Rapid purification and properties of human glycodelin (endometrial alpha2-globulin)

Affinity purification of native glycodelin from amniotic fluid for biological investigations and development of a glycodelin ELISA for clinical studies

INTRODUCTION

Glycodelin is a glycoprotein with different oligosaccharides that are responsible for its diverse biological functions in contraception and immunosuppression. Therefore, it is necessary to have access to adequate amounts of glycodelin with retained carbohydrate structure for functional studies because the carbohydrate part can be lacking or be insufficient in recombinant glycodelin from prokaryotic and eukaryotic cell systems.

METHODS AND RESULTS

Native glycodelin was purified from amniotic fluid by a series of affinity chromatography steps and had many glycosylated forms verified by mass spectrometry. About 7.5 mg glycodelin was obtained from 1.5 L amniotic fluid. No high molecular mass forms of glycodelin were found in amniotic fluid. Aliquots of the purified glycodelin were used as an immunogen in rabbits for antibody production against glycodelin and a calibrator in a highly sensitive glycodelin enzyme-linked immunosorbent assay (ELISA) with a detection limit of about 1 μg/L.

CONCLUSIONS

Native glycodelin was purified from amniotic fluid and used as an immunogen for raising a rabbit antibody against glycodelin and a calibrator in a highly sensitive glycodelin ELISA. We found no high molecular mass forms of glycodelin in amniotic fluid. Aliquots of the purified glycodelin were set aside for functional studies which are in progress.

Human amniotic glycodelin actively regulates changes in β-catenin immunoreactivity in cultured human umbilical vein endothelial cells (HUVEC)

OBJECTIVE

Assessment of the capacity of Glycodelin A (GdA) to modulate the aggregation of cultured human umbilical vein endothelial cells.

METHODS

Highly purified Glycodelin A (GdA) from late first trimester amniotic fluid has been added to cultured cells and its biological activity has been observed with immunofluorescent staining of β-catenin molecules.

RESULTS

GdA induces translocation of β-catenin molecules promoting cell-to-cell adhesion and formation of adherents junctions through cytoskeletal reorganization.

CONCLUSION

These data provide further mechanistic insight into the specificity of cell-to-cell adhesion, thus corroborating the role of GdA in promoting angiogenesis.

Glycodelin: a major lipocalin protein of the reproductive axis with diverse actions in cell recognition and differentiation

Glycodelin is a glycoprotein that belongs to the lipocalin superfamily. Depending on glycosylation, glycodelin appears in various isoforms. In the uterus, glycodelin-A is the major progesterone-regulated glycoprotein secreted into uterine luminal cavity by secretory/decidualized endometrial glands. The other tissues expressing glycodelin include fallopian tubes, ovary, breast, seminal vesicle, bone marrow, and eccrine glands. Glycodelin-A potently and dose-dependently inhibits human sperm-egg binding, whereas differently glycosylated glycodelin-S from seminal plasma has no such effect. Absence of contraceptive glycodelin-A in the uterus during periovulatory midcycle is consistent with an open "fertile window." Glycodelin induced by local or systemic administration of progestogens may potentially reduce the fertilizing capacity of sperm in any phase of the menstrual cycle. Glycodelin also has immunosuppressive activity. Its high concentration at the fetomaternal interface may contribute to protection of the embryonic semiallograft. Besides being an epithelial differentiation marker, glycodelin appears to play a role in glandular morphogenesis, as transfection of glycodelin cDNA into a glycodelin-negative breast cancer cells resulted in formation of gland-like structures, restricted proliferation, and induction of other epithelial markers. These various properties, as well as the chemistry, biology, and clinical aspects of glycodelin, continue to be areas of active investigation reviewed in this communication.

Glycodelin: a reproduction-related lipocalin

Glycodelin, a human lipocalin, is a major endometrial protein with at least two differentially glycosylated isoforms. Glycodelin-A (GdA) is purified from human mid-trimester amniotic fluid, where it is secreted from the decidualized endometrium. Glycodelin-S (GdS) is synthesized in the male reproductive tract, mainly in the seminal vesicles, and secreted into seminal plasma. These two glycodelin isoforms, glycosylated in a completely different manner, serve as a good model for studying the effects of glycosylation on protein function and physicochemical properties. We have reviewed here the structure, expression and biological functions of glycodelin.

Effect of pH on the structure and aggregation of human glycodelin A. A comparison with beta-lactoglobulin A

The effect of pH on the structure of glycodelin A (GdA) and of beta-lactoglobulin A (beta-LgA) has been investigated by means of circular dichroism, steady state fluorescence, synchrotron radiation small angle X-ray scattering (SR-SAXS) and gel permeation chromatography. The comparison between GdA and beta-LgA shows that, at pH 7.0, both proteins are dimers with an extended content of beta-sheet conformation, but pH 2.0 and 9.0 yield a different secondary, tertiary and quaternary structural organisation. Whilst beta-LgA is a monomer, that conserves beta-sheet conformation at pH 2.0 and 9.0, GdA has a stable dimeric structure at alkaline pH, but at pH 2.0 increases its alpha-helix content and it aggregates soon. SR beam has been used to perform SAXS comparative measurements of the two proteins. SR-SAXS data provide the radius of gyration and the radii of the cross-section and of the thickness. GdA aggregation at acid pH has been characterised by calculating the distance distribution function (P(r)). Isoelectric focusing and chromatofocusing data show a different charge distribution on the surfaces of the two proteins, supporting the hypothesis that the presence of oligosaccharides deeply influences the conformational state and the aggregation process of GdA at different pH values. In particular, the presence of sialic acid residues, within the oligosaccharide moiety of the GdA, might be responsible for the differences observed between the two proteins.

Structural properties of human glycodelin A in water and in water-alcohol mixtures: a comparison with bovine beta-lactoglobulin A

Human glycodelin A (GdA) is a glycoprotein that is highly homologous to bovine beta-lactoglobulin A (beta-LgA) because the amino acid sequences are 50-60% identical. The structural characteristics of human GdA and beta-LgA were compared in water and 2-propanol/water solutions. Circular dichroism spectra reveal that in water the two proteins have a very similar beta-sheet secondary structure. In the presence of 2-propanol/water mixtures (up to 50% v/v) the alpha-helix structure of both proteins increases. A further increase in the alcohol percentage of the solvent (up to 80% v/v 2-propanol) causes the formation of a new folded tertiary structure containing mainly beta-sheet features. Synchrotron radiation small angle X-ray scattering indicates that, in a neutral pH aqueous solution, GdA is a dimer. Its radius of gyration value (Rg), 25.1+/-0.4 A, is greater than that of beta-LgA (21.1+/-0.3 A), probably because of the contribution of polysaccharides bound to Asn-28 and Asn-63 residues of GdA. Conversely, small angle X-ray scattering and gel permeation chromatography data on GdA in 2-propanol have revealed a massive aggregation of the protein.

Glycodelin and beta-lactoglobulin, lipocalins with a high structural similarity, differ in ligand binding properties

Human glycodelin, a lipocalin with a high amino acid similarity to beta-lactoglobulins, appears as various glycoforms with different biological activities in endometrium (glycodelin-A) and seminal plasma (glycodelin-S). We found that the structures of these glycodelins and beta-lactoglobulin are similar. Despite this structural similarity, unlike beta-lactoglobulin, glycodelin-A binds neither retinoic acid nor retinol. It was impossible to detect any endogenous retinoids or steroids in any of the two purified glycodelins. Both their glycoforms share similar thermodynamic parameters of reversible denaturation suggesting that native folding of glycodelin-A and glycodelin-S is not influenced by the differences in glycosylation or by ligand binding.