Fast and selective protein modification with iron-substituted polyoxometalates via a radical pathway

Oxidative modifications of proteins are crucial post-translational modifications that profoundly impact their structure, function, and turnover. Developing chemical methods that selectively induce oxidative protein modifications and cleavage would significantly facilitate elucidation of these oxidative processes, benefiting our understanding of disease mechanisms, identifying novel therapeutic targets, and advancing biotechnological applications. In this work, we demonstrate that all-inorganic discrete polyoxometalate (POM) clusters stabilize redox active metal centers such as Fe(III) and Mn(III) under physiological pH and temperature (pH = 7.5, 37 °C), enabling the generation of reactive oxygen species (ROS) under mild aqueous conditions. Specifically, we show that catalytic amounts of the iron-substituted POM K₇[Fe^III(α₂-P₂W₁₇O₆₁)(H₂O)] (Fe^IIIWD), in the presence of ascorbate (Asc), rapidly induce selective oxidation and cleavage of hen egg-white lysozyme (HEWL) in four narrow regions of the protein sequence. The protein cleavage sites are all located near the interaction sites of M^IIIWD (M = Mn or Fe) catalysts with the protein surface. In contrast, the manganese-substituted POM K₇[Mn^III(α₂-P₂W₁₇O₆₁)(H₂O)] (Mn^IIIWD) shows no similar catalytic activity, pointing towards a different radical mechanism. These findings highlight the potential of well-tailored inorganic clusters to facilitate selective catalytic processes, enabling iron to target specific regions of a protein sequence without relying on coordination sites on the protein surface, while offering flexibility in reaction conditions.