Effects of Nanoparticle Electrostatics and Protein-Protein Interactions on Corona Formation: Conformation and Hydrodynamics.

All-atom molecular dynamics simulations of plasma proteins (human serum albumin, fibrinogen, immunoglobulin gamma-1 chain-C, complement C3, and apolipoprotein A-I) adsorbed onto 10 nm sized cationic, anionic, and neutral polystyrene (PS) particles in water are performed. In simulations of a single protein with a PS particle, proteins eventually bind to all PS particles, regardless of particle charge, in agreement with experiments showing the binding between anionic proteins and particles, which is further confirmed by calculating the binding free energies from umbrella sampling simulations. Simulations of mixtures of multiple proteins and a PS particle show the formation of the protein layer on the surface via the adsorption competition between proteins, which influences the binding affinity and structure of adsorbed proteins. In particular, diffusivities are much higher for proteins bound to the particle surface or to the boundary of the protein layer than for those bound to both the particle surface and other proteins, indicating the dependence of protein mobility on their positions in the layer. These findings help to explain in detail experimental observations regarding the replacement of plasma proteins at the early stage of corona formation and the difference in the binding strength of proteins in inner and outer protein-layers.