Regioselective Zr₅ Nanocluster Photocatalyst for Precise Protein Editing Under Mild Conditions

Understanding the impact of oxidative modifications on protein structure and function is of central importance in protein chemistry, necessitating precise and controlled methods for introducing such modifications. Herein, we report a strategy for regioselective chemical editing of a protein using a novel Zr₅ nanocluster as a visible-light photocatalyst. The  [Zr^IV ₅(μ─ΟΗ)₂(μ─Ο)₂(μ₃─Ο)Cl₂(H₂O)₆(μ-η¹,η²,η¹-tBu-dihyde-O,O',O″)₅] (Zr₅) cluster features a unique [Zr₅O₅] structural motif and its electronic structure and light absorption properties were fully analyzed and reproduced through Time-dependent density functional theory (DFT) calculations. Zr₅ exhibits exceptional photophysical properties, including the optical gap of 2.01 eV, the lowest reported to date for a zirconium-oxo cluster. Under light irradiation at 370 nm, Zr₅ mediates the regioselective cleavage and oxidative side-chain modification of hen egg white lysozyme, producing fragments which are ideal for middle-down proteomics applications. Combined DFT and experimental approaches indicate that Zr₅ efficiently produces reactive oxygen species that mediate protein oxidation and cleavage. Comprehensive characterization confirmed the cluster's stability under reaction conditions, with no detectable structural changes or dissolution, enabling its reuse for multiple times without loss of catalytic efficiency. The unique photocatalytic properties of Zr₅ offer new opportunities for precise protein functionalization and pave the way for extending them to other classes of molecular transformations.