Secondary Structural Changes in Protein as a Result of Electroadsorption at Aqueous-Organogel Interfaces

The adsorption of proteins at aqueous-organic interfaces offers the possibility to examine protein structural rearrangements upon interaction with lipophilic phases, without modifying the bulk protein or relying on a solid support. The aqueous-organic interface has already provided a simple means of protein detection, often involving adsorption and ion complexation; however, little is yet known about the protein structure at such interfaces. This work focuses on the interaction between proteins and an electrified aqueous-organic interface via controlled protein electroadsorption. Four proteins known to be electroactive at such interfaces were studied: lysozyme, myoglobin, cytochrome c and hemoglobin. Following controlled protein electrodeposition onto the interface, ex situ structural characterization of the proteins by FTIR spectroscopy was undertaken, focusing on secondary traits within the amide I band. The structural variations observed included unfolding to form aggregated anti-parallel beta-sheets, where the rearrangement was specifically dependent on the interaction with the organic phase. This was supported by MALDI-ToF MS measurement, which showed the formation of protein-anion complexes for three of these proteins, and molecular dynamics simulations, which modelled the structure of lysozyme at an aqueous-organic interface. Based on these findings, the modulation of protein secondary structure by interfacial electrochemistry opens up unique prospects to selectivly modify proteins.