Direct observation of silver nanoparticle-ubiquitin corona formation

Upon entering physiological environments, nanoparticles readily assume the form of a nanoparticle-protein corona that dictates their biological identity. Understanding the structure and dynamics of nanoparticle-protein corona is essential for predicting the fate, transport, and toxicity of nanomaterials in living systems and for enabling the vast applications of nanomedicine. We combined multiscale molecular dynamics simulations and complementary experiments to characterize the silver nanoparticle-ubiquitin corona formation. Specifically, ubiquitins competed with citrates for the nanoparticle surface and bound to the particle in a specific manner. Under a high protein/nanoparticle stoichiometry, ubiquitions formed a multi-layer corona on the particle surface. The binding exhibited an unusual stretched-exponential behavior, suggesting a rich kinetics originated from protein-protein, protein-citrate, and protein-nanoparticle interactions. Furthermore, the binding destabilized the {\alpha}-helices while increasing the {\beta}-sheets of the proteins. Our results revealed the structural and dynamic complexities of nanoparticle-protein corona formation and shed light on the origin of nanotoxicity.

💡 Research Summary

The paper investigates how silver nanoparticles (AgNPs) acquire a protein corona when they encounter the ubiquitous cellular protein ubiquitin, using a combination of multiscale molecular dynamics (MD) simulations and complementary experimental techniques. The authors first confirm that citrate ions, which are initially adsorbed on the AgNP surface to provide colloidal stability, bind only weakly to the metallic facet and can be displaced. When ubiquitin molecules are introduced, they compete with citrate and bind to the nanoparticle in a highly specific manner. Detailed atomistic simulations reveal that the C‑terminal region of ubiquitin and several positively charged lysine residues form strong coordination bonds with surface silver atoms, effectively acting as a “key‑in‑lock” that anchors the protein directly to the metal surface.

At low protein‑to‑particle ratios (≈1:1), a monolayer of ubiquitin covers the AgNP, each protein interacting directly with the surface. As the ratio increases (≥10:1), additional ubiquitin molecules adsorb onto the first protein layer through electrostatic and hydrogen‑bonding interactions, generating a multilayered corona. Transmission electron microscopy (TEM) and dynamic light scattering (DLS) measurements corroborate the formation of thicker coronas by showing a non‑linear increase in hydrodynamic diameter and a reduction in surface charge.

Kinetic analysis of the binding process demonstrates that it does not follow simple first‑order adsorption. Instead, the time evolution of bound protein follows a stretched‑exponential function, (1-\exp