Bioaccumulation of Arsenic by Engineered Escherichia coli Cells Expressing Rice Metallothionein Isoforms.

Metallothioneins (MTs) are low-molecular weight cysteine (Cys)-rich proteins with high metal-binding capacity. Based on the Cys arrangement in their amino acid sequences, plant MTs are categorized into four classes. This study evaluated the ability of genetically engineered Escherichia coli cells, which express four rice MT isoforms as fusion proteins with glutathione-S-transferase (GST), to remove arsenic. As compared with control strain, the expression of GST-OsMT1, GST-OsMT2, GST-OsMT3, and GST-OsMT4 resulted in 8-, 5.6-, 3-, and 1.1-fold-higher As3+ accumulation. The recombinant GST-OsMT isoforms were purified using affinity chromatography and their apo-forms were prepared. The ability of the GST-OsMT2 isoform to bind with As3+ in vitro was also confirmed by ultraviolet (UV) absorption spectra recorded after the reconstitution of apo-proteins with As3+. However, the formation of complexes of other MT isoforms with arsenic was not observed.