Contrasting effects of nanoparticle binding on protein denaturation

Understanding the interactions between nanoparticles (NPs) and proteins is essential for the design of bionanotechnology and biomedicine and for delineating the biological implications of nanomaterials for safe nanotechnology. In the present study we have examined protein denaturation in the presence of NPs, using the high-throughput technique of differential scanning fluorometry. Specifically, the melting temperature of human immunoglobulin (IgG) rose from 59.5 to 68.5 °C while that of lysozyme dropped from 74.0 to 68.8 °C for increasing NP:protein molar ratios. This contrast in protein stability was further examined by circular dichroism spectroscopy and Thioflavin T measurements, where a marked increase inβ-sheets as well as amyloid fibrillation occurred in lysozyme while small changes were seen in the secondary structure of IgG. Our immunoassays further revealed a greatly elevated cytokine production in the cells treated with fullerol-lysozyme and a mostly unchanged TNF-α secretion in THP-1 cells exposed to fullerol-IgG, suggesting a connection between changes in protein secondary structure induced by fullerol binding and their triggered immune responses. These contrasting effects imply that, due to their finite solubility and size NPs display the duality of both a particle and a chemical and, therefore, do not conform to the conventional role of a ligand in protein stabilization.