A Novel Conformation-Dependent Monoclonal Antibody Specific to the Native Structure of β-Lactoglobulin and Its Application

Molten globules are thought to be general intermediates in protein folding and unfolding. β-lactoglobulin (β-LG) is one of the major bovine whey proteins, constituting ∼10 to 15% of total milk proteins. We have recently identified β-LG as a superior marker for evaluating thermally processed milk. Strand D of β-LG participates in irreversible thermal unfolding as probed by a monoclonal antibody (mAb) specific to thermally denatured β-LG. In the present study, we used native β-LG as an immunogen to test the hypothesis that a specific mAb against the native β-LG could be established. As result, a mAb (4H11E8) directed against the native structure of β-LG was made. The antibody did not recognize the heat-denatured form of β-LG, such as its dimer and aggregates. Immunoassay using this “native” mAb showed that the stability of β-LG was at temperatures ≤70°C. β-Lactoglobulin began to deteriorate between 70 and 80°C over time. The denaturation was correlated with the transition temperature of β-LG. Further chemical modification of Cys (carboxymethylation) or positively charged residues (acetylation) of β-LG totally abolished its immunoreactivity, confirming the conformation-dependent nature of this mAb. Using competitive ELISA, the 4H11E8 mAb could determine the native β-LG content in commercially processed milks. Concentrations of native β-LG varied significantly among the local brands tested. From a technological standpoint, the mAb prepared in this study is relevant to the design and operation of appropriate processes for thermal sanitation of milk and of other dairy products.