Glycan characterization of pregnancy-specific glycoprotein 1 and its identification as a novel Galectin-1 ligand

Abstract

Pregnancy-specific beta 1 glycoprotein (PSG1) is secreted from trophoblast cells of the human placenta in increasing concentrations as pregnancy progresses, becoming one of the most abundant proteins in maternal serum in the third trimester. PSG1 has seven potential N-linked glycosylation sites across its four domains. We carried out glycomic and glycoproteomic studies to characterize the glycan composition of PSG1 purified from serum of pregnant women and identified the presence of complex N-glycans containing poly LacNAc epitopes with α2,3 sialyation at four sites. Using different techniques, we explored whether PSG1 can bind to galectin-1 (Gal-1) as these two proteins were previously shown to participate in processes required for a successful pregnancy. We confirmed that PSG1 binds to Gal-1 in a carbohydrate-dependent manner with an affinity of the interaction of 0.13 μM. In addition, we determined that out of the three N-glycosylation-carrying domains, only the N and A2 domains of recombinant PSG1 interact with Gal-1. Lastly, we observed that the interaction between PSG1 and Gal-1 protects this lectin from oxidative inactivation and that PSG1 competes the ability of Gal-1 to bind to some but not all of its glycoprotein ligands.

Role of galectin-glycan circuits in reproduction: from healthy pregnancy to preterm birth (PTB)

“…PSGs contain multiple potential N-glycosylation sequences and also potential sites for O-glycosylation and evidence of glycosylation have been indicated by lectin binding studies [151]. Recently, we have characterized PSG1 n detail in terms of its glycosylation [152]. We showed that PSG1 contains multi-antennary complex N-glycans with high levels of α2-3 sialic acid capping.…”

Evolution of Placental Hormones: Implications for Animal Models

“…These appear to attract, activate, and induce apoptosis of maternal immune cells that might otherwise attack invading trophoblast ( 134 ). Intriguingly, PSG-1 is a ligand for galectin-1 ( 135 ).…”

Medawar’s PostEra: Galectins Emerged as Key Players During Fetal-Maternal Glycoimmune Adaptation

“…The high expression level of PSG1 during the third trimester permitted the isolation of native PSG1 from pooled serum of pregnant women using affinity chromatography allowing for a comprehensive glycomic and glycoproteomic investigation of the native protein ( 234 ). PSG1 has seven potential N-linked glycosylation sites across its four Ig-like domains designates as N, A1, A2 and B2 but only four sites mapping to the N, A1 and A2 domains of the protein were confirmed to be occupied by glycans ( 234 ). The presence of multiantennary and poly-N-acetyl-lactosamine (LacNac) elongated moieties with mainly alpha2,3-linked sialic acid terminals, suggested that PSG1 could interact with members of the galectin family.…”

“…Gal-1 binds to native and recombinant PSG1 in a carbohydrate-dependent manner, demonstrated by the inhibition of PSG1-gal-1 binding by lactose and failure of PSG1 generated in insect cells or N-acetylglucosaminlytransferase I (GnTI)-deficient cells, which carry only mannose-type glycans, to interact with gal-1. In addition, removal of N-linked oligosaccharides from the N- and A2- PSG1 domains by treatment with the amidase PNGase F prevented their binding to gal-1 ( 234 ). Changes in glycosylation could add further complexity to the regulation of important biological processes in pregnancy known to be regulated by both extracellular galectins and their ligands, including the PSGs.…”