Beta-lactoglobulin structural rearrangement at interfaces: relevance to its immunogenic behavior

The physiological properties of many proteins, relies on their behavior at the molecular scale, which often is affected by their surface interactions. A central issue for the in vivo action of allergens, but also of antibacterial or otherwise bioactive peptides, is the surface behavior in terms of interaction with other molecules and surfaces present in the same environment. -lactoglobulin (BLG) is the major bovine whey protein. A 36 kDa dimer of identical subunits, BLG is considered the major milk allergen. A general relationship between structure and immunoreactivity of milk proteins has not been established. The aim of this work is to understand whether and how the BLG conformational changes derived from the interaction with two model hydrophobic interfaces (a liquid oil-in-water nanoemulsion, and solid latex nanoparticles), can modulate its immunoreactivity and its absorption by human cells involved in the immune response. Conformational changes in the absorbed protein were demonstrated through spectroscopic and limited proteolysis/MS approaches. ELISA experiments demonstrated that immunoreactivity of BLG increases upon adsorption on either liquid/liquid or solid/liquid hydrophobic interfaces, likely as a consequence of recognition of cognate regions of the protein by the antibodies. Indeed, after hydrolysis with trypsin, the overall immunoreactivity of the absorbed protein remains high compared with that of the protein hydrolyzed in solution. Also, the kinetics of internalization by monocytes of BLG adsorbed on the oil nanodroplets is with respect to free BLG, which is absorbed more efficiently and rapidly than BLG adsorbed on an emulsion interface. Competition experiments, carried out by adding free unlabeled protein to both free and emulsion BLG systems shows how the free protein seems to acts as an enhancer for the internalization of the oil-bound protein. Whether these evidences indicate independent patterns for intracellular uptake of free and nanoparticulate-bound BLG remains to be verified.