Effect of Infrared Light on Protein Behavior in Contact with Solid Surface

Adsorption of proteins at a solid surface affects characteristics of the surface (e.g. its biocompatibility) and functionality of the immobilized biomacromolecules. The latter is defined by the type of binding sites, protein conformation and its structural flexibility that enable functional motions to occur. Protein motions are only possible at certain level of hydration. Furthermore, water molecules act as lubricant facilitating sliding along solid surface. In this work we explore the potential of a remote physical trigger –a non-ionizing infrared radiation (IR) to affect protein-surface interactions. We report on IR-induced changes of hydrophilicity of the protein coatings on silica nanoparticles, impact of IR on monitored in-situ dynamic adsorption of proteins on silica surface and effect of IR on conformational state of adsorbed proteins. Our results indicate that IR can protect proteins from surface denaturation depending on the presence of strongly hydrated amino acid residues. Preservation of native fold results in protein coatings of higher hydrophilicity. IR can also facilitate displacement of surface activespecies that became adsorbed to protein apolar compartments and couldotherwise promote denaturation. Apart from supporting native conformation, their removalincreases protein-water interfacial tension and therefore promotes aggregation (hydrophobic attraction) of the protein-coated nanoparticles. By its ability to affect protein conformational state and interfacial characteristics (such as effective protein-water affinity) IR radiation can therefore modulate protein interactions.