Protein Corona Formation on Cadmium-Bearing Nanoparticles: Important Role of Facet-Dependent Binding of Cysteine-Rich Proteins.

Cadmium-bearing nanoparticles, such as nanoparticulate cadmium selenide (CdSe) and cadmium sulfide (CdS), widely exist in the environment and originate from both natural and anthropogenic sources. Risk assessment of these nanoparticles cannot be accurate without taking into account the properties of the protein corona that is acquired by the nanoparticles upon biouptake. Here, we show that the compositions of the protein corona on CdSe/CdS nanoparticles are regulated collectively by the surface atomic arrangement of the nanoparticles and the abundance and distribution of cysteine moieties of the proteins in contact with the nanoparticles. A proteomic analysis shows that the observed facet-dependent preferential binding of proteins is mostly related to the cysteine contents of the proteins, among commonly recognized protein properties controlling the formation of the protein corona. Theoretical calculations further demonstrate that the atomic arrangement of surface Cd atoms, as dictated by the exposed facets of the nanoparticles, controls the specific binding mode of the S atoms in the disulfide bonds of the proteins. Supplemental protein adsorption experiments confirm that disulfide bonds remain intact during protein adsorption, making the binding of protein molecules sensitive to the abundance and distribution of Cd-binding moieties and possibly molecular rigidity of the proteins. The significant conformational changes of adsorbed proteins evidenced from a circular dichroism spectroscopy analysis suggest that disrupting the structural stability of proteins may be an additional risk factor of Cd-bearing nanoparticles. These findings underline that the unique properties and behaviors of nanoparticles must be fully considered when evaluating the biological effects and health risks of metal pollutants.