Biosynthesis of sialylated and fucosylated selectin ligands of HL-60 cellsin vitro - Midchain alpha 3-fucose units inhibit terminal alpha 6-sialylation but not alpha 3-sialylation of polylactosamines

Polylactosamines Neu5Ac alpha 2-3'Lex beta 1-3'Lex beta 1-3'Lex and Neu5Ac alpha 2-3'LN beta 1-3'Lex beta 1-3'Lex [Lex, Gal beta 1-4(Fuc alpha 1-3)Glc NAc; LN, Gal beta 1-4GlcNAc] decorate selectin counterreceptors in human HL -60 cells. Here, me show that HL-60 cell lysates catalyze distal alpha 3-si alylation of LN beta 1-3'LN beta 1-3'LN and LN beta 1-3'Lex beta 1-3'Lex ef ficiently, outlining two potential sets of biosynthetic pathways leading to the selectin ligands, In one set, alpha 3-sialylation precedes internal fu cosylation of the polylactosamine backbone, whereas in the other one, inter nal fucosylation is initiated before alpha 3-sialylation, In contrast to al pha 3-sialylation, LN beta 1-3'Lex beta 1-3'Lex was alpha 6-sialylated much less efficiently than LN beta 1-3'LN beta 1-3'LN by HL-60 cell lysates, He nce, internal fucosylation may regulate the extent of alpha 6-sialylation o f polylactosamines in these cells, (C) 1999 Federation of European Biochemi cal Societies.