Effect of carbon black nanoparticles on the albumin secondary structure

Nano-particulate air pollutants-particularly fine particle matter (PM2.5)-may cause several health issues, such as the accumulation of misfolded proteins in developing brains. However, the physicochemical molecular mechanism underlying nanoparticle (NP) toxicity remains poorly understood. This study investigates the effects of carbon black (CB) NPs (CB-NPs), with different surface properties and particle sizes, on the secondary structure of bovine serum albumin (BSA) using Fourier transform infrared and circular dichroism (CD) spectroscopic techniques, complemented by molecular dynamics (MD) simulations. The BSA sample incubated with CB-NPs exhibited no significant change when analyzed with excess BSA unbound to the NPs; however, CD spectroscopy revealed that Printex 90-a CB-NP with a smaller primary particle size and a more defective graphene structure-induced a notable change in the secondary structure of the adsorbed BSA. This change was characterized by a decrease in α-helix content and an increase in β-sheets. MD simulations further supported these findings, signifying that BSA monomers were adsorbed onto the CB-NP surface, leading to restricted protein mobility. This study provides crucial molecular-level insight into the role of carbonaceous NPs in triggering protein unfolding, a crucial step in NP toxicity.