Glycodelin from seminal plasma is a differentially glycosylated form of contraceptive glycodelin-A

Glycodelin-A is a human amniotic fluid-derived glycoprotein with contraceptive and immunosuppressive activities. An immunoreactive form of glycodelin was detected in seminal plasma over a decade ago, but definitive characterization of this glycoprotein was not pursued. We considered it unlikely that the seminal plasma of fertile men would contain an appreciable amount of contraceptive glycodelin-A. To address this issue we purified seminal plasma glycodelin (glycodelin-S) and performed comparative studies with glycodelin-A. Glycodelin-S behaved differently when compared with glycodelin-A during sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) and isoelectric focusing but identically after enzymatic deglycosylation. N-terminal sequencing of glycodelin-A and glycodelin-S gave identical results, and digestion with trypsin gave identical peptide fragments. The glycoproteins were also found to be indistinguishable from each other based upon immunological analyses. These results indicate that glycodelin-S and glycodelin-A have similar overall protein structure, suggesting the likelihood that these glycoproteins are differentially glycosylated forms of very similar proteins. This latter possibility is supported by lectin binding studies indicating that, unlike glycodelin-A, glycodelin-S does not manifest any affinity for lectins from Wisteria floribunda or Sambucus nigra. The results of sugar analysis and neuraminidase digestion also lead us to conclude that glycodelin-S and glycodelin-A are differentially glycosylated forms of similar proteins. Our evidence indicates that glycodelin-A mediated its biological activities via its unusual oligosaccharide sequences that are not associated with glycodelin-S. In lectin-immunoassay no appreciable amount of contraceptive glycodelin-A was found in the 22 seminal plasma samples studied.