The role of GST omega in metabolism and detoxification of arsenic in clam Ruditapes philippinarum

The major hazard of arsenic in living organisms is increasingly being recognized. Marine mollusks are apt to accumulate high levels of arsenic, but knowledge related to arsenic detoxification in marine mollusks is still less than sufficient. In this study, arsenic bioaccumulation as well as the role of glutathione S-transferase omega (GST Omega) in the process of detoxification were investigated in the Ruditapes philippinarum clam after waterborne exposure to As(III) or As(V) for 30 days. The results showed that the gills accumulated significantly higher arsenic levels than the digestive glands. Arsenobetaine (MB) and dimethylarsenate (DMA) accounted for most of the arsenic found, and monomethylarsonate (MMA) can be quickly metabolized. A subcellular distribution analysis showed that most arsenic was in biologically detoxified metal fractions (including metal-rich granules and metallothionein-like proteins), indicating their important roles in protecting cells from arsenic toxicity. The relative mRNA expressions of two genes encoding GST Omega were up-regulated after arsenic exposure, and the transcriptional responses were more sensitive to As(III) than As(V). The recombinant GST Omega s exhibited high activities at optimal conditions, especially at 37 degrees C and pH 4-5, with an As(V) concentration of 60 mM. Furthermore, the genes encoding GST Omega significantly enhance the arsenite tolerance but not the arsenate tolerance of E. call AW3110 (DE3) (Delta arsRBC). It can be deduced from these results that GST Omega s play an important role in arsenic detoxification in R. philippinarum.