Abstract
Gas-phase hydrazinolysis was used to analyze the glycoform of the O-linked oligosaccharide of human serum IgA 1. In our previous report, only one glycoform was obtained from the IgA1 of healthy individuals. However, it was found to be composed of heterogeneous IgAl components having mutually different glycoforms. First, the IgA 1 was separated into two subfractions having different affinities toward jacalin. Among them, the high-affinity subfraction was mainly composed of polymerized IgA1. Comparative study of the carbohydrate chain showed a relative abundance of Galβ1, 3GalNAc in the polymerized form. A simultaneous analysis of the N-glycan of these subfractions was also carried out. Three major components, two biantennary and one triantennary oligosaccharides, were obtained from both subfractions and the relative contents of these components were almost the same. On the other hand, IgA 1 was artificially polymerized by heating at 63°C for 2h. The heat-stable IgA 1 was separated from the heat-aggregated material on a Sephacryl S-300 column. The obtained heat-stable IgA 1 (approximately 20%) was not further aggregated by more heating under the same conditions. The heat-stable IgA 1 contained a much higher amount of the sialylated Galβ1, 3GalNAc. Thus, it was shown that the degree of completeness of the hinge O-linked oligosaccharide might be correlated with the stability and polymerization process of the IgAl molecule.
