Effects of divalent cations on the physical, conformational and immunological properties of bovine allergen β-lactoglobulin aggregates

Abstract

β-lactoglobulin is a major allergen in whey and always forms aggregates under different conditions. In our study, four kinds of divalent cations (Cu2+, Mg2+, Zn2+ and Ca2+) were used to induce the aggregation of β-lactoglobulin. The molecular interactions and characteristics, thermal stability and conformational structure of aggregates were monitored by silver staining, RP-HPLC, differential scanning calorimetry and spectroscopic methods, respectively. The immunological properties of Cu2+-induced β-lactoglobulin aggregates and dimers were evaluated in a Balb/c mouse model. The results showed that Cu2+ promoted the highest β-lactoglobulin dimer levels compared with other metal ions. The thermal stability of aggregates induced by the four ions was more stable than that of native protein. The specific molecular interaction of aggregates induced by Mg2+, Zn2+ and Ca2+ was disulfide bonding, while Cu2+-induced β-lactoglobulin aggregates were connected by disulfide bonds combined with other bonds. Specially, Cu2+-induced dimer showed decreased allergenicity and a shift from the Th2 response to the Th1 response that balances homeostasis compared with native BLG and Cu2+-induced aggregates. The results may provide a possible method to alleviate the allergenicity of bovine β-lactoglobulin by forming more dimers.