Studies on the relationship between structure and IgE-binding ability of Parietaria judaica allergen I

The main allergen of Parietaria judaica pollen, Par j I, is a glycopolypeptide with mol. wt about 10,000. It shows a considerable charge heterogeneity which is mostly due to the carbohydrate prosthetic groups, since treatment with trifluoromethanesulfonic acid yielded a deglycosylated protein with 8500 mol. wt that displayed only a few bands on IEF, in a narrow pH-region around 5.0. Deglycosylated Par j I exhibited a specific allergenic activity slightly lower than that of native Par j I; however, no allergenic determinants should be located on the sugar moiety since both native and deglycosylated Par j I inhibited up to a similar extent the binding of specific human IgE to P. judaica-coated wells in ELISA. The decrease of specific allergenic activity following deglycosylation could be ascribed to conformational changes evidenced by CD experiments. On the other hand, fluorescence spectroscopy showed that Par j I bears unidentified yellow-brown chromophores strongly linked to the polypeptide chain. These chromophores were not removed by TFMS treatment. Finally, reduction and alkylation caused the complete loss of allergenic activity, showing that disulphide bridges are essential for the IgE-binding ability of Par j I.