Engineered proteoliposome transporter for treatment of cesium contaminated water

Radioactive cesium (¹³⁷Cs) released from nuclear power plants and nuclear accidents continues to be a worldwide concern, and its removal from water remains a difficult problem. Here, we present the development of an innovative method to remove Cs⁺ present at low concentrations in water. To achieve this, a proteoliposome transporter was engineered, composed of a membrane-bound potassium uptake protein, Kup from E. coli, which was reconstituted into a liposome vesicle. Cs⁺ removal (10-100 µg/L) was demonstrated by incubating the constructed proteoliposome in lab-fortified water, followed by ultracentrifugation to remove captured Cs⁺. Inductively coupled plasma mass spectrometry (ICP-MS) results from testing water spiked with 100 µg/L Cs⁺ revealed that adding increasing volumes of proteoliposome solution (containing 0.015-1.2 mg of Kup membrane transporter) resulted in 0.29-12.7% removal in a linear fashion. Proteoliposome addition (containing 0.015-0.3 mg of Kup membrane transporter) to water spiked with 10 µg/L Cs⁺ resulted in 0.65-3.43% removal, while removal by protein-free liposomes was negligible at 0.03%. These results suggest that Kup transporters inserted into the liposomes are mainly responsible for the removal efficiencies. Consequently, a desired removal efficiency can be achieved by adding a higher volume of constructed proteoliposome and subsequently higher mg of Kup transporter to the contaminated water. This provides new insight on the effectiveness and applicability of proteoliposome transporters, and an alternative and a novel contribution to emerging technologies in removing cesium or other metal contaminants undergoing transmembrane transport.