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International audience; In-solution small-angle X-ray and neutron scattering (SAXS/SANS) have become popular methods to characterize the structure of membrane proteins, solubilized by either detergents or nanodiscs. SANS studies of protein-detergent complexes usually require deuterium-labeled proteins or detergents, which in turn often lead to problems in their expression or purification. Here, we report an approach whose novelty is the combined analysis of SAXS and SANS data from an unlabeled membrane protein complex in solution in two complementary ways. First, an explicit atomic analysis, including both protein and detergent molecules, using the program WAXSiS, which has been adapted to predict SANS data. Second, the use of MONSA which allows one to discriminate between detergent head- and tail-groups in an ab initio approach. Our approach is readily applicable to any detergent-solubilized protein and provides more detailed structural information on protein-detergent complexes from unlabeled samples than SAXS or SANS alone.

International audience; Although soil characteristics modulate metal mobility and bioavailability to organisms, they are often ignored in the risk assessment of metal transfer. This paper aims to determine the ability of chemical methods to assess and predict cadmium (Cd), lead (Pb) and zinc (Zn) environmental bioavailability to the land snail Cantareus aspersus. Snails were exposed in the laboratory for 28 days to 17 soils from around a former smelter. The soils were selected for their range of pH, organic matter, clay content, and Cd, Pb and Zn concentrations. The influence of soil properties on environmental availability (estimated using HF-HClO(4), EDTA, CaCl(2), NH(4)NO(3), NaNO(3), free ion activity and total dissolved metal concentration in soil solution) and on environmental bioavailability (modelled using accumulation kinetics) was identified. Among the seven chemical methods, only the EDTA and the total soil concentration can be used to assess Cd and Pb environmental bioavailability to snails (r²(adj)=0.67 and 0.77, respectively). For Zn, none of the chemical methods were suitable. Taking into account the influence of the soil characteristics (pH and CEC) allows a better prediction of Cd and Pb environmental bioavailability (r²(adj)=0.82 and 0.83, respectively). Even though alone none of the chemical methods tested could assess Zn environmental bioavailability to snails, the addition of pH, iron and aluminium oxides allowed the variation of assimilation fluxes to be predicted. A conceptual and practical method to use soil characteristics for risk assessment is proposed based on these results. We conclude that as yet there is no universal chemical method to predict metal environmental bioavailability to snails, and that the soil factors having the greatest impact depend on the metal considered.

International audience; The neurotoxic l-2-amino-3-methylaminopropionic acid (BMAA) was hypothesized to be involved in sporadic cases of amyotrophic lateral sclerosis (ALS). Studies highlighting a possible implication of environmental factors in the incidence of sporadic ALS have become more numerous over recent years. Over the past years, the most widely used method for quantifying BMAA was based on the derivatization of this polar and basic molecule with a fluorescent compound (6-aminoquinolonyl-N-hydroxysuccinimidyl, 6-AQC). This derivatization allows the retention of the conjugate by reversed-phase liquid chromatography and its detection by fluorescence. Nevertheless, recent findings have shown that this method applied to complex samples may cause false positive responses. We therefore developed an analytical procedure for the determination of underivatized BMAA at trace level in complex environmental matrices (river water, cyanobacteria and biofilm) using solid-phase extraction (SPE) based on mixed mode sorbent to concentrate and clean up real samples. Analyzes were performed by hydrophilic interaction chromatography (HILIC) coupled to electrospray ionization and tandem mass spectrometry used in multiple reaction monitoring scan mode. Analytical procedures were validated for the different natural samples using the total error approach. BMAA can be quantified by these reliable and highly selective analytical methods in a range of only a few ng mL(-1) in river water and a few ng mg(-1) dry weight in cyanobacteria and biofilm matrices.

International audience; Size exclusion chromatography coupled online to a Tetra Detector Array in combination with analytical ultracentrifugation (or with quasi-elastic light scattering) is a useful methodology to characterize hydrodynamic properties of macromolecules, including intrinsically disordered proteins. The time-averaged apparent hydration and the shape factor of proteins can be estimated from the measured parameters (molecular mass, intrinsic viscosity, hydrodynamic radius) by these techniques. Here we describe in detail this methodology and its application to characterize hydrodynamic and conformational changes in proteins.