Protein Recognition and Amyloid Remodeling Governed by Paddlewheel Diruthenium Coordination Chemistry

Paddlewheel diruthenium (Ru2) complexes are promising modulators of protein aggregation due to their tunable coordination chemistry and dual-action properties. Here, we investigate the interaction of five Ru2 complexes with hen egg white lysozyme (HEWL), an amyloid model, to elucidate their antiaggregation capabilities. High-resolution X-ray crystallography shows that all complexes preferentially bind to Asp119 and, in some cases, Asp101, through coordination to the Ru2 core while preserving the overall protein fold. Both covalent and noncovalent interactions are observed, depending on ligand environment and steric effects. Solution studies confirm the formation of HEWL-Ru2 adducts under both neutral and acidic conditions. Functional assays demonstrate that all Ru2 complexes effectively inhibit HEWL fibrillogenesis, as indicated by reduced ThT fluorescence and the absence of large aggregates in dynamic light scattering measurements. Disaggregation of preformed fibrils was more variable, with the complex bearing vacant axial sites showing the highest activity. Circular dichroism and scanning electron microscopy analyses reveal that these compounds redirect aggregation toward noncanonical morphologies rather than fully dissolving fibrils. Cytotoxicity assays confirm reduced HEWL-induced cellular toxicity. Overall, our findings establish a correlation between ligand composition, coordination behavior, protein binding, and antiamyloid activity, providing a framework for designing Ru2-based multifunctional modulators of protein aggregation.