Studies on heavy metals effects on Mytilus galloprovincialis sperm chromatin proteins and on DNA

Heavy metal pollution has become one of the most serious environmental problems in the world that brought threat to human health and ecological security. To monitor sea levels of heavy metals we used as specific bioindicator Mytilus galloprovincialis whose sperm chromatin is organized mainly by three protamine-like proteins (PLII, PLIII and PLIV). These proteins protect DNA from a variety of potentially dangerous reactive species but chromatin packaging doesn’t protect DNA from metal ion-dependent damage in the presence of hydroxyl radicals. We report the effects induced by Cu2+, Ni2+ and Cd2 ions on DNA and on Mytilus galloprovincialis’ PLII and PLIII. Self-association ability of PLII and PLIII mediated by Cd2+, Ni2+ and Cu2+ show that Cd2+ causes only PLII aggregation to a greater extend respect to Ni2+ that induces a mild aggregation of both PLII and PLIII; Cu2+, instead, doesn’t produce any type of aggregates. In vivo studies show that these heavy metals affect PLII, PLIII and PLIV state and properties. While nickel produces an increase of DNA binding affinity for both PLII and PLIII cadmium causes a decrease of PLII DNA binding affinity but an increase for PLIII. Copper and cadmium promote hydrogen peroxide damage of DNA also in the presence of protamine-like proteins while nickel doesn’t. All these effects can lead an anomalous chromatin packaging and a reduction of the reproductive fitness in Mytilus galloprovincialis and other organisms exposed to the same toxicants.