O-LINKED TRISACCHARIDE AND N-LINKED POLY-N-ACETYLLACTOSAMINYL GLYCANSARE PRESENT ON MOUSE ZP2 AND ZP3

Mammalian oocytes are surrounded by an extracellular glycocalyx, the z ona pellucida (ZP). in the mouse, the ZP is composed of three glycopro teins, designated mZP1, mZP2, and mZP3. Extensive studies in this spec ies have resulted in the identification of primary (mZP3) and secondar y (mZP2) receptors for spermatozoa. In this paper we present evidence for the occurrence of poly-N-acetyllactosaminyl glycans and an O-linke d trisaccharide on mZP2 and mZP3. When exhaustively digested with endo -beta-galactosidase, an enzyme known to cleave repeating units of acet yllactosamine (3Gal beta 1,4GlcNAc beta 1), mZP2 and mZP3 showed an ap parent reduction in size by 23 kDa and 16 kDa, respectively. Experimen tal evidence included in this report indicates that polylactosaminyl g lycans are present on N-linked sugar chains. In addition, O-linked sug ar chains of mZP3 have been characterized. First, treatment of de-N-gl ycosylated mZP3 with O-glycanase in the presence of exo-glycosidases ( sialidase, alpha-L-fucosidase, and N-acetylglucosaminidase) caused an apparent reduction in its size by 2-3 kDa as determined by SDS-PAGE. S econd, treatment of the de-N-glycosylated mZP3 with mild alkali in the presence of 1 M (NaBH4)-H-3 released radiolabeled oligosaccharide (OS ) that eluted from a high-resolution Bio-Gel P-4 column at the positio n of a trisaccharide. The radiolabeled OS had the following structure: GlcNAc --> Gal beta 1,3GalNAcol, The structure was established by siz ing on the Bio-Gel P-4 column, followed by examination of the suscepti bility of the OS to exo-glycosidases and by its adsorbability to immob ilized lectin (PNA). Potential roles of N-linked and O-linked sugar ch ains in sperm-egg interaction are herein discussed.