Influence of structural details in modeling electrostatically driven protein adsorption

Mechanistic modeling of protein adsorption has evolved to include increasingly detailed descriptions of protein structure in an effort to capture experimentally observed behavior. This has been especially true of electrostatically driven adsorption, for which colloidal models have been used frequently. These efforts have focused on adsorption of proteins to oppositely charged surfaces and often capture the experimental trends even with gross simplification of protein structure. As a more stringent test of model sensitivity to structural details, we have modeled the patch-controlled adsorption of basic proteins on anion-exchange surfaces, where a small number of negative charges on the protein surface lead to a net attraction between the net positively charged protein and the positively charged surface. We account in detail for the protein shape and charge distribution and examine the role of the assumed surface description. A model assuming a uniformly charged surface is unable to predict electrostatically driven adsorption observed experimentally, whereas models accounting for the discreteness of charge on the adsorbent are able to explain some of the anomalous experimental trends. Although our results show that fine details of the models are crucial in correctly describing adsorption behavior under these unusual conditions, they also suggest that when the protein and the surface are oppositely charged, model calculations can be quite robust to model idealizations.