Evidence of oxidative stress in wild freshwater mussels (Lasmigona costata) exposed to urban-derived contaminants.

The physiological effect of complex mixtures of anthropogenic contaminants on aquatic organisms is not well understood. This study employed a suite of sub-cellular biomarkers and general health measurements to assess the effect of urban-derived contaminants on wild freshwater mussels. Adult Lasmigona costata were collected from four sites in the Grand River (ON, Canada) that receive incremental amounts of municipal wastewater effluents and road runoff. Biomarkers of metal exposure, oxidative stress, and general health were examined in the gills of wild mussels. Concentrations of nine metals as well as the metal-binding protein, metallothionein (MT), were significantly higher (p<0.05) in mussels living downstream of the urban area. For example the concentrations of Pb, Cr and Zn were five-fold, and Ag more than 20 fold higher in mussels collected downstream of 11 municipal wastewater treatment plants and four cities compared to levels in upstream mussels. Downstream mussels showed evidence of oxidative stress, such that lipid peroxidation (LPO) (as thiobarbiturate reactive substances) was significantly elevated and the antioxidant capacity against peroxyl radicals (ACAP) was significantly decreased (p<0.01) in downstream mussels compared to upstream mussels. Regarding general health indicators, although gill lipid concentrations were similar across sites, protein concentration was significantly (p<0.001) higher in mussels collected from the upstream reference site compared to all downstream sites. The trends observed indicate that there are physiological effects in mussels associated with chronic exposure to complex urban inputs and that some biomarkers respond to municipal wastewater effluent and road runoff exposure in a cumulative manner. The observed oxidative stress response (ACAP) along with the elevation in MT, suggest that even though the defense mechanisms in the chronically exposed mussels have been activated, there is still an excess of reactive oxygen species that result in oxidative damage. The physiological effects of exposure reported in this study correspond with previously reported whole-organism impacts and declines in freshwater mussel populations in the urban-impacted region of this watershed.

Peptides with the same composition, hydrophobicity, and hydrophobic moment bind to phospholipid bilayers with different affinities.

We investigated the dependence of membrane binding on amino acid sequence for a series of amphipathic peptides derived from δ-lysin. δ-Lysin is a 26 amino acid, N-terminally formylated, hemolytic peptide that forms an amphipathic α-helix bound at membrane-water interfaces. A shortened peptide, lysette, was derived from δ-lysin by deletion of the four N-terminal amino acid residues. Five variants of lysette were synthesized by altering the amino acid sequence such that the overall hydrophobic moment remained essentially the same for all peptides. Peptide-lipid equilibrium dissociation constants and helicities of peptides bound to zwitterionic lipid vesicles were determined by stopped-flow fluorescence and circular dichroism. We found that binding to phosphatidylcholine bilayers was a function of the helicity of the bound peptide alone and independent of the a priori hydrophobic moment or the ability to form intramolecular salt bridges. Molecular dynamics (MD) simulations on two of the peptides suggest that sequence determines the insertion depth into the bilayer. The location of the two aspartate residues at the C-terminus of lysette-2 leads to a loss of helical content in the simulations, which correlates with faster desorption from the bilayer as compared to lysette. We also found a systematic deviation of the experimentally determined dissociation constant and that predicted by the Wimley-White interfacial hydrophobicity scale. The reason for the discrepancy remains unresolved but appears to correlate with a predominance of isoleucine over leucine residues in the lysette family of peptides.