Glycobiology Advance Access originally published online on October 19, 2007
Glycobiology 2008 18(1):42-52; doi:10.1093/glycob/cwm113
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A Tetraantennary Glycan with Bisecting N-Acetylglucosamine and the Sda Antigen is the Predominant N-Glycan on Bovine Pregnancy-Associated Glycoproteins
3 Abteilung Neuroanatomie, Medizinische Hochschule Hannover, 30625 Hannover, Germany
4 Division of Molecular Biosciences, Faculty of Natural Sciences, Imperial College, London SW7 2AZ, UK
5 Abteilung für Toxikologie, Medizinische Hochschule Hannover, 30625 Hannover, Germany
6 Klinik für Geburtshilfe, Gynäkologie und Andrologie der Groß- und Kleintiere, Justus-Liebig-Universität Giessen, 35392 Giessen, Germany
7 Department of Basic Animal and Veterinary Sciences, Faculty of Life Sciences, University of Copenhagen, Denmark
8 Institut für Veterinäranatomie, Justus-Liebig-Universität Giessen, 35392 Giessen, Germany
2 To whom correspondence should be addressed. Tel: +44 11595 16464 Fax: +44 11595 16415; e-mail: karl.klisch{at}nottingham.ac.uk
Received on May 21, 2007; revised on September 14, 2007; accepted on October 1, 2007
Pregnancy-associated glycoproteins (PAGs) are major secretory proteins of trophoblast cells in ruminants. Binucleate trophoblast giant cells (BNCs) store these proteins in secretory granules and release them into the maternal organism after fusion with maternal uterine epithelial cells. By matrix assisted laser desorption ionisation-mass spectrometry (MALDI-MS) analysis and linkage analysis, we show that by far, the most abundant N-glycan of PAGs in midpregnancy is a tetraantennary core-fucosylated structure with a bisecting N-acetylglucosamine (GlcNAc). All four antennae consist of the Sda-antigen (NeuAc
2-3[GalNAcβ1-4]Galβ1-4GlcNAc-). Immunohistochemistry with the mono- clonal antibody CT1, which recognizes the Sda-antigen, shows that BNC granules contain the Sda-antigen from gestation day (gd) 32 until a few days before parturition. Lectin histochemistry with Maackia amurensis lectin (MAL), which binds to
2-3sialylated lactosamine, shows that BNC granules are MAL-positive prior to gd 32 and also at parturition. The observed tetraantennary glycan is a highly unusual structure, since during the synthesis of N-glycans, the insertion of a bisecting GlcNAc inhibits the activity of the GlcNAc-transferases that leads to tri- and tetraantennary glycans. The study defines the substantial changes of PAG N-glycosylation in the course of pregnancy. This promotes the hypothesis that PAGs may have different carbohydrate-mediated functions at different stages of pregnancy.
Key words: cattle / gestation / glycosylation / mass spectrometry / placenta
1Present address: School of Veterinary Medicine and Science, University of Nottingham, Loughborough LE11 5RD, UK