  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.
