin A from Clostridium difficile (TcdA-A2). The CaR-ESI-MS results revealed that CTB5 binds to six of the gangliosides (GM1, GM2, GM3, GD1a, GD1b, and GT1b), while TcdA-A2 binds to five of them (GM1, GM2, GM3, GD1a, and GT1b). These findings are consistent with the measured binding specificities of these proteins for ganglioside oligosaccharides. Screening mixtures of lipids extracted from porcine brain and a human epithelial cell line against CTB5 revealed binding to multiple GM1 isoforms as well as to fucosyl-GM1, which is a known ligand. Finally, a comparison of the present results with data obtained with the CaR-ESI-MS assay implemented using nanodiscs (NDs) revealed that the PDs exhibited similar or superior performance to NDs for protein-GL binding measurements.

Nanodiscs and electrospray ionization mass spectrometry: a tool for screening glycolipids against proteins.

Electrospray ionization-mass spectrometry (ESI-MS) is extensively employed to detect and quantify protein-carbohydrate interactions in vitro and is increasingly used to screen carbohydrate libraries against target proteins. However, current ESI-MS methods are limited to carbohydrate ligands that are relatively soluble in water and are, therefore, not generally suitable for studying protein interactions with glycolipids, an important class of cellular receptors. Here, we describe a catch-and-release (CaR)-ESI-MS assay, which exploits nanodiscs (NDs) to solubilize glycolipids and mimic their natural cellular environment, suitable for screening libraries of glycosphingolipids (GSL) against proteins to identify specific interactions and to rank their relative affinities. Using the B subunit homopentamers of cholera toxin and heat labile toxin as model GSL-binding proteins, the CaR-ESI-MS was applied to NDs containing mixtures of gangliosides. The results demonstrate that the CaR-ESI-MS assay can simultaneously detect both high and low affinity GSL ligands using either a library of NDs that each contains one GSL or incorporating a mixture of GSLs into a single ND. Moreover, the relative abundances of the released ligands appear to reflect their relative affinities in solution. Application of the CaR-ESI-MS assay using NDs containing gangliosides extracted from porcine brain led to the discovery of a neolacto GSL as a cholera toxin ligand, highlighting the power of the assay for identifying specific protein-glycolipid interactions from biologically relevant mixtures.

Synthesis of efficient N-containing TiO2 photocatalysts with high anatase thermal stability and the effects of the nitrogen residue on the photoinduced charge separation.

Efficient N-containing TiO(2) nanoparticles with high anatase thermal stability were synthesized via a hexamethylenetetramine (HMT)-modified sol-hydrothermal process. The results showed that modification with proper amounts of HMT is effective in increasing the onset temperature of the phase transformation of TiO(2) from anatase to rutile. The enhancement of the anatase thermal stability of the modified TiO(2) was attributed to ammonia produced slowly by hydrolysis of the HMT molecules in the sol-hydrothermal process and, additionally, to the residual nitrogen species after the thermal treatment at high temperatures, as indicated by the XPS examination. Compared with the unmodified TiO(2), the modified TiO(2) obtained by a thermal treatment at high temperatures exhibited good photocatalytic performance under UV light and was found to even be superior to the commercially available P25-TiO(2). It was suggested that the residual N species (Ti-O-N), formed after the thermal treatment at high temperatures, along with the mixed phase composition, large surface area and the increase in the thermal stability, were responsible for the enhanced photocatalytic activity of modified TiO(2). It was demonstrated, by means of the surface photovoltage responses of the modified TiO(2) in different atmospheres along with the aid of an outer electric field, that the residual N species could effectively capture the photoinduced holes, which was favorable for the effective separation of the photoinduced charges. This work provides a feasible route to fabricate high-performance TiO(2)-based functional nanomaterials with high anatase thermal stability.

Liposome electrokinetic chromatography based in vitro model for early screening of the drug-induced phospholipidosis risk.

Drug-induced phospholipidosis (PLD) is a storage disorder of lysosomes characterized by the excessive accumulation of phospholipids as a result of improper medical treatments. Although few evidences have supported that PLD can induce significant pathological consequences, this potential toxicity indeed can put off the drug discovery process. In this research, a high-throughput liposome electrokinetic chromatography (LEKC) method was validated to evaluate the PLD risk of drug candidates by screening drug-phospholipid interaction, which correlates to the phospholipidosis inducing risk. A statistical analysis based on the Spearman's correlation test showed that the retention factors (log k) of the tested drugs in the LEKC system and the literature reported in vivo and in vitro PLD data were highly correlated. In order to investigate the predictability of LEKC, the effect of liposome composition such as the molar ratio of phospholipids and the addition of cholesterol were also discussed in this study. The results indicated that the LEKC method could offer a fast, reliable and cost-effective screening tool for early prediction of the PLD inducing potential of drug candidates.