Immunoglobulins against gp273, the ligand for sperm–egg interaction in the mollusc bivalve Unio elongatulus, are directed against charged O‐linked oligosaccharide chains bearing a Lewis‐like structure and interact with epitopes of the human zona pellucida

Abstract

In oocytes of the mollusc bivalve Unio elongatulus, gp273 is the ligand molecule for sperm-egg interaction and binding is mediated by its O-glycans. A serum raised against this protein enabled its localization in the crater region, the area of the vitelline coat where sperm recognition occurs, and showed that after cyanogen bromide fragmentation, the anti-gp273 epitope(s) was retained by a peptide where the O-glycans are localized. In this article, we utilized purified anti-gp273 immunoglobulins to characterize the corresponding epitope by: (i) immunoblotting analysis of the protein after removal of O- and N-glycans; (ii) solid phase binding analysis of anti-gp273 IgG to gp273 N- and O-glycans; and (iii) binding analysis of the same antibody to commercially available oligosaccharides. The results showed that the epitope consists of O-glycans and contains a Lewis-like structure with fucose as determinant. Anti-gp273 IgG were then used to investigate human zona pellucida by immunoelectronmicroscopy and immunoblotting. Epitopes recognized by the antibody were demonstrated on the outer surface of the zona pellucida and shown to belong to a zona pellucida protein having electrophoretic mobility similar to human ZP3. Since human sperm specifically bind to gp273, and anti-gp273 interferes with this binding a functional role for these epitopes is suggested.

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

“…Proteinecarbohydrate complementarity appears to be conserved in fertilization processes throughout the whole evolutionary scale (Dale, 1991). Sperm receptors include glycosidases that act as lectin-like molecules that recognize glycoconjugates on the egg coat leading to spermeegg binding (Hoshi et al, 1985;Tulsiani et al, 1997;Abascal et al, 1998;Martinez et al, 2000;Miranda et al, 2000;Mengerink and Vacquier, 2001;Focarelli et al, 2003;Koyanagi and Honegger, 2003;Zitta et al, 2006;Venditti et al, 2010;Clark, 2013Clark, , 2014. The molecular mechanism regarding fertilization in insects is still poorly understood.…”

“…Fucose is a common component of the glycan chains of glycoproteins and glycolipids, and many works have shown that L-fucose residues are present on the gamete surface and play roles in gamete recognition (Becker and Lowe, 2003;Flechon et al, 2003;Focarelli et al, 2003;Jimenez-Movilla et al, 2004;Tanghe et al, 2004).…”

Sulphated glycoconjugates are powerful inhibitors of spermatozoa binding to the vitelline envelope in amphibian eggs

“…Consistently, for D. pictus , previous studies (Infante et al, 2004) showed no cross‐reactivity with anti‐ U. elongatus gp273 antibodies. The latter recognize glycans containing a Lewis‐like structure with fucose as the determinant (Focarelli et al, 2003). Moreover, metaperiodate trials support the conclusion that, in spermatozoa—VE binding, sugar radicals such as hydroxy groups are not implicated.…”

“…Interestingly, sulphate fucose was also shown to be involved in the spermatozoa— zona ‐free hamster interaction (Dravland and Mortimer, 1988). In humans and U. elongatus , spermatozoa selectin‐like molecules are involved in binding to the zona (Oehninger, 2001) or to the VE (Focarelli et al, 2003) respectively. In U. elongatus , gp273, the VE ligand, contains a Lewis‐like structure with fucose as determinant (Focarelli et al, 2003).…”

Distribution, crypticity, stability, and localization of α‐L‐fucosidase of mouse cauda epididymal sperm

“…Fucose residues have been detected in the ZP and cortical granules of oocytes (El‐Mestrah and Kan, 2002; Jiménez‐Movilla et al, 2004). Epitopes containing fucose in Lewis‐like structures are involved in human gamete interaction (Focarelli et al, 2003). Tanghe et al (2004b) showed that L ‐fucose inhibited the penetration rate of sperm into oocytes in bovine in vitro fertilization (IVF).…”