Determination of orientation and adsorption-induced changes in the tertiary structure of proteins on material surfaces by chemical modification and peptide mapping

The labeling of amino acid residues followed by peptide mapping via mass spectrometry (AAL/MS) is a promising technique to provide detailed information on the adsorption-induced changes in its solvent accessibility. However, the potential of this method for the study of adsorbed protein structure is largely undeveloped at this time. The objective of this research was therefore to extend these capabilities by developing and applying AAL/MS techniques for a range of amino acid types to identify the dominant configurations of an adsorbed protein on a material surface. In this study, the configuration of hen egg white lysozyme (HEWL) adsorbed on fused silica glass, high-density polyethylene (HDPE) and poly(methyl methacrylate) (PMMA) was mapped by combining the labeling profiles obtained from five amino acid labels, which were independently applied. In order to be able to combine the results from the different amino acid labeling processes, the intensity of the HEWL segment without the target amino acids was used as an internal control to normalize the intensity shifts to an equivalent level. The resulting quantitative differences in the normalized amino acid profiles were then used to provide insights into adsorbed orientation, protein–protein interactions and adsorption-induced tertiary unfolding of HEWL, which were found to be distinctly different between the fused silica glass, HDPE and PMMA surfaces. The developed technique has the potential for broad application and for expansion to additional targeted amino acids to provide highly detailed information on the adsorbed state of any protein on any given surface.