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Front. Mol. Biosci. | doi: 10.3389/fmolb.2019.00073

Probing Metal Ion Discrimination in a Protein Designed to Bind Uranyl Cation with Femtomolar Affinity

 Marie Hoarau1, Karl J. Koebke2,  Zhan Chen1 and  Neil Marsh1*
  • 1University of Michigan, United States
  • 2Michigan Medicine, University of Michigan, United States

The design of metal-binding sites in proteins that combine high affinity with high selectivity for the desired metal ion remains a challenging goal. Recently, a protein designed to display femtomolar affinity for UO22+, dubbed “Super Uranyl-binding Protein” (SUP), was described, with potential applications for removing UO22+ in water. Although it discriminated most metal ions present in seawater, the protein showed a surprisingly high affinity for Cu2+ ions. Here, we have investigated Cu2+ binding to SUP using a combination of electron paramagnetic resonance, fluorescence and circular dichroism spectroscopies. Our results provide evidence for two Cu2+ binding sites on SUP that are distinct from the UO22+ binding site, but one of which interferes with UO22+ binding. They further suggest that in solution the protein’s secondary structure changes significantly in response to binding UO22+; in contrast, the crystal structures of the apo- and holo-protein are almost superimposable. These results provide insights for further improving the selectivity of SUP for UO22+, paving the way towards protein-based biomaterials for decontamination and/or recovery of uranium.

Keywords: Protein engeineering, Metalloproteins, Helical bundle proteins, EPR spectra of Cu(II) complexes, Metal ion selectivity

Received: 25 Jun 2019; Accepted: 07 Aug 2019.

Copyright: © 2019 Hoarau, Koebke, Chen and Marsh. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence: Prof. Neil Marsh, University of Michigan, Ann Arbor, 48109, Michigan, United States, nmarsh@umich.edu