Pregnancy-Specific Glycoprotein (PSG) in Baboon (Papio hamadryas): Family Size, Domain Structure, and Prediction of a Functional Region in Primate PSGs1

Abstract

Pregnancy-specific glycoprotein (PSG) constitutes a major component of serum of pregnant women and appears to be essential for a successful pregnancy. Its function is, however, still unknown. Because of the evolutionary divergence between human and rodent PSG, functional studies may require a primate animal model. We have characterized PSG transcripts in a baboon placenta cDNA library and analyzed baboon genomic DNA. The main PSG isoform had the domain structure N-A1-B2-C similar to the human type IIa isoform. The type I isoform (N-A1-A2-B2-C) was also expressed. Fifteen similar PSG genes were identified of which at least nine were simultaneously expressed in third trimester baboon placenta. Thus, the baboon PSG family was as complex as that of humans. Recombinant baboon PSG (isoform IIa) had a molecular weight of 38 kDa and reacted with antibodies against human PSG. Comparative analysis of 43 N-domain amino acid sequences of PSG from four species and nine primate carcinoembryonic antigen subgroup N domain sequences identified a number of residues in the GFCC'C" ss-sheet and FG loop that are probable candidates for PSG binding to its putative ligand.

An abundant placental transcript containing an IAP-LTR is allelic to mouse pregnancy-specific glycoprotein 23 (Psg23): cloning and genetic analysis

“…Whilst this finding is consistent with a number of possible integrin-mediated functions, including a disintegrin type function, several studies failed to find an integrin-related mode of action of PSGs (Zhou and Hammarstrom, 2001). However, a recent report of mouse Psg binding to integrin-associated CD9 (Waterhouse et al, 2002), lends further support to the speculation that Psg RGD-like motifs are functional, and suggests that more detailed studies of these motifs are warranted.…”

Pregnancy-Specific Glycoproteins Bind Integrin αIIbβ3 and Inhibit the Platelet—Fibrinogen Interaction

“…Snake venoms contain disintegrin proteins that bind integrins and disrupt cell - extracellular matrix interactions or blood clotting mechanisms and, analogously, we and others have hypothesised that PSGs may function as secreted integrin ligands that disrupt integrin function and thereby facilitate invasion of maternal tissues by fetal trophoblast, or disrupt other integrin mediated functions in maternal tissues [6], [24]. We noted that PSG1 has a KGD rather than an RGD motif and, based on the presence of a KGD motif in barbourin, a platelet integrin αIIbβ3 antagonist found in pygmy rattlesnake ( S. m. barbouri ) venom [25], we tested whether PSG1 may be a selective αIIbβ3 ligand.…”

Adaptive Immune Responses During Pregnancy

“…81 It has been reported that PSG1a can turn macrophages tolerogenic and increase their ability to produce IL-10 and TGFbeta. 82,83 PSGs and particularly PSG-1a can inhibit T-cell proliferation but not directly, they rather do this via macrophages (reviewed in Martinez). Similarly to what is reported for Gal-1 54 and HO-1 27 among others, PSG1a seems to modulate DC phenotype and maturation that finally promotes the secretion of IL-17.…”