Structural and functional changes of bovine beta-lactoglobulin after adsorption on hydrophobic surfaces : influence of the sorbent material and size

INTRODUCTION: Adsorption of protein molecules on interfaces occurs in natural and man-made systems, and plays a central role in many events related to human health, to food science, and to environmental issues (1,2). Structural rearrangements upon contact with the sorbent phase may affect the protein's biological activities (allergenicity, bioavailability, ability to bind micro- and macromolecular ligands). The surface characteristics of the sorbent material play a key role in the form and extent of these rearrangements. Knowledge of these phenomena may allow to predict or modulate the protein functional behavior after adsorption (3). In this work structural and functional changes undergone by bovine beta-lactoglobulin (BLG) - a relevant food allergen - upon adsorption on different materials and size hydrophobic surfaces (46 nm and 200 nm polystyrene nanoparticles or oil-in-water microemulsions) were evaluated by means of intrinsic fluorescence spectroscopy, binding of fluorescent probes, accessibility of cysteine thiols, and limited proteolysis followed by MALDI-TOF and LC-MS identification of released peptides. Changes in immunoreactivity were evaluated by competitive ELISA using epitope-specific monoclonal antibodies. RESULTS: The results indicate that BLG undergoes an extended stretch of the native structure after adsorption on hydrophobic surfaces, exposing regions buried from the aqueous media in the native structure. Hydrolysis of BLG stuck on different surfaces results into different peptide patterns, but for a single peptide – that may be a common region interacting with the sorbent phase. Immunoreactivity of BLG is markedly altered upon absorption. The amplitude of the observed differences is also depending on the nature of the sorbent material. All these results corroborate the central role of the nature and of the size of the sorbent material, as determinants of the type and extent of BLG structural rearrangements. In silico surface denaturation simulation is running in order to have an overview on the overall structural modification process.