Human zona pellucida recognition associated with removal of sialic acid from human sperm surface

Abstract

The ability of human spermatozoa recovered from highly motile sperm fractions to bind wheat germ agglutinin (WGA) after discontinuous Percoll gradient centrifugation was studied. WGA could bind to almost all motile spermatozoa, whereas fewer than 25% of spermatozoa could bind peanut (PNA) and concanavalin A (Con A) agglutinin, two lectins that specifically bind acrosomal membranes. After removal of the plasma membrane with 0.04% Triton X100, WGA, PNA and Con A bound more than 80% of spermatozoa, but binding sites for WGA on the anterior acrosomal region were markedly reduced. The expression of sialic acid on human sperm plasma membrane was demonstrated, since WGA, which specifically recognizes both sialic acid (NeuNAc) and N-acetylglucosamine (GlcNAc), bound almost all intact motile spermatozoa, whereas succinylated WGA, which recognizes only GlcNAc, bound less than 10% of intact motile spermatozoa. Moreover, binding of WGA was compared with that of three other lectins (Sambucus nigra, SNA; Maackia amurensis, MAL and Limulus polyphemus, LPA) with specificity for different NeuNAc linkages. Only SNA, which requires the presence of the disaccharide structure NeuNAc alpha(2,6) Gal/GalNAc, showed a positive correlation with sperm motility as observed with WGA. Moreover, there was a strong inhibition of WGA binding on spermatozoa preincubated with bovine submaxillary mucin containing (2,6)-linked NeuNAc. These results demonstrate the presence of NeuNAc alpha(2,6) Gal/GalNAc glycoconjugate sequences on the plasma membrane of the motile human spermatozoon.(ABSTRACT TRUNCATED AT 250 WORDS)