Abstract
The Pacific oyster, Crassostrea gigas, is a traditional food worldwide. The soft body of the oyster can easily accumulate heavy metals such as cadmium (Cd). To clarify the molecular mechanism of Cd accumulation in the viscera of C. gigas, we identified Cd-binding proteins. 5,10,15,20-Tetraphenyl-21H,23H-porphinetetrasulfonic acid, disulfuric acid, tetrahydrate, and Cd-binding competition experiments using immobilized metal ion affinity chromatography revealed the binding of water-soluble high molecular weight proteins to Cd, including C. gigas protein disulfide isomerase (cgPDI). Liquid chromatography–tandem mass spectrometry (LC–MS/MS) analyses revealed two CGHC motifs in cgPDI. The binding between Cd and rcgPDI was confirmed through a Cd-binding experiment using the TPPS method. Isothermal titration calorimetry (ITC) revealed the binding of two Cd ions to one molecule of rcgPDI. Circular dichroism (CD) spectrum and tryptophan fluorescence analyses demonstrated that the rcgPDI bound to Cd. The binding markedly changed the two-dimensional or three-dimensional structures. The activity of rcgPDI measured by a PDI Activity Assay Kit was more affected by the addition of Cd than by human PDI. Immunological analyses indicated that C. gigas contained cgPDI at a concentration of 1.0 nmol/g (viscera wet weight). The combination of ITC and quantification results revealed that Cd-binding to cgPDI accounted for 20% of the total bound Cd in the visceral mass. The findings provide new insights into the defense mechanisms of invertebrates against Cd.
Highlights
The Pacific oyster, Crassostrea gigas, is a traditional food worldwide
Cd content was highest in the viscera, and the accumulated amount was larger in the order of mantle, gills, and muscle (Fig. 1b)
Since the weight of the viscera is approximately five-times that of the gills, the accumulation of Cd would be greatest in the viscera
Summary
The Pacific oyster, Crassostrea gigas, is a traditional food worldwide. The soft body of the oyster can accumulate heavy metals such as cadmium (Cd). The third group, rcgPDI + Cd treated with Chelex reagent, comprised rcgPDI dissolved in ultrapure water with the addition of Cd at a final concentration of 1 mM, followed by treatment with Chelex as described above.
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