Variety and microheterogeneity in the carbohydrate chains of glycoproteins

Targeting Glycoproteins as a therapeutic strategy for diabetes mellitus and its complications

OBJECTIVES

Glycoproteins are organic compounds formed from proteins and carbohydrates, which are found in many parts of the living systems including the cell membranes. Furthermore, impaired metabolism of glycoprotein components plays the main role in the pathogenesis of diabetes mellitus. The aim of this study is to investigate the influence of glycoprotein levels in the treatment of diabetes mellitus.

METHODS

All relevant papers in the English language were compiled by searching electronic databases, including Scopus, PubMed and Cochrane library. The keywords of glycoprotein, diabetes mellitus, glycan, glycosylation, and inhibitor were searched until January 2019.

RESULTS

Glycoproteins are pivotal elements in the regulation of cell proliferation, growth, maturation and signaling pathways. Moreover, they are involved in drug binding, drug transportation, efflux of chemicals and stability of therapeutic proteins. These functions, structure, composition, linkages, biosynthesis, significance and biological effects are discussed as related to their use as a therapeutic strategy for the treatment of diabetes mellitus and its complications.

CONCLUSIONS

The findings revealed several chemical and natural compounds have significant beneficial effects on glycoprotein metabolism. The comprehension of glycoprotein structure and functions are very essential and inevitable to enhance the knowledge of glycoengineering for glycoprotein-based therapeutics as may be required for the treatment of diabetes mellitus and its associated complications. Graphical abstract.

Glycoproteins functionalized natural and synthetic polymers for prospective biomedical applications: A review

Glycoproteins have multidimensional properties such as biodegradability, biocompatibility, non-toxicity, antimicrobial and adsorption properties; therefore, they have wide range of applications. They are blended with different polymers such as chitosan, carboxymethyl cellulose (CMC), polyvinyl pyrrolidone (PVP), polycaprolactone (PCL), heparin, polystyrene fluorescent nanoparticles (PS-NPs) and carboxyl pullulan (PC) to improve their properties like thermal stability, mechanical properties, resistance to pH, chemical stability and toughness. Considering the versatile charateristics of glycoprotein based polymers, this review sheds light on synthesis and characterization of blends and composites of glycoproteins, with natural and synthetic polymers and their potential applications in biomedical field such as drug delivery system, insulin delivery, antimicrobial wound dressing uses, targeting of cancer cells, development of anticancer vaccines, development of new biopolymers, glycoproteome research, food product and detection of dengue glycoproteins. All the technical scientific issues have been addressed; highlighting the recent advancement.

How sweet it is! Cell wall biogenesis and polysaccharide capsule formation in Cryptococcus neoformans

Cryptococcus neoformans is a pathogenic fungus responsible for severe opportunistic infections. The most prominent feature of this yeast is its elaborate polysaccharide capsule, a complex structure that is required for virulence. The capsule is intimately associated with the cell wall, which underlies the capsule and offers the organism strength and flexibility in potentially hostile environments. Both structures are primarily composed of polysaccharides, offering a glimpse of the tremendous variation inherent in natural carbohydrate structures and their multiple biological functions. The steps in cell wall and capsule biosynthesis and assembly pose fascinating questions of metabolism, enzymology, cell biology, and regulation; the answers have potential application to treatment of a deadly infection. This article reviews current knowledge of cryptococcal cell wall and capsule biosynthesis and outstanding questions for the future.

Analysis of the microheterogeneity of the IgA1 hinge glycopeptide having multiple O-linked oligosaccharides by capillary electrophoresis

It was found that the self-aggregation of IgA1 was closely connected with the glycoform of a mucin-type sugar chain on its hinge portion. In this report, normal human serum IgA1 was separated into two subfractions by a jacalin column. The elution condition, 25 mM galactose, used here was similar to that reported for the glycoprotein with a single mucin-type sugar chain per molecule. The IgA1 eluted under this condition was substantially the monomeric form. In contrast, the remaining IgA1 eluted from the column with 0. 8 M galactose was substantially the aggregated form. An analytical method for the microheterogeneity of the IgA1 hinge glycopeptide (HGP33) was developed to determine the difference between these IgA1 fractions by capillary electrophoresis (CE). Native HGP33 from both IgA1 fractions was separated into peaks 1-11, depending on their glycoforms. Because the sialic acid-rich component migrated slowly on CE, the 25 mM fraction was abundant in the sialic acid-rich components (peaks 7-11), but the 0.8 M fraction was abundant in the sialic acid-poor components (peaks 1-4). Comparison of the number of sugar chains per hinge peptide indicated that the 25 mM fraction was relatively well glycosylated. Thus, application of CE analysis to the HGP33 indicated that the monomeric IgA1 was composed of a relatively complete molecule with respect to the glycoform rather than the aggregated IgA1.

Protein Glycosylation and Diseases: Blood and Urinary Oligosaccharides as Markers for Diagnosis and Therapeutic Monitoring

Background: N- and O-oligosaccharide variants on glycoproteins (glycoforms) can lead to alterations in protein activity or function that may manifest themselves as overt disease.

Approach: This review summarizes those diseases that are known to be the result of an inherited or acquired glycoprotein oligosaccharide structural alteration and that are diagnosed in blood or urine by chemical characterization of that oligosaccharide alteration.

Content: The biochemical synthesis steps and catabolic pathways important in determining glycoprotein function are outlined with emphasis on alterations that lead to modified function. Clinical and biochemical aspects of the diagnosis are described for inherited diseases such as I-cell disease, congenital disorders of glycosylation, leukocyte adhesion deficiency type II, hereditary erythroblastic multinuclearity with a positive acidified serum test, and Wiskott-Aldrich syndrome. We also review the laboratory use of measurements of glycoforms related to acquired diseases such as alcoholism and cancer.

Conclusions: Identification of glycoprotein glycoforms is becoming an increasingly important laboratory contribution to the diagnosis and management of human diseases as more diseases are found to result from glycan structural alterations.

alpha-Gal epitopes in animal tissue glycoproteins and glycolipids

alpha-Gal terminated saccharides are present on the cell surface both as glycolipids and glycoproteins in all mammals except Old World monkeys and humans. The structural diversity among identified saccharides terminated by this epitope in animal tissues is steadily increasing. The majority of these saccharides have the alpha-Gal linked to lactosamine but other core saccharides exist. The alpha-Gal terminated saccharides are recognized by the immune system as a specific antigen and antibodies directed to the alpha-Gal, which do not cross-react with the classic blood group B trisaccharide, are found in man and Old World monkeys. Similar to other complex carbohydrate cell surface antigens, the alpha-Gal epitope is heterogeneously distributed in different organs and in different cells within an organ. It is present on the vascular endothelium and it is the primary target for human naturally occurring antibodies following pig to primate/man xenotransplantation leading to hyperacute rejection of the graft. Important for the future will be to further structurally characterize this antigen system, its cellular/subcellular distribution, and to identify possible of additional glycosyltransferases, related to the already described alpha 1,3galactosyltransferase that may explain the structural diversity. Such information will be of importance in the studies of, for example, the pathogenesis of autoimmune diseases and for the production of genetically modified pigs to prevent xenograft rejection.

The carbohydrate moiety of alpha-galactosidase from Trichoderma reesei

Alpha-galactosidase from Trichoderma reesei is a glycoprotein that contains O- and N-linked carbohydrate chains. There are 6 O-linked glycans per protein molecule that are linked to serine and threonine and can be released by beta-elimination. Among these are monomers: D-glucose, D-mannose, and D-galactose; dimers: alpha1-6 D-mannopyranosyl-alpha-D-glycopyranoside and alpha1-6 D-glucopyranosyl-alpha-D-galactopyranoside and one trimer: alpha-D-glucopyranosyl-alpha1-2 D-mannopyranosyl-alpha1-6 D-galactopyranoside. N-linked glycans are of the mannose-rich type and may be released by treating the protein with Endo-beta-N-acetyl glycosaminidase F or by hydrozinolysis. The enzyme was deglycosylated with Endo-beta-N-acetyl glycosaminidase F as well as with a number of exoglycosidases that partially remove the terminal residues of O-linked glycans. The effect of enzymatic deglycosylation on the properties of alpha-galactosidase has been considered. The effects of tunicamycin and 2-deoxyglucose on the secretion and glycosylation of the enzyme during culture growth have been analysed. The presence of two glycoforms of alpha-galactosidase differing in the number of N-linked carbohydrate chains and the microheterogeneity of the carbohydrate moiety of the enzyme are described.

Thermal resistance of pantetheine hydrolase

Pantetheine hydrolase from pig kidney shows a very high resistance to denaturation with chemical denaturants, being unfolded at concentrations of guanidinium chloride higher than 6.5 M. On the contrary, chemical inactivation, followed by recording catalytic activity, occurs before conformational changes can be detected by fluorimetric or spectroscopic measurements. The enzyme resists temperatures as high as 80 degrees C, as monitored by second derivative spectroscopy and circular dichroism. Activity increases with temperature to an optimum of about 70 degrees C recording the initial velocity. The enzyme behaves very differently against chemical denaturants or against temperature denaturation. These results are unusual for a mesophilic protein.

Epithelial glucosphingolipid expression as a determinant of bacterial adherence and cytokine production

D-Threo-1-phenyl-2-decanoylamino-3-morpholino-1-propanol (PDMP) is a structural analog of ceramide that inhibits glucosylation of this molecule and thus of glucosphingolipid (GSL) expression by living cells. In this study, we used PDMP to slow the synthesis of the globoseries of GSLs (globo-GSLs) (derived from the precursor Gal alpha 1-4Gal beta 1-4Glc-ceramide) by cultured human kidney and large intestinal epithelial cells. The aim was to deplete the cells of receptors for P-fimbriated Escherichia coli and to examine the effects on the bacterially induced cytokine response. The mammalian cells (A498, HT-29, and Caco2) were cultured in the presence of PDMP in order to deplete them of GSLs. The cells were then subjected to GSL analysis or used to test bacterial adherence and cytokine production. The globo-GSLs were identified by thin-layer chromatography. Bacterial adherence was quantitated by microscopy, and interleukin-6 secretion was quantitated by the B9 bioassay. The interaction of bacteria with the globo-GSLs was studied by using E. coli strains and recombinant clones expressing P fimbriae. E. coli strains expressing type 1 fimbriae binding to mannose-containing glycoproteins were used as controls. PDMP treatment was found to reduce the content of the globo-GSLs in mammalian cells and the adherence of P-fimbriated E. coli to these cells. In contrast, PDMP treatment had no effect on the adherence of type 1-fimbriated E. coli or their activation of cytokine production by A498 cells. P-fimbriated E. coli elicited an interleukin-6 response in the A498 cells; this response was reduced after treatment with PDMP. The results emphasize the role of GSLs as receptors for P-fimbriated E. coli and for the cytokine response elicited by attaching bacteria.

Analysis of porcine gastric mucus glycoprotein added to a culture medium of Streptomyces sp. OH-11242 as the only source of carbon

1. In the process of obtaining the degradation enzymes of mucus glycoprotein, porcine gastric mucus glycoprotein (PGM), added as the only source of carbon, was removed from the culture medium of Streptomyces sp. OH-11242 [Iwase et al. (1988) Biochem. biophys. Res. Commun. 151, 422-428] and analysed. 2. The amino acid and carbohydrate compositions of porcine gastric mucus glycoprotein (PGM-m) recovered from a culture medium were similar to those of original PGM. 3. However, the elution profile of PGM-m on Sephacryl S-400 differed from that of PGM and closely resembled that of performic acid-treated PGM or protease-treated PGM. 4. Either of these corresponded to the so-called subunit of approximately 550,000 in mol. wt, as reported by Scawen and Allen [(1977) Biochem. J. 163, 363-368]. 5. Performic acid treatment of PGM-m led to the production of a smaller unit (unit m) having a mol. wt of about 72,000. Separate treatment of different sized components prepared from PGM-m showed the above unit m to be produced from each molecule. 6. Thus, PGM-m is a molecule partly modified by various glycosidases including endo-alpha-N-acetylgalactosaminidase and exposure of the modified part to performic acid results in oxidation. 7. Production of unit m from both larger and smaller molecules indicates the part susceptible to performic acid to exist at regular intervals on the mucus glycoprotein molecule.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of the N-Linked Oligosaccharide Structures of the Two Major Human Myelin Glycoproteins MAG and P0: Assessment and Relative Occurrence of Oligosaccharide Structures by Serial Lectin Affinity Chromatography of14C-Glycopeptides

The N-linked oligosaccharide structures of human myelin-associated glycoprotein (MAG) and P0 have been characterized by serial lectin affinity chromatography (SLAC) of 14C-glycopeptides. 14C-Glycopeptides were prepared from purified MAG derivative and P0 by extensive proteolytic digestion and N-14C-acetylation. Assuming that all the 14C-glycopeptides were radiolabelled to the same specific radioactivity, the relative occurrence of the oligosaccharide structures was correlated to the amount of incorporated radioactivity. Sixteen and 15 fractions were generated by SLAC of MAG and P0 14C-glycopeptides, respectively. Despite this tremendous structural heterogeneity, the oligosaccharide "fingerprints" of MAG and P0 obtained by SLAC displayed similarities: (a) of the three types of N-linked oligosaccharides, the complex type accounted for 80.4% and 94.9% of MAG and P0 radioactivity, respectively; (b) biantennary complex oligosaccharides were the major structures present on MAG and P0; (c) approximately 60% of MAG and P0 oligosaccharides possessed a bisecting N-acetylglucosamine residue; and (d) large amounts of oligosaccharides with an alpha(1-6)fucose residue were found in both MAG and P0 and, noticeably, approximately 25% of the tri- and/or tetraantennary and approximately 90% of the bisected biantennary oligosaccharides of both glycoproteins contained alpha(1-6)fucose residues in the core. This study demonstrates that MAG and P0, both belonging to the immunoglobulin superfamily, display structural similarities in their N-linked oligosaccharide contents.

The determination of asialoglycoforms of serum glycoproteins by lectin blotting with Ricinus communis agglutinin

Serum proteins were fractionated by polyacrylamide gel electrophoresis under denaturing conditions and transferred to nitrocellulose membranes. The blotted polypeptides were probed with biotinylated Ricinus communis lectin (RCA120) followed by streptavidin/alkaline phosphatase. This procedure detected five asialoglycoproteins (alpha 2-macroglobulin, transferrin, alpha 1-antitrypsin, alpha 1-antichymotrypsin and haptoglobin beta chain). The asialoform of the alpha 1-trypsin inhibitor was found to be decreased in inflammation.

Hypogalactosylation of immunoglobulin G sugar chains and elevated serum interleukin 6 in Castleman's disease

Immunoglobulin G (IgG) molecule has two N-linked complex type oligosaccharides, consisting of a mixture of at least 12 different structures. The pattern of these oligosaccharides is fairly constant in healthy individuals. In three patients with Castleman's disease, in whom serum interleukin 6 (IL-6) levels were elevated, agalactosyl species of serum IgG oligosaccharides were markedly increased as compared to those of normal healthy controls. A close relationship between increased IL-6 and altered IgG oligosaccharide structure is suggested.

Secretory immunoglobulin A carries oligosaccharide receptors for Escherichia coli type 1 fimbrial lectin

Type 1 fimbriae with mannose-specific lectins are widely distributed among members of the family Enterobacteriaceae and confer the ability to attach to a range of host cells, including colonic epithelial cells. The mucosal surfaces are protected by secretory immunoglobulin A (IgA), which agglutinates microorganisms and prevents their attachment to host epithelial cells. This action has been attributed to a specificity of the antigen-combining site of mucosal immunoglobulins for bacterial and viral surface components. Here, we report a novel mechanism for the antibacterial effect of secretory IgA. Secretory IgA and IgA myeloma proteins, especially those of the IgA2 subclass, were shown to possess carbohydrate receptors for the mannose-specific lectin of type 1-fimbriated Escherichia coli. The presence of the high-mannose oligosaccharide chain Man alpha 1-6(Man alpha 1-3)Man alpha 1-6(Man alpha 1-3)Man beta 1-4GlcNAc beta 1-4GlcNAc correlated with binding activity. The interaction between bacterial mannose-specific lectins and IgA receptor oligosaccharide resulted in agglutination of the bacteria and in inhibition of bacterial attachment to colonic epithelial cells. Thus, this interaction could form the basis for a broad antibacterial function of secretory IgA against enterobacteria regardless of the specificity of antibody molecules.

The epitope(s) recognized by HNK-1 antibody and IgM paraprotein in neuropathy is present on several N-linked oligosaccharide structures on human P0 and myelin-associated glycoprotein

The mouse monoclonal antibody HNK-1 and the human monoclonal IgM antibody present in patients with polyneuropathy both recognize carbohydrate epitope(s) on human myelin-associated glycoprotein and P0. In the present study, the oligosaccharide structures that bear the antibody epitope(s) were investigated. The extracellular derivative of myelin-associated glycoprotein (dMAG) was purified by immunoaffinity chromatography. P0 was electroeluted from gel slices. Western blot analysis of whole glycoproteins demonstrated that the epitopes for HNK-1 and the human monoclonal IgM antibody were different. The glycopeptides obtained by proteolysis of purified dMAG and P0 were separated and characterized by affinity chromatography on concanavalin A-Sepharose. Both dMAG and P0 displayed heterogeneity in their oligosaccharide structures, i.e., they both contained mainly tri- and tetraantennary oligosaccharides (approximately 80%), although biantennary (10%) and high-mannose and/or hybrid (10%) oligosaccharides were present. The human monoclonal IgM antibody epitope was present on all types of isolated oligosaccharide structures from either dMAG and P0. The HNK-1 epitope was present on all types of oligosaccharide structures of dMAG, whereas it was present only on tri- and tetraantennary structures of P0.

Structural analysis of the carbohydrate chains of a mouse monoclonal IgM antibody

A mouse monoclonal IgM antibody, directed against human blood group B determinant, was isolated from hybridoma culture growth medium. Chemical analysis indicated presence of N- and O-linked oligosaccharides. The N- and O-linked carbohydrate chains were liberated using two different conditions of reductive alkaline degradation. Structural analysis was carried out on the isolated chains using chemical analysis, 500-MHz 1H-NMR spectroscopy and fast-atom-bombardment mass spectrometry. The following composite structures of the N-linked chains were found: (formula; see text) where R = OH for biantennary structures and R = Neu5Ac alpha 2-3Gal beta 1-4 GlcNAc beta 1- or Neu5Ac alpha 2-3Gal beta 1-3[Neu5Ac alpha 2-6]GlcNAc beta 1- for triantennary structures. The O-linked oligosaccharides, found in the light chains, were shown to have the structure Neu5Ac alpha 2-3Gal beta 1-3GalNAc. The native IgM antibody could be separated on a concanavalin-A-Sepharose column into two subfractions, differing in the presence of a high-mannose-type oligosaccharide.

Serum level of cryptic tumor antigens in breast cancer patients as determined by two monoclonal antibodies (M85/F36) and its comparison with CA 15-3

An enzyme immunoassay system that measures cryptic epitopes on breast cancer mucinlike antigens (BCM-EIA) was evaluated in a double-blind manner in sera from 58 normal blood donors, 36 sex- and age-matched controls, 36 patients with benign breast diseases, and 47 patients with breast cancer. Two murine monoclonal antibodies, M85 (IgM) as the solid-phase and F36/22 (IgG3) as the probe, were used in the configuration of the assay kit. The assay additionally utilized neuraminidase to remove terminal sialic acid from carbohydrate side-chains to expose cryptic epitopes that were masked in serum specimens. BCM-EIA monoclonal assay from the normal healthy blood donors resulted in 17.34 +/- 7.04 units/ml (mean +/- 1 S.D.) with an upper normal cutoff of 31.4 units/ml. The distributions of serum BCM in the sex- and age-matched controls (17.77 +/- 11.17) and benign breast diseases (14.34 +/- 11.46) were similar to that of normal blood donors. A mean value of 66.04 units/ml and 27.74 units/ml was obtained from breast cancer patients with active disease and without evidence of disease, respectively, a level much greater than those of normals, controls, and benign breast diseases. Simultaneous analysis of CA 15-3, a putative breast tumor marker, in the normal donors and breast cancer patients revealed correlation regression of (CA 15-3) = 0.876 (BCM) + 1.972, r = 0.856; and (CA 15-3) = 0.66 (BCM) + 16.094, r = 0.730, respectively. These data showed that there is a statistically significant correlation of CA 15-3 and BCM in normal blood donors' specimens.(ABSTRACT TRUNCATED AT 250 WORDS)