Proteins are natural polymers which under physiological conditions fold into complex three-dimensional structures. The sequence of amino acids determines the primary structure, the arrangement of fragments of the amino acid chains into α-helices or β-sheets represent the secondary structure elements of a protein. A three-dimensional structure of a protein is known as a tertiary structure. Under pathological conditions, some proteins undergo irreversible changes in their secondary and tertiary structure. In this work, we investigate the adsorption process of a model protein: lysozyme on the gold surface from electrolyte solutions of different pH and ionic strengths. Multi-Parameter Surface Plasmon Resonance (MP-SPR) and Quartz Crystal Microbalance (QCM-D) results show that the maximum adsorption efficiency was obtained at the pH=10, which corresponds to lysozyme’s isoelectric point. Results of MP-SPR and QCM-D methods allow for the calculation of the hydration level of lysozyme’s layer. Amide I’ mode of proteins is of great analytical importance because it provides information on the secondary structure elements of a protein. The conformation of adsorbed on the gold surface lysozyme was examined using Polarization-Modulation Infrared Reflection Absorption-Spectroscopy (PM-IRRAS). The analysis of the amide I’ mode region of the PM-IRRA spectra shows that the secondary structure of the adsorbed protein differs from the conformation found in the solution phase (examined by CD). Furthermore, we investigated the impact of the surface charge density on the gold electrode on the adsorption process of lysozyme. To modulate the surface charge density of the gold surface electrochemical control was used. The structure of the adsorbed protein depends on both the surface charge density and pH of the electrolyte solution. Most substantial structural changes are observed when lysozyme adsorbs on the positively charged surface from acidic (pH=4) as well as on negatively charged surface from basic (pH=9) condition. The electrostatic attraction determines not only the amount but also the conformation of the adsorbed protein.

Changes in protein’s secondary structure as a result of its interaction with a gold surface

2019 Spring National Meeting

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