Chemoenzymatic synthesis of a sialylated diantennary N-glycan linked to asparagine

A partial structure of many glycoproteins, a glycosylated asparagine carrying a complex type undecasaccharide N-glycan (Neu5Ac(alpha 2-6)Gal(beta 1-4)GlcNAc(beta 1-2)Man alpha 1-3) [Neu5Ac(alpha 2-6)Gal(beta 1-4)GlcNAc(beta 1-2)Man(alpha 1-6)]Man(beta 1-4) GlcNAc(beta 1-4)GlcNAc-Asn) was obtained by total synthesis. As a starting material served a chemically synthesized diantennary heptasaccharide azide which was deprotected in a three-step sequence in high yield. The reduction of the anomeric azide was accomplished with propanedithiol in methanol-ethyldiisopropylamine. Coupling of the glycosyl amine to an activated aspartic acid gave the benzyl protected asparagine conjugate. After removal of the six benzyl functions the resulting free heptasaccharide asparagine was elongated enzymatically in the oligosaccharide part. The use of beta-1,4-galactosyltransferase and alpha-2,6-sialytransferase in the presence of alkaline phosphatase allowed the efficient transfer of four sugar units to the acceptor resulting in a full length N-glycan, a sialyated diantennary undecasaccharide-asparagine of the complex type.

Observation of unique cross-linked lattices between multiantennary carbohydrates and soybean lectin. Presence of pseudo-2-fold axes of symmetry in complex type carbohydrates

The tetrameric lectin from Glycine max (soybean) (SBA) has been shown to cross-link and precipitate with N-linked multiantennary complex type oligosaccharides containing nonreducing terminal Gal residues (Bhattacharyya, L., Haraldsson, M., & Brewer, C. F. (1988) Biochemistry 27, 1034-1041). In the present study, negative stain electron micrographs of the precipitates of SBA with a series of naturally occurring and synthetic multiantennary carbohydrates with terminal Gal or GalNAc residues show the presence of highly ordered cross-linked lattices for many of the complexes. The precipitates of SBA with a "bisected" and "nonbisected" N-linked biantennary complex type oligosaccharide containing Gal residues at the nonreducing termini show similar two-dimensional patterns. However, the pattern observed for the precipitates of a tetraantennary complex type oligosaccharide with SBA is distinct from those of the two biantennary carbohydrates. Furthermore, the precipitates formed between the lectin and a synthetic O-linked biantennary ("cluster") glycoside with terminal GalNAc residues show a pattern that is different from those above. Four biantennary pentasaccharide analogs of the blood group I antigen containing beta-LacNAc moieties at the 2,3-, 2,4-, 2,6-, and 3,6-positions of the core Gal also showed ordered patterns in their precipitates with SBA. X-ray crystallographic data and mixed quantitative precipitation profiles of binary mixtures of the four analogs demonstrate that each analog possesses a unique cross-linked lattice with the protein. A common structural feature of the naturally occurring and synthetic carbohydrates that show highly organized cross-linked lattices with SBA is the presence of a pseudo-2-fold axis of symmetry in each oligosaccharide relating the terminal binding epitopes on each arm. This suggests that the symmetry features of certain naturally occurring branch chain oligosaccharides facilitate formation of highly ordered, homogeneous cross-linked complexes with specific lectins.

Observation of unique cross-linked lattices between multiantennary carbohydrates and soybean lectin. Presence of pseudo-2-fold axes of symmetry in complex type carbohydrates

The tetrameric lectin from Glycine max (soybean) (SBA) has been shown to cross-link and precipitate with N-linked multiantennary complex type oligosaccharides containing nonreducing terminal Gal residues (Bhattacharyya, L., Haraldsson, M., & Brewer, C. F. (1988) Biochemistry 27, 1034-1041). In the present study, negative stain electron micrographs of the precipitates of SBA with a series of naturally occurring and synthetic multiantennary carbohydrates with terminal Gal or GalNAc residues show the presence of highly ordered cross-linked lattices for many of the complexes. The precipitates of SBA with a "bisected" and "nonbisected" N-linked biantennary complex type oligosaccharide containing Gal residues at the nonreducing termini show similar two-dimensional patterns. However, the pattern observed for the precipitates of a tetraantennary complex type oligosaccharide with SBA is distinct from those of the two biantennary carbohydrates. Furthermore, the precipitates formed between the lectin and a synthetic O-linked biantennary ("cluster") glycoside with terminal GalNAc residues show a pattern that is different from those above. Four biantennary pentasaccharide analogs of the blood group I antigen containing beta-LacNAc moieties at the 2.3-, 2.4-, 2.6-, and 3.6-positions of the core Gal also showed ordered patterns in their precipitates with SBA. X-ray crystallographic data and mixed quantitative precipitation profiles of binary mixtures of the four analogs demonstrate that each analog possesses a unique cross-linked lattice with the protein.(ABSTRACT TRUNCATED AT 250 WORDS)

Stepwise synthesis of a GalNAc-containing cluster glycoside ligand of the asialoglycoprotein receptor

A series of peptidylglycoside derivatives, including the tris(GalNAc-aminohexyl) glycoside of tyrosyl(glutamyl)-glutamate (1) which is known to have sub-nanomolar affinity for the asialoglycoprotein receptor (ASGPr), have been synthesized using the protected tetra-O-acetyl aminohexyl glycoside (9) of N-acetylgalactosamine. The N-succinyl derivative of 1 was also prepared, providing a derivative for bioconjugate formation via carboxyl activation of the glycopeptide. Use of the protected glycoside 9 affords synthetic intermediates with increased solubility in organic solvents that are easier to purify and use in subsequent synthetic manipulations in comparison with compounds containing unprotected glycosides. These synthetic procedures will be generally applicable to the preparation of related compounds to probe binding to the ASGPr and the use of these cluster glycosides as ligands for targeted delivery to the liver.

Selective inhibition of N-acetylglucosamine and galactose-specific lectins including the 14-kDa vertebrate lectin by novel synthetic biantennary oligosaccharides

A novel series of synthetic biantennary tri-, penta- and hepta-saccharides with terminal beta-GlcNAc, beta-LacNAc and alpha NeuAc(2,6)beta LacNAc residues, respectively, [LacNAc = Gal beta (1,4)Glc-NAc] connected to a core Gal residue were evaluated for their inhibitory potencies for specific plant and animal lectins. Six isomeric trisaccharides with two beta-GlcNAc residues at the 2,3-, 2,4-, 2,6-, 3,4-, 3,6-, or 4,6-positions of the core Gal were tested for their hemagglutination inhibition activities against two GlcNAc-specific lectins, Griffonia simplicifolia II (GS II) and wheat germ agglutinin (WGA). The 2,3-, 2,4-, 2,6- and 3,6-trisaccharides inhibited WGA 12-50 times more strongly than GlcNAc, whereas only weak or no inhibition was observed with GS II. The 3,4- and 4,6-trisaccharides did not inhibit either of the lectins. Six biantennary isomeric pentasaccharides containing two terminal beta-LacNAc residues with branching patterns similar to the trisaccharides showed selective hemagglutination inhibition of five Gal/GalNAc-specific plant lectins and the 14-kDa Gal-specific calf spleen lectin. The plant lectins include the soybean agglutinin (SBA), ricin agglutinin-I (RCA-I), and three Erythrina lectins with similar specificities: Erythrina indica (EIL), E. corallodendron (ECorL), and E. cristagalli (ECL). The 2,3-pentasaccharide inhibited only SBA and the 14-kDa lectin, and thus was a selective inhibitor among the plant lectins. The 2,6-pentasaccharide inhibited SBA, ECL and the 14-kDa lectin, but not RCA-I or the two other Erythrina lectins. The 4,6-pentasaccharide did not inhibit any of the plant lectins, but was a specific inhibitor of the 14-kDa calf spleen lectin. Synthetic heptasaccharides analogs with 2,4-, 2,6-, 3,6- and 4,6-branching patterns and terminal alpha(2,6)NeuAc residues all showed 25-fold stronger inhibition against the alpha(2,6)sialic-acid-specific elderberry (Sambucus nigra L.) bark lectin as compared to a monovalent disaccharide alpha NeuAc(2,6)beta GalOR. The lack of inhibition of alpha NeuAc(2,6)beta GalOR derivatives methylated at the C6 of the Gal residue and a sulfur-linked thiosialoside derivative demonstrates that the 2,6-anomeric linkage region is important for lectin recognition. Selective inhibition of the Gal/GalNAc-specific lectins was observed for two isomeric C6 methyl-substituted Gal derivatives of methyl beta-LacNAc which possess different preferred rotamer orientations about the C5-C6 bond of the Gal residue.

Binding and precipitating activities of Erythrina lectins with complex type carbohydrates and synthetic cluster glycosides. A comparative study of the lectins from E. corallodendron, E. cristagalli, E. flabelliformis, and E. indica

Erythrina lectins possess similar structural and carbohydrate binding properties. Recently, tri- and tetra-antennary complex type carbohydrates with non-reducing terminal galactose residues have been shown to be precipitated as tri- and tetravalent ligands, respectively, with certain Erythrina lectins [Bhattacharyya L, Haraldsson M, Brewer CF (1988) Biochemistry 27:1034-41]. The present work describes a comparative study of the binding and precipitating activities of four Erythrina lectins, viz., E. corallodendron, E. cristagalli, E. flabelliformis, and E. indica, with multi-antennary complex type carbohydrates and synthetic cluster glycosides. The results show that though their binding affinities are very similar, the Erythrina lectins show large differences in their precipitating activities with the carbohydrates. The results also indicate significant dependence of the precipitating activities of the lectins on the core structure of the carbohydrates. These findings provide a new dimension to the structure-activity relationship of the lectins and their interactions with asparagine-linked carbohydrates.

Inhibition of adenylyl cyclase activity in rat corpora luteal tissue by glycopeptides of human chorionic gonadotropin and the alpha-subunit of human chorionic gonadotropin

Indirect evidence has indicated that the carbohydrate moieties of the glycoprotein hormones are involved in the activation of the receptor-adenylyl cyclase system of reproductive tissues. In the present study, we have isolated the glycopeptides (GP) from human chorionic gonadotropin (hCG), the alpha-subunit of hCG, fetuin, and bovine gamma-globulin (b gamma G). These along with a number of synthetic oligosaccharides were tested for their ability to inhibit adenylyl cyclase (AC). There was less than 0.001% cross-reactivity of the GP from hCG, hCG alpha, fetuin, and b gamma G when tested in a double-antibody hCG radioimmunoassay or rat corpora lutea radioreceptor assay. The GP of fetuin, b gamma G, and the synthetic oligosaccharides did not inhibit AC activity of 2000 g corpora lutea membranes when coincubated with 100 ng of hCG/mL (ED50). However, when the GP of hCG and hCG alpha were included with intact hCG, there was a dose-related inhibition. Inhibition of cyclase activity was enhanced when the hCG GP were desialylated. This occurred without a change in the lag time of hCG activation which was calculated to be 1-1.5 min. Changing the concentration of ATP and Mg2+ did not affect the inhibitory effects of the hCG alpha GP on hCG-stimulated AC activity. Inhibition by hCG GP followed uncompetitive kinetics. The inhibition by the GP of hCG seems to be restricted to the LH/hCG-stimulatable AC system because the same dosage of hCG GP which inhibited the rat luteal AC system did not have any effect on the rat hepatocyte AC system when coincubated with glucagon or on NaF-stimulated activity in luteal membranes.(ABSTRACT TRUNCATED AT 250 WORDS)

Carbohydrate binding studies on the lectin from Datura stramonium seeds

The carbohydrate-binding properties of the Datura stramonium seed lectin were studied by equilibrium dialysis, quantitative precipitation of natural and synthetic glycoproteins, and hapten inhibition of precipitation. The dimeric lectin (Mr = 86,000) possesses two carbohydrate-binding sites for N,N'N",N"'- tetraacetylchitotetritol /mol protein, with an apparent Ka = 8.7 X 10(3) M-1 at 4 degrees C. Whereas fetuin and orosomucoid reacted poorly with the Datura lectin, the asialo derivatives of these glycoproteins gave strong precipitation with the lectin. Carcinoembryonic antigen, type 14 pneumococcal capsular polysaccharide, and bovine serum albumin, highly substituted with N,N'- diacetylchitobiose units, also precipitated the lectin. Of the homologous series of chitin oligosaccharides tested, N,N',N"'- triacetylchitotriose was over 6-fold more potent than the disaccharide (N,N'- diacetylchitobiose ) which, in turn, was 90 times more reactive than N-acetyl-D-glucosamine. N-Acetyllactosamine [beta-D-Gal-(1----4)-D-GlcNAc] was also a potent inhibitor of Datura lectin being equivalent to N,N'- diacetylchitobiose . The requirement for an N-acetyl-D-glucosaminyl unit linked at the C-4 position was established. The biantennary pentasaccharide (penta-2,6) was a 500-fold more potent inhibitor than N-acetyllactosamine, suggesting that it might interact with both saccharide-binding sites of the Datura lectin simultaneously.

Synthesis of a nona- and an undeca-saccharide that form part of the complex type of carbohydrate moiety of glycoproteins

Silver trifluoromethanesulfonate-promoted condensation of 3,6-di-O-acetyl-2-deoxy-2-phthalimido-4-O-(2,3,4,6-tetra-O-acetyl-beta-D- galactopyranosyl)-beta-D-glucopyranosyl bromide with benzyl 2,4,-di-O-benzyl-6-O-(3,4-di-O-benzyl-alpha-D-mannopyranosyl)-3-O-(3,6-di-O- benzyl-alpha-D-mannopyranosyl)-alpha-D-mannopyranoside gave nonasaccharide and undecasaccharide derivatives. The nonasaccharide 2 and the undecasaccharide 3 were obtained by removal of the protecting groups followed by N-acetylation. (formula; see text).