INFLUENCE OF STRUCTURAL DETAILS IN MODELING ELECTROSTATICALLY DRIVEN PROTEIN ADSORPTION

Mechanistic modeling of protein adsorption has evolved to include incr easingly detailed descriptions of protein structure in an effort to ca pture experimentally observed behavior. This has been especially true of electrostatically driven adsorption, for which colloidal models hav e been used frequently. These efforts have focused on adsorption of pr oteins to oppositely charged surfaces and often capture the experiment al trends even with gross simplification of protein structure. As a mo re stringent test of model sensitivity to structural details, we have modeled the patch-controlled adsorption of basic proteins on anion-exc hange surfaces, where a small number of negative charges on the protei n surface lead to a net attraction between the net positively charged protein and the positively charged surface. We account in detail for t he protein shape and charge distribution and examine the role of the a ssumed surface description. A model assuming a uniformly charged surfa ce is unable to predict electrostatically driven adsorption observed e xperimentally, whereas models accounting for the discreteness of charg e on the adsorbent are able to explain some of the anomalous experimen tal trends. Although our results show that fine details of the models are crucial in correctly describing adsorption behavior under these un usual conditions, they also suggest that when the protein and the surf ace are oppositely charged, model calculations can be quite robust to model idealizations.