title: Sulphated glycoconjugates are powerful inhibitors of spermatozoa binding to the vitelline envelope in amphibian eggs.
abstract: BACKGROUND
  In amphibians, the role of sulphated glycans has not been determined in spermatozoa-egg interaction, although they are known to be involved in other systems. In previous studies, it was found that, in Discoglossus pictus, a VE (vitelline envelope) glycoprotein of 63 kDa exhibits high homology to Xenopus laevis gp69/gp64 and to ZP2 of mammals. gp63 and a glycoprotein of 75 kDa are both capable of binding the spermatozoa in in vitro assays and, having similar peptide maps and different glycosylation, are probably two glycoforms of the same protein.
  
  
  RESULTS
  In the present study, binding assays performed by treating dejellied eggs with metaperiodate suggest that hydroxy groups of sugars are not directly involved in spermatozoa-vitelline envelope binding. Competition assays between dejellied eggs and spermatozoa preincubated with dextran, dextran sulphate or fucoidan indicated that sulphated oligosaccharides have an inhibitory effect on spermatozoa binding. In similar competition assays, Le(x) (Lewis(x)) trisaccharide 3'-sulphate inhibited spermatozoa binding to VE in contrast with 3'-sialyl-Le(x) tetrasaccharide. Assays performed with gp75- or gp63-coated beads and spermatozoa treated with fucoidan or dextran sulphate indicated that sulphated oligosaccharides competitively inhibit spermatozoa binding to gp75-coated beads, yet not to gp63-coated beads. Finally, solubilized VE digested with N-glycosidase F retains the inhibitory activity in spermatozoa-VE binding assays in contrast with VE treated with alpha-N-acetylgalactosaminidase.
  
  
  CONCLUSIONS
  It was concluded that VE sulphate groups are involved in spermatozoa binding. These groups are present in gp75 glycoconjugates and are probably located in O-linked glycoconjugates.
authors.affiliation: Dipartimento di Biologia Evolutiva e Comparata, Università di Napoli Federico II, Napoli, Italy.
authors.forename: Mariangela
authors.initials: M
authors.lastname: Caputo
authors.forename: Stefania
authors.initials: S
authors.lastname: Riccio
authors.forename: Paolo
authors.initials: P
authors.lastname: Paglierucci
authors.forename: Loredana
authors.initials: L
authors.lastname: Tretola
authors.forename: Clementina
authors.initials: C
authors.lastname: Diglio
authors.forename: Rosa
authors.initials: R
authors.lastname: Carotenuto
authors.forename: Nadia
authors.initials: N
authors.lastname: De Marco
authors.forename: Chiara
authors.initials: C
authors.lastname: Campanella
mesh_terms: D000663:Amphibians; D000818:Animals; D001667:Binding, Competitive; D016264:Dextran Sulfate / Q000737:chemistry / Q000494:pharmacology; D003911:Dextrans / Q000737:chemistry; D004305:Dose-Response Relationship, Drug; D004527:Egg Proteins / Q000737:chemistry; D004591:Electrophoresis, Polyacrylamide Gel; D005260:Female; D006001:Glycoconjugates / Q000494:pharmacology*; D008297:Male; D008562:Membrane Glycoproteins / Q000737:chemistry; D009844:Oligosaccharides / Q000737:chemistry; D010063:Ovum / Q000378:metabolism; D010449:Peptide Mapping; D043524:Peptide-N4-(N-acetyl-beta-glucosaminyl) Asparagine Amidase / Q000378:metabolism; D010455:Peptides / Q000737:chemistry; D011134:Polysaccharides / Q000737:chemistry / Q000494:pharmacology; D011485:Protein Binding; D020033:Protein Isoforms; D011956:Receptors, Cell Surface / Q000737:chemistry / Q000378:metabolism; D013084:Sperm-Ovum Interactions / Q000187:drug effects; D013094:Spermatozoa / Q000378:metabolism*; D013455:Sulfur / Q000737:chemistry*; D014817:Vitelline Membrane / Q000378:metabolism*; D014982:Xenopus laevis; D000072216:Zona Pellucida Glycoproteins
chemical_list: D003911:Dextrans; D004527:Egg Proteins; D006001:Glycoconjugates; D008562:Membrane Glycoproteins; D009844:Oligosaccharides; D010455:Peptides; D011134:Polysaccharides; D020033:Protein Isoforms; D011956:Receptors, Cell Surface; D000072216:Zona Pellucida Glycoproteins; C035027:egg surface sperm receptor; D013455:Sulfur; D016264:Dextran Sulfate; C007789:fucoidan; D043524:Peptide-N4-(N-acetyl-beta-glucosaminyl) Asparagine Amidase