Purification and characterization of endo-beta-galactosidase from Escherichia freundii induced by hog gastric mucin

Expression of Podocalyxin Potentially Decorated With Low-sulfated Keratan Sulfate in Human Testicular Embryonal Carcinoma

SummaryWe previously demonstrated that among various histological types of human testicular germinal cell tumors (GCTs), embryonal carcinoma (EC) preferentially expresses low-sulfated keratan sulfate (KS) consisting of repeating N-acetyllactosamine (LacNAc) disaccharide units composed of galactose and 6-O-sulfated N-acetylglucosamine (GlcNAc), which is recognized by the R-10G antibody. Recently, we generated another anti-low-sulfated KS monoclonal antibody, 294-1B1. Immunohistochemical analysis of testicular GCTs (n=83) revealed that the low-sulfated KS recognized by 294-1B1 is also preferentially expressed in EC but minimally in other GCT histological types. Moreover, immunolabeling with R-10G and 294-1B1 antibodies was resistant to peptide-N-glycosidase F digestion, and EC was not stained with the MECA-79 antibody, indicating that low-sulfated KS expressed in EC contains mucin-type core 2 O-glycans carrying GlcNAc-6-O-sulfated oligo-LacNAc. Double immunofluorescence staining showed that R-10G and 294-1B1 antibody signals colocalized with those for podocalyxin (PODXL). Furthermore, western blot analysis of recombinant human PODXL•IgG fusion proteins secreted from low-sulfated KS-expressing human embryonic kidney 293T cells revealed that PODXL functions as a core protein for low-sulfated KS. Taken together, these findings strongly suggest that the PODXL glycoform decorated with low-sulfated KS is preferentially expressed in human testicular EC and may therefore serve as a diagnostic marker for this malignancy.

Expression of low-sulfated keratan sulfate in non-mucinous ovarian carcinoma

Keratan sulfate glycosaminoglycan is composed of repeating N-acetyllactosamine (LacNAc) disaccharide units consisting of galactose (Gal) and N-acetylglucosamine (GlcNAc), both often 6-O-sulfated. Sulfate contents of keratan sulfate are heterogeneous depending upon the origins. In this study, keratan sulfate is classified as either highly sulfated (in which both GlcNAc and Gal residues are 6-O-sulfated) or low-sulfated (in which only GlcNAc residues are 6-O-sulfated). It is reported that highly sulfated keratan sulfate detected by the 5D4 monoclonal antibody is preferentially expressed in normal epithelial cells lining the female genital tract and in their neoplastic counterparts; however, expression of low-sulfated keratan sulfate in either has not been characterized. In the present study, we generated the 294-1B1 monoclonal antibody, which selectively recognizes low-sulfated keratan sulfate, and performed precise glycan analysis of sulfated glycans expressed on human serous ovarian carcinoma OVCAR-3 cells. We found that OVCAR-3 cells do not express highly sulfated keratan sulfate but rather express low-sulfated form, which was heterogeneous in 294-1B1 reactivity. Comparison of mass spectrometry spectra of sulfated glycans in 294-1B1-positive versus -negative OVCAR-3 cells indicated that the 294-1B1 epitope is likely at least 2, and possibly 3 or more, tandem GlcNAc-6-O-sulfated LacNAc units. Then, using the 294-1B1 antibody, we performed quantitative immunohistochemical analysis of 40 specimens from patients with ovarian cancer, consisting of 10 each of serous, endometrioid, clear cell, and mucinous carcinomas, and found that among them low-sulfated keratan sulfate was widely expressed in all but mucinous ovarian carcinoma.

Apical Membrane Expression of Distinct Sulfated Glycans Is a Characteristic Feature of Ductules and Their Reactive and Neoplastic Counterparts

Intrahepatic bile ducts transport bile between bile canaliculi and the extrahepatic bile duct. The luminal surface of this tract is lined by a layer of biliary epithelial cells, or cholangiocytes, which secrete mucins consisting of scaffold proteins and O-glycosidically linked carbohydrate side chains. Although mucin core proteins have been extensively investigated, the structure and function of carbohydrate side chains have not. Here, we demonstrate that distinct sulfated glycans positive for MECA-79, R-10G, and 297-11A, but not 5D4, monoclonal antibodies are expressed in the cytoplasm of cells of large-sized ducts and in the apical membrane of cells in ductules, and that R-10G immunolabeling is partially eliminated by endo-β-galactosidase digestion, supporting the presence of N-acetylglucosamine-6-O-sulfated N-acetyllactosamine structures. We observed comparable apical membrane-predominant staining in ductular reactions seen during regeneration that occurs in various liver diseases and in cholangiolocarcinoma, a subtype of small duct-type intrahepatic cholangiocarcinoma (iCCA). Apical membrane expression of distinct sulfated glycans in large duct-type iCCA was negligible. Intriguingly, under pathological conditions, endo-β-galactosidase digestion almost completely eliminated R-10G immunoreactivity. These findings suggest that apical membrane expression of distinct sulfated glycans is a characteristic feature of ductules and their reactive and neoplastic counterparts.

Core 2 β1,6-N-acetylglucosaminyltransferases accelerate the escape of choriocarcinoma from natural killer cell immunity

Hyperglycosylated human chorionic gonadotropin (H-hCG) is secreted from choriocarcinoma and contains a core2 O-glycan formed by core2 β1,6-N-acetylglucosaminyl transferase (C2GnT). Choriocarcinoma is considered immunogenic as it is gestational and contains paternal chromosomal components. Here we examined the function of C2GnT in the evasion of choriocarcinoma cells from natural killer (NK) cell-mediating killing. We determined that C2GnT is highly expressed in malignant gestational trophoblastic neoplasms. C2GnT KO downregulates core2 O-glycan expression in choriocarcinoma cells, which are more efficiently killed by NK cells than control cells. C2GnT KO cell containing tumor necrosis factor-related apoptosis inducing ligand have lower viability than control cells. Additionally, poly-N-acetyllactosamine in core2 branched oligosaccharides on MHC class I-related chain A (MICA) and mucin1 (MUC1) is significantly reduced in C2GnT KO cells. Meanwhile, the cumulative survival rate of nude mice inoculated with C2GnT KO tumors was higher than that of the control group. These findings suggest that choriocarcinoma cells may escape NK cell-mediated killing via glycosylation of MICA and MUC1.

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C2GnT knockout reduces core2 O-glycan expression in choriocarcinoma cells

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C2GnT KO cells are more readily killed by NK cells

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C2GnT KO cells containing TRAIL have lower viability than controls

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MHC class I-related chain A and MUC1 glycosylation is reduced in C2GnT KO cells

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Survival rate of nude mice inoculated with C2GnT KO tumors is higher than controls

Enzymatic Synthesis of Oligosaccharides and Neoglycoconjugates

Oligosaccharides involved in glycoconjugates play important roles in a number of biological events. To elucidate the biological functions of oligosaccharides, sufficient quantities of structurally defined oligosaccharides, are of limited availability by traditional purification methods, are required. Hence, chemical and enzymatic syntheses of oligosaccharides are becoming increasingly important in glycobiology and glycotechnology. In addition, oligosaccharides often occur as glycoconjugates attached to proteins or lipids. Hence, the development of simple and effective methods for synthesizing neoglycoconjugates such as neoglycoprotein and neoglycolipids is essential for an understanding of the biological function of these molecules. Here we review the most recent developments in the enzymatic synthesis of oligosaccharides and neoglycoconjugates.

Attenuation of fibroblast growth factor signaling by poly-N-acetyllactosamine type glycans

Fibroblast growth factors (FGFs) and their receptors are expressed in a variety of mammalian tissues, playing a role in development and cell proliferation. While analyzing human sperm motility, we found that sperm treated with endo-β-galactosidase (EBG), which specifically hydrolyzes poly-N-acetyllactosamine type glycans (polyLacs), enhanced motility. Mass spectrometry analysis revealed that sperm-associated polyLacs are heavily fucosylated, consistent with Lewis Y antigen. Immunohistochemistry of epididymis using an anti-Lewis Y antibody before and after EBG treatment suggested that polyLacs carrying the Lewis Y epitope are synthesized in epididymal epithelia and secreted to seminal fluid. EBG-treated sperm elevated cAMP levels and calcium influx, indicating activation of fibroblast growth factor signaling. Seminal fluid polyLacs bound to FGFs in vitro, and impaired FGF-mediated signaling in HEK293T cells.

Loss of effector function of human cytolytic T lymphocytes is accompanied by major alterations in N- and O-glycosylation

Most human tumors are not eliminated by the immune system, and therapeutic vaccination shows poor results, a fact that can be explained at least partially by an immunosuppressive tumor microenvironment that is abundant in galectin-3. On cytolytic T lymphocyte (CTL) clones, maintained in culture by regular stimulation, recently activated CTLs present low effector functions. However, these functions are restored after a short treatment with LacNAc. The latter, which is in agreement with the glycoprotein-galectin lattice concept involving reduced motility, poses the question why galectin-3 ligands improve effector functions. We employed ultrasensitive MALDI-TOF-MS on resting and recently activated CTL clones combined with various glycosidase digestions and GC-MS linkage analyses. Our results showed that compared with the resting CTLs, the N-glycans of the recently activated CTLs consisted of (i) larger LacNAc oligomers of which a significant portion was longer than four-units and (ii) more multi-antennary structures. Interestingly, our results showed that the poly-LacNAc appeared to be equally distributed on all available N-glycan branches and not selectively enriched on a specific branch. The above structural alterations in the recently activated CTLs are expected to increase the galectin-3-LacNAc lattices and multivalent interactions and, therefore, reduce the motility of surface glycoproteins, such as the T-cell receptor. These findings suggest that the loss of effector functions on CTLs may be linked to reduced motility of surface glycoproteins. In addition, our results showed that recently activated CTLs had a reduced abundance of NeuAcα2,6-linked N-glycans and an increased abundance of disialylated core 1 and monosialylated core 2 O-glycan structures.

Endo-beta-galactosidases and keratanase

This overview covers the endo-beta-galactosidases; enzyme is capable of hydrolyzing a wide range of glycoconjugates. Endo-beta-galactosidases from numerous sources are discussed in terms of their substrate specificities and substrates, as well as their practical research applications.

Mucin dynamics and microbial populations in chicken small intestine are changed by dietary probiotic and antibiotic growth promoter supplementation

The mucous layer that covers the intestinal absorptive surface acts as a barrier against bacterial translocation. The chicken gut contains a diverse bacterial population which interacts with the mucous layer. In this report, we studied the effect of changing the intestinal microbial populations on mucin dynamics by feeding 1-d-old chicks a control diet or that diet containing either antibiotic growth promoter (AGP) or a probiotic product for 14 d. Dietary AGP increased the proportions of Bifidobacterium species in the duodenum compared with the other groups. In AGP-fed chicks, the villous surface area was increased in the jejunum, goblet cell density was greater in the jejunum and ileum, and mucin glycoprotein levels in the duodenum were lower than in the other groups (P < 0.05). Feeding AGP increased the expression of mucin mRNA in the jejunum and ileum compared with controls. The dietary probiotic increased the proportion of Lactobacillus species in the ileum compared with the controls (P < 0.05) and significantly enlarged the goblet cell "cup" area throughout the small intestine compared with the other groups. Expression of mucin mRNA and the levels of mucin glycoprotein were greater in the jejunum of the probiotic-fed chicks compared with controls (P < 0.05). Neither the probiotic nor AGP treatments affected the thickness of the mucous adherent layer. These results indicate that both probiotic and AGP altered processes of mucin biosynthesis and/or degradation mediated via changes in the intestinal bacterial populations. These modifications in mucin dynamics influence gut function and health and may change nutrient uptake.

Enzymatic synthesis of poly-N-acetyllactosamines as potential substrates for endo-β-galactosidase-catalyzed hydrolytic and transglycosylation reactions

Enzymatic synthesis of GlcNAc-terminated poly-N-acetyllactosamine beta-glycosides GlcNAcbeta1,3(Galbeta1,4GlcNAcbeta1,3)(n)Galbeta1,4GlcNAcbeta-pNP (n=1-4) was demonstrated using a transglycosylation reaction of Escherichia freundii endo-beta-galactosidase. The enzyme catalyzed a transglycosylation reaction on GlcNAcbeta1,3Galbeta1,4GlcNAcbeta-pNP (1), which served both as a donor and an acceptor, and converted 1 into p-nitrophenyl beta-glycosides GlcNAcbeta1,3(Galbeta1,4GlcNAcbeta1,3)(1)Galbeta1,4GlcNAcbeta-pNP (2), GlcNAcbeta1,3(Galbeta1,4GlcNAcbeta1,3)(2)Galbeta1,4GlcNAcbeta-pNP (3), GlcNAcbeta1,3(Galbeta1,4GlcNAcbeta1,3)(3)Galbeta1,4GlcNAcbeta-pNP (4) and GlcNAcbeta1,3(Galbeta1,4GlcNAcbeta1,3)(4)Galbeta1,4GlcNAcbeta-pNP (5). When 2 was used as an initial substrate, it led to the preferential synthesis of nonasaccharide beta-glycoside 4 to heptasaccharide beta-glycoside 3. This suggests that 4 is directly synthesized by transferring the tetrasaccharide unit GlcNAcbeta1,3Galbeta1,4GlcNAcbeta1,3Gal to nonreducing end GlcNAc residue of 2 itself. The efficiency of production of poly-N-acetyllactosamines by E. freundii endo-beta-galactosidase was significantly enhanced by the addition of BSA and by a low-temperature condition. Resulting 2 and 3 were shown to be useful for studying endo-beta-galactosidase-catalyzed hydrolytic and transglycosylation reactions.

Kinetic studies on endo-beta-galactosidase by a novel colorimetric assay and synthesis of N-acetyllactosamine-repeating oligosaccharide beta-glycosides using its transglycosylation activity

Novel chromogenic substrates for endo-beta-galactosidase were designed on the basis of the structural features of keratan sulfate. Galbeta1-4GlcNAcbeta1-3Galbeta1-4GlcNAcbeta-pNP (2), which consists of two repeating units of N-acetyllactosamine, was synthesized enzymatically by consecutive additions of GlcNAc and Gal residues to p-nitrophenyl beta-N-acetyllactosaminide. In a similar manner, GlcNAcbeta1-3Galbeta1-4GlcNAcbeta-pNP (1), GlcNAcbeta1-3Galbeta1-4Glcbeta-pNP (3), Galbeta1-4GlcNAcbeta1-3Galbeta1-4Glcbeta-pNP (4), Galbeta1-3GlcNAcbeta1-3Galbeta1-4Glcbeta-pNP (5), and Galbeta1-6GlcNAcbeta1-3Galbeta1-4Glcbeta-pNP (6) were synthesized as analogues of 2. Endo-beta-galactosidases released GlcNAcbeta-pNP or Glcbeta-pNP in an endo-manner from each substrate. A colorimetric assay for endo-beta-galactosidase was developed using the synthetic substrates on the basis of the determination of p-nitrophenol liberated from GlcNAcbeta-pNP or Glcbeta-pNP formed by the enzyme through a coupled reaction involving beta-N-acetylhexosaminidase (beta-NAHase) or beta-d-glucosidase. Kinetic analysis by this method showed that the value of Vmax/Km of 2 for Escherichia freundii endo-beta-galactosidase was 1.7-times higher than that for keratan sulfate, indicating that 2 is very suitable as a sensitive substrate for analytical use in an endo-beta-galactosidase assay. Compound 1 still acts as a fairly good substrate despite the absence of a Gal group in the terminal position. In addition, the hydrolytic action of the enzyme toward 2 was shown to be remarkably promoted compared to that of 4 by the presence of a 2-acetamide group adjacent to the p-nitrophenyl group. This was the same in the case of a comparison of 1 and 3. Furthermore, the enzyme also catalysed a transglycosylation on 1 and converted it into GlcNAcbeta1-3Galbeta1-4GlcNAcbeta1-3Galbeta1-4GlcNAcbeta-pNP (9) and GlcNAcbeta1-3Galbeta1-4GlcNAcbeta1-3Galbeta1-4GlcNAcbeta1-3Galbeta1-4GlcNAcbeta-pNP (10) as the major products, which have N-acetyllactosamine repeating units.

Keratan sulfate disaccharide composition determined by FACE analysis of keratanase II and endo-beta-galactosidase digestion products

Many tissues contain glycoproteins and proteoglycans, which are substituted with N-or O-linked keratan sulfate, a glycosaminoglycan in which the lactosamine (-galbeta1,4glcNAc-) disaccharide backbone is variably modified by sulfation, fucosylation, and sialylation. We report here a rapid, sensitive, and quantitative procedure for obtaining a complete disaccharide compositional analyses for keratan sulfates after FACE separation of products generated by hydrolysis of the glycosaminoglycans with B. fragillis keratanase II and E. freundii endo-beta-galactosidase. Seven digestion end products are separable in a single electrophoretic step using Monosaccharide composition gels. These are: the unsulfated disaccharide, glcNAcbeta1,3gal, the fucosylated trisaccharide, galbeta1,2[fucalpha1,3]glcNAc6S, the mono- and disulfated disaccharides, galbeta1,4glcNAc6S or gal6Sbeta1,4glcNAc6S from the chain interior, and the sialylated mono- and disulfated trisaccharides neuAalpha2,3galbeta1,4glcNAc6S or neuAalpha2,3gal6Sbeta1,4glcNAc6S from the nonreducing terminus. FACE analyses also revealed the presence of a contaminant beta-galactosidase activity in keratanase II enzyme preparations which cleaves the disaccharide, galbeta1,4glcNAc6S to its constituent monosaccharides, gal and glcNAc6S. It was particularly prominent at enzyme concentrations > 2 mU per nmole substrate glcNH(2) or after prolonged digestion times (> 12 h), and was not inhibitable by thiogalactosides or N-acetyl-lactosamine. As these monosaccharide products would not be detectable using the commonly described analytical methods for KS hydrolase products, such as (1)H-NMR and HPLC analyses, our data illustrate that the FACE procedure represents an improved approach for accurate compositional microanalyses of corneal and skeletal keratan sulfates, especially applicable to experimentation involving small amounts (1-2 microg) of this glycosaminoglycan.

Analytical method for keratan sulfates by high-performance liquid chromatography/turbo-ionspray tandem mass spectrometry

We established a highly sensitive LC/MS/MS method for the analysis of the disaccharides produced from keratan sulfates (KS). It was revealed that the disaccharides produced by keratanase II enzymatic digestion of KS could be determined with high sensitivity by the negative-ion mode of multiple reaction monitoring. Furthermore, monosulfated and disulfated disaccharides can be separated using a short column of Capcell Pak NH2 UG80 (35 mm x 2 mm i.d.). The complete analysis of one sample can be performed within 5 min. The assay method was validated and showed satisfactory sensitivity, precision, and accuracy, which enabled quantitation at subpicomole levels. From the results of analyses of KS obtained from cornea, nasal cartilage, and brain, it was found that the degree of sulfation at the C-6 position of the galactose residues differed among those samples in the following order: nasal cartilage > cornea > brain. Our analytical method is very useful for the analyses of KS in various biological materials and for comparison of the degree of sulfation of KS from various biological samples.

Identification and characterization of three novel beta 1,3-N-acetylglucosaminyltransferases structurally related to the beta 1,3-galactosyltransferase family

We have isolated three types of cDNAs encoding novel beta1,3-N-acetylglucosaminyltransferases (designated beta3Gn-T2, -T3, and -T4) from human gastric mucosa and the neuroblastoma cell line SK-N-MC. These enzymes are predicted to be type 2 transmembrane proteins of 397, 372, and 378 amino acids, respectively. They share motifs conserved among members of the beta1,3-galactosyltransferase family and a beta1,3-N-acetylglucosaminyltransferase (designated beta3Gn-T1), but show no structural similarity to another type of beta1,3-N-acetylglucosaminyltransferase (iGnT). Each of the enzymes expressed by insect cells as a secreted protein fused to the FLAG peptide showed beta1,3-N-acetylglucosaminyltransferase activity for type 2 oligosaccharides but not beta1,3-galactosyltransferase activity. These enzymes exhibited different substrate specificity. Transfection of Namalwa KJM-1 cells with beta3Gn-T2, -T3, or -T4 cDNA led to an increase in poly-N-acetyllactosamines recognized by an anti-i-antigen antibody or specific lectins. The expression profiles of these beta3Gn-Ts were different among 35 human tissues. beta3Gn-T2 was ubiquitously expressed, whereas expression of beta3Gn-T3 and -T4 was relatively restricted. beta3Gn-T3 was expressed in colon, jejunum, stomach, esophagus, placenta, and trachea. beta3Gn-T4 was mainly expressed in brain. These results have revealed that several beta1,3-N-acetylglucosaminyltransferases form a family with structural similarity to the beta1,3-galactosyltransferase family. Considering the differences in substrate specificity and distribution, each beta1,3-N-acetylglucosaminyltransferase may play different roles.

Poly-N-acetyllactosamine extension in N-glycans and core 2- and core 4-branched O-glycans is differentially controlled by i-extension enzyme and different members of the beta 1,4-galactosyltransferase gene family

Poly-N-acetyllactosamines are attached to N-glycans, O-glycans, and glycolipids and serve as underlying glycans that provide functional oligosaccharides such as sialyl Lewis(X). Poly-N-acetyllactosaminyl repeats are synthesized by the alternate addition of beta1,3-linked GlcNAc and beta1,4-linked Gal by i-extension enzyme (iGnT) and a member of the beta1,4-galactosyltransferase (beta4Gal-T) gene family. In the present study, we first found that poly-N-acetyllactosamines in N-glycans are most efficiently synthesized by beta4Gal-TI and iGnT. We also found that iGnT acts less efficiently on acceptors containing increasing numbers of N-acetyllactosamine repeats, in contrast to beta4Gal-TI, which exhibits no significant change. In O-glycan biosynthesis, N-acetyllactosamine extension of core 4 branches was found to be synthesized most efficiently by iGnT and beta4Gal-TI, in contrast to core 2 branch synthesis, which requires iGnT and beta4Gal-TIV. Poly-N-acetyllactosamine extension of core 4 branches is, however, less efficient than that of N-glycans or core 2 branches. Such inefficiency is apparently due to competition between a donor substrate and acceptor in both galactosylation and N-acetylglucosaminylation, since a core 4-branched acceptor contains both Gal and GlcNAc terminals. These results, taken together, indicate that poly-N-acetyllactosamine synthesis in N-glycans and core 2- and core 4-branched O-glycans is achieved by iGnT and distinct members of the beta4Gal-T gene family. The results also exemplify intricate interactions between acceptors and specific glycosyltransferases, which play important roles in how poly-N-acetyllactosamines are synthesized in different acceptor molecules.

Poly-N-acetyllactosamine synthesis in branched N-glycans is controlled by complemental branch specificity of I-extension enzyme and beta1,4-galactosyltransferase I

Poly-N-acetyllactosamine is a unique carbohydrate that can carry various functional oligosaccharides, such as sialyl Lewis X. It has been shown that the amount of poly-N-acetyllactosamine is increased in N-glycans, when they contain Galbeta1-->4GlcNAcbeta1-->6(Galbeta1-->4GlcNAcbeta1 -->2)Manalpha1-->6 branched structure. To determine how this increased synthesis of poly-N-acetyllactosamines takes place, the branched acceptor was incubated with a mixture of i-extension enzyme (iGnT) and beta1, 4galactosyltransferase I (beta4Gal-TI). First, N-acetyllactosamine repeats were more readily added to the branched acceptor than the summation of poly-N-acetyllactosamines formed individually on each unbranched acceptor. Surprisingly, poly-N-acetyllactosamine was more efficiently formed on Galbeta1-->4GlcNAcbeta1-->2Manalpha-->R side chain than in Galbeta1-->4GlcNAcbeta1-->6Manalpha-->R, due to preferential action of iGnT on Galbeta1-->4GlcNAcbeta1-->2Manalpha-->R side chain. On the other hand, galactosylation was much more efficient on beta1,6-linked GlcNAc than beta1,2-linked GlcNAc, preferentially forming Galbeta1-->4GlcNAcbeta1-->6(GlcNAcbeta1-->2)Manalph a1-->6Manbeta -->R. Starting with this preformed acceptor, N-acetyllactosamine repeats were added almost equally to Galbeta1-->4GlcNAcbeta1-->6Manalpha-->R and Galbeta1-->4GlcNAcbeta1-->2Manalpha-->R side chains. Taken together, these results indicate that the complemental branch specificity of iGnT and beta4Gal-TI leads to efficient and equal addition of N-acetyllactosamine repeats on both side chains of GlcNAcbeta1-->6(GlcNAcbeta1-->2)Manalpha1-->6Manbet a-->R structure, which is consistent with the structures found in nature. The results also suggest that the addition of Galbeta1-->4GlcNAcbeta1-->6 side chain on Galbeta1-->4GlcNAcbeta1-->2Man-->R side chain converts the acceptor to one that is much more favorable for iGnT and beta4Gal-TI.

Regulation of I-branched poly-N-acetyllactosamine synthesis. Concerted actions by I-extension enzyme, I-branching enzyme, and beta1,4-galactosyltransferase I

I-branched poly-N-acetyllactosamine is a unique carbohydrate composed of N-acetyllactosamine branches attached to linear poly-N-acetyllactosamine, which is synthesized by I-branching beta1, 6-N-acetylglucosaminyltransferase. I-branched poly-N-acetyllactosamine can carry bivalent functional oligosaccharides such as sialyl Lewisx, which provide much better carbohydrate ligands than monovalent functional oligosaccharides. In the present study, we first demonstrate that I-branching beta1, 6-N-acetylglucosaminyltransferase cloned from human PA-1 embryonic carcinoma cells transfers beta1,6-linked GlcNAc preferentially to galactosyl residues of N-acetyllactosamine close to nonreducing terminals. We then demonstrate that among various beta1, 4-galactosyltransferases (beta4Gal-Ts), beta4Gal-TI is most efficient in adding a galactose to linear and branched poly-N-acetyllactosamines. When a beta1,6-GlcNAc branched poly-N-acetyllactosamine was incubated with a mixture of beta4Gal-TI and i-extension beta1,3-N-acetylglucosaminyltransferase, the major product was the oligosaccharide with one N-acetyllactosamine extension on the linear Galbeta1-->4GlcNAcbeta1-->3 side chain. Only a minor product contained galactosylated I-branch without N-acetyllactosamine extension. This finding was explained by the fact that beta4Gal-TI adds a galactose poorly to beta1,6-GlcNAc attached to linear poly-N-acetyllactosamines, while beta1, 3-N-acetylglucosaminyltransferase and beta4Gal-TI efficiently add N-acetyllactosamine to linear poly-N-acetyllactosamines. Together, these results strongly suggest that galactosylation of I-branch is a rate-limiting step in I-branched poly-N-acetyllactosamine synthesis, allowing poly-N-acetyllactosamine extension mostly along the linear poly-N-acetyllactosamine side chain. These findings are entirely consistent with previous findings that poly-N-acetyllactosamines in human erythrocytes, PA-1 embryonic carcinoma cells, and rabbit erythrocytes contain multiple, short I-branches.

Synthesis of poly-N-acetyllactosamine in core 2 branched O-glycans. The requirement of novel beta-1,4-galactosyltransferase IV and beta-1,3-n-acetylglucosaminyltransferase

Poly-N-acetyllactosamine is a unique carbohydrate composed of N-acetyllactosamine repeats and provides the backbone structure for additional modifications such as sialyl Lex. Poly-N-acetyllactosamines in mucin-type O-glycans can be formed in core 2 branched oligosaccharides, which are synthesized by core 2 beta-1,6-N-acetylglucosaminyltransferase. Using a beta-1, 4-galactosyltransferase (beta4Gal-TI) present in milk and the recently cloned beta-1,3-N-acetylglucosaminyltransferase, the formation of poly-N-acetyllactosamine was found to be extremely inefficient starting from a core 2 branched oligosaccharide, GlcNAcbeta1-->6(Galbeta1-->3)GalNAcalpha-->R. Since the majority of synthesized oligosaccharides contained N-acetylglucosamine at the nonreducing ends, galactosylation was judged to be inefficient, prompting us to test novel members of the beta4Gal-T gene family for this synthesis. Using various synthetic acceptors and recombinant beta4Gal-Ts, beta4Gal-TIV was found to be most efficient in the addition of a single galactose residue to GlcNAcbeta1-->6(Galbeta1-->3)GalNAcalpha-->R. Moreover, beta4Gal-TIV, together with beta-1,3-N-acetylglucosaminyltransferase, was capable of synthesizing poly-N-acetyllactosamine in core 2 branched oligosaccharides. On the other hand, beta4Gal-TI was found to be most efficient for poly-N-acetyllactosamine synthesis in N-glycans. In contrast to beta4Gal-TI, the efficiency of beta4Gal-TIV decreased dramatically as the acceptors contained more N-acetyllactosamine repeats, consistent with the fact that core 2 branched O-glycans contain fewer and shorter poly-N-acetyllactosamines than N-glycans in many cells. These results, as a whole, indicate that beta4Gal-TIV is responsible for poly-N-acetyllactosamine synthesis in core 2 branched O-glycans.

The centrally acting beta1,6N-acetylglucosaminyltransferase (GlcNAc to gal). Functional expression, purification, and acceptor specificity of a human enzyme involved in midchain branching of linear poly-N-acetyllactosamines

In the present experiments the cDNA coding for a truncated form of the beta1,6N-acetylglucosaminyltransferase responsible for the conversion of linear to branched polylactosamines in human PA1 cells was expressed in Sf9 insect cells. The catalytic ectodomain of the enzyme was fused to glutathione S-transferase, allowing effective one-step purification of the glycosylated 67-74-kDa fusion protein. Typically a yield of 750 microg of the purified protein/liter of suspension culture was obtained. The purified recombinant protein catalyzed the transfer of GlcNAc from UDP-GlcNAc to the linear tetrasaccharide Galbeta1-4GlcNAcbeta1-3Galbeta1-4GlcNAc, converting the acceptor to the branched pentasaccharide Galbeta1-4GlcNAcbeta1-3(GlcNAcbeta1-6)Galbeta1-4 GlcNAc as shown by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry, degradative experiments, and 1H NMR spectroscopy of the product. By contrast, the recombinant enzyme did not catalyze any reaction when incubated with UDP-GlcNAc and the trisaccharide GlcNAcbeta1-3Galbeta1-4GlcNAc. Accordingly, we call the recombinant beta1,6-GlcNAc transferase cIGnT6 to emphasize its action at central rather than peridistal galactose residues of linear polylactosamines in the biosynthesis of blood group I antigens. Taken together this in vitro expression of I-branching enzyme, in combination with the previously cloned enzymes, beta1,4galactosyltransferase and beta1, 3N-acetylglucosaminyltransferase, should allow the general synthesis of polylactosamines based totally on the use of recombinant enzymes.

Expression cloning of cDNA encoding a human beta-1,3-N-acetylglucosaminyltransferase that is essential for poly-N-acetyllactosamine synthesis

The structure and biosynthesis of poly-N-acetyllactosamine display a dramatic change during development and oncogenesis. Poly-N-acetyllactosamines are also modified by various carbohydrate residues, forming functional oligosaccharides such as sialyl Lex. Herein we describe the isolation and functional expression of a cDNA encoding beta-1,3-N-acetylglucosaminyltransferase (iGnT), an enzyme that is essential for the formation of poly-N-acetyllactosamine. For this expression cloning, Burkitt lymphoma Namalwa KJM-1 cells were transfected with cDNA libraries derived from human melanoma and colon carcinoma cells. Transfected Namalwa cells overexpressing the i antigen were continuously selected by fluorescence-activated cell sorting because introduced plasmids containing Epstein-Barr virus replication origin can be continuously amplified as episomes. Sibling selection of plasmids recovered after the third consecutive sorting resulted in a cDNA clone that directs the increased expression of i antigen on the cell surface. The deduced amino acid sequence indicates that this protein has a type II membrane protein topology found in almost all mammalian glycosyltransferases cloned to date. iGnT, however, differs in having the longest transmembrane domain among glycosyltransferases cloned so far. The iGnT transcript is highly expressed in fetal brain and kidney and adult brain but expressed ubiquitously in various adult tissues. The expression of the presumed catalytic domain as a fusion protein with the IgG binding domain of protein A enabled us to demonstrate that the cDNA encodes iGnT, the enzyme responsible for the formation of GlcNAcbeta1 --> 3Galbeta1 --> 4GlcNAc --> R structure and poly-N-acetyllactosamine extension.

Mimecan, the 25-kDa corneal keratan sulfate proteoglycan, is a product of the gene producing osteoglycin

Bovine cornea contains three unique keratan sulfate proteoglycans (KSPGs), of which two (lumican and keratocan) have been characterized using molecular cloning. The gene for the third protein (KSPG25) has not been identified. This study examined the relationship between the KSPG25 protein and the gene for osteoglycin, a 12-kDa bone glycoprotein. The N-terminal amino acid sequence of KSPG25 occurs in osteoglycin cDNA cloned from bovine cornea. The osteoglycin amino acid sequence makes up the C-terminal 47% of the deduced sequence of the KSPG25 protein. Antibodies to osteoglycin reacted with intact corneal KSPG, with KSPG25 protein, and with a 36-kDa protein, distinct from lumican and keratocan. KSPG25-related proteins, not modified with keratan sulfate, were also detected in several connective tissues. Northern blot analysis showed mRNA transcripts of 2.4, 2.5, and 2.6 kilobases in numerous tissues with the 2.4-kilobase transcript enriched in ocular tissues. Ribonuclease protection analysis detected several protected KSPG25 mRNA fragments, suggesting alternate splicing of KSPG25 transcripts. We conclude that the full-length translation product of the gene producing osteoglycin is a corneal keratan sulfate proteoglycan, also present in many non-corneal tissues without keratan sulfate chains. The multiple size protein products of this gene appear to result from in situ proteolytic processing and/or alternative splicing of mRNA. The name mimecan is proposed for this gene and its products.

Synthesis of corneal keratan sulfate proteoglycans by bovine keratocytes in vitro

Keratan sulfate proteoglycans (KSPGs) are the major proteoglycans of the cornea and are secreted by keratocytes in the corneal stroma. Previous studies have been able to show only transient secretion of KSPG in cell culture. In this study, cultures of bovine keratocytes were found to secrete the three previously characterized KSPG proteins into culture medium. Reactivity with monoclonal antibody I22 demonstrated substitution of these proteins with keratan sulfate chains. KSPG constituted 15% of the proteoglycan metabolically labeled with [35S]sulfate in keratocyte culture medium. This labeled KSPG contained keratan sulfate chains of 4700 Da compared to 21,000 Da for bovine corneal keratan sulfate. Labeled keratan sulfate from cultures contained nonsulfated, monosulfated, and disulfated disaccharides that were released by digestion with endo-beta-galactosidase or keratanase II. Nonsulfated disaccharides were relatively more abundant in keratan sulfate from culture than in corneal keratan sulfate. These results show that cultured bovine keratocytes maintain the ability to express all three of the known KSPG proteins, modified with keratan sulfate chains and sulfated on both N-acetylglucosamine and galactose moieties. KSPG made in vitro differs from that found in vivo in the length and sulfation of its keratan sulfate chains. The availability of cell cultures secreting corneal keratan sulfate proteoglycans provides an opportunity to examine biosynthesis and control of this important class of molecules.

Molecular cloning and tissue distribution of keratocan. Bovine corneal keratan sulfate proteoglycan 37A

Previous studies showed that the keratan sulfate-containing proteoglycans of bovine corneal stroma contain three unique core proteins designated 37A, 37B, and 25 (Funderburgh, J. L., Funderburgh, M. L., Mann, M. M., and Conrad, G. W. (1991) J. Biol. Chem. 266, 14226-14231). Degenerate oligonucleotides designed from amino acid sequences of the 37A protein were used to screen a cDNA expression library from cultured bovine keratocytes. A cDNA clone coding for keratocan, a 37A protein, was isolated and sequenced. The deduced keratocan amino acid sequence is unique but related to two other keratan sulfate-containing proteins, lumican (the 37B core protein) and fibromodulin. These three proteins share approximately 35% amino acid identity and a number of conserved structural features. Northern hybridization and immunoblotting of tissue extracts found keratocan distribution to be more limited than that of lumican or fibromodulin. Keratocan is abundant in cornea and sclera and detected in much lesser amounts in skin, ligament, cartilage, artery, and striated muscles. Only in cornea was keratocan found to contain large, sulfated keratan sulfate chains. Keratocan, like lumican, is a core protein of a major corneal proteoglycan but is present in non-corneal tissues primarily as a nonsulfated glycoprotein.

The Beta-subunit of the rabbit H,K-ATPase:a glycoprotein with all terminal lactosamine units capped with alpha-linked galactose residues

The beta-subunit of the gastric H,K-ATPase is the most abundant glycoprotein in the tubulovesicular compartment of the acid-secreting parietal cells. The oligosaccharides of the beta-subunit have been shown to contain fucose, N-acetylglucosamine, mannose, galactose, and N-acetylgalactosamine. Previous studies have shown that the rabbit beta-subunit is devoid of N-acetylneuraminic acid. Here we report the structural features of the N-linked oligosaccharides of the beta-subunit from rabbit H,K-ATPase. We used glycosidase digestions and analysis by high-pH anion-exchange chromatography with pulsed amperometric detection and matrix-assisted laser desorption/ionization mass spectrometry to analyze the peptide-N4-(N-acetyl-beta-D-glucosaminyl)asparagine amidase (PNGase F)- and endo-beta-N-acetylglucosaminidase H (Endo H)-released oligosaccharides. The studies showed that the oligosaccharides of the beta-subunit are a mixture of both oligomannosidic and lactosamine-type structures. The high-mannose structures were identified as Man5Man8GlcNAc2 species. A striking finding was that all the branches of the lactosamine-type structures were terminated with Galalpha-->Galbeta-->GlcNAc extensions. All of the lactosamine-type structures were found to be core fucosylated and some of them contained one to three lactosamine repeats. We propose that a part of the adaptation of the gastric beta-subunit to the acidic environment of the stomach is through providing acid-stable terminal residues on the oligosaccharides.

Purification of preparative quantities of group B Streptococcus type III oligosaccharides

Many bacterial capsular polysaccharides are regularly repeating units of oligosaccharides. Bacterial oligosaccharides have been used in neoglycoconjugate vaccines and as reagents in the study of specific antibody binding. Unfortunately, separation methods have not been adequate for the purification of preparative quantities of bacterial oligosaccharides. Here we describe a size-exclusion procedure that resulted in the resolution of group B Streptococcus type III oligosaccharides composed of 4-25 sugars.

Biosynthesis of sialyl-oligomeric-Lewisx and VIM-2 epitopes: site specificity of human milk fucosyltransferase

In a previous study we have established the order of fucosylation of a trimer of Gal beta 1-->4GlcNAc (LacNAc) linked to a synthetic hydrophobic aglycon, (LacNAc)3-[(trifluoroacetamido)phenyl]ethyl, by a partially purified alpha 3-fucosyltransferase preparation from normal human milk [De Vries, Th., Norberg, T., Lönn, H., & van den Eijnden, D. H. (1993) Eur. J. Biochem. 216, 769-777]. Using the same fucosyltransferase preparation, we have now studied the fucosylation of the oligosaccharide NeuAc alpha 2-->3(LacNAc)3-Me. This compound was generated from the asialo analogue by use of an alpha 3-sialyltransferase preparation from human placenta. The location of the fucose residues in the monofucosylated and difucosylated intermediate products was determined by analyzing digests obtained after endo-beta-galactosidase treatment using HPLC on amino-bonded silica. In addition, the fucosylated NeuAc alpha 2-->3(LacNAc)3-Me structures were characterized by high-pH anion-exchange chromatography with pulsed amperometric detection and were identified by 400-MHz 1H-NMR spectroscopy. Intermediate products included oligosaccharides that contained the VIM-2, sialyl-LewisX, and sialyl-dimeric-LewisX epitopes. The final product was identified as the sialyl-trimeric-LewisX oligosaccharide. Kinetic analysis of the fucosylation reaction indicated that there is a significant difference in the rate of transfer of the first, second, and third fucose residues onto the acceptor molecule. Transfer of the first fucose occurred to either of the three GlcNAc residues in NeuAc alpha 2-->3(LacNAc)3-Me with only a modest preference for the proximal and medial residues. A similar slight preference for these GlcNAc residues was found for the attachment of the second fucose residue.(ABSTRACT TRUNCATED AT 250 WORDS)

Tools to cleave glycoproteins

There are a variety of enzymes available that are able to cleave glycoproteins, including enzymes that are specific for carbohydrate-carbohydrate linkages, carbohydrate-protein bonds and the peptide backbone. Such enzymes are useful for determining the sites of glycosylation within proteins, and for releasing glycan structures for subsequent carbohydrate analysis. One protease has been identified as being specific for O-sialoglycoproteins and can be used to identify such molecules and their epitope regions. The lack of cytotoxicity and the narrow specificity of this enzyme provides an improved method for the immunomagnetic selection of human bone-marrow stem-cells.

Glycosidase and sulfatase activities and their possible role in keratan sulfate degradation in metamorphosing bonefish (Albula sp.) leptocephali

During metamorphosis of leptocephalous larvae of the bonefish (Albula sp.), keratan sulfate, the principal glycosaminoglycan of the extracellular gelatinous body matrix, is degraded. Artificial substrates have been utilized to demonstrate the presence of β-N-acetylglucosaminidase, β-galactosidase and sulfatase activities in whole-body homogenates of early metamorphosing leptocephali. The concerted action of these enzymes has been shown to degrade the keratan sulfate polymer in other tissues. This paper describes the extraction, partial purification and some of the physical and kinetic properties of these enzymes. Additionally, starch gel electrophoresis was used to follow glycosidase activities in early, intermediate and advanced metamorphosing larvae. No differences were observed in electrophoretic migration or banding pattern of either β-N-acetylglucosaminidase or β-galactosidase during metamorphosis.

Glycosphingolipid patterns in human promyelocytic HL-60 leukemia cells susceptible or resistant to differentiation induction by phorbol 12-myristate 13-acetate

The patterns of glycosphingolipids (GSLs) were analyzed in an HL-60 cell variant, HL-205, which is susceptible to phorbol 12-myristate 13-acetate (PMA)-induced monocyte/macrophage differentiation, and in an HL-60 cell variant, HL-525, which is resistant to such differentiation. The amounts and types of the GSLs were similar in both the HL-205 and HL-525 cells and they resemble those of granulocytes. Treatment with 3 nM PMA caused the susceptible HL-205 cells (but not the resistant cells) to acquire a new GSL pattern which resembles that of monocytes. This new pattern was characterized by increases in the level of a neutral GSL, Gb3Cer, from trace levels to 0.05 mg/10(9) cells and of an acidic GSL, GM3 ganglioside, from 0.03 to 0.33 mg/10(9) cells. The increases in the level of this ganglioside were found to be due to an increase in CMP-N-acetylneuraminic acid:lactosylceramide sialyltransferase activity. These results indicate an association between PMA-induced terminal differentiation along the monocyte/macrophage cell lineage and PMA-evoked increases in specific GSLs, GM3 in particular, which is due to a rise in the activity of its synthetic enzyme.

alpha-D-galactose-bearing glycoproteins on the surface of stimulated murine peritoneal macrophages. Biochemical and immunochemical characterization of purified glycoproteins

Two glycoproteins were isolated from lysates of thioglycollate-stimulated, murine peritoneal macrophages by affinity chromatography on immobilized Griffonia simplicifolia I lectin and by preparative SDS/PAGE. The glycoproteins were readily labeled on the surface of intact macrophages with 3H and 125I. The labeled glycoproteins migrated as broad bands of molecular mass 92-109 kDa and 115-125 kDa. The mobility of the glycoproteins decreased only slightly after reduction with dithiothreitol, indicating the absence of intersubunit disulfide bridges. The 92-kDa and 115-kDa glycoproteins had pI 5.2-5.4 and pI less than or equal to 4, respectively. Digestion of both glycoproteins with alpha-galactosidase released 23% of their 3H content and abolished their ability to bind to the G. simplicifolia I lectin, showing that they contain terminal alpha-D-galactosyl groups. After reduction with 2-mercaptoethanol, each glycoprotein fraction was sensitive to N-glycanase; the 115-kDa glycoproteins produced a smear with the front at approximately 67 kDa, whereas the 92-kDa glycoprotein gave two bands of 61 kDa and 75 kDa. Unreduced glycoproteins were insensitive to N-glycanase, suggesting the presence of intramolecular disulfide bonds. Although each glycoprotein fraction was sensitive to endoglycosidase H, this enzyme produced only slight changes in molecular mass when compared with N-glycanase. From these results as well as from the specificity of the enzymes involved, it is concluded that each glycoprotein fraction contains complex-type oligosaccharides and a small amount of high-mannose and/or hybrid-type oligosaccharides. While each glycoprotein fraction was bound to Datura stramonium lectin, they failed to react with anti-[i-(Den)] serum and their digestion with endo-beta-galactosidase did not cause a band shift in SDS/PAGE. Taken together, these results suggest the presence of N-acetyllactosamine units which are not arrayed in linear form but occur as single units, bound either to C2 and C6, or to C2 and C4, or both, of outer mannosyl residues on complex-type oligosaccharides. The glycoprotein(s) fraction precipitated with anti-[I (Step)] serum, suggesting the presence of branched lactosaminoglycans. Digestion of both glycoprotein fractions with a mixture of sialidase and O-glycanase did not alter their mobility in SDS/PAGE, suggesting a lack or low content of O-linked trisaccharides and tetrasaccharides. Each glycoprotein fraction was bound specifically to Sambucus nigra and Maackia amurensis immobilized lectins, indicating the presence of sialic acid linked alpha 2,6 to subterminal D-galactose or N-acetylgalactosamine residues, and alpha 2,3 to N-acetyllactosamine residues, respectively.

Alpha-D-galactosylation of surface fucoglycoconjugate(s) upon stimulation/activation of murine peritoneal macrophages

Murine resident macrophages express, on their surface, carbohydrate epitopes which undergo changes during their stimulation/activation as monitored by binding of 125I labelled Evonymus europaea and Griffonia simplicifolia I-B4 lectins. Treatment of the stimulated macrophages with coffee bean alpha-galactosidase abolished binding of the GS I-B4 isolectin and changed the binding pattern of the Evonymus lectin. The affinity (Ka) of Evonymus lectin for alpha-galactosidase-treated macrophages decreased approximately 23-fold, from 1.25 x 10(8) M-1 to 5.5 x 10(6) M-1. Subsequent digestion of alpha-galactosidase-treated macrophages with alpha-L-fucosidase from Trichomonas foetus, further reduced binding of Evonymus lectin. Resident macrophages showed the same pattern of Evonymus lectin binding, with the same affinity, as alpha-galactosidase-treated, stimulated macrophages. These results, together with a consideration of the carbohydrate binding specificity of the Evonymus lectin which, in the absence of alpha-D-galactosyl groups, requires alpha-L-fucosyl groups for binding, indicate the presence, on resident macrophages, of glycoconjugates with terminal alpha-L-fucosyl residues. It is also concluded that during macrophage stimulation/activation alpha-D-galactosyl residues are added to this glycoconjugate and that they form part of the receptor for Evonymus lectin. The same glycoconjugate(s) is/are also expressed on the activated macrophage IC-21 cell line which exhibits the same characteristics as that of stimulated peritoneal macrophages, i.e., it contains alpha-D-galactosyl end groups and is resistant to the action of trypsin. Both lectins were also specifically bound to Corynaebacterium parvum activated macrophages.

Demonstration of a keratan sulfate-containing proteoglycan in atherosclerotic aorta

Proteoglycans were isolated from either grossly normal or atherosclerotic pigeon aortas after extraction with 4 M guanidine hydrochloride and purification by ion-exchange and size-exclusion chromatography. The small-size proteoglycans (Kav 0.4, on Sepharose CL-4B) from both normal and atherosclerotic tissue contained primarily a dermatan sulfate proteoglycan with an intact molecular size of 220-330 kd and a 45-kd core protein. In addition to the dermatan sulfate proteoglycan, the preparation contained a proteoglycan recognized by monoclonal antibody (MAb) 5-D-4, indicating the presence of sulfated poly-N-acetyllactosamine sequences common to corneal and cartilage keratan sulfate. Electrophoresis on sodium dodecyl sulfate-polyacrylamide gel revealed a polydisperse proteoglycan of 60-150 kd that was recognized by MAb 5-D-4. Significantly greater immunoreactivity with MAb 5-D-4 was observed for atherosclerotic compared with normal artery. After endo-beta-D-galactosidase treatment of the proteoglycan from atherosclerotic aorta, diminished MAb 5-D-4 reactivity observed by both Western blot analysis and enzyme-linked immunosorbent assay demonstrated that the material was keratan sulfate. Endo-beta-D-galactosidase treatment of the intact proteoglycan generated core proteins of 28 and 38 kd. These studies suggest the presence of one or more keratan sulfate proteoglycans in grossly normal and atherosclerotic arteries. Immunochemical data suggest that sulfation of the keratan sulfate proteoglycan may be greater in atherosclerotic aorta.

Determination of the branch location of extra N-acetyllactosamine units in sialo N-linked tetraantennary oligosaccharides

An approach is presented for the determination of the branch location of 1 or 2 extra N-acetyllactosamine units in sialo N-linked carbohydrate chains from glycoproteins. Tetraantennary oligosaccharides containing extra N-acetyllactosamine units were digested with endo-beta-galactosidase, followed by treatment with N-acetyl-beta-glucosaminidase, yielding products which could be analysed by 1H-NMR spectroscopy, thereby giving conclusive data about the location of the extra units in the intact structures.

The S-type lectin from calf heart tissue binds selectively to the carbohydrate chains of laminin

We report that the S-type lectin in calf heart tissue, termed calf heart agglutinin (CHA), binds to immobilized mouse laminin in ligand blotting and solid-phase radioligand binding assays. When compared with other glycoproteins, radioiodinated CHA binds preferentially to immobilized laminin. The binding is saturable with a Kd of 9.2 x 10(-7) M and is competitively inhibited by nonradiolabeled CHA as well as a similar lectin from porcine heart tissue. Both lactose and N-acetyllactosamine are good inhibitors of binding to laminin but binding is not inhibited by heparin. Exoglycosidase treatments demonstrated that the binding of radioiodinated CHA to laminin is not dependent on terminal sialyl-, fucosyl-, beta- or alpha-linked galactosyl residues, whereas treatment of laminin with endo-beta-galactosidase significantly decreases the lectin binding. Thus, CHA binds selectively to the poly-N-acetyllactosamine chains on complex-type Asn-linked oligosaccharides in laminin.