Tumor cells as the origin of elevated serum alpha1,3fucosyltransferase in association with malignancy

We have previously reported that the elevated activities of serum alpha 1,3fucosyltransferase reverted to normal levels after curative removal of the tumors. To determine the origin of elevated serum alpha 1,3fucosyltransferase, blood samples were obtained from both the drainage vein and the artery in patients with different stages of colorectal cancer at surgery. The enzyme levels in all samples from the drainage vein were found to be higher than the levels in the artery that fed the tumor. Hence, the origin of elevated alpha1,3fucosyltransferase in serum was thought to be the tumor rather than the liver that is the normal source of serum alpha1,3fucosyltransferase. When serum samples not only from colorectal cancer patients but also from patients with gastric, liver, lung, pancreas, bladder and esophagus cancer were treated with anti-FUTVI antibody, the measured activities of alpha1,3fucosyltransferase were markedly reduced. Further, secretion of alpha1,3fucosyltransferase from human colorectal carcinoma cells was also detected in the culture medium by Western immuno-blot analysis with anti-FUTVI antibody.

Human ovarian cancer, lymphoma spleen, and bovine milk GlcNAc:beta1,4Gal/GalNAc transferases: two molecular species in ovarian tumor and induction of GalNAcbeta1,4Glc synthesis by alpha-lactalbumin

Affinity Gel-UDP was utilized to purify GlcNAc:beta1,4Gal/GalNAc transferases (Ts) from human lymphoma spleen, ovarian tumor, and ovarian cancer sera. Mn(2+) was found to be an absolute requirement for activity. Two molecular species containing both beta1,4Gal/GalNAc-T activities were discernible when the purified ovarian tumor microsomal enzyme was subjected to Sephacryl S-100 HR column chromatography as well as native polyacylamide gel-electrophoresis. Acceptor specificity studies of the affinity-purified lymphoma spleen and ovarian tumor microsomal enzymes and the conventionally purified, as well as the cloned, bovine milk GlcNAc:beta1,4Gal-Ts using a number of synthetic acceptors showed that the beta(1,6)-linked GlcNAc moiety to alpha-GalNAc was the most efficient acceptor. As compared to the purified milk enzyme, the recombinant form exhibited sixfold GlcNAc:beta1,4 GalNAc-T activity and up to eightfold GlcNAc6SO3beta-:beta1,4Gal-T activity. Further, the recombinant enzyme catalyzed the transfer of GalNAc to the terminal beta-linked GlcNAc6SO3 moiety. Alpha-lactalbumin (alpha-LA) inhibited up to 85%, the transfer of Gal to the GlcNAc moiety linked either to Man or GlcNAc. On the contrary, alpha-LA had no significant influence on the transfer of GalNAc to the above acceptors. alpha-LA had no appreciable effect on the recombinant enzyme, except for the transfer of Gal or GalNAc to Glc. Both alpha- and beta-glucosides, as well as alpha-N-acetylglucosaminide, did not serve as acceptors.

Human lung adenocarcinoma alpha1,3/4-L-fucosyltransferase displays two molecular forms, high substrate affinity for clustered sialyl LacNAc type 1 units as well as mucin core 2 sialyl LacNAc type 2 unit and novel alpha1,2-L-fucosylating activity

Human lung tumor alpha1,3/4-L-fucosyltransferase (FT) was purified (2000-fold, 29% recovery) from 290 g of tissue by including a chromatography step on Affinity Gel-GDP. Two molecular forms (FTA, larger size carrying 15% alpha1,4-FT activity; FTB, the major form with 85% activity) were separated by further fractionation on a Sephacryl S-100 HR column. A difference in the electrophoretic mobilities of these two activities was also found on native polyacrylamide gel electrophoresis (PAGE). Both forms were devoid of typical alpha1,2-fucosylating activity but were associated with the novel alpha1,2-fucosylating ability of converting the Lewis a determinant to Lewis b. Based on percentage activity toward 2-O-MeGalbeta1,3GlcNAcbeta-O-Bn, both forms exhibited the same extent of activity toward various acceptors, which included sulfated, sialylated, or methylated LacNAc type 1 or type 2 as well as mucin core 2 acceptors. However, FTA and FTB exhibited a difference in their ability to act on mucin core 2 3'-sialyl LacNAc (activities 24.2% and 40.8%, respectively, as compared to 2-O-MeGalbeta1,3GlcNAcbeta-O-Bn). The unsubstituted LacNAc type 1 acceptors were 15-20 times as active as the corresponding LacNAc type 2 acceptors. The 3-O-substitution on the beta1,4-linked Gal (methyl, sulfate, or sialyl) in mucin core 2 acceptors increased the efficiency of these acceptors five- to eightfold. The most efficient acceptor for FTA and FTB was 3-O-sulfoGalbeta1,3GlcNAcbeta-O-Al (K(m) 100 and 47 microM, respectively). The K(m) (mM) values for 2-O-methyl Galbeta1,3GlcNAcbeta-O-Bn and 3-O-sialyl Galbeta1,3GlcNAcbeta-O-Bn were 0.40 and 2.5 (FTA) and 0.16 and 0.67 (FTB), respectively. The 35-kDa glycoprotein ancrod (from Malayan pit viper venom) containing 36% complex N-glycans with the antennae NeuAcalpha2,3Galbeta1,3GlcNAcbeta- acted as the best macromolecular acceptor substrate (K(m): 45 microM), as examined with FTB. On desialylation the acceptor efficiency dropped to approximately 50% (K(m) for asialo ancrod: 167 microM). Sialylglycoproteins, such as carcinoembryonic antigen, fetuin, and bovine alpha(1)-acid glycoprotein, were better acceptors than asialo fetuin. On the contrary, fetuin triantennary glycopeptide containing predominantly NeuAcalpha2,3Galbeta1,4GlcNAcbeta- was only 55% active as compared to the asialo glycopeptide (K(m): 1.43 and 0.63 mM, respectively). Thus, the human lung tumor alpha1,3/4-L-FT has the potential to generate clustered sialyl Lewis a and Lewis b determinants in N-glycans and sialyl Lewis x determinant in mucin core 2 structures.

Molecular analysis of plasma alpha 1,3-fucosyltransferase deficiency and development of the methods for its genotyping

Four patients with mental illness were found to be deficient in plasma alpha1,3-fucosyltransferase for the first time in Japan [Exp Clin Immunogenet 1999;16:125-130]. Complete sequencing of FUT6 genes in these individuals revealed the presence of two point mutations, i.e., G739 to A (Glu-->247 to Lys) and C945 to A (Tyr-->315 to stop). In addition to two reported alleles having G739 to A (pf1) and G739 to A and C945 to A (pf3), a new mutated allele having C945 to A (pf2) was found to be present and all the individuals who lack alpha1,3-fucosyltransferase activity in plasma were found to possess pf genes homozygously (pf/pf). In order to detect such lethal mutations in FUT6 genes easily, PCR-RFLP methods have also been developed and applied for the screening of FUT6 deficiency in a large number of samples which resulted in the demonstration of three additional FUT6-deficient individuals. The absence of alpha1,3-fucosylated molecules on alpha(1)-acid glycoprotein in plasma from all the 7 individuals was confirmed to result from the plasma alpha1,3-fucosyltransferase deficiency.

A new method for assaying adhesion of cancer cells to the greater omentum and its application for evaluating anti-adhesion activities of chemically synthesized oligosaccharides

A new ex vivo method for assaying adhesion of cancer cells to the greater omentum has been developed using mouse greater omentum and [3H]labelled human gastric and mouse colorectal cancer cells. Since the adhesion rates were found to increase up to 18 h and labelled cells seemed to be stable during the period, the present method could be useful for investigating adhesion of cancer cells to the greater omentum, which must occur at the first step of the peritoneal dissemination. The adhesion of cancer cells to the greater omentum was inhibited by a series of chemically synthesized oligosaccharides and Gal beta1,3[3OMeGal beta1,4GlcNAc beta1,6]alphaBn was found to be the best inhibitor. The anti-tumor effect of this novel tetrasaccharide in vivo was shown in preliminary experiments using Balb/c mice and colon26 cells.

The 2-naphthylmethyl (NAP) group in carbohydrate synthesis: first total synthesis of the GlyCAM-1 oligosaccharide structures

Total syntheses of the GlyCAM-1 (glycosylation-dependent cell adhesion molecule-1) oligosaccharide structures: [alpha-NeuAc-(2 --> 3)-beta-Gal-(1 --> 4)-[alpha-Fuc-(1 --> 3)]-beta-(6-O-SO3Na)-GlcNAc-(1 --> 6)]-[alpha-NeuAc-(2 --> 3)-beta-Gal-(1 --> 3)]-alpha-GalNAc-OMe (1) and [alpha-NeuAc-(2 --> 3)-beta-Gal-(1 --> 4)-[alpha-Fuc-(1 --> 3)]-beta-GlcNAc-(1 --> 6)]-[alpha-NeuAc-(2 3)-beta-Gal-(1 --> 3)]-alpha-GalNAc-OMe (2) through a novel sialyl LewisX tetrasaccharide donor are described. Employing sequential glycosylation strategy, the starting trisaccharide was regio- and stereoselectively constructed through coupling of a disaccharide imidate with the monosaccharide acceptor phenyl-6-O-naphthylmethyl-2-deoxy-2-phthalimido-1-thio-beta-D-glucopyranoside with TMSOTf as a catalyst without affecting the SPh group. The novel sialyl Lewisx tetrasaccharide donor 3 was then obtained by alpha-L-fucosylation of trisaccharide acceptor with the 2,3,4-tri-O-benzyl-1-thio-beta-L-fucoside donor. The structure of the novel sialyl Lewisx tetrasaccharide was established by a combination of 2D DQF-COSY and 2D ROESY experiments. Target oligosaccharides 1 and 2 were eventually constructed through heptasaccharide which was obtained by regioselective assembly of advanced sialyl Lewisx tetrasaccharide donor 3 and a sialylated trisaccharide acceptor in a predictable and controlled manner. Finally, target heptasaccharides 1 and 2 were fully characterized by 2D DQF-COSY, 2D ROESY, HSQC, HMBC experiments and FAB mass spectroscopy.

Chemical synthesis of sulfated oligosaccharides with a beta-D-Gal-(1-->3)

The syntheses of two sulfated pentasaccharides: beta-D-Gal6SO3Na-(1-->3)-[beta-D-Gal-(1-->4)-alpha-L-Fuc-(1-->3)-beta-D-Glc-NAc-(1-->6)]-alpha-D-GalNAc-->OMe (1) and beta-D-Gal6SO3Na-(1-->3)-[beta-D-Gal-(1-->4)-alpha-L-Fuc-(1-->3)-beta-D-Glc-NAc6SO3Na-(1-->6)]-alpha-D-GalNAc-->OMe (2) by using Lewisx trisaccharides 12 and 16 as glycosyl donors are described. Sulfated oligosaccharides 1-2 and intermediate compounds are fully characterized by 2D 1H-1H DQF-COSY and 2D ROESY experiments.

Chemical synthesis of a core 2 branched pentasaccharide containing a carboxylate group

Design and synthesis of a carboxylate-containing pentasaccahride 1 with the Galbeta(1-4) (Fucalpha1-3)GlcNAcbeta(1-6)[3-[1-carboxymethyl]-Galbeta+ ++(1-3)]GalNAcalpha-OMe sequence, which is obtained through regioselective coupling of the 6-OH of a novel acceptor 9 with Lewis(x) donor 10 catalyzed by NIS-TfOH are described.

Total synthesis of sialylated and sulfated oligosaccharide chains from respiratory mucins

The total syntheses of several complex oligosaccharide moieties that occur in the core structure of sulfated mucins are reported. A trisaccharide acceptor was obtained through regio- and stereoselective sialylation of methyl (6-O-pivaloyl-beta-D-galactopyanosyl)(1-->3)-4,6-O-benzylidene-2-a cetamido-2-deoxy-alpha-D-galactopyranoside with a novel sialyl donor. A tetrasaccharide, pentasaccharide, and hexasaccharide were constructed in predictable and controlled manner with high regio- and stereoselectivity after the successful preparation and employment of a disaccharide donor, trisaccharide donor, disaccharide acceptor, and trisaccharide acceptor building blocks. Finally, a mild oxidative cleaving method was adopted for the selective removal of 2-naphthylmethyl (NAP) in the presence of benzyl groups.

A convergent synthesis of trisaccharides with alpha-Neu5Ac-(2 --> 3)-beta-D-gal-(1 --> 4)-beta-D-GlcNAc and alpha-Neu5Ac-(2 --> 3)-beta-D-gal-(1 --> 3)-alpha-D-GalNAc sequences

The syntheses of three trisaccharides: alpha-Neu5Ac-(2 --> 3)-beta-D-Gal-(1 --> 4)-beta-D-GlcNAc --> OMe, alpha-Neu5Ac-(2 --> 3)-beta-D-Gal6SO3Na-(1 --> 4)-beta-D-GlcNAc --> OMe, and alpha-Neu5Ac-(2 --> 3)-beta-D-Gal-(1 --> 3)-alpha-D-GalNAc --> OBn were accomplished by using either methyl (phenyl 5-acetamido-4,7,8,9-tetra-O-acetyl-3,5-dideoxy-2-thio-beta-D-glycero-D-g alacto-2-nonulopyranoside)onate or methyl (phenyl N-acetyl-5-acetamido-4,7,8,9-tetra-O-acetyl-3,5-dideoxy-2-thio-beta-D-gl ycero-D-galacto-2-nonulopyranoside)onate as the sialyl donor. The N,N-diacetylamino sialyl donor appears to be more reactive than its parent acetamido sugar when allowed to react with an disaccharide acceptor under the same glycosylation conditions. The trisaccharides, as well as the intermediate products, were fully characterized by 2D DQF 1H-1H COSY and 2D ROESY spectroscopy.

N-p-nitrobenzyloxycarbonyl galactosamine imidate as a glycosyl donor for the efficient synthesis of mucin core-2 analogue

An efficient synthesis of the mucin core-2 analogue 1a was accomplished using N-p-nitrobenzyloxycarbonyl(PNZ)-protected trichloroacetimidate 4 as a novel glycosyl donor.

Mammalian Notch1 is modified with two unusual forms of O-linked glycosylation found on epidermal growth factor-like modules

Notch is a large cell-surface receptor known to be an essential player in a wide variety of developmental cascades. Here we show that Notch1 endogenously expressed in Chinese hamster ovary cells is modified with O-linked fucose and O-linked glucose saccharides, two unusual forms of O-linked glycosylation found on epidermal growth factor-like (EGF) modules. Interestingly, both modifications occur as monosaccharide and oligosaccharide species. Through exoglycosidase digestions we determined that the O-linked fucose oligosaccharide is a tetrasaccharide with a structure identical to that found on human clotting factor IX: Sia-alpha2,3-Gal-beta1, 4-GlcNAc-beta1,3-Fuc-alpha1-O-Ser/Thr. The elongated form of O-linked glucose appears to be a trisaccharide. Notch1 is the first membrane-associated protein identified with either O-linked fucose or O-linked glucose modifications. It also represents the second protein discovered with an elongated form of O-linked fucose. The sites of glycosylation, which fall within the multiple EGF modules of Notch, are highly conserved across species and within Notch homologs. Since Notch is known to interact with its ligands through subsets of EGF modules, these results suggest that the O-linked carbohydrate modifications of these modules may influence receptor-ligand interactions.

An efficient synthesis of two monosulfated trisaccharides with the Galbeta1,3GlcNacbeta1,3Galbeta-O-allyl backbone

The GlcNAcbeta(1-->3) Gal linked disaccharide 7 was synthesized as key building blocks for the construction of target monosulfated trisaccharides 1 and 2 using oxazoline 3 as glycosyl donor promoted by BF3 x Et2O.

Characterization of distinct Gal:3-O-sulfotransferase activities in human tumor epithelial cell lines and of calf lymph node GlcNAc : 6-O-sulfotransferase activity

We found earlier in human breast and colon tumors, an augmented level of Gal : 3-O-sulfotransferase activities showing, respectively, an acceptor preference to blood group T-hapten (Group A enzymes) or Galbeta1,4GlcNAc (Group B enzymes) on the mucin Core 2 structure [Chandrasekaran EV, Jain RK, Vig R, and Matta KL (1997) Glycobiology 7: 753-68]. The present study reports these enzyme activities in human tumor cell lines and additional tumor specimens. The human colon tumor epithelial cell lines, akin to their parent tumors, express Group B enzyme activity. The acceptor specificity and kinetic properties, such as divalent metal ion activation and pH dependent activity profile, of the colon cancer line LS180 enzyme activity are identical to those of colon tissue specimens. Consistent with breast tumor specimens, the Group A enzyme activity is present in human breast tumor epithelial cell lines, with some exceptions. The Gal : 3-O-sulfotransferases show specific binding to Aleuria aurantia lectin, suggesting the presence of asparagine linked carbohydrate chains containing an inner core alpha1,6-fucosyl residue on these enzymes. Calf lymph nodes contain GlcNAc : 6-O-sulfotransferase as well as Group A Gal : 3-O-sulfotransferase activities, which differ in pH dependent profiles, pH optima (7.6 and 7.0, respectively) and the influence of Mn2+.

Cell surface n-acetylneuraminic acid alpha2,3-galactoside-dependent intercellular adhesion of human colon cancer cells

Sialoglycans on the cell surface of human colon cancer (HCC) cells have been implicated in cellular adhesion and metastasis. To clarify the role of N-acetylneuraminic acid (NeuAc) linked alpha2,3 to galactose (Gal) on the surface of HCC cells, we studied the intercellular adhesion of HCC cell lines expressing increasing NeuAcalpha2,3Gal-R. Our model system consisted of the HCC SW48 cell line, which inherently possesses low levels of cell surface alpha2,3 and alpha2,6 sialoglycans. To generate SW48 clonal variants with elevated cell surface NeuAcalpha2,3Gal-R linkages, we transfected the expression vector, pcDNA3, containing either rat liver cDNA encoding Galbeta1,3(4)GlcNAc alpha2,3 sialyltransferase (ST3Gal III) or human placental cDNA encoding Galbeta1,3GalNAc/Galbeta1,4GlcNAc alpha2,3 sialyltransferase (ST3Gal IV) into SW48 cells. Selection of neomycin-resistant clones (600 microgram G418/ml) having a higher percentage of cells expressing NeuAcalpha2,3Gal-R (up to 85% positive Maackia amurenis agglutinin staining compared with 30% for wild type cells) was performed. These ST3Gal III and ST3Gal IV clonal variants demonstrated increased adherence to IL-1beta-activated human umbilical vein endothelial cells (HUVEC) (up to 90% adherent cells compared with 63% for wild type cells). Interestingly, ST3Gal III and ST3Gal IV clonal variants also bound non-activated HUVEC up to 4-fold more effectively than wild type cells. Cell surface NeuAcalpha2,3Gal-R expression within the various SW48 clonal variants correlated directly with increased adhesion to HUVEC (r=0.84). Using HCC HT-29 cells, which express high levels of surface NeuAcalpha2,3Gal-R, addition of synthetic sialyl, sulfo or GalNAc Lewis X structures were found to specifically inhibit intercellular adhesion. At 1.0mM, NeuAcalpha2,3Galbeta1,3(Fucalpha1, 4)GlcNAc-OH and Galbeta1,4(Fucalpha1,3)GlcNAcbeta1,6(SE-6Galbeta1++ +, 3)GalNAcalpha1-O-methyl inhibited HT-29 cell adhesion to IL-1beta-stimulated HUVEC by 100% and 68%, respectively. GalNAcbeta1, 4(Fucalpha1,3)GlcNAcbeta1-O-methyl and GalNAcbeta1,4(Fucalpha1, 3)GlcNAcbeta1,6Manalpha1,6Manbeta1-0-C30H61, however, did not possess inhibitory activity. In conclusion, these studies demonstrated that cell surface NeuAcalpha2,3Gal-R expression is involved in HCC cellular adhesion to HUVEC. These specific carbohydrate-mediated intercellular adhesive events may play an important role in tumor angiogenesis, metastasis and growth control.

Synthesis of Gal-beta-(1-->4)-GlcNac-beta-(1-->6)-[Gal-beta-(1-->3]-GalNAc-alpha- OBn oligosaccharides bearing O-methyl or O-sulfo groups at C-3 of the Gal residue: specific acceptors for Gal: 3-O-sulfotransferases

Our recent studies have revealed the existence of two distinct Gal: 3-O-sulfotransferases capable of acting on the C-3 position of galactose in a Core 2 branched structure, e.g., Galbeta1-->4GlcNAcbeta1-->6(Galbeta1-->3)GalNacalph a1-->OBenzyl as acceptor to give 3-O-sulfoGalbeta1-->4GlcNAcbeta1-->3(Galbeta1-->3)G alNAcalpha1-->OB 20 and Galbeta1-->4GlcNAcbeta1-->6(3-O-sulfoGalbeta1-->3)G alNAcalpha1-->OB 23. We herein report the synthesis of these two compounds and also that of other modified analogs that are highly specific acceptors for the two sulfotransferases. Appropriately protected 1-thio-glycosides 7, 8, and 10 were employed as glycosyl donors for the synthesis of our target compounds.

Synthesis of oligosaccharides containing beta-D-Gal-(1-->3)-O-(6-O-sulfo-beta-D-GlcNAc) as a terminal unit

The chemical synthesis of beta-D-Gal-(1-->3)-6-O-SO3Na-beta-D-GlcNAc-(1-->6)-alpha-D-Man-O-+ ++C6H4NO2 (1) and beta-D-Gal-(1-->3)-6-O-SO3Na-beta-D-GlcNAc-(1-->2)-alpha-D-Man-OMe (2) is reported using a key glycosyl donor, phenyl O-(2,3,4,6-tetra-O-acetyl-beta-D-galactopyranosyl)-(1-->3)-4,6-di-O- chloroacetyl-2-deoxy-2-phthalimido-1-thio-beta-D-glucopyranoside (3).

Inhibition of L- and P-selectin by a rationally synthesized novel core 2-like branched structure containing GalNAc-Lewisx and Neu5Acalpha2-3Galbeta1-3GalNAc sequences

The selectins interact in important normal and pathological situations with certain sialylated, fucosylated glycoconjugate ligands containing sialyl Lewisx(Neu5Acalpha2-3Galbeta1-4(Fucalpha1-3)GlcN Ac). Much effort has gone into the synthesis of sialylated and sulfated Lewisxanalogs as competitive ligands for the selectins. Since the natural selectin ligands GlyCAM-1 and PSGL-1 carry sialyl Lewisxas part of a branched Core 2 O-linked structure, we recently synthesized Galbeta1-4(Fucalpha1-3)GlcNAcbeta1-6(SE-3Galbeta1++ +-3)GalNAc1alphaOMe and found it to be a moderately superior ligand for L and P-selectin (Koenig et al. , Glycobiology 7, 79-93, 1997). Other studies have shown that sulfate esters can replace sialic acid in some selectin ligands (Yeun et al. , Biochemistry, 31, 9126-9131, 1992; Imai et al. , Nature, 361, 555, 1993). Based upon these observations, we hypothesized that Neu5Acalpha2-3Galbeta1-3GalNAc might have the capability of interacting with L- and P-selectin. To examine this hypothesis, we synthesized Galbeta1-4(Fucalpha1-3)GlcNAcbeta1-6(Neu5Acalpha2++ +-3Galbeta1-3)-GalNAc alpha1-OB, which was found to be 2- to 3-fold better than sialyl Lexfor P and L selectin, respectively. We also report the synthesis of an unusual structure GalNAcbeta1-4(Fucalpha1- 3)GlcNAcbeta1-OMe (GalNAc-Lewisx-O-methyl glycoside), which also proved to be a better inhibitor of L- and P-selectin than sialyl Lewisx-OMe. Combining this with our knowledge of Core 2 branched structures, we have synthesized a molecule that is 5- to 6-fold better at inhibiting L- and P-selectin than sialyl Lewisx-OMe, By contrast to unbranched structures, substitution of a sulfate ester group for a sialic acid residue in such a molecule resulted in a considerable loss of inhibition ability. Thus, the combination of a sialic acid residue on the primary (beta1-3) arm, and a modified Lexunit on the branched (beta1-6) arm on an O-linked Core 2 structure generated a monovalent synthetic oliogosaccharide inhibitor superior to SLexfor both L- and P-selectin.

Binding of synthetic sulfated ligands by human splenic galectin 1, a beta-galactoside-binding lectin

The carbohydrate-binding site of galectin 1, a vertebrate beta-galactoside-binding lectin, has a pronounced specificity for the betaGal(1-->3)- and betaGal(1-->4)GlcNAc sequences. The binding inhibition study reported herein was carried out to determine whether sulfation of saccharides would influence their binding by galectin 1. The presence of 6'-OSO3- on LacNAc greatly reduces the inhibitory potency relative to LacNAc. 3'-OSO3-LacNAc, 3'-OSO3-Galbeta(1-->3)GlcNAc(beta)1-OBzl and 3-OSO3-Galbeta1-OMe are more potent inhibitors than the non-sulfated parent compounds. Surprisingly, 2'-OSO3-LacNAc showed over 40 fold less inhibitory potency relative to LacNAc. Ovarian carcinoma A121 cells were shown to synthesize sulfated macromolecules that bind to galectin 1. Modulation in vivo of saccharide sulfation may lead to modulation of galectin 1 interaction with glycoconjugates; hence, sulfation could play a role in modulating lectin functions.

Fucosylation of disaccharide precursors of sialyl LewisX inhibit selectin-mediated cell adhesion

We showed previously that HL-60 and F9 mouse embryonal carcinoma cells will take up and deblock peracetylated Galbeta1-4GlcNAcbeta-O-naphthalenemethanol (Galbeta1-4GlcNAc-NM) and use the disaccharide as a primer of oligosaccharide chains (Sarkar, A. K., Fritz, T. A., Taylor, W. H., and Esko, J. D. (1995) Proc. Natl. Acad. Sci. U. S. A. 92, 3323-3327). We now report that another disaccharide, acetylated GlcNAcbeta1-3Gal-naphthalenemethanol (GlcNAcbeta1-3Gal-NM), has even greater potency and that both compounds will inhibit sialyl LewisX (sLex)-dependent cell adhesion. When fed to U937 cells, acetylated forms of Galbeta1-4GlcNAc-NM and GlcNAcbeta1-3Gal-NM primed oligosaccharides in a dose-dependent manner. Analysis of compounds assembled on Galbeta1-4GlcNAc-NM showed only one product, namely Galbeta1-4(Fucalpha1-3)GlcNAc-NM. In contrast, GlcNAcbeta1-3Gal-NM generated Galbeta1-4GlcNAcbeta1-3Gal-NM, Galbeta1-4(Fucalpha1-3)GlcNAcbeta1-3Gal-NM, NeuAcalpha2-3Galbeta1-4GlcNAcbeta1-3Gal-NM, and NeuAcalpha2-3Galbeta1-4(Fucalpha1-3)GlcNAcbeta1- 3Gal-NM. Both compounds decreased the incorporation of [3H]fucose into cellular glycoconjugates, without affecting the incorporation of [3H]mannosamine, a precursor of sialic acid residues. Moreover, the overall extent of sialylation was not affected based on the reactivity of cells to fluorescein isothiocyanate-conjugated Maackia amurensis lectin. Priming inhibited expression of sLex on cell surface glycoconjugates, which reduced E-selectin-dependent cell adhesion to tumor necrosis factor-alpha-activated human umbilical vein endothelial cells. GlcNAcbeta1-3Gal-NM and Galbeta1-4GlcNAc-NM represent starting points for making enzyme-specific, site-directed inhibitors of glycosyltransferases that could act in living cells.

The enzymatic sulfation of glycoprotein carbohydrate units: blood group T-hapten specific and two other distinct Gal:3-O-sulfotransferases as evident from specificities and kinetics and the influence of sulfate and fucose residues occurring in the carbohydrate chain on C-3 sulfation of terminal Gal

Enzymatic 3-O-sulfation of terminal beta-Gal residues was investigated by screening sulfotransferase activity present in 37 human tissue specimens toward the following synthesized acceptor moieties: Galbeta1,3GalNAc alpha-O-Al, Galbeta1,4GlcNAcbeta-O-Al, Galbeta1,3GlcNAcbeta-O-Al, and mucin-type Galbeta1,4GlcNAcbeta1,6(Galbeta1,3)GalNAc alpha-O-Bn structures containing a C-3 methyl substituent on either Gal. Two distinct types of Gal: 3-O-sulfotransferases were revealed. One (Group A) was specific for the Galbeta1, 3GalNAc alpha- linkage and the other (Group B) was directed toward the Galbeta1,4GlcNAc branch beta1,6 linked to the blood group T hapten. Enzyme activities found in breast tissues were unique in showing a strict specificity for the T-hapten. Galbeta-O-allyl or benzyl did not serve as acceptors for Group A but were very active with Group B. An examination of activity present in six human sera revealed a specificity of the serum enzyme toward beta1,3 linked Gal, particularly, the T-hapten without beta1,6 branching. Group A was highly active toward T-hapten/acrylamide copolymer, anti-freeze glycoprotein, and fetuin O-glycosidic asialo glycopeptide; less active toward fetuin triantennary asialo glycopeptide; and least active toward bovine IgG diantennary glycopeptide. Group B was moderately and highly active, respectively, with the latter two glycopeptides noted and least active with the first two. Competition experiments performed with Galbeta1,3GalNAc alpha-O-Al and Galbeta1,4GlcNAcbeta1,6(Galbeta1,3)GalNAc alpha-O-Bn having a C-3 substituent (methyl or sulfate) on either Gal reinforced earlier findings on the specificity characteristics of Group A and Group B. Group A displayed a wider range of optimal activity (pH 6.0-7.4), whereas Group B possessed a peak of activity at pH 7.2. Mg2+ stimulated Group A 55% and Group B 150%, whereas Mn+2 stimulated Group B 130% but inhibited Group A 75%. Ca2+ stimulated Group B 100% but inhibited Group A 35%. Group A and Group B enzymes appeared to be of the same molecular size (<100,000 Da) as observed by Sephacryl S-100 HR column chromatography. The following effects upon Gal: 3-O-sulfotransferase activities by fucose, sulfate, and other substituents on the carbohydrate chains were noted. (1) A methyl or GlcNAc substituent on C-6 of GalNAc diminished the ability of Galbeta1,3GalNAc alpha-O-Al to act as an acceptor for Group A. (2) An alpha1,3-fucosyl residue on the beta1,6 branch in the mucin core structure did not affect the activity of Group A toward Gal linked beta1,3 to GalNAc alpha-. (3) Lewis x and Lewis a terminals did not serve as acceptors for either Group A or B enzymes. (4) Elimination of Group B activity on Gal in the beta1,6 branch owing to the presence of a 3-fucosyl or 6-sulfo group on GlcNAc did not hinder any action toward Gal linked beta1,3 to GalNAc alpha. (5) Group A activity on Gal linked beta1,3 to GalNAc remained unaffected by 3'-sulfation of the beta1,6 branch. The reverse was true for Group B. (6) The acceptor activity of the T-hapten was increased somewhat upon C-6 sulfation of GalNAc, whereas, C-6 sialylation resulted in an 85% loss of activity. (7) A novel finding was that Galbeta1,4GlcNAcbeta-O-Al and Galbeta1,3GlcNAcbeta-O-Al, upon C-6 sulfation of the GlcNAc moiety, became 100% inactive and 5- to 7-fold active, respectively, in their ability to serve as acceptors for Group B.

Selectin inhibition: synthesis and evaluation of novel sialylated, sulfated and fucosylated oligosaccharides, including the major capping group of GlyCAM-1

Selectins interact with glycoconjugate ligands in important normal and pathological situations. While high affinity recognition of natural ligands is associated with alpha 1-3(4)fucosylated, alpha 2-3sialylated (and/or sulfated) lactosamine sequences, small oligosaccharides that potently inhibit the selectins have not been found. One possibility suggested by other investigators is that high affinity may require unusual sequences not yet tested, for example, the "major capping group" (6'-sulfo-sialyl Le(x)) of the L-selectin ligand GlyCAM-1. To explore this possibility, we synthesized a spectrum of novel synthetic and semisynthetic oligosaccharides related to those on natural ligands. In studying these molecules, we noted that binding of recombinant soluble selectins to immobilized sialyl Le(a) or 3'-sulfo-Le(x) is markedly inhibited by concentrations of chloride above the physiological range. This indicates the ionic nature of the interactions, and shows that buffers typically used in screening assays for inhibitors are not optimal. Using parameters that more closely approximate physiological conditions, we confirmed that alpha 2-3-linked sialic acids, and alpha 1-3(4)fucosylation are important for recognition. Similar results obtained with both types of immobilized targets for the three selectins indicated that the binding sites for sialic acid and sulfate are very close, or identical. While O-sulfate esters mostly improved L- and P-selectin recognition, effects depended upon their position and number. Furthermore, sulfation can also impart some "negative" specificity: the major capping group does not interact with E-selectin. The branched Core 2 sequence seemed to enhance L- and P-selectin binding, however, the best inhibitors still appeared to be sialyl Le(a) and 3'-sulfo-Le(x), with the aglycone group of the latter affecting binding. Of particular note, the "major capping group" of GlyCAM-1 was not an unusually potent nor highly selective inhibitor of L-selectin, even when studying the interaction of L-selectin with native GlyCAM-1 itself.

Inhibition of human HT-29 colon carcinoma cell adhesion by a 4-fluoro-glucosamine analogue

Cell surface glycoconjugates play an important role in cellular recognition and adhesion. Modification of these structures in tumour cells could affect tumour cell growth and behaviour, including metastasis. 2-Acetamido-1,3,6-tri-O-acetyl-4-deoxy-4-fluoro-alpha-D-glycopyranose (4-F-GlcNAc) was synthesized as a potential inhibitor and/or modifier of tumour cell glycoconjugates. The effect of this sugar analogue on the adhesive properties of human colon carcinoma HT-29 cells was evaluated. Treatment of HT-29 cells with 4-F-GlcNAc led to reduced cell surface expression of terminal lactosamine, sialy-Le(x) and sialyl-Le(a), as determined by Western blotting and flow cytometry. The aberrant expression of these oligosaccharide structures on the HT-29 cell surface resulted in: (1) decreased E-selectin mediated adhesion of human colon cells to human umbilical cord endothelial cells (HUVEC); (2) impaired adhesion of HT-29 cells to beta-galactoside binding lectin, galectin-1; and (3) reduced ability to form homotypic aggregates. After exposure to 4-F-GlcNAc, lysosomal associated membrane proteins (lamp) 1 and 2, and carcinoembryonic antigen (CEA) detected in HT-29 cells were of lower molecular weight, probably due to impaired glycosylation. These results strongly suggest that modification of tumour cell surface molecules can alter tumour cell adhesion and that tumour cell surface oligosaccharides may be suitable targets for therapeutic exploitation.

Inhibition of anti-Gal IgG binding to porcine endothelial cells by synthetic oligosaccharides

Rejection of pig-to-human or pig-to-primate xenografts is mediated by the natural anti-Gal antibody, which interacts with alpha-galactosyl epitopes (i.e., Gal alpha1-3Gal beta1-4GlcNAc-R) abundantly expressed on porcine cells. The objective of this study was to determine the ability of various synthetic oligosaccharides to inhibit the binding of anti-Gal IgG molecules to porcine endothelial cells in vitro. Such inhibition ultimately may help to reduce or to prevent the in vivo antibody-dependent cell cytotoxicity (ADCC) reaction. In the absence of complement-mediated hyperacute rejection, the ADCC induced by anti-Gal IgG molecules is likely to cause the chronic rejection of xenografts. The synthetic free alpha-galactosyl epitope (Gal alpha1-3Gal beta1-4GlcNAc) was found to be 300-fold more effective than melibiose or alpha-methyl galactoside in inhibiting anti-Gal binding to porcine endothelial cells, and to prevent >90% of the antibody binding at a concentration of 1 mM. The disaccharide Gal alpha1-3Gal was ten-fold less effective than the free alpha-galactosyl epitope. Accordingly, the affinity of the disaccharide to anti-Gal, as measured by equilibrium dialysis, was seven-fold lower than that of the trisaccharide. The effective concentration of oligosaccharides inhibiting anti-Gal is independent of the antibody affinity, but is dependent on the concentration of the antibody. Based on the small difference in affinity between Gal alpha1-3Gal beta1-4GlcNAc and Gal alpha1-3Gal beta1-4GIc, and the large difference in the price of N-acetyllactosamine vs. lactose, it is suggested that lactose may be considered as an appropriate starting material for synthesizing large amounts of a trisaccharide that effectively neutralizes anti-Gal.

Specificity analysis of three clonal and five non-clonal alpha 1,3-L-fucosyltransferases with sulfated, sialylated, or fucosylated synthetic carbohydrates as acceptors in relation to the assembly of 3'-sialyl-6'-sulfo Lewis x (the L-selectin ligand) and related complex structures

Unique specificities of the cloned alpha 1,3-L-fucosyltransferases (FTs), FT III (Lewis type), FT IV (myeloid type), and FT V (plasma type), and the alpha 1,3-FTs of Colo 205 (colon carcinoma), HL 60 (myeloid), B142 (lymphoid), EKVX (lung carcinoma), and calf mesenteric lymph nodes (CMLN) were discerned with sulfated, sialylated, and/or fucosylated Gal beta 1,3/4GlcNAc beta-based acceptor moieties. (a) FT V was 1.0-, 20.8-, and 4.6-fold active in forming Lewis x, Lewis y, and 3'-alpha-galactosyl Lewis x, respectively. (b) FT III and FT V formed approximately 4-fold 3'-sulfo Lewis x, as compared to 3'-sialyl Lewis x. (c) FT IV showed great efficiency in forming 3'-sulfo Lewis x (249%) and Lewis x (345%) in mucin-type branched chains. (d) FT III, FT IV, and FT V formed 19%, 62%, and 47% 6-sulfo Lewis x as compared to Lewis x. (e) 6'-Sulfo Lewis x and 3'-sialyl-6'-sulfo Lewis x (GLYCAM ligand) were not synthesized from their immediate precursors by FT III, FT IV, or FT V. (f) FT III, FT IV, and FT V were 311%, 9%, and 188% active, respectively, with 2'-fucosyl lactose but were not active with 2'- fucosyl-6'-sulfo lactose. (g) FT III and FT V were 7.0- and 0.5-fold active in forming Lewis a as compared to Lewis x, whereas, FT IV was inactive. (h) FT III was -2.0-fold more active in forming 3'-alpha-galactosyl Lewis a than Lewis b. (i) FT III synthesized 6-sialyl Lewis a (40% efficiency as compared to Lewis a) from 6-sialyl type 1. (j) FT III did not act on 6'-sulfo or 6'-sialyl type 1 but was 106% and 22% active with 3'-sulfo and 6-sulfo type 1, respectively. (k) The Colo 205 FT activities with type 1 compounds almost paralleled that of FT III except for the low activity (9%) with Gal beta 1,3(NeuAc alpha 2, 6)GlcNAc beta-O-Bn, but with type 2 considerable differences between Colo 205 FT and FT III were noticed. (l) The alpha 1,3-FTs of CMLN, HL60, B142, and EKVX were 1.2-1.7 times active with Fuc alpha 1,2Gal beta 1,4GlcNAc beta- O-pNP and Gal alpha 1,3Gal beta 1,4 GlcNAc beta-O-Bn with respect to Gal beta 1,4GlcNAc beta-O-Al. (m) Both CMLN and HL60 FTs were 2-fold active with 3-sulfoGal beta 1,4GlcNAc in a mucin-type branch structure such as 3-sulfoGal beta 1,4GlcNAc beta 1,6(Gal beta 1,3)GalNAc alpha-O-Bn. (n) The 3'-sulfoLacNAc/acrylamide copolymer, either as an acceptor or as a competitive inhibitor, had the potential to distinguish myeloid type alpha 1,3-FT from the plasma type.

Characterization of the specificities of human blood group H gene-specified alpha 1,2-L-fucosyltransferase toward sulfated/sialylated/fucosylated acceptors: evidence for an inverse relationship between alpha 1,2-L-fucosylation of Gal and alpha 1,6-L-fucosylation of asparagine-linked GlcNAc

The assembly of complex structures bearing the H determinant was examined by characterizing the specificities of a cloned blood group H gene-specified alpha 1,2-L-fucosyltransferase (FT) toward a variety of sulfated, sialylated, or fucosylated Gal beta 1,3/4GlcNAc beta- or Gal beta 1,3GalNAc alpha-based acceptor structures. (a) As compared to the basic type 2, Gal beta 1,4GlcNAc beta-(K(m) = 1.67 mM), the basic type 1 was 137% active (K(m) = 0.83 mM). (b) On C-6 sulfation of Gal, type 1 became 142.1% active and type 2 became 223.0% active (K(m) = 0.45 mM). (c) On C-6 sulfation of GlcNAc, type 2 showed 33.7% activity. (d) On C-3 or C-4 fucosylation of GlcNAc, both types 1 and 2 lost activity. (e) Type 1 showed 70.8% and 5.8% activity, respectively, on C-6 and C-4 O-methylation of GlcNAc. (f) Type 1 retained 18.8% activity on alpha 2,6-sialylation of GlcNAc. (g) Terminal type 1 or 2 of extended chain had lower activity. (h) With Gal in place of GlcNAc in type 1, the activity became 43.2%. (i) Compounds with terminal alpha 1,3-linked Gal were inactive. (j) Gal beta 1,3GalNAc alpha- (the T-hapten) was approximately 0.4-fold as active as Gal beta 1,4GlcNAc beta-. (k) C-6 sulfation of Gal on the T-hapten did not affect the acceptor activity. (l) C-6 sulfation of GalNAc decreased the activity to 70%, whereas on C-6 sulfation of both Gal and GalNAc the T-hapten lost the acceptor ability. (m) C-6 sialylation of GalNAc also led to inactivity. (n) beta 1,6 branching from GalNAc of the T-hapten by a GlcNAc residue or by units such as Gal beta 1, 4GlcNAc-, Gal beta 1,4(Fuc alpha 1,3)GlcNAc-, or 3-sulfoGal beta 1,4GlcNAc- resulted in 111.9%, 282.8%, 48.3%, and 75.3% activities, respectively. (o) The enhancement of enzyme affinity by a sulfo group on C-6 of Gal was demonstrated by an increase (approximately 5-fold) in the K(m) for Gal beta 1,4GlcNAc beta 1,6(Gal beta 1,3)GalNAc alpha-O-Bn in presence of 6-sulfoGal beta 1,- 4GlcNAc beta-O-Me (3.0 mM). (p) Among the two sites in Gal beta 1, 4GlcNAc beta 1,6(Gal beta 1,3) GalNAc alpha-O-Bn, the enzyme had a higher affinity ( > 3-fold) for the Gal linked to GlcNAc. (q) With respect to Gal beta 1,- 3GlcNAc beta-O-Bn (3.0 mM), fetuin triantennary asialo glycopeptide (2.4 mM), bovine IgG diantennary glycopeptide (2.8 mM), asialo Cowper's gland mucin (0.06 mM), and the acrylamide copolymers (0.125 mM each) containing Gal beta 1,3GlcNAc beta-, Gal beta 1,3(6-sulfo)GlcNAc beta-, Gal beta 1,3GalNAc alpha-, Gal beta 1,3Gal beta-, or Gal alpha 1,3Gal beta- units were 153.6%, 43.0%, 6.2%, 52.5%, 94.9%, 14.7%, 23.6%, and 15.6% active, respectively. (r) Fucosylation by alpha 1,2-L-FT of the galactosyl residue which occurs on the antennary structure of the bovine IgG glycopeptide was adversely affected by the presence of an alpha 1,6-L-fucosyl residue located on the distant glucosaminyl residue that is directly attached to the asparagine of the protein backbone. This became evident from the 4-fold activity of alpha 1,2-L-FT toward bovine IgG glycopeptide after approximately 5% removal of alpha 1,6-linked Fuo.

Chemical synthesis of a hexasaccharide comprising the Lewisx determinant linked beta-(1-->6) to a linear trimannosyl core and the precursor pentasaccharide lacking fucose

Phenyl 2,3,4-tri-O-acetyl-6-O-chloroacetyl-1-thio-alpha,beta-mannopyranoside (5) was condensed with benzyl O-(2,3,4-tri-O-benzyl-beta-D-mannopyranosyl)-(1-->6)-2,3,4-tri-O-benzyl- alpha-D- mannopyranoside (12) in the presence of NIS-triflic acid to give, after removal of the chloroacetyl group, the key intermediate, benzyl O-(2,3,4-tri-O-acetyl-alpha-D-mannopyranosyl)-(1-->6)-O-(2,3,4-tri-O-ben zyl- beta-D-mannopyranosyl)-(1-->6)-2,3,4-tri-O-benzyl-alpha-D-mannopyranosid e (14). A similar condensation of 6 and 7 with acceptor 14, followed by the removal of protecting groups, afforded 16 and 18, respectively. These compounds are expected to be useful in specificity studies of an antibody raised against a related, synthetic antigen that we are currently investigating.

Synthesis of precursors for the dimeric 3-O-SO3Na Lewis X and Lewis A structures

Stereoselective syntheses of 3-O-SO3Na-beta-Gal-(1-->4)-beta-GlcNAc- (1-->3)-beta-Gal-(1-->4)-GlcNAc-beta-OBn (15) and 3-O-SO3Na-beta-Gal-(1-->3)-beta-GlcNAc-(1-->3)-beta-Gal-(1-->3)- beta-GlcNAc-(1-->3)-beta-Gal-(1-->4)-Glc-beta-OBn (25) were accomplished through the use of two novel glycosyl donors, namely, ethyl O-(2,6-di-O-acetyl-3,4-O-isopropylidene-beta-D- galactopyranosyl)-(1-->4)-3-O-acetyl-2-deoxy-2-phthalimido-1-thio-6-O- trimethylacetyl-beta-D-glucopyranoside (8). and ethyl O-(2,6-di-O-acetyl-3,4-O-isopropylidene-beta-D-galactopyranosyl)- (1-->3)-4-O-acetyl-2-deoxy-2-phthalimido-1-thio-6-O-trimethylace tyl-beta-D-glucopyranoside (18).

Synthetic mucin fragments: synthesis of O-sulfo and O-methyl derivatives of allyl O-(beta-D-galactopyranosyl)-(1-->3)-2-acetamido-2-deoxy-alpha-D- galactopyranoside as potential compounds for sulfotransferases

Allyl 2-acetamido-4,6-O-(4-methoxybenzylidene)-2-deoxy-alpha-D-galact opy ranoside (1) was condensed with either 2,3,4,6-tetra-O-acetyl-alpha-D-galactopyranosyl bromide (2) or 2,3,4-tri-O-benzoyl-6-O-bromoacetyl-alpha-D-galactopyranosyl bromide (14) in the presence of mercuric cyanide. Selective substitution with methyl, sulfo or both at desired positions, followed by the removal of protecting groups, afforded allyl O-(beta-D-galactopyranosyl)-(1-->3)-2-acetamido-2-deoxy-6-O-methyl-alpha -D- galactopyranoside (5), allyl O-(6-O-sulfo-beta-D-galactopyranosyl sodium salt)-(1-->3)-2-acetamido-2-deoxy-6- O-methyl-alpha-D-galactopyranoside (10), allyl O-(beta-D-galactopyranosyl)-(1-->3)-2-acetamido-2-deoxy-6-O-sulfo-alpha- D- galactopyranoside sodium salt (13), allyl O-(6-O-sulfo-beta-D-galactopyranosyl sodium salt)-(1-->3)-2-acetamido-2-deoxy- alpha-D-galactopyranoside (17) and allyl O-(3-O-sulfo-beta-D-galactopyranosyl sodium salt)-(1-->3)-2-acetamido-2-deoxy- alpha-D-galactopyranoside (22). The structures of compounds 5, 10, 13, 17 and 22 were established by 13C NMR and FAB mass spectroscopy.

Characterization of a novel mucin sulphotransferase activity synthesizing sulphated O-glycan core 1,3-sulphate-Gal beta 1-3GalNAc alpha-R

A novel sulphotransferase (sulpho-T) activity from rat colonic mucosa was characterized using O-glycan core 1 substrate, Gal beta 1-3GalNAc alpha-benzyl. Derivatives of Gal beta 1-3GalNAc- were used to demonstrate that the 3- and 4-hydroxyl of Gal and the 2-acetamido group of the GalNAc residue of Gal beta 1-3GalNAc alpha-benzyl substrates were important for activity. Sulphated product using Gal beta 1-3GalNAc alpha-benzyl as substrate was analysed by ion spray mass spectrometry, methylation analysis, high-pH anion-exchange chromatography and beta-galactosidase digestion. The results suggested that sulphate was added to the 3-position of the Gal residue. The synthesis of core 2 from core 1 by UDP-GlcNAc: Gal beta 1-3GalNAc beta 6-GlcNAc-transferase was inhibited by sulphation of the Gal residue, indicating that GlcNAc beta 1-6 branching has to precede sulphation in the O-glycan core 1 processing pathway. These data demonstrate several novel pathways in the synthesis of sulphated mucin-type oligosaccharides.

Synthesis of oligosaccharide substrates for N-linked glycoprotein processing enzymes

The stereoselective syntheses of one pentasaccharide and one tetrasaccharide containing the Glc-alpha-(1-->3)-Man-alpha moiety as their terminal unit, as well as one tetrasaccharide and one trisaccharide containing the Man-alpha-(1-->2)-Man-alpha terminal unit were accomplished through the utilization of two key glycosyl donors, namely, 4-pentenyl 3-O-acetyl-2,4,6-tri-O-benzyl-alpha-D-mannopyranoside and ethyl 2-O-acetyl-3,4,6-tri-O-benzyl-1-thio-alpha-D-mannopyranoside.

Substrate specificity and inhibition of UDP-GlcNAc:GlcNAc beta 1-2Man alpha 1-6R beta 1,6-N-acetylglucosaminyltransferase V using synthetic substrate analogues

UDP-GlcNAc:GlcNAc beta 1-2Man alpha 1-6R (GlcNAc to Man) beta 1,6- N-acetylglucosaminyltransferase V (GlcNAc-T V) adds a GlcNAc beta 1-6 branch to bi- and triantennary N-glycans. An increase in this activity has been associated with cellular transformation, metastasis and differentiation. We have used synthetic substrate analogues to study the substrate specificity and inhibition of the partially purified enzyme from hamster kidney and of extracts from hen oviduct membranes and acute myeloid leukaemia leukocytes. All compounds with the minimum structure GlcNAc beta 1-2Man alpha 1-6Glc/Man beta-R were good substrates for GlcNAc-T V. The presence of structural elements other than the minimum trisaccharide structure affected GlcNAc-T V activity without being an absolute requirement for activity. Substrates with a biantennary structure were preferred over linear fragments of biantennary structures. Kinetic analysis showed that the 3-hydroxyl of the Man alpha 1-3 residue and the 4-hydroxyl of the Man beta- residue of the Man alpha 1-6(Man alpha 1-3)Man beta-R N-glycan core are not essential for catalysis but influence substrate binding. GlcNAc beta 1-2(4,6-di-O-methyl-)Man alpha 1-6Glc beta-pnp was found to be an inhibitor of GlcNAc-T V from hamster kidney, hen oviduct microsomes and acute and chronic myeloid leukaemia leukocytes.

Expression of blood group Lewis b determinant from Lewis a: association of this novel alpha (1,2)-L-fucosylating activity with the Lewis type alpha (1,3/4)-L-fucosyltransferase

Blood group H type 1 [Fuc alpha (1,2)Gal beta (1,3)GlcNAc beta-->] is known as the precursor structure of the blood group determinant, Lewis b [Fuc alpha (1,2)Gal beta (1,3)(Fuc alpha (1,4))GlcNAc beta-->]. Recently, a new biosynthetic route for Lewis b from Lewis a [Gal beta (1,3)(Fuc alpha (1,4))GlcNAc-->] was identified in human gastric carcinoma cells, colon carcinoma Colo 205, and ovarian tumor. The present study demonstrates the association of this new type of alpha (1,2)-L-fucosyltransferase (FT) activity with the Lewis-type alpha (1,3/4)-L-FT as follows: (i) the alpha (1,4)- and novel alpha (1,2)-FT activities of Colo 205 were much less inhibited than the alpha (1,3)-FT activity by N-ethylmaleimide [Ki(microM) = 714.0, 119.0, and 6.5 respectively]. (ii) The alpha (1,4)- and novel alpha (1,2)-FT activities emerged from a Sephacryl S-200 column in identical positions. (iii) A specific inhibitor (copolymer from 3-sulfo-Galbeta(1,3)GlcNAcbeta-O-allyl and acrylamide) of alpha(1,4)-FT activity inhibited both alpha(1,4)- and alpha(1,2)-FT activities in Sephacryl S-200 column effluent to almost the same extent (approximately 80%); (iv) separation of the Lewis-type alpha(1,3/4)-FT from the plasma-type alpha(1,3)-FT by specific elution of the affinity column (bovine IgG glycopep-Sepharose) with lactose and further purification on a Sephacryl S-100 HR column showed that (a) the alpha(1,3)-FT activity was the inherent capacity of the Lewis-type FT (Colo 205 fraction L) since approximately 90% of both the alpha(1,4)- and alpha(1,3)-FT activities is inhibited by the copolymer, (b) the unique ability of catalyzing the alpha(1,2)-L-fucosylation of Gal in Lewis a structure and also the alpha(1,3)-L-fucosylation of Glc in lactose-based structure belonged to the Lewis type enzyme (Colo 205 fraction L), (c) a measurement of the [14C]fucosyl products arising from the two acceptors Galbeta(1,3)(4,6-di-O-Me)GlcNAcbeta-O-Bn and 3-sulfo-Galbeta(1,3)GlcNAcbeta-O-A1 (specific for alpha(1,2) and alpha(1,4), respectively) taken in the same incubation mixture showed mutual inhibition by the acceptors ([Km for the alpha(1,4)-specific acceptor, 3-sulfo-Galbeta(1,3)GlcNAcbeta-O-A], increased from 32 to 50 microM in the presence of 7.5 mM Galbeta(1,3)(4,6-di-O-Me)GlcNAcbeta-O-Bn, whereas Ki for the mutual inhibition of alpha(1,2)-FT activity by the former was 102 microM], and (d) the Lewis-type FT, in contrast to the plasma type FT, was highly effective in fucosylating complex glycopeptides. (iv) A cloned FT (FT III:Lewis type) and the Colo 205 Lewis-type FT (fraction L) showed similar activities toward various acceptors; the enzymatic product resulting from the action of cloned FT on Galbeta(1,3)(Fucalpha(1,4))GlcNAc-beta-O-Bn was identified by FAB mass spectrometry as the difucosyl compound. (v) An examination of six human cell lines indicated that the novel alpha(1,2)-FT activity associates with the alpha(1,4)-FT activity.

Genetic and enzymatic evidence for Lewis enzyme expression in Lewis-negative cancer patients

It has been observed that the frequency of individuals with Lewis-negative erythrocytes is significantly higher in cancer patients than in healthy controls. In this study, 20 of the 66 (30.3%) patients with various cancers were typed as Lewis negative from their erythrocytes, while the same frequency in healthy controls was 11.1%. These 20 patients were divided into three groups based on the presence of Lewis blood group antigens and alpha 1-->4-fucosyltransferase in their salivas: group I, 6 patients who had both Lewis antigens and alpha 1-->4-fucosyltransferase activity; group II, 8 patients who had no Lewis antigens but possessed alpha 1-->4-fucosyltransferase activity; group III, 6 patients who had neither Lewis antigens nor alpha 1-->4-fucosyltransferase activity. The genotyping of Le genes by the PCR-RFLP methods, which have been developed and established by us recently, demonstrated that all 14 patients from groups I and II possess Le gene homozygously (Le/Le) or heterozygously (Le/le), whereas all 6 patients from group III were le/le homozygotes. Only the 6 patients from group III were identified as the genuine Lewis-negative individuals. The immunohistochemical staining of the colorectal tumors also showed that the Lewis antigens could be detected on the tumors from groups I and II but not from group III.

Characterization of sialyloligosaccharide binding by recombinant soluble and native cell-associated CD22. Evidence for a minimal structural recognition motif and the potential importance of multisite binding

CD22, a B cell-specific receptor of the immunoglobulin superfamily, has been demonstrated to bind to oligosaccharides containing alpha 2-6-linked sialic acid (Sia) residues. Previously, we demonstrated that the minimal structure recognized by this lectin is the trisaccharide Sia alpha 2-6Gal beta 1-4GlcNAc, as found on N-linked, O-linked, or glycolipid structures (Powell, L., and Varki, A. (1994) J. Biol. Chem. 269, 10628-10636). Here we utilize a soluble immunoglobulin fusion construct (CD22Rg) to determine directly by equilibrium dialysis the stoichiometry (2:1) and dissociation constant (32 microM) for Neu5Ac alpha 2-6Gal beta 1-4Glc binding. Inhibition assays performed with over 30 different natural and synthetic sialylated and/or sulfated compounds are utilized to define in greater detail specific structural features involved in oligosaccharide-protein binding. Specifically, the critical features required for binding include the exocyclic hydroxylated side chain of the Sia residue and the alpha 2-6 linkage position to the underlying Gal unit. Surprisingly, alterations of the 2-, 3-, and 4-positions of the latter residue have limited effect on the binding. The nature of the residue to which the Gal is attached may affect binding. Bi(alpha 2-6)-sialylated biantennary oligosaccharides are capable of simultaneously interacting with both lectin sites present on the dimeric CD22Rg fusion construct, giving a marked improvement in binding over monosialylated compounds. Furthermore, data are presented indicating that full-length native CD22, expressed on the surface of Chinese hamster ovary cells, is structurally and functionally a multimeric protein, demonstrating a higher apparent affinity for multiply sialylated compounds over monosialylated compounds. These observations provide a mechanism for strong CD22-dependent cell adhesion despite the relatively low Kd for protein-sugar binding.

Selectin ligands and tumor-associated carbohydrate structures: specificities of alpha 2,3-sialyltransferases in the assembly of 3'-sialyl-6-sialyl/sulfo Lewis a and x, 3'-sialyl-6'-sulfo Lewis x, and 3'-sialyl-6-sialyl/sulfo blood group T-hapten

The sequence in the assembly of the functional unit of selectin ligands containing sulfate, sialic acid, and fucose and also tumor-associated O-glycan structures was studied by examining the specificities of alpha 2,3-sialyltransferases (ST). The first enzyme, porcine liver ST, was 57, 37, and 79% active (Km: 0.105, 0.420, and 0.200 mM), respectively, toward 6-sulfo, 6-sialyl, or 6-O-methyl derivatives of the Gal beta 1,3GalNAc alpha- unit; C-3 or C-6 substitution on Gal abolished sialylation. An acrylamide copolymer (MW approximately 40,000) containing approximately 40 T-haptens and asialo Cowper's gland mucin (MW approximately 200,000) containing approximately 48 T-haptens was 5-fold more active as an acceptor as compared to Gal beta 1, 3GalNAc alpha-O-Al on a molecular weight basis. The second enzyme, a cloned alpha-2,3-ST specific for lactose-based structure, was 70, 102, and 108% active (Km: 0.500, 0.210, and 0.330 mM), respectively, toward 6-sialyl, 6-sulfo, or 6-O-methyl derivatives of the Gal beta 1,3GlcNAc beta- unit; C-3 and C-6 substitution on Gal abolished sialylation. Gal beta 1,4GlcNAc beta- and its 6-sulfo derivative were approximately 20% active; the Lewis a structure, Gal beta 1,3- (Fuc alpha 1,4)GlcNAc beta-, was not an acceptor. The acrylamide copolymers containing approximately 40 units of Gal beta 1,3GlcNAc beta-, Gal beta 1,3(6-sulfo)GlcNAc beta-, or fetuin triantennary asialo or bovine IgG diantennary glycopeptides were respectively 5.9-, 5.4-, 0.7-, and 0.1-fold as active. A transfer of 7-9 mol of NeuAc per mole of the above copolymers was catalyzed by this ST, the sialyl linkage being susceptible to alpha 2,3-specific sialidase. A partially purified Colo 205 Lewis type (alpha 1, 3/4) fucosyltransferase catalyzed the formation of 3'-sialyl-6-sulfo Lewis a from [9-3H]NeuAc alpha 2, 3Gal beta 1, 3(6-sulfo)GlcNAc beta-O-Allyl and copolymer containing [9-3H]NeuAc alpha 2, 3Gal beta 1, 3(6-sulfo)GlcNAc beta- units, using GDP[14C]Fuc as fucosyl donor. The third enzyme, HL-60 ST, was 103% active with Gal beta 3(6-sulfo)GalNAc alpha- but was only 8% active with 6-sialo compound; it showed 11.6-fold greater activity with the copolymer of T-hapten. Further, we observed the alpha 2,3 sialylation of Gal beta 1,4GlcNAc beta- but not Gal beta 1,3GlcNAc beta- by HL60-ST, consistent with the occurrence of 3'-sialyl LacNAc and 3'-sialyl Lewis x units in leukosialin of HL60.(ABSTRACT TRUNCATED AT 400 WORDS)

Use of sialylated or sulfated derivatives and acrylamide copolymers of Gal beta 1,3GalNAc alpha- and GalNAc alpha- to determine the specificities of blood group T- and Tn-specific lectins and the copolymers to measure anti-T and anti-Tn antibody levels in cancer patients

Sialylated or sulfated derivatives and acrylamide copolymers of blood group T-(Gal beta 1,3GalNAc alpha-) and Tn-(GalNAc alpha) haptens were studied for their interaction with the lectins of peanut (PNA), Agaricus bisporus-(ABA), Helix pomatia-(HPA) and Vicia villosa B4-(VVA), using asialo Cowper's gland mucin (ACGM), which contains both T and Tn epitopes, as the coating substrate in enzyme linked lectin assay. Both T and Tn copolymers (-40 haptens) showed high affinity and strict specificity; although the T-copolymer at 0.05-0.07 microM concentration caused 50% inhibition of interaction of either PNA or ABA with ACGM, there was little inhibition of the HPA and VVA interactions even at over 100 times that concentration. The Tn-copolymer at 0.02-0.05 microM inhibited HPA or VVA interaction with ACGM by 50% but gave virtually no inhibition of PNA and ABA binding. Sialyl, sulfate or methyl group substitution on C-6 of GalNAc of the T-haptene did not prevent interaction with PNA but almost abolished interaction with ABA. In contrast, sialyl or sulfate group on C-6 and sulfate on C-3 of Gal in Gal beta 1,3GalNAc alpha- inhibited almost completely the interaction of PNA with ACGM but had only a slight effect on the interaction of ABA; C-6 substitution with either sialic acid or sulfate on GalNAc alpha- almost abolished the interaction of both HPA and VVA with ACGM.(ABSTRACT TRUNCATED AT 250 WORDS)

Alterations of O-glycan biosynthesis in human colon cancer tissues

Human colon cancer is associated with antigenic and structural changes in mucin-type carbohydrate chains (O-glycans). To elucidate the control of the biosynthesis of these O-glycans is colon cancer, we have studied glycosyltransferase and sulphotransferase activities involved in the assembly of elongated O-glycan structures. We analysed homogenates prepared from cancer tissue, adjacent normal and distal normal tissue from 20 patients. Several transferase activities showed pronounced changes in cancer tissue. The changes correlate with previous findings of a loss of O-glycans in cancer mucins, but did not always correlate with levels of Tn, sialyl-Tn, T and Lex antigens in homogenates or with the differentiation status and Duke's stages of the cancer tissue or the patient's blood type, sex and age. UDP-GlcNAc: Gal NAc-R beta 3-N-acetylglucosaminyltransferase (where GlcNAc is N-acetyl-D-glucosamine and GalNAc is N-acetyl-D-galactosamine) synthesizing O-glycan core 3, GlcNAc beta 1-3GalNAc-, CMP-sialic acid: GalNAc-peptide alpha 6-sialyltransferase synthesizing the sialyl-Tn antigen and sulphotransferase activities towards O-glycan core 1, Gal beta 1-3GalNAc-, were found to be decreased in cancer. UDP-GlcNAc: Gal beta 1-3GalNAc beta 6-N-acetylglucosaminyltransferase was also decreased in cancer concomitant with a loss of the ability to synthesize the I antigen and core 4, GlcNAc beta 1-6(GlcNAc beta 1-3) GalNAc-, CMP-sialic acid: Gal beta 1-3GalNAc-R alpha 3-sialyltransferase and GDP-fucose: Gal beta-R alpha 2-fucosyltransferase, synthesizing the blood group H determinant, were found to be 4- and 3- to 8-fold increased, respectively, in cancer compared to normal tissue. The data suggest that the biosynthesis of antigens and mucin-bound O-glycan structures in colon cancer is subject to complex control mechanisms.

Synthesis of alpha-D-galactopyranosyl-linked oligosaccharides containing the alpha-Gal-->beta-Gal-->GlcNAc sequence employing methyl-2,3,4,6-tetra-O-(4-methoxybenzyl)-1-thio-beta-D-galactopyranosid e as an efficient glycosyl donor

Synthesis of two trisaccharides and a tetrasaccharide, namely, alpha-Gal-(1-->3)-beta-Gal-(1-->3)-GlcNAc-beta-OBn (6), alpha-Gal-(1-->3)-beta-Gal-(1-->4)-GlcNAc-beta-OBn (9) and alpha-Gal-(1-->3)-beta-Gal-(1-->4)-GlcNAc-beta-(1-->6)-GalNAc- alpha-OBn (19) was accomplished through development and utilization of a key alpha-galactosyl donor, methyl 2,3,4,6-tetra-O-(4- methoxybenzyl)-1-thio-beta-D-galactopyranoside (1).

O-glycan biosynthesis in human colorectal adenoma cells during progression to cancer

A human colonic adenoma cell line PC/AA derived from a familial polyposis coli patient was passaged in culture to form an intermediate premalignant clonogenic variant AA/C1 and, upon treatment with differentiating and carcinogenic agents, a cell line AA/C1/SB10 which is tumourigenic in nude mice. These three mucin-secreting cell lines have been used as a model to study the changes in O-glycan biosynthesis during the progression to cancer. Several glycosyltransferases involved in the synthesis, elongation and termination of the common O-glycan core structures were found to decrease in the progression sequence towards adenocarcinoma. Higher activity of a number of enzymes was seen in the intermediate cell line. O-glycan biosynthesis in the original PC/AA cell line was closest to the normal human colonic phenotype, since all four common mucin O-glycan cores and their extended structures could be synthesized; core 3 beta 3-GlcNAc-transferase and alpha 6-sialytransferase acting on GalNAc-mucin were still detectable and core 2 beta 6-GlcNAc-transferase activity was accompanied by core 4 and I beta 6-GlcNAc-transferase activities. During progression towards adenocarcinoma, the expression of alpha 6-sialyltransferase, core 3 beta 3-GlcNAc-transferase, core 4 and I beta 6-GlcNAc-transferases were turned off. Using monoclonal antibodies, Tn antigen, sialyl-Tn antigen, O-acetyl-sialomucin and sialyl-Lea determinants were not detected in secreted or cellular mucin isolated from any of the cell lines. The exposure of MUC1 epitopes was seen in the malignant line, whereas sialyl-Lex determinants were found only in the premalignant PC/AA line. Sulfotransferase activities using core 1 substrate, Gal beta 1-3GalNAc alpha-benzyl, were high in PC/AA cells and progressively decreased upon development to adenocarcinoma, and this decrease correlated with mucin sulfation. In summary, the synthesis of less abundant, sialylated, fucosylated and extended, unbranched core 1 structures should be facilitated in the malignant cells. This is the first report of glycosyltransferase changes in human premalignant cells developing to tumourigenic cells. The data demonstrate that these cell lines are an excellent model to study the changes and regulation of mucin oligosaccharide biosynthesis during progression to cancer.

A biosynthetic control on structures serving as ligands for selectins: the precursor structures, 3-sialyl/sulfo Gal beta 1, 3/4GlcNAc beta-0-R, which are high affinity substrates for alpha 1, 3/4-L-fucosyltransferases, exhibit the phenomenon of substrate inhibition

The present study reports a control on the biosynthesis of fucosylated structures, serving as ligands for selectins by demonstrating the potential of 3-sialyl or 3-sulfo Gal beta 1, 3/4GlcNAc beta-containing glycoconjugates as high affinity substrates for alpha 1, 3/4-L-fucosyltransferases and as substrate inhibitors at higher concentrations. The synthetic sulfated saccharides and the triantennary sialoglycopeptide from fetuin were potent competitive inhibitors of the transfer of fucose to non-anionic saccharide acceptors and the corresponding triantennary asialoglycopeptide respectively catalyzed by a partially purified alpha 1, 3/4-L-fucosyltransferase preparation from Colo 205 (specific activity:transfer of 113.1 nmol Fuc to 2'-FucosylLacNAc per h per mg protein); Ki for the inhibitions by triantennary sialoglycopeptide, 3-SulfoGal beta 1, 3GlcNAc beta-0-Allyl and a copolymer from 3-SulfoGal beta 1, 3GlcNAc beta-0-Allyl and acrylamide were 51.9 microM, 500 microM and 67.0 microM, respectively. Further, the alpha 1,3-specific anionic acceptor, 3'-SulfoLacNAc, also inhibited the alpha 1,4- activity; Km for the alpha 1,4-specific acceptor, 2-methylGal beta 1, 3GlcNAc beta-0-Bn increased from 0.40 mM to 1.35 mM in presence of 3.0 mM 3'-sulfoLacNAc, whereas Ki for the mutual inhibition of alpha 1,3-activity by the former was found to be high (3.64 mM). Furthermore, the phenomenon of substrate inhibition, serving as acceptors at lower concentrations and as inhibitors at higher concentrations, was exhibited by the anionic acceptors; the Hill plots gave the Ki values 342.7 microM, 13.03 mM and 13.36 mM respectively for fetuin triantennary sialo glycopeptide, 3'-sulfoLacNAc and 3-sulfoGal beta 1, 3GlcNAc beta-0-Allyl.

Inhibition of UDP-GlcNAc:Gal beta 1-3GalNAc-R (GlcNAc to GalNAc) beta 6-N-acetylglucosaminyltransferase from acute myeloid leukaemia cells by photoreactive nitrophenyl substrate derivatives

Cells from patients with acute myeloid leukaemia (AML) contain an abnormally high UDP-GlcNAc: Gal beta 1-3GalNAc-R (GlcNAc to GalNAc) beta 6-N-acetylglucosaminyltransferase (core 2 beta 6-Gn-T) activity. Upon UV irradiation at 350 nm, the substrate Gal beta 1-3GalNAc alpha-p-nitrophenyl acted as an effective inhibitor for this enzyme but not for several other transferases. Preincubation with Gal beta 1-3GalNAc alpha-benzyl but not GalNAc alpha-benzyl protected core 2 beta 6-Gn-T from inhibition indicating that the inhibitor is specific for the substrate binding site of core 2 beta 6-Gn-T. A number of other nitrophenyl-sugar derivatives similarly acted as inhibitors for core 2 beta 6-Gn-T. GalNAc alpha-pnp at higher concentrations also inactivated UDP-Gal: GalNAc-R beta 3-galactosyltransferase from rat liver and AML cells and inhibition could be reduced by substrate protection. These results suggest that pnp-sugar derivatives may prove useful as specific inhibitors of glycosyltransferases and as affinity labels.

Lactose as affinity eluent and a synthetic sulfated copolymer as inhibitor, in conjunction with synthetic and natural acceptors, differentiate human milk Lewis-type and plasma-type alpha-L-fucosyltransferases

Human milk Lewis-type (alpha 1,3/4) fucosyltransferase (FT) was separated from the plasma-type by chromatography on bovine IgG glycopep-Sepharose using lactose as the selective eluent and further purified on a column of Sephacryl S-100 HR. The alpha 1,3-FT activity towards 2'-fucosyllactose was found to be associated with alpha 1,4-FT activity. The inherency of N-acetyl-glucosaminide alpha 1,3-L-FT activity in the Lewis-type FT was shown by a) the emergence of both alpha 1,3- and alpha 1,4-FT activities from the Sephacryl S-100 HR column in the same position; b) the inhibition of the alpha 1,3-FT activity in the Lewis-type FT by alpha 1,4-FT specific inhibitor namely a copolymer from 3-sulfoGal beta 1,3GlcNAc beta-O-Allyl and acrylamide; c) the inhibition of alpha 1,4 activity in the Lewis-type FT by alpha 1,3-FT specific acceptor. Fetuin triantennary sialoglycopeptide, the corresponding asialo glycopeptide, and bovine IgG diantennary glycopeptide served as acceptors for both FTs, the Lewis-type FT being far more active than the plasma type FT towards the triantennary sialoglycopeptide.

Preferred conformations and dynamics of five core structures of mucin type O-glycans determined by NMR spectroscopy and force field calculations

Glycosyltransferases acting on O-glycans have been shown to exhibit distinct specificity for the carbohydrate and the peptide moiety of their substrates. As an approach to study the 3-dimensional interactions between enzymes and O-glycan substrates, we determined the preferred conformations of five oligosaccharide-core structures of mucin type glycoproteins by NMR spectroscopy and by static and dynamic force field calculations. Seven oligosaccharides, representing five basic core structures, were investigated: Gal beta (1-3)GalNAc alpha Bzl (1, core 1), GlcNAc beta (1-6)[Gal beta (1-3)]GalNAc alpha Bzl (2, core 2), GlcNAc beta (1-3)GalNAc alpha Bzl (3, core 3), GlcNAc beta (1-6)[GlcNAc beta (1-3)]GalNAc alpha Bzl (4, core 4), GlcNAc beta (1-6)GalNAc alpha Bzl (5, core 6), the elongated core 2, Gal beta (1-4)GlcNAc beta (1-6)[Gal beta (1-3)]GalNAc alpha pNp (6) and GalNAc alpha-Bzl (7). The dynamic behaviour of the molecules was studied by Metropolis Monte Carlo (MMC) simulations. Experimental coupling constants, chemical shift changes, and NOEs were compared with results from static energy minimizations and dynamic MMC simulations and show a good agreement. MMC simulations show that the (1-6) linkage is much more flexible than the (1-3) or the (1-4) linkages. The preferred conformations of the disaccharides (1) and (3) show only slight differences due to the additional N-acetyl group in (3). The conformational equilibrium of beta (1-3) glycosidic bonds of 1 and 3 was not affected by attaching a beta (1-6) linked GlcNAc unit to the GalNAc residue in 2 and 4. However, experimental and theoretical data show that the beta (1-6) linkages of the trisaccharides 2 and 4, which carry an additional beta (1-3) linked glycosyl residue, change their preferred conformations when compared with (5). The 6-branch also shows significant interactions with the benzyl aglycon altering the preferred conformation of the hydroxymethyl group of the GalNAc to a higher proportion of the gt conformer. The (1-6) linkage of 2, 4, and 6 can have two different families of conformations of which the lower energy state is populated only to about 20% of the time whereas the other state with a relative enthalpy of approximately 4 kcal mol-1 is populated to 80%. This fact demonstrates that the two conformational states have different entropy contents. Entropy is implicitly included in MMC simulations but cannot be derived from energy minimizations.

Processing O-glycan core 1, Gal beta 1-3GalNAc alpha-R. Specificities of core 2, UDP-GlcNAc: Gal beta 1-3 GalNAc-R(GlcNAc to GalNAc) beta 6-N-acetylglucosaminyltransferase and CMP-sialic acid: Gal beta 1-3GalNAc-R alpha 3-sialyltransferase

To elucidate control mechanisms of O-glycan biosynthesis in leukemia and to develop biosynthetic inhibitors we have characterized core 2 UDP-GlcNAc:Gal beta 1-3GalNAc-R(GlcNAc to GalNAc) beta 6-N-acetylglucosaminyltransferase (EC 2.4.1.102; core 2 beta 6-GlcNAc-T) and CMP-sialic acid: Gal beta 1-3GalNAc-R alpha 3-sialyltransferase (EC 2.4.99.4; alpha 3-SA-T), two enzymes that are significantly increased in patients with chronic myelogenous leukemia (CML) and acute myeloid leukemia (AML). We observed distinct tissue-specific kinetic differences for the core 2 beta 6-GlcNAc-T activity; core 2 beta 6-GlcNAc-T from mucin secreting tissue (named core 2 beta 6-GlcNAc-T M) is accompanied by activities that synthesize core 4 [GlcNAc beta 1-6(GlcNAc beta 1-3)GalNAc-R] and blood group I [GlcNAc beta 1-6(GlcNAc beta 1-3)Gal beta-R] branches; core 2 beta 6-GlcNAc-T in leukemic cells (named core 2 beta-GlcNAc-T L) is not accompanied by these two activities and has a more restricted specificity. Core 2 beta 6-GlcNAc-T M and L both have an absolute requirement for the 4- and 6-hydroxyls of N-acetylgalactosamine and the 6-hydroxyl of galactose of the Gal beta 1-3GalNAc alpha-benzyl substrate but the recognition of other substituents of the sugar rings varies, depending on the tissue. alpha 3-sialyltransferase from human placenta and from AML cells also showed distinct specificity differences, although the enzymes from both tissues have an absolute requirement for the 3-hydroxyl of the galactose residue of Gal beta 1-3GalNAc alpha-Bn. Gal beta 1-3(6-deoxy)GalNAc alpha-Bn and 3-deoxy-Gal beta 1-3GalNAc alpha-Bn competitively inhibited core 2 beta 6-GlcNAc-T and alpha 3-sialyltransferase activities, respectively.