Plasma protein adsorption on TiO2 nanoparticles: Impact of surface adsorption on temperature-dependent structural changes

Abstract

Protein adsorption on metal oxide nanoparticle surfaces is crucial to the behavior of oxide nanoparticles in biological systems. In this study, attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy was used for the first time to probe differences in the temperature-dependent conformational changes of two plasma proteins, bovine serum albumin (BSA) and fibrinogen (Fib), in solution and adsorbed on titanium dioxide nanoparticle (ca. 20 nm in diameter) surfaces. ATR-FTIR spectra and autocorrelation moving window two-dimensional correlation (MW2D) spectroscopy were used to identify the denaturation temperature range of these two proteins in aqueous solution and adsorbed. Generalized two-dimensional correlation spectroscopy (2DCOS) was done to investigate the protein unfolding pathway. The results show that the thermostability of BSA changed when adsorbed on the surface whereas there was no difference for solution phase Fib and adsorbed on TiO2. The most notable fact was that solution BSA underwent significant structural changes upon adsorption whereas adsorbed Fib did not. Upon heating adsorbed BSA, no further changes occurred while BSA in solution thermally denatured. In contrast, solution and adsorbed Fib had identical denaturation temperatures and similar sequential secondary structural changes with increasing temperature. These studies show quantitatively, for the first time, that there are differences in the temperature-dependent structural changes of proteins adsorbed on nanoparticles surfaces and these changes depend on the initial interaction with the nanoparticle surface. Overall, the results of this study provide new insights into understanding the effects of temperature on the structure of adsorbed protein on nanoparticle surfaces and the range of different behaviors that can occur.