Sulphated glycoconjugates are powerful inhibitors of spermatozoa binding to the vitelline envelope in amphibian eggs.
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.
Caputo
Mariangela
M
Dipartimento di Biologia Evolutiva e Comparata, Università di Napoli Federico II, Napoli, Italy.
Riccio
Stefania
S
Paglierucci
Paolo
P
Tretola
Loredana
L
Diglio
Clementina
C
Carotenuto
Rosa
R
De Marco
Nadia
N
Campanella
Chiara
C
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
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