Title
Impacts of glycation and transglutaminase-catalyzed glycosylation with glucosamine on the conformational structure and allergenicity of bovine β-lactoglobulin
Author
Fangzhou Yuan, Ishfaq Ahmed, Liangtao Lv, Zhaojie Li, Zhenxing Li, Hong Lin, Hang Lin, Jinxia Zhao, Shenglan Tian, Jia Ju Ma
Year
2018
Journal
Food & Function
Abstract
β-lactoglobulin (β-LG) is recognized as the major milk allergen. In this study, the effects of transglutaminase (TGase) and glucosamine (GlcN)-catalyzed glycosylation and glycation on the conformational structure and allergenicity of β-lactoglobulin (β-LG) were investigated. The formations of cross-linked peptides were demonstrated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), and GlcN-conjugated modification was identified using matrix-assisted laser desorption ionization-time of flight-mass spectrometry (MALDI-TOF-MS). Structural analysis revealed that glycosylation and glycation of β-LG induced unfolding of the primary protein structure followed by loss of secondary structure. As revealed by the circular dichroism (CD) spectroscopies, glycosylated β-LG exhibited highest increase in the β-sheets from 32.6 % to 40.4 % (25 °C) and 44.2 % (37 °C), and the percentage of α-helices decreased from 17.7 % to 14.4 % (25 °C) and 12.3 % (37 °C), respectively. The tertiary and quaternary structures of β-LG also changed significantly during glycosylation and glycation, along with reduced free amino groups and variation in surface hydrophobicity. Immunoblotting and indirect enzyme-linked immuno sorbent assay (ELISA) analyses demonstrated that the lowest IgG- and IgE-binding capacities of β-LG were obtained following glycosylation at 37 °C, which were 52.7 % and 56.3 % lower than that of the native protein in a respective way. The reduction in the antigenicity and potential allergenicity of glycosylated β-LG were more pronounced compared to TGase treated- and glycated β-LG, which correlated well with the structural changes. These results suggest that TGase-catalyzed glycosylation has more potential compared to glycation for mitigating the allergenic potential of milk products.
Instrument
J-815
Keywords
Circular dichroism, Secondary structure, Thermal stability, Chemical stability, Food science, Biochemistry