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Thermodynamic Analysis of Protein-Nanoparticle Interactions Links Binding Affinity and Structural Stability
Summary
Using model proteins with systematically altered surface charges, researchers showed that polystyrene nanoparticles destabilize protein structure upon contact, and that how strongly a protein binds to a nanoparticle surface predicts how much it will unfold. When nanoplastics enter biological fluids, they become coated in a protein 'corona' that determines how cells recognize and respond to them, so understanding the binding thermodynamics helps predict nanoplastic toxicity and biological behavior. This work builds a framework for forecasting which proteins are most vulnerable to disruption by nanoplastics—relevant to understanding their health effects.
When nanoparticles and nanoplastics enter biological fluids, their surfaces are rapidly coated with proteins, forming a corona that governs biological responses. However, understanding protein-surface interaction energetics remains a significant challenge. Here, we examine how protein charge distribution affects adsorption to polystyrene nanoparticles (PSNPs) by generating a series of lysine-to-alanine variants of the GB3 protein. This approach is unique because it explores how systematic perturbations in a controlled model protein influence protein-surface interactions. Using isothermal titration calorimetry (ITC), we found that the K19A variant binds most strongly to both nonfunctionalized and carboxylate-functionalized PSNPs. ITC thermograms indicate that K19A forms a stable monolayer, while other variants exhibit multilayer adsorption. The folded protein structure suggests that removing lysine at position 19 creates a flatter, more neutral interaction surface that promotes efficient initial binding. Fluorescence denaturation experiments show that PSNPs destabilize GB3 protein variants, and the binding free energy correlates strongly with protein unfolding (r = 0.82, p < 0.01 for carboxylate-functionalized PSNPs and r = 0.76, p < 0.03 for nonfunctionalized PSNPs). These results reveal how protein stability and charge distribution shape adsorption thermodynamics, informing frameworks for predicting protein-surface interactions.
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