Fucosyltransferase substrate specificity and the order of fucosylation in invertebrates

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Abstract
Core α1,6-fucosylation is a conserved feature of animal N-linked oligosaccharides being present in both invertebrates and vertebrates. To prove that the enzymatic basis for this modification is also evolutionarily conserved, cDNAs encoding the catalytic regions of the predicted Caenorhabditis elegans and Drosophila melanogaster homologs of vertebrate α1,6-fucosyltransferases (E.C. 2.4.1.68) were engineered for expression in the yeast Pichia pastoris. Recombinant forms of both enzymes were found to display core fucosyltransferase activity as shown by a variety of methods. Unsubstituted nonreducing terminal GlcNAc residues appeared to be an obligatory feature of the substrate for the recombinant Caenorhabditis and Drosophila α1,6-fucosyltransferases, as well as for native Caenorhabditis and Schistosoma mansoni core α1,6-fucosyltransferases. On the other hand, these α1,6-fucosyltransferases could not act on N-glycopeptides already carrying core α1,3-fucose residues, whereas recombinant Drosophila and native Schistosoma core α1,3-fucosyltransferases were able to use core α1,6-fucosylated glycans as substrates. Lewis-type fucosylation was observed with native Schistosoma extracts and could take place after core α1,3-fucosylation, whereas prior Lewis-type fucosylation precluded the action of the Schistosoma core α1,3-fucosyltransferase. Overall, we conclude that the strict order of fucosylation events, previously determined for fucosyltransferases in crude extracts from insect cell lines (core α1,6 before core α1,3), also applies for recombinant Drosophila core α1,3- and α1,6-fucosyltransferases as well as for core fucosyltransferases in schistosomal egg extracts.