Conformation transitions of adsorbed proteins by interfacial forces at an air-liquid interface and their effect on the catalytic activity of proteins

An efficient method to monitor and control the secondary structures of globular proteins is developed by adsorption of proteins from a bulk solution onto an air-liquid interface. By controlling the concentration of a protein in the aqueous phase, as well as the attractive force exerted by the template layer, the adsorption of proteins can be classified into two stages according to the variation of surface pressure. In the first stage, the proteins adsorb as a single-molecular layer. The interface-molecule interactions induce a structural transition of the adsorbed proteins into a beta-sheet conformation (alpha/beta < 0.1). The second stage is initiated by further adsorption of proteins onto the interface, forming multilayer proteins, and triggering a conformational transition into alpha-helix (alpha/beta > 10). The glucose sensing experiments demonstrate that GOx with alpha-helix conformation has a much higher sensitivity than beta-sheet GOx, attributed to its lower charge transfer resistance at the GOx-electrolyte interface. The present study not only provides a new approach to monitor, control, and design protein conformations, but also raises the importance of adsorption states of proteins in performing bio-activities at bio-interfaces.