FTIR-ATR and radiolabeling study of the adsorption of ribonuclease A onto hydrophilic surfaces: Correlation between the exchange rate and the interfacial denaturation

The kinetic aspects of the exchange mechanism and of the ongoing structural modification with interfacial residence time for ribonuclease A adsorbed on hydrophilic surfaces are investigated. This is done by means of radiolabeling and FTIR-ATR techniques. An important decrease of the protein exchange ability and increase of the irreversibly bound protein fraction with adsorption time is found. These observations are compared with a decrease of the relative content of beta-sheet and an increase in turns and unordered structures in the adsorbed protein layer. Both the exchange process and the structural modifications vary with comparable characteristic times, on the order of 20 h for the exchange process on the TiO2 surface and 10-15 h for the structural modifications on the germanium one. These data suggest that the decrease in the protein exchange ability results from important structural changes following adsorption, which corresponds to a decrease of the ordered structure of the protein.