Harvesting Uranium From The Sea

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Harvesting Uranium From The Sea
AsianScientist (Oct. 3, 2014) – Scientists have designed a protein that can bind to uranyl with extremely high affinity, making it possible to tap into the rich uranyl resources of the sea. This research has been published in the journal Nature Chemistry.
Uranium is the key element used in nuclear energy industry. It has been estimated that there are about 4.5 billion tons of uranium dissolved in the world’s oceans—nearly 1,000 times as much of the worldwide reserves of uranium on land—thought to be an inexhaustible supply.
Efforts to extract uranyl, the predominant aerobic form of uranium, from seawater date back many decades. So far, though, all solutions have been cost prohibitive. The problem is that the concentration of uranyl is extremely low (3.2 ppb, approximately 14 nM), compared with other metals with a similar size and charge, which requires the uranyl extraction ligands to be very potent and selective.
Turning to proteins, researchers including Professor Lai Luhua’s group at the Center for Quantitative Biology, Peking University used a computational algorithm to guide the engineering of a protein that selectively binds uranyl with a very high affinity (7.4 fM), calling it Super Uranyl-binding Protein (SUP).
Based on the computational “protein key residues grafting” strategy established by Professor Lai’s lab for protein-protein interaction design, they developed a computational screening algorithm called URANTEIN to search the Protein Data Bank for proteins that could accommodate uranyl.
Ten promising candidates were selected, among which four showed binding to uranyl with Kd values of ~100 nM and below. One of the candidates was further optimized with several rounds of amino acid residue mutations, bringing the binding affinity down from 37nM to 7.4 fM (femtomolar) with high selectivity.
SUP’s high-resolution crystal structure revealed a binding-site geometry similar to that predicted by the URANTEIN model, proving the rationality of the protein design strategy. Furthermore, the team genetically expressed SUP on the surface of E. coli and found that this bacterial system could extract uranyl selectively from synthetic seawater very efficiently. This is the first known demonstration of a bacterial system used to mine ocean-based uranium, which is cheaper than existing methods.
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