For many years, polyclonal antibodies raised against the plant glycoprotein horseradish peroxidase have been used to specifically stain the neural and male reproductive tissue of Drosophila melanogaster. This epitope is considered to be of carbohydrate origin, but no glycan structure from Drosophila has yet been isolated that could account for this cross-reactivity. Here we report that N-glycan core ␣1,3-linked fucose is, as judged by preabsorption experiments, indispensable for recognition of Drosophila embryonic nervous system by anti-horseradish peroxidase antibody. Further, we describe the identification by matrix-assisted laser desorption-ionization time-of-flight mass spectrometry and high performance liquid chromatography of two Drosophila N-glycans that, as already detected in other insects, carry both ␣1,3-and ␣1,6-linked fucose residues on the proximal core GlcNAc. Moreover, we have isolated three cDNAs encoding ␣1,3-fucosyltransferase homologues from Drosophila. One of the cDNAs, when transformed into Pichia pastoris, was found to direct expression of core ␣1,3-fucosyltransferase activity. This recombinant enzyme preferred as substrate a biantennary core ␣1,6-fucosylated N-glycan carrying two non-reducing N-acetylglucosamine residues (GnGnF 6 ; K m 11 M) over the same structure lacking a core fucose residue (GnGn; K m 46 M). The Drosophila core ␣1,3-fucosyltransferase enzyme was also shown to be able to fucosylate N-glycan structures of human transferrin in vitro, this modification correlating with the acquisition of binding to anti-horseradish peroxidase antibody.Glycoproteins from plants and invertebrates are often highly immunogenic and many antibodies (both IgG and IgE) directed against them bind to core ␣1,3-fucose and/or 1,2-xylose residues of their N-linked oligosaccharides (1-7); since these modifications are present across plant species and one or the other modification is present in a number of invertebrates, these antibodies are highly cross-reactive. Indeed, polyclonal antibodies to horseradish peroxidase (anti-HRP) 1 have been used for nearly two decades to specifically stain neurons, and their growth pathways, in Drosophila melanogaster (8 -11); similar staining has also been described in grasshopper (11), whereas in Caenorhabditis elegans 10% of neurons are stained by this antibody (12). A number of proteins in Drosophila, such as an Na ϩ ,K ϩ ATPase christened Nervana, a receptor tyrosine phosphatase, and cell adhesion molecules (e.g. fasciclin I and II, neurotactin and neuroglian), have been found to bind anti-HRP (9 -11, 13, 14); however, no data on their glycosylation have been described. A number of Drosophila nac (neurally altered carbohydrate) mutants have been described, which are defective in anti-HRP staining of adult flies and display wing morphological defects (15) and, when under cold stress, some minor behavioral and eye developmental abnormalities (9). Neither the affected gene(s) nor the underlying biochemical defect(s) have been identified.As compared with the amount o...
