Identification of uranyl-binding proteins in Arabidopsis thaliana cells exposed to uranium: Insights from a metalloproteomic analysis and characterization of Glycine-Rich RNA-binding protein 7 (GRP7).

Uranium (U) is a naturally occurring radionuclide that poses chemotoxic threats to living organisms, including plants. Despite its environmental relevance, the molecular mechanisms underlying U toxicity in plant cells are not well understood. In this study, we used an integrative metalloproteomic strategy integrating chromatographic fractionation with high-resolution proteomics and inductively coupled plasma mass spectrometry to identify cellular protein targets of uranyl (U(VI)) in cultured Arabidopsis thaliana cells. This approach led to the identification of 57 candidate U-binding proteins, suggesting a broad potential for U-protein interactions in plant systems. Among these, the Glycine-Rich RNA-binding Protein 7 (GRP7), a multifunctional protein implicated in RNA processing, stress responses, and circadian regulation, emerged as a particularly compelling candidate. We purified recombinant GRP7 and demonstrated its ability to bind U(VI) with a 1:2 (protein:metal) stoichiometry in vitro. Structural investigation using solution-state nuclear magnetic resonance (NMR) spectroscopy revealed the dynamic nature of the interaction and pinpointed specific residues involved in U(VI) coordination at two distinct sites. Importantly, we showed that U(VI) binding disrupts the RNA-binding function of GRP7, suggesting a molecular mechanism by which U exposure may impair gene regulation in plants. These findings provide the first detailed molecular insight into U-protein interaction in plants and suggest that GRP7 may play a critical role in mediating U-induced toxicity through interference with RNA metabolism. This work paves the way for future studies on U toxicity and tolerance in plants, with potential implications for environmental risk assessment and phytoremediation strategies.