Understanding Cooperative Protein Adsorption Events at the Microscopic Scale: A Comparison between Experimental Data and Monte Carlo Simulations

Cooperative effects play a vital role in protein adsorption events on biological interfaces. Despite a number of studies in this field molecular adsorption mechanisms that include cooperativity are still under debate. In this work we use a Monte Carlo-type simulation to explore the microscopic details behind cooperative protein adsorption. The simulation was designed to implement our previously proposed mechanism through which proteins are not necessarily rejected if they approach the surface to an occupied region. Instead, we suggest that proteins can be tracked laterally for a certain distance due to the influence of preadsorbed proteins in order to reach the nearest available binding site. The simulation results were compared with experimental data obtained by using the supercritical angle fluorescence (SAF) microscopy technique. It was found that the tracking distance may be up to 2.5 times the protein's diameter depending on the investigated system. The general validity of this tracking mechanism is supported by a number of linear or upward concave adsorption kinetics reported in the literature which are consistent with our simulation results. Furthermore, the self-organization of proteins adsorbing under cooperative conditions on the surface is shown to necessarily cause density inhomogeneities in the surface distribution of proteins which is also in agreement with experimental observations.