Structural analysis of murine zone pellucida glycans -: Evidence for the expression of core 2-type O-glycans and the Sda antigen

Murine sperm initiate fertilization by binding to specific oligosaccharides linked to the zona pellucida, the specialized matrix coating the egg. Biophysical analyses have revealed the presence of both high mannose and complex-type N-glycans in murine zona pellucida, The predominant high mannose-type glycan had the composition Man(5)GlcNAc(2), but larger oligosaccharides of this type were also detected. Biantennary, triantennary, and tetraantennary complex-type N-glycans were found to be terminated with the following antennae: Gal beta 1-4GlcNAc, NeuAc alpha 2-3Gal beta 1-4GlcNAc, NeuGc alpha 2-3Gal beta 1-4GlcNAc, the Sd(a) antigen (NeuAc alpha 2-3[GalNAc beta 1-4]Gal beta 1-4GlcNAc, NeuGc alpha 2-3[GalNAc beta 1-4]Gal beta 1-4GlcNAc), and terminal GlcNAc, Polylactosamine-type sequence was also detected on a subset of the antennae. Analysis of the O-glycans indicated that the majority were core 2-type (Gal beta 1-4GlcNAc beta 1-6[Gal beta 1-3]GalNAc). The beta 1-linked branches attached to these Q-glycans were terminated with the same sequences as the N-glycans, except for terminal GlcNAc. Glycans bearing Gal beta 1-4GlcNAc beta 1-6 branches have previously been suggested to mediate initial murine gamete binding. Oligosaccharides terminated with GalNAc beta 1-4Gal have been implicated in the secondary binding interaction that occurs following the acrosome reaction. The significant implications of these observations are discussed.