Molecular-Level Characterization of Protein-Nanoparticle Interactions: Orientation, Deformation and Matrix Effects

The adsorption of a corona has major impacts on the environmental fate of a released nanoparticle. While numerous techniques have been developed or adapted to determine corona composition, a detailed understanding of the forces that drive adsorption is lacking. Characterizing nanoparticle-corona complexes typically requires that the complex is isolated from the bulk medium prior to analysis, which can disrupt native interactions. To achieve a more detailed picture of protein-particle interactions, protein footprinting methods that were initially developed to investigate protein-protein interactions have been employed by us and others. Through the chemical labeling of solvent-exposed residues, molecular-level interactions can be obtained. Using a combination of protein footprinting and simulation, we previously showed preferential sites of interaction between cytochrome c (cyt c) and negatively charged gold nanoparticles, as well as evidence of protein deformation on the particle surface. Herein, we expand our investigation into a suite of proteins with differing propensity for deformation, as previously reported from acid exposure studies, and evaluate how matrix components affect protein binding orientation and/or deformation. We found that all three model proteins—cytochrome c, b-lactogloublin, and albumin—bound to nanoparticles through residues within flexible loop regions, that their secondary structure is unlikely to experience substantial deformation but may instead undergo localized conformational changes to enable additional residues to contact the particle surface, and that the protein complexes sometimes partially unfold (or deform) during the binding to the nanoparticle.