Abstract
We have recently demonstrated that a human amniotic fluid-derived glycoprotein, glycodelin-A (GdA; previously known as PP14 or PAEP), potently inhibits gamete binding in an established sperm-egg binding system and expresses immunosuppressive activities directed against a variety of different immune cell types. GdA has high mannose-, hybrid-, and complex-type biantennary oligosaccharides including structures with fucosylated or sialylated N, N'-diacetyllactosediamine (GalNAcbeta1-4GlcNAc) sequences, which are rare in other human glycoproteins. We now report the characterization of glycodelin-S (GdS). This is a human seminal plasma glycoprotein that is immunologically indistinguishable from GdA, but unlike the latter, does not inhibit human sperm-zona pellucida binding under hemizona assay conditions. Analysis of the N-glycans of GdS by mass spectrometry revealed that all glycoforms of GdS are different from those of GdA. GdS glycans are unusually fucose-rich, and the major complex-type structures are biantennary glycans with Lewisx (Galbeta1-4(Fucalpha1-3)GlcNAc) and Lewisy (Fucalpha1-2Galbeta1-4(Fucalpha1-3)GlcNAc) antennae. It is probable that these highly fucosylated epitopes contribute to the immunosuppressive activity of human seminal plasma and to the low immunogenicity of sperm. This study provides the first evidence for gender-specific glycosylation that may serve to regulate key processes involved in human reproduction.
Highlights
We have recently demonstrated that a human amniotic fluid-derived glycoprotein, glycodelin-A (GdA; previously known as PP14 or PAEP), potently inhibits gamete binding in an established sperm-egg binding system and expresses immunosuppressive activities directed against a variety of different immune cell types
This study provides the first evidence for gender-specific glycosylation that may serve to regulate key processes involved in human reproduction
Immunological and molecular biological analyses have suggested that glycodelin is expressed in tissues other than the endometrium (16, 17), and significantly, a glycoprotein that cross-reacted with antibodies to GdA was detected in human seminal plasma over a decade ago (16)
Summary
GdA, glycodelin-A; GdS, glycodelin-S; FAB-MS, fast atom bombardment mass spectrometry; LC-ES-MS, liquid chromatography-electrospray mass spectrometry; GC-MS, gas chromatography-mass spectrometry; PNGase F, peptide N-glycosidase F. immunodiffusion and tandem-crossed electrophoresis studies, which suggests that GdS and GdA are very closely related proteins (16, 19). Recent analysis of GdS indicates that the protein component of GdS is very similar to that of GdA based upon peptide mapping, N-terminal sequencing, and immune binding studies using specific polyclonal and monoclonal antibodies (19). Lectin binding and endo/exoglycosidase digestion studies (19) suggested that the observed differences in size and charge between GdS and GdA could be due to differential glycosylation, implying that human male and female reproductive tissues are capable of glycosylating the protein differently. We have employed similar strategies to define the N-glycan structures in GdS and their sites of attachment. This study provides the first evidence for gender-specific glycosylation that may serve to regulate key processes involved in human reproduction
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