Silica Nanoparticle Size Influences the Structure and Enzymatic Activity of Adsorbed Lysozyme

TLDR

The study examines how silica nanoparticle size influences the structure and enzymatic activity of adsorbed lysozyme. Adsorption of lysozyme on silica nanoparticles is size‑dependent, with 4‑nm particles forming complexes, 20‑nm particles yielding monolayer adsorption, and 100‑nm particles producing multilayer adsorption; larger particles and lower pH cause greater loss of α‑helix and enzymatic activity, correlating with decreased protein function.

Abstract

Adsorption of chicken egg lysozyme on silica nanoparticles of various diameters has been studied. Special attention has been paid to the effect of nanoparticle size on the structure and function of the adsorbed protein molecules. Both adsorption patterns and protein structure and function are strongly dependent on the size of the nanoparticles. Formation of molecular complexes is observed for adsorption onto 4-nm silica. True adsorptive behavior is evident on 20- and 100-nm particles, with the former resulting in monolayer adsorption and the latter yielding multilayer adsorption. A decrease in the solution pH results in a decrease in lysozyme adsorption. A change of protein structure upon adsorption is observed, as characterized by a loss in α-helix content, and this is strongly dependent on the size of the nanoparticle and the solution pH. Generally, greater loss of α helicity was observed for the lysozyme adsorbed onto larger nanoparticles under otherwise similar conditions. The activity of lysozyme adsorbed onto silica nanoparticles is lower than that of the free protein, and the fraction of activity lost correlates well with the decrease in α-helix content. These results indicate that the size of the nanoparticle, perhaps because of the contributions of surface curvature, influences adsorbed protein structure and function.