The abundance of additional N-acetyllactosamine units in N-linked tetraantennary oligosaccharides of human Tamm-Horsfall glycoprotein is a donor-specific feature

Previously, treatment of Tamm-Horsfall glycoprotein (THp) from differentdonors with endo-beta-galactosidase has been shown to liberate a tetra- anda Sd(a)-active pentasaccharide, concluding the presence of N-linkedcarbohydrate chains containing additional N - acetyllactosamine units.These type of oligosaccharides were not found in a detailed structureelucidation of the carbohydrate moiety of THp of one male donor, suggestinga donor-specific feature for these type of structures. Therefore, THp wasisolated from four healthy male donors and each subjected toendo-beta-galactosidase treatment in order to release these tetra- andSd(a)-active pentasaccharide. Differences were observed in the total amountof released tetra- and Sda-active pentasaccharide of the used donors (42,470, 478, 718 microg/100 mg THp), indicating that the presence of repeatingN-acetyllactosamine units incorporated into the N-glycan moiety of THp isdonor specific. Furthermore, a higher expression of the Sd(a) determinanton antennae which display N-acetyllactosamine elongation was observed,suggesting a better accessibility for thebeta-N-acetylgalactosaminyltransferase. In order to characterize theN-glycans containing repeating N- acetyllactosamine units, carbohydratechains were enzymatically released from THp and isolated. Thetetraantennary fraction, which accounts for more than 33% of the totalcarbohydrate moiety of THp, was used to isolate oligosaccharides containingadditional N - acetyllactosamine units. Five N-linked tetraantennaryoligosaccharides containing a repeating N-acetyllactosamine unit wereidentified, varying from structures bearing four Sd(a) determinants tostructures containing no Sd(a) determinant (see below). One compound wasused in order to specify the branch location of the additional N-acetyllactosamine unit, and it appeared that only the Gal-6' and Gal-8'residues were occupied by a repeating N -acetyllactosamine unit.