Purification and properties of N-acetylglucosaminide alpha 1----3-fucosyltransferase from embryonal carcinoma cells

Embryoglycan: a highly branched poly-N-acetyllactosamine in pluripotent stem cells and early embryonic cells

Embryonal carcinoma cells, stem cells of teratocarcinomas, are pluripotent stem cells and also prototypes of embryonic stem cells. Embryonal carcinoma cells contain large amounts of a highly branched poly-N-acetyllactosamine called embryoglycan, which has a molecular weight of approximately 10,000 or greater, and is asparagine-linked. This glycan was found by analyses of fucose-labeled glycopeptides, and its characteristics were established by biochemical analyses. The content of embryoglycan progressively decreases during the in vitro differentiation of embryonal carcinoma cells. Embryoglycan is also abundant in mouse embryonic stem cells and preimplantation mouse embryos, and decreases during embryogenesis. Embryoglycan carries a number of carbohydrate markers of murine pluripotent stem cells. Lewis x markers, such as SSEA-1, 4C9 antigen, and binding sites for Lotus tetragonolobus agglutinin are of particular importance. 4C9 antigenicity requires clustering of Lewis x, best accomplished by poly-N-acetyllactosamine branching, whereas SSEA-1 does not. Although in vivo evidence is lacking, these epitopes have been suggested to participate in cell-to-cell and cell-to-substratum adhesion. Other markers on embryoglycan include α-galactosyl antigens such as ECMA-2, and binding sites for Dolichos biflorus agglutinin, the epitope of which is considered to be identical to Sd^a antigen, namely, GalNAcβ1-4(NeuAcα2-3)Galβ1-4GlcNAc. While embryoglycan is also present in human teratocarcinoma cells, the carbohydrate markers characterized in human pluripotent stem cells to date are largely carried by glycolipids and keratan sulfate. Information on embryoglycan and markers carried by it may assist in the development of new markers of human pluripotent stem cells and their progenies.

Glycodelin-A interacts with fucosyltransferase on human sperm plasma membrane to inhibit spermatozoa-zona pellucida binding

Fertilization depends on successful binding of the spermatozoa to the zona pellucida of the oocyte. Glycodelin-A inhibits spermatozoa-zona pellucida binding. Previous data showed that glycodelin-A receptor(s) and zona pellucida protein receptor(s) on human spermatozoa are closely related. Using a chemical cross-linking approach, the glycodelin-A-sperm receptor complex was isolated. The receptor was identified to be fucosyltransferase-5 (FUT5) by mass spectrometry and confirmed with the use of anti-FUT5 antibodies. Sperm FUT5 was an externally oriented integral membrane protein in the acrosomal region of human spermatozoa. Biologically active FUT5 was purified from spermatozoa. Co-immunoprecipitation confirmed the interaction between glycodelin-A and sperm FUT5. Solubilized zona pellucida reduced the binding of glycodelin-A to sperm FUT5. An anti-FUT5 antibody and FUT5 acceptor blocked the binding of glycodelin-A to spermatozoa and the zona binding inhibitory activity of glycodelin-A. Sperm FUT5 bound strongly to intact and solubilized human zona pellucida. The equilibrium dissociation constant of sperm FUT5 binding to solubilized zona pellucida was 42.82 pmol/ml. These observations suggest that human sperm FUT5 is a receptor of glycodelin-A and zona pellucida proteins, and that glycodelin-A inhibits spermatozoa-zona binding by blocking the binding of sperm FUT5 to the zona pellucida.

Protein-bound carbohydrates on cell-surface as targets of recognition: an odyssey in understanding them

Multidisciplinary approaches by a number of investigators have established that cell-surface carbohydrates are integral components of recognition systems regulating survival, migration, adhesion, growth and differentiation of various cells. Our own experience and contributions to this exciting field are described. We discovered Endo D as the first endoglycosidase acting on glycoproteins, found complementary specificity of two endoglycosidases (Endo D and Endo H), and applied these enzymes for glycoprotein research. Endo-beta-galactosidase C, which hydrolyzes Galalpha1-3Galbeta1-4GlcNAc xenoantigenic determinant, was later found and molecularly cloned. We also found highly branched poly-N-acetyllactosamines in early embryonic cells, and demonstrated developmentally regulated carbohydrate changes during early mammalian development. The binding site for Dolichos biflorus agglutinin was introduced as a new differentiation marker. Basigin and embigin, two related members of the immunoglobulin superfamily, a sialomucin MGC-24 and other glycoproteins were discovered as carriers of developmentally regulated carbohydrate markers. We proposed enhancement of integrin action as a function of sugar chains with Lewis X epitope, and observed a relationship between the expression of carbohydrate markers and invasive properties of human carcinoma. Midkine, a heparin-binding growth factor, was discovered more recently and its interaction with heparin and oversulfated chondroitin sulfate was elucidated. N-Acetylglucosamine-6-sulfotransferase was cloned and used to reconstitute L-selectin ligands. Gene knockout was applied to reveal in vivo function of basigin, syndecan-4 and chondroitin 6-sulfate. Throughout my research on all these subjects, I have been fortunate in obtaining unexpected observations and enjoying fruitful collaborations.

Protein N-glycosylation: molecular genetics and functional significance

Protein N-glycosylation is a metabolic process that has been highly conserved in evolution. In all eukaryotes, N-glycosylation is obligatory for viability. It functions by modifying appropriate asparagine residues of proteins with oligosaccharide structures, thus influencing their properties and bioactivities. N-glycoprotein biosynthesis involves a multitude of enzymes, glycosyltransferases, and glycosidases, encoded by distinct genes. The majority of these enzymes are transmembrane proteins that function in the endoplasmic reticulum and Golgi apparatus in an ordered and well-orchestrated manner. The complexity of N-glycosylation is augmented by the fact that different asparagine residues within the same polypeptide may be modified with different oligosaccharide structures, and various proteins are distinguished from one another by the characteristics of their carbohydrate moieties. Furthermore, biological consequences of derivatization of proteins with N-glycans range from subtle to significant. In the past, all these features of N-glycosylation have posed a formidable challenge to an elucidation of the physiological role for this modification. Recent advances in molecular genetics, combined with the availability of diverse in vivo experimental systems ranging from yeast to transgenic mice, have expedited the identification, isolation, and characterization of N-glycosylation genes. As a result, rather unexpected information regarding relationships between N-glycosylation and other cellular functions--including secretion, cytoskeletal organization, proliferation, and apoptosis--has emerged. Concurrently, increased understanding of molecular details of N-glycosylation has facilitated the alignment between N-glycosylation deficiencies and human diseases, and has highlighted the possibility of using N-glycan expression on cells as potential determinants of disease and its progression. Recent studies suggest correlations between N-glycosylation capacities of cells and drug sensitivities, as well as susceptibility to infection. Therefore, knowledge of the regulatory features of N-glycosylation may prove useful in the design of novel therapeutics. While facing the demanding task of defining properties, functions, and regulation of the numerous, as yet uncharacterized, N-glycosylation genes, glycobiologists of the 21st century offer exciting possibilities for new approaches to disease diagnosis, prevention, and cure.

Clinical aspects of glycoprotein biosynthesis

Glycoproteins are widely distributed among species in soluble and membrane-bound forms, associated with many different functions. The heterogenous sugar moieties of glycoproteins are assembled in the endoplasmic reticulum and in the Golgi and are implicated in many roles that require further elucidation. Glycoprotein-bound oligosaccharides show significant changes in their structures and relative occurrences during growth, development, and differentiation. Diverse alterations of these carbohydrate chains occur in diseases such as cancer, metastasis, leukemia, inflammatory, and other diseases. Structural alterations may correlate with activities of glycosyltransferases that assemble glycans, but often the biochemical origin of these changes remains unclear. This suggests a multitude of biosynthetic control mechanisms that are functional in vivo but have not yet been unraveled by in vitro studies. The multitude of carbohydrate alterations observed in disease states may not be the primary cause but may reflect the growth and biochemical activity of the affected cell. However, knowledge of the control mechanisms in the biosynthesis of glycoprotein glycans may be helpful in understanding, diagnosing, and treating disease.

Differentiative changes in fucosyltransferase activity in newborn rat epidermal cells

An enzymatic activity catalyzing the transfer of L-fucose from GDP-L-fucose to a glycoprotein that is associated with the surfaces of the basal cells has been found in the membranous fraction of the cutaneous epidermis from the newborn rat. This fucosyltransferase which is located in the differentiated cells alters the acceptor glycoprotein's lectin-binding specificity from the Isolectin I-B4 of Griffonia simplicifolia (GS I-B4) to the Agglutinin I of Ulex europeus (UEA) and could be responsible for the same change in lectin-binding specificity that occurs as the epidermal basal cell differentiates. Another membraneous fucosyltransferase that can use asialofetuin--but not the GS I-B4-binding glycoprotein--as an acceptor, is also present in the membraneous fraction.

Occurrence and specificities of α3-fucosyltransferases

The Le(x) (CD15) carbohydrate antigen and sialylated and oligomeric derivatives thereof have been implicated in cell adhesion processes. Expression of these antigens is developmentally regulated and (re)occurrence of several members of this group has been reported in malignant transformation of cells. Studies on the enzymology and genetics of alpha 3-fucosyltransferases, glycosyltransferases that play a key role in the biosynthesis of these antigens, would yield insight in the regulation of expression of these carbohydrate structures. In this paper the existing literature on these enzymes is reviewed and placed in the context of cell adhesion and malignancy.

Immunohistochemical localization of the carbohydrate antigen 4C9 in the mouse embryo: a reliable marker of mouse primordial germ cells

Expression of 4C9, a Lex[Gal beta 1----4(Fuc alpha 1----3)GlcNAc] antigen, during mouse embryogenesis was studied by immunohistochemical methods. Distribution of 4C9 was similar to, but not identical with that of SSEA-1 (stage-specific embryonic antigen-1). Notably, 4C9 was detected in some of the inner cell mass cells of late blastocysts, ectoderm cells migrating from the primitive streak to the mesoderm space and primordial germ cells just formed from the migrating cells. Thus, 4C9 was considered to be continuously expressed in the cell lineage starting at the totipotent 8 cell stage and leading to primordial germ cells. While 4C9 gradually decreased from the surface of primordial germ cells after they have settled in the gonad, the antigen remained in cytoplasmic granules for some period in a sex determined manner. In male gonads, cytoplasmic granules positive for 4C9 tended to be polarized to one side of cytoplasm. The 4C9 reactive material completely disappeared from male germ cells by day 16 of gestation. In female gonads, granules scattered throughout the cytoplasm and cell surface were positive for 4C9. On day 16 of gestation the cell surface antigenicity was lost, but some cytoplasmic antigenicity still remained. As above, 4C9 is a reliable marker to study the origin, migration and differentiation of primordial germ cells, and to distinguish male and female germ cells. By immunoelectron microscopy, 4C9 was detected at the plasma membrane, the Golgi apparatus, and dense-cored vesicles in primordial germ cells on 10-11 days of gestation.

Purification of the N-acetylglucosaminide alpha(1-3/4)fucosyltransferase of human milk

The N-acetylglucosaminide alpha(1-3/4)fucosyltransferase has been purified 1.8 x 10(6)-fold from human milk by ion-exchange chromatography, affinity chromatography on GDP-agarose and HPLC. The alpha(1-3/4)fucosyltransferase behaves in gel filtration-HPLC as a molecule of M(r) 98,000, and differs from the alpha(1-3)fucosyltransferase which behaves like a molecule of about M(r) 47,000. The enzyme is a glycoprotein, and the purified preparation appears in SDS polyacrylamide gel electrophoresis as a band of M(r) 44,000. The results present the first purification of human milk alpha(1-3/4)fucosyltransferase to apparent homogeneity, and suggest that the alpha(1-3/4)- and alpha(1-3)fucosyltransferase of human milk differ in their native molecular sizes, the former being a dimer of two subunits.

Developmentally regulated expression of cell surface carbohydrates during mouse embryogenesis

Cell surface carbohydrates undergo marked alterations during mouse embryogenesis. In preimplantation embryos, many carbohydrate markers show stage-specific expression in diverse ways. In early postimplantation embryos, certain carbohydrate markers are localized in defined regions in the embryo. Important carriers of stage-specific carbohydrates are the lactoseries structure (Gal beta 1----4GlcNAc) and the globoseries structure (Gal alpha 1----4Gal). Notably, the glycoprotein-bound large carbohydrate of poly-N-acetyllactosamine-type ([Gal beta 1----4GlcNAc beta 1----3]n) carries a number of markers preferentially expressed in early embryonic cells. These markers are of practical value in analyzing embryogenesis and cell differentiation. For example, in order to monitor in vitro differentiation of multipotential embryonal carcinoma cells, stage-specific embryonic antigen-1 (SSEA-1) and the Lotus agglutinin receptor have been used as markers of the undifferentiated cells, and the Dolichos agglutinin receptor has been used as a marker of extraembryonic endoderm cells. Developmental control of cell surface carbohydrates is attained by controlled expression of activities of key glycosyltransferases; for example, the activity of N-acetylglucosaminide alpha 1----3 fucosyltransferase is lost during in vitro differentiation of embryonal carcinoma cells to parietal endoderm cells, in parallel to the disappearance of SSEA-1. Accumulating evidence suggests that poly-N-acetyllactosamine-type glycans that are abundant in early embryonic cells are involved in cell surface recognition of these cells.

Mutants of embryonal carcinoma cells defective in the expression of embryoglycan

Embryonal carcinoma cells defective in the expression of developmentally regulated carbohydrate epitope of teratocarcinoma cells (TEC-1) were isolated from mutagenized P19X1 and P19S1801A1 cells by a single-step selection technique using monoclonal antibody TEC-01 conjugated to plant toxin ricin. Three independently isolated mutant cell lines were characterized in detail. Analysis of the expression of the TEC-1 epitope in somatic cell hybrids constructed between wild-type and mutant cells and between two mutant cell types revealed that the mutant phenotypes are recessive and that the mutants belong to, at least, two complementation groups. Each mutant cell line exhibited a unique binding pattern of four monoclonal antibodies and five lectins, and different properties of large glycopeptides were distinguished by Sephadex G-50 column chromatography. The combined data suggest that our mutants identify three genes involved in the synthesis of embryoglycan, one of which appears to be the regulatory or structural gene for fucosyltransferase. One mutant cell line was completely deprived of embryoglycan and several carbohydrate structures typical of early embryonic and embryonal carcinoma cells; however, the cells were similar to parental cells in their morphology, their ability to form aggregates when cultured in suspension, their ability to differentiate into neuron-like cells after treatment with retinoic acid, and their ability to form tumors composed of embryonal carcinoma cells. Thus, embryoglycan is not required for the expression of a number of properties of the embryonal carcinoma phenotype.

Purification and separation of two soluble fucosyltransferase activities of small intestinal mucosa

1. Rat small intestinal soluble fucosyltransferase is purified more than 2000-fold using chromatographic procedures with DEAE-cellulose, CM-cellulose, GDP-Sepharose and Concanavalin A-Sepharose. 2. Chromatography on Sephadex G15 of the final enzymatic fraction clearly separates two activities: a first peak incorporates fucose on asialoserotransferrin and a second peak on asialofetuin. 3. The use of small saccharidic acceptors (phenylgalactose, lactose, lacto-N-fucopentaose I) and the analysis of fucosylated asialoglycoproteins indicate that the first activity corresponds to an alpha-(3/4)-fucosyltransferase and the second one to an alpha-(1-2)-fucosyltransferase. 4. Protein analysis by polyacrylamide gel electrophoresis in the presence of SDS for each enzyme shows two bands corresponding to a mol. wt of about 65,000 and 70,000. The two enzymes have the same sensitivity to the action of N-ethylmaleimide.