Identification of Different Sources and Forms of Arsenic in the Vicinity of Ore Mining in Serbia

Plant available arsenic (As) is not defined by its total content but by the various forms in soil. The aims of this study were to determine the amounts of As phases in soils extracted in the vicinity of the antimony mines; to study soil surface processes affecting formation of most mobile phases of As and the identification of sources of As phases in C soil horizon. Five fractions of soil As were determined by sequential extraction analyses (As F1, As F 2, As F 3, As F 4 and As F 5) in A and C horizons. The identification of the origin of As fractions were made by mean of principal component analyses (PCA) including Pearson correlations. The amount of the most mobile forms of As (As F1 and F2) was below 1%. The content of As F1, As F2 and As F4 decrease with soil depth, while aqua regia As and phases F3 and F5 increase with depth. Principal component analyses (PCA) showed that the content of As F2 is affected by anthropogenic factor and the content of As F4 by biological factor. In C horizon, As F2 and F4 are influenced by the leaching processes in soil. Arsenic F5 is bound to sediment rocks. The soil surface processes increases the availability of As in soil. The most mobile forms of As were found in deeper soil horizon that is due to the leaching of As with water from biological sources. The content of semi available phase of As F3 increases with depth, with stronger bounds due to the linkage to the amorphous Fe hydroxides

Molecular determinants of sphingomyelin specificity of a eukaryotic pore-forming toxin.

Sphingomyelin (SM) is abundant in the outer leaflet of the cell plasma membrane, with the ability to concentrate in so-called lipid rafts. These specialized cholesterol-rich microdomains not only are associated with many physiological processes but also are exploited as cell entry points by pathogens and protein toxins. SM binding is thus a widespread and important biochemical function, and here we reveal the molecular basis of SM recognition by the membrane-binding eukaryotic cytolysin equinatoxin II (EqtII). The presence of SM in membranes drastically improves the binding and permeabilizing activity of EqtII. Direct binding assays showed that EqtII specifically binds SM, but not other lipids and, curiously, not even phosphatidylcholine, which presents the same phosphorylcholine headgroup. Analysis of the EqtII interfacial binding site predicts that electrostatic interactions do not play an important role in the membrane interaction and that the two most important residues for sphingomyelin recognition are Trp(112) and Tyr(113) exposed on a large loop. Experiments using site-directed mutagenesis, surface plasmon resonance, lipid monolayer, and liposome permeabilization assays clearly showed that the discrimination between sphingomyelin and phosphatidylcholine occurs in the region directly below the phosphorylcholine headgroup. Because the characteristic features of SM chemistry lie in this subinterfacial region, the recognition mechanism may be generic for all SM-specific proteins

Identification of Different Sources and Forms of Arsenic in the Vicinity of Ore Mining in Serbia

Plant available arsenic (As) is not defined by its total content but by the various forms in soil. The aims of this study were to determine the amounts of As phases in soils extracted in the vicinity of the antimony mines; to study soil surface processes affecting formation of most mobile phases of As and the identification of sources of As phases in C soil horizon. Five fractions of soil As were determined by sequential extraction analyses (As F1, As F 2, As F 3, As F 4 and As F 5) in A and C horizons. The identification of the origin of As fractions were made by mean of principal component analyses (PCA) including Pearson correlations. The amount of the most mobile forms of As (As F1 and F2) was below 1%. The content of As F1, As F2 and As F4 decrease with soil depth, while aqua regia As and phases F3 and F5 increase with depth. Principal component analyses (PCA) showed that the content of As F2 is affected by anthropogenic factor and the content of As F4 by biological factor. In C horizon, As F2 and F4 are influenced by the leaching processes in soil. Arsenic F5 is bound to sediment rocks. The soil surface processes increases the availability of As in soil. The most mobile forms of As were found in deeper soil horizon that is due to the leaching of As with water from biological sources. The content of semi available phase of As F3 increases with depth, with stronger bounds due to the linkage to the amorphous Fe hydroxides

Molecular recognition of a single sphingolipid species by a protein’s transmembrane domain

Functioning and processing of membrane proteins critically depend on the way their transmembrane segments are embedded in the membrane. Sphingolipids are structural components of membranes and can also act as intracellular second messengers. Not much is known of sphingolipids binding to transmembrane domains (TMDs) of proteins within the hydrophobic bilayer, and how this could affect protein function. Here we show a direct and highly specific interaction of exclusively one sphingomyelin species, SM 18, with the TMD of the COPI machinery protein p24 (ref. 2). Strikingly, the interaction depends on both the headgroup and the backbone of the sphingolipid, and on a signature sequence (VXXTLXXIY) within the TMD. Molecular dynamics simulations show a close interaction of SM 18 with the TMD. We suggest a role of SM 18 in regulating the equilibrium between an inactive monomeric and an active oligomeric state of the p24 protein, which in turn regulates COPI-dependent transport. Bioinformatic analyses predict that the signature sequence represents a conserved sphingolipid-binding cavity in a variety of mammalian membrane proteins. Thus, in addition to a function as second messengers, sphingolipids can act as cofactors to regulate the function of transmembrane proteins. Our discovery of an unprecedented specificity of interaction of a TMD with an individual sphingolipid species adds to our understanding of why biological membranes are assembled from such a large variety of different lipids