Abstract
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 , dubbed “Super Uranyl-binding Protein” (SUP), was described, with potential applications for removing 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 binding site, but one of which interferes with binding. They further suggest that in solution the protein's secondary structure changes significantly in response to binding ; 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 , paving the way toward protein-based biomaterials for decontamination and/or recovery of uranium.
Highlights
Proteins have evolved to bind metal ions with remarkable selectivity
Potential applications of uranium-binding proteins include biosensing and bio-remediation of uranium-contaminated environments that may result from the use of depleted uranium in munitions and from uranium processing associated with nuclear weapons and nuclear fuel manufacture (Bhalara et al, 2014; Newsome et al, 2014; Xie et al, 2019)
We proposed to study UO22+ binding to Super Uranyl-binding Protein” (SUP) at pH 7.5 using circular dichroism (CD)
Summary
Proteins have evolved to bind metal ions with remarkable selectivity. Proteins exercise exquisite control over the reactivity of the metals they bind, for example fine-tuning properties such as Lewis acidity, oxidation state, and redox potential. The design of proteins (and nucleic acids) that bind uranium has been of particular interest, given that this element is an essential component in nuclear weapons and nuclear reactors (Handley-Sidhu et al, 2010). Potential applications of uranium-binding proteins include biosensing and bio-remediation of uranium-contaminated environments that may result from the use of depleted uranium in munitions and from uranium processing associated with nuclear weapons and nuclear fuel manufacture (Bhalara et al, 2014; Newsome et al, 2014; Xie et al, 2019)
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