Surface Attachment Enhances the Thermodynamic Stability of ProteinL

Despite the importance of protein-surface interactions in both biology and biotechnology, our understanding of their origins is limited due to a paucity of experimental studies of the thermodynamics behind such interactions. In response, we have characterized the extent to which interaction with a chemically well-defined macroscopic surface alters the stability of proteinL. To do so, we site-specifically attached a redox-reporter-modified protein variant to a hydroxy-terminated monolayer on a gold surface and then used electrochemistry to monitor its guanidine denaturation and determine its folding free energy. Comparison with the free energy seen in solution indicates that interaction with this surface stabilizes the protein by 6kJmol(-1), a value that is in good agreement with theoretical estimates of the entropic consequences of surface-induced excluded volume effects, thus suggesting that chemically specific interactions with this surface (e.g., electrostatic interactions) are limited in magnitude.