Drosophila sperm surface alpha-L-fucosidase interacts with the egg coats through its core fucose residues

Sperm-oocyte interaction during fertilization is multiphasic, with multicomponent events, taking place between egg's glycoproteins and sperm surface receptors. Protein-carbohydrate complementarities in gamete recognition have observed in cases throughout the whole evolutionary scale. Sperm-associated alpha-L-fucosidases have been identified in various organisms. Their wide distribution and known properties reflect the hypothesis that fucose and alpha-L-fucosidases have fundamental function(s) during gamete interactions. An alpha-L-fucosidase has been detected as transmembrane protein on the surface of spermatozoa of eleven species across the genus Drosophila. Immunofluorescence labeling showed that the protein is localized in the sperm plasma membrane over the acrosome and the tail, in Drosophila melanogaster. In the present study, efforts were made to analyze with solid phase assays the oligosaccharide recognition ability of fruit fly sperm alpha-L-fucosidase with defined carbohydrate chains that can functionally mimic egg glycoconjugates. Our results showed that alpha-L-fucosidase bound to fucose residue and in particular it prefers N-glycans carrying core alpha 1,6-linked fucose and core alpha 1,3-linked fucose in N-glycans carrying only a terminal mannose residue. The ability of sperm alpha-L-fucosidase to bind to the micropylar chorion and to the vitelline envelope was examined in in vitro assays in presence of alpha-L-fiicosidase, either alone or in combination with molecules containing fucose residues. No binding was detected when alpha-L-fucosidase was pre-incubated with fucoidan, a polymer of alpha-L-fucose and the monosaccharide fucose. Furthermore, egg labeling with anti-horseradish peroxidase, that recognized only core alpha 1,3-linked fucose, correlates with alpha-L-fucosidase micropylar binding. Collectively, these data support the hypothesis of the potential role of this glycosidase in sperm egg interactions in Drosophila. (C) 2015 Elsevier Ltd. All rights reserved.