Intact Golgi synthesize complex branched O-linked chains on glycoside primers: evidence for the functional continuity of seven glycosyltransferases and three sugar nucleotide transporters

We examined the functional co-localization and continuity of glycosyltransferases and sugar nucleotide transporters in the Golgi of two Chinese hamster ovary (CHO) cell lines that synthesize different types of O-linked oligosaccharides. CHO cells normally synthesize primarily Sia2,3Galbeta1,3GalNAc- on glycoproteins. CHO cells transfected with core-2 GlcNAc transferase (Core 2) can synthesize glycoproteins containing branched O-linked oligosaccharides with poly-N-acetyllactosamines. CHO lines incubated with [(3)H]galactose and GalNAc-alpha-phenyl (GAP) as a primer, synthesize labeled glycoside products that faithfully resemble those found on the endogenous acceptors: CHO cells make Sia2,3[(3)H]Gal(beta)1,3GAP, while CHO Core2 cells synthesize GAPs with complex branched chains including poly-N-acetyllactosamines. To determine if isolated Golgi preparations make similar products, we prepared Golgi by established homogenization methods, documented their intactness, and added tracer UDP-[(3)H]Gal, unlabeled sugar nucleotides, and GAP. CHO Golgi preparations synthesized only Sia2,3[(3)H]Gal(beta)1,3GAP. CHO Core2, also made this product and a small amount of Core-2 GlcNAc transferase-dependent products. No endogenous glycoproteins were labeled. However, when either cell line was gently permeabilized with streptolysin-O or given hypo-osmotic shock, both GAP and endogenous acceptors were efficiently glycosylated within an intact functional Golgi lumen and remained there. Significantly, Golgi from CHO Core2 cells made mostly branched GAP products including some with poly-N-acetyllactosamines as complex as those made and secreted by living cells incubated with GAP. These results suggest that the lumen of the Golgi apparatus is functionally continuous or interconnected. Once glycosides diffuse into the Golgi lumen, they have access to all the sugar nucleotide transporters and glycosyltransferases used for complex GAP-based products without requiring metabolic energy or inter-vesicular transport. Glycosylation of artificial acceptors could be used to track the functional continuity or co-localization of multiple glycosyltransferases and transporters under conditions where Golgi morphology disintegrates and/or reappears.

Aglycone structure influences alpha-fucosyltransferase III activity using N-acetyllactosamine glycoside acceptors

We showed previously that Chinese hamster ovary cells took up and utilized a variety of N-acetylglucosaminides as primers of oligosaccharide biosynthesis (Ding et al., 1999, J. Carbohydr. Chem., 18:471-475). In this study, a library of N-acetylglucosaminides was enzymatically galactosylated in vitro to yield type 2 chain N-acetyllactosaminides bearing a variety of aglycones. Those disaccharides are potential acceptors for fucosyltransferases. As an extension of the previous study, we tested the type 2 chain disaccharyl glycosides (Galbeta1,4-GlcNAcbeta-R) for their aglycone-dependent acceptor specificity for alpha-L-fucosyltransferase III (Fuc-TIII). The enzyme activity significantly depended on the aglycone structures, suggesting that, in addition to the polar groups on the sugar moiety, the hydrophobic aglycone can substantially contribute to recognition in this reaction.

Direct utilization of mannose for mammalian glycoprotein biosynthesis

Direct utilization of mannose for glycoprotein biosynthesis has not been studied because cellular mannose is assumed to be derived entirely from glucose. However, animal sera contain sufficient mannose to force uptake through glucose-tolerant, mannose-specific transporters. Under physiological conditions this transport system provides 75% of the mannose for protein glycosylation in human hepatoma cells despite a 50- to 100-fold higher concentration of glucose. This suggests that direct use of mannose is more important than conversion from glucose. Consistent with this finding the liver is low in phosphomannose isomerase activity (fructose-6-P<->mannose-6-P), the key enzyme for supplying glucose-derived mannose to the N-glycosylation pathway. [2-3H] Mannose is rapidly absorbed from the intestine of anesthetized rats and cleared from the blood with a t1/2of 30 min. After a 30 min lag, label is incorporated into plasma glycoproteins, and into glycoproteins of all organs during the first hour. Most (87%) of the initial incorporation occurs in the liver, but this decreases as radiolabeled plasma glycoproteins increase. Radiolabel in glycoproteins also increases 2- to 6-fold in other organs between 1-8 h, especially in lung, skeletal muscle, and heart. These organs may take up hepatic-derived radiolabeled plasma glycoproteins. Significantly, the brain, which is not exposed to plasma glycoproteins, shows essentially no increase in radiolabel. These results suggest that mammals use mannose transporters to deliver mannose from blood to the liver and other organs for glycoprotein biosynthesis. Additionally, contrary to expectations, most of the mannose for glycoprotein biosynthesis in cultured hepatoma cells is derived from mannose, not glucose. Extracellular mannose may also make a significant contribution to glycoprotein biosynthesis in the intact organism.

UDP-GlcNAc:Ser-protein N-acetylglucosamine-1-phosphotransferase from Dictyostelium discoideum recognizes serine-containing peptides and eukaryotic cysteine proteinases

Phosphoglycosylation catalyzed by UDP-GlcNAc:Ser-protein N-acetylglucosamine-1-phosphotransferase (Ser:GlcNAc phosphotransferase) adds GlcNAcalpha-1-P to peptidyl-Ser of selected Dictyostelium discoideum proteins. Lysosomal cysteine proteinase (CP), proteinase-1(CP7), is the major phosphoglycosylated protein in bacterially grown amoebae. GlcNAc-1-P is added within a Ser-rich domain containing SSS, SGSG, or SGSQ repeated motifs that are not found in other papain-like CPs. We studied the substrate specificity of the transferase using peptides containing these motifs and 12 other peptides with one or more Ser residues. Phosphoglycosylation is comparable for all three Dictyostelium CP motifs, but it is not restricted to them. Flanking residues in the other peptides strongly influence phosphoglycosylation efficiency. Dictyostelium microsomal membranes also phosphoglycosylate endogenous acceptors, and some of these acceptors occur as an 18 S complex with the transferase. CP-serine motif peptides inhibit endogenous acceptor phosphoglycosylation weakly (30-40%) at 800 microM, whereas catalytically inactive proteinase-1(CP7) and other non-phosphoglycosylated eukaryotic CPs, lacking the serine domain, inhibit transferase activity at 1-4 microM. SDS denaturation destroys the inhibitory potential of all CPs showing that transferase recognizes a conformation-dependent feature that is shared by all. Proteinase-1(CP7) expressed in Escherichia coli lacks GlcNAc-1-P, but it is a substrate for Ser:GlcNAc phosphotransferase, Km = 5.6 microM. Thus, Ser:GlcNAc phosphotransferase recognizes both acceptor peptide sequences and a conformational feature of eukaryotic CPs. This may be physiologically important for establishing or maintaining non-overlapping groups of GlcNAc-1-P- and Man-6-P-modified Dictyostelium proteins that reside in functionally distinct endo-lysosomal vesicles.

Human fibroblasts prefer mannose over glucose as a source of mannose for N-glycosylation. Evidence for the functional importance of transported mannose

Mannose in N-linked oligosaccharides is assumed to be derived primarily from glucose through phosphomannose isomerase (PMI). The discovery of mammalian mannose-specific transporters that function at physiological concentrations suggested that mannose might directly contribute to oligosaccharide synthesis. To determine the relative contribution of glucose and mannose, human fibroblasts were labeled with either [2-3H]mannose or [1,5,6-3H]glucose at the same specific activity, and the N-linked chains were released by PNGase F digestion. Most of the trichloroacetic acid-precipitable [3H]mannose label was released by this digestion, but only about 10% of the trichloroacetic acid-precipitable material was released from cells labeled with [1,5,6-3H]glucose. Both sugars labeled a similar array of oligosaccharides, and acid hydrolysis of these chains showed that [2-3H]mannose contributed 65-75% of the [3H]mannose in cells labeled for 1 h, despite the 100-fold higher concentration of exogenous glucose. Mannose consumption and [2-3H]mannose utilization were within the range of rates expected for mannose transport via the mannose-specific transporter. About 7-14% of the [2-3H]mannose is used for glycosylation, while the rest (86-93%) is catabolized to 3H2O via PMI. Increasing the exogenous mannose concentration beyond mannose transporter saturation results in the conversion of >99% of [2-3H]mannose into 3H2O. Long term labeling of cells with [2-3H]mannose showed that the specific activity of mannose in glycoproteins reached 77% of the specific activity of [2-3H]mannose added to the medium. These results show that when fibroblasts are provided with physiological concentrations of mannose, they use the mannose-specific transporter to supply the majority of mannose needed for glycoprotein synthesis. PMI may normally be used to catabolize excess mannose rather than to primarily supply Man-6-P for glycoprotein synthesis.

Abnormal metabolism of mannose in families with carbohydrate-deficient glycoprotein syndrome type 1

Patients with carbohydrate-deficient glycoprotein syndrome (CDGS) Type 1 underglycosylate many glycoproteins by failing to add entire N-linked carbohydrate chains to them. The primary defect in these patients has been reported as a > 90% deficiency in phosphomannomutase activity (PMM), the enzyme that converts mannose-6-phosphate to mannose-1-phosphate. This lesion reduces both the amount and the size of the lipid-linked oligosaccharide precursor. We have now analyzed the activity of PMM and the level of glycosylation in cultured fibroblasts as well as the level of blood mannose in seven CDGS Type 1 patients and their parents. All of these patients were approximately 95% deficient in PMM activity and their parents had an average of 51% of control PMM activity. Furthermore, parental fibroblasts showed reduced glycosylation and a higher proportion of truncated N-linked chains compared to those made by control fibroblasts. Addition of 0.25 mM mannose to the culture medium corrected both the underglycosylation and size of the oligosaccharide chains in CDGS Type 1 patients and their parents. Finally, serum from CDGS patients had considerably reduced mannose levels (5-40 microM) compared to normal controls (40-80 microM) and some parents were below normal (16-103 microM). These results suggest that the reduced blood mannose level is a consequence of the PMM deficiency. This is the first inherited disorder in human metabolism that shows a decrease in available mannose. Increasing blood mannose levels might correct some protein underglycosylation in these patients.

Oral ingestion of mannose elevates blood mannose levels: a first step toward a potential therapy for carbohydrate-deficient glycoprotein syndrome type I

Carbohydrate-deficient glycoprotein syndrome type I (CDGS) is an inherited metabolic disorder with multisystemic abnormalities resulting from a failure to add entire N-linked oligosaccharide chains to many glycoproteins. Fibroblasts from these patients also abnormally glycosylate proteins, but this lesion is corrected by providing 250 microM mannose to the culture medium. This correction of protein glycosylation suggests that providing dietary mannose to elevate blood mannose concentrations might also remedy some of the underglycosylation observed in these patients. We find that ingested mannose is efficiently absorbed and increases blood mannose levels in both normal subjects and CDGS patients. Blood mannose levels increased in a dose-dependent fashion with increasing oral doses of mannose (0.07-0.21 g mannose/kg body weight). Peak blood mannose concentrations occurred at 1-2 h following ingestion and the clearance half-time was approximately 4 h. Doses of 0.1 g mannose/ kg body weight given at 3-h intervals maintained blood mannose concentrations at levels 3- to 5-fold higher than the basal level in both normal controls (approximately 55 microM) and CDGS patients. No side effects were observed for this dosage regimen. These results establish the feasibility of using mannose as a potential therapeutic dietary supplement (nutraceutical) to treat CDGS patients.

Enzymatic assay of D-mannose in serum

We describe a new and improved enzymatic assay for determining the concentration of D-mannose in sera. Serum D-glucose is selectively converted to glucose-6 phosphate with the highly specific thermostable glucokinase (EC 2.7.1.2) from Bacillus stearothermophilus. The anionic reaction products and excess substrates are removed by a rapid and simple anion-exchange chromatography step in microcentrifuge spin columns. D-Mannose in the glucose-depleted sample is then assayed spectrophotometrically by using coupled enzymatic reactions. The quantitative elimination of glucose from the serum samples allowed the accurate and reproducible assay of serum mannose in the 0-200 mumol/L range. Recovery of mannose added to serum (5-200 mumol/L) was 94% +/- 4.4%. The intraassay CV was 6.7% at 40 mumol/L mannose (n = 5; 39.6 +/- 1.6 mumol/L) and 4.4% at 80 mumol/L (n = 11; 75.0 +/- 1.8 mumol/L); the interassay CV at these concentrations was 12.2% (n = 7; 36.9 +/- 2.1 mumol/L) and 9.8% (n = 7; 74.2 +/- 2.7 mumol/L), respectively. Sera from 11 healthy human volunteers contained an average of 54.1 +/- 11.9 mumol/L mannose (range 36-81 mumol/L).

A lysosomal cysteine proteinase from Dictyostelium discoideum contains N-acetylglucosamine-1-phosphate bound to serine but not mannose-6-phosphate on N-linked oligosaccharides

Previous studies showed that vegetative Dictyostelium discoideum cells make a lysosomal proteinase, proteinase-1, that contains multiple GlcNAc-alpha-1-P residues in phosphodiester linkage to serine. We extended these studies and, in contrast to earlier reports, found that proteinase-1 contains 7.5 mol of Fuc, 8 mol of Man, 2 mol of Xyl, and 30 mol of GlcNAc per calculated mol of protein but no Man-6-P residues. The protein binds to concanavalin A and wheat germ agglutinin lectin affinity columns, and PNGase-F digestion released most of the mannose and xylose but little of the GlcNAc. beta-Elimination under reducing conditions released only GlcNAc-alpha-1-P. There was no evidence for the release of disaccharides or of fucitol. A rabbit antiserum and monoclonal antibodies prepared against proteinase-1 recognize GlcNAc-alpha-1-P residues in immunoblots and are specifically competed by UDP-GlcNAc or GlcNAc-alpha-1-P. Use of other monoclonal antibodies showed the presence of mannose-6-sulfate on N-linked sugar chains, and alpha-fucose residues on the protein. Thus, proteinase-1 has at least two types of modifications: Glc NAc-alpha-1-P-Ser, which we call phosphoglycosylation, and N-linked oligosaccharides. This is the first purified lysosomal enzyme in Dictyostelium that does not contain Man-6-P residues. The GlcNAc-alpha-1-P-specific antibodies also recognize a group of developmentally regulated proteins, especially enriched in vegetative cells. Some of them are also lysosomal cysteine proteinases, and all bind to the GlcNAc-alpha-1-P-specific monoclonal antibody but not to the mammalian CI-Man-6-P receptor. Conversely, lysosomal enzymes that have Man-6-P do not bind to the GlcNAc-alpha-1-P-specific antibody. An exception to this is beta-N-acetylglucosaminidase, where 15% of the activity binds to this antibody. Thus, there appear to be two sets of lysosomal enzymes with distinct post-translational modifications.

A new approach to mapping co-localization of multiple glycosyl transferases in functional Golgi preparations

We have developed a new method to co-localize multiple glycosyl transferases in different Golgi compartments. The approach relies on the proven ability of intact, sealed rat liver Golgi preparations to concentrate exogenous labeled sugar nucleotides into the lumen where they glycosylate either endogenous or artificial acceptors. The premise is that if two glycosyl transferases are co-localized within the same compartment, they will compete for the limited amount of transported donor. If the donor is consumed in glycosylating a permeable artificial glycoside within a Golgi compartment, it will be unavailable to glycosylate endogenous products within that same compartment. The greater the degree of transferase co-localization, the greater the potential decrease in glycosylation of endogenous acceptors. We provide an example consistent with these predictions. Adding 1 microM UDP[3H]Gal to Golgi preparations followed by a chase with a cocktail of unlabeled sugar nucleotides labels mostly endogenous N-linked oligosaccharides containing both beta 1,3- and beta 1,4[3H]Gal residues with and without sialic acid. Addition of increasing amounts of 4-methylumbelliferyl-beta-xyloside (Xyl beta MU) produces [3H]Gal1 beta, 4Xyl beta MU and leads to a reciprocal decrease in labeling of a restricted set of the endogenous acceptors. This decrease is preferential for [3H]Gal beta 1-->3GlcNAc beta 1-->R and, to a lesser extent, [3H]Gal beta 1-->4GlcNAc beta 1-->R structures in neutral and mono-sialylated oligosaccharides; synthesis of these structures in di- and tri-sialylated oligosaccharides was unaffected. These preferential decreases are not seen in detergent permeabilized, sugar nucleotide transport-independent Golgi incubations, and are not due to inhibition by the Gal beta 1,4Xyl beta MU product. These results argue that there is significant overlap in the functional co-localization of sialyl and galactosyltransferases in rat liver Golgi preparations and that GAG chain core specific Galactosyltransferase I is co-localized with subsets of N-glycan Gal beta 1,3 and Gal beta 1,4 transferases. This approach can be used with other glycosides and sugar nucleotides to map and co-localize other glycosyl transferases. The functional compartments defined by this approach may or may not correspond entirely with morphologically defined Golgi domains.

Human melanoma and Chinese hamster ovary cells galactosylate n-alkyl-beta-glucosides using UDP gal:GlcNAc beta 1,4 galactosyltransferase

We previously showed that human melanoma, CHO and other cells can convert beta-xylosides into structural analogs of ganglioside GM3. We have investigated several potential acceptors including a series of n-alkyl-beta-D-glucosides (n = 6-9). All were labeled with 3H-galactose when incubated with human melanoma cells. Octyl-beta-D-glucoside (Glc beta Octyl) was the best acceptor, whereas neither octyl-alpha-D-glucoside nor N-octanoyl-methylglucamine (MEGA 8) were labeled. Analysis of the products by a combination of chromatographic methods and specific enzyme digestions showed that the acceptors first received a single Gal beta 1,4 residue followed by an alpha 2,3 linked sialic acid. Synthesis of these products did not affect cell viability, adherence, protein biosynthesis, or incorporation of radiolabeled precursors into glycoprotein, glycolipid or proteoglycans. To determine which beta 1,4 galactosyl transferase synthesized Gal beta 1,4Glc beta Octyl, we analyzed similar incubations using CHO cells and a mutant CHO line (CHO 761) which lacks GAG-core specific beta 1,4 galactosyltransferase. The mutant cells showed the same level of incorporation as the control, eliminating this enzyme as a candidate. Thermal inactivation kinetics using melanoma cell microsomes and rat liver Golgi to galactosylate Glc beta Octyl showed the same half-life as UDP-Gal:GlcNAc beta 1,4 galactosyltransferase, whereas LacCer synthase was inactivated at a much faster rate. We show that Glc beta Octyl is a substrate for purified bovine milk UDP-Gal:GlcNAc beta 1,4 galactosyltransferase. Furthermore, the galactosylation of Glc beta Octyl by CHO cell microsomes can be competitively inhibited by GlcNAc or GlcNAc beta MU. These results indicate that UDP-Gal:GlcNAc beta 1,4 galactosyltransferase is the enzyme used for the synthesis of the alkyl lactosides when cells or rat liver Golgi are incubated with alkyl beta glucosides.

Characterization, subcellular localization, and developmental regulation of a cysteine proteinase from Dictyostelium discoideum

Previous studies showed that vegetative cells of Dictyostelium discoideum make a cysteine proteinase called proteinase-1, which contains multiple residues of GlcNAc-1-P linked directly to peptidyl serines. As a prelude to understanding the function of this novel carbohydrate modification, we purified and extensively characterized this proteinase in terms of its enzymatic activity, subcellular localization, and developmental regulation. The purified enzyme has an apparent molecular weight of 38 kDa in heat-denatured, reducing SDS/PAGE and 55 kDa under nonreducing conditions. Native gel electrophoresis and isoelectric focusing revealed two protein bands with equal activity and having pI values of 2.5 and 2.6. Even more complex patterns are found in non-heat-denatured SDS/PAGE gels. However, partial amino acid sequencing of the purified protein gave predominantly a single sequence. The enzyme is inhibited by trans-epoxysuccinyl-L-leucylamido-(4-guanidino) butane, Na-p-tosyl-L-lysine chloromethyl ketone, N-tosyl-L-phenylalanine chloromethyl ketone, and leupeptin, has a pH optimum of 5.0, and cofractionates with lysosomal enzymes in bacterially grown cells. It appears to comprise about 90% of the total cysteine proteinase activity in cells at a time when the cells have just finished clearing the bacterial lawn. Prior to this point and after the onset of development, its level is 2- to 20-fold lower. This remarkably fine regulation parallels the developmental regulation of other cysteine proteinases in Dictyostelium. Based on these results it appears that proteinase-1 may be primarily used for specialized proteolysis just before the onset of development rather than for simply digesting the bacteria for food.

A novel method to co-localize glycosaminoglycan-core oligosaccharide glycosyltransferases in rat liver Golgi. Co-localization of galactosyltransferase I with a sialyltransferase

4-Methylumbelliferyl-beta-xyloside (Xyl beta MU) primes glycosaminoglycan synthesis by first serving as an acceptor for the addition of 2 galactoses and 1 glucuronic acid residue to make the typical core structure, GlcUA beta 1, 3Gal beta 1,3Gal beta 1,4Xyl beta MU. To investigate the relative localization of these biosynthetic enzymes, intact and properly oriented rat liver Golgi preparations were incubated with Xyl beta MU and 1 microM UDP-[3H]Gal and then chased with 5 microM of unlabeled UDP-Gal, UDP-GlcUA, UDP-GlcNAc, UDP-GalNAc, and CMP-Neu5Ac. Under these conditions, no intervesicular transport occurs and acceptor labeling depends entirely upon transporter-mediated delivery of the labeled sugar nucleotides into the lumen of a vesicle and co-localization of the appropriate glycosyltransferases. The labeled products were isolated from the incubation medium and from within the Golgi and their structures analyzed by C18, anion-exchange, and amine adsorption high performance liquid chromatography in combination with glycosidase digestions. Surprisingly, the major products within the Golgi were two sialylated xylosides (Sia alpha 2,3Gal beta 1,4Xyl-beta MU and Sia alpha 2,8Sia alpha 2,3Gal beta 1,4Xyl beta MU) rather than the expected group of partially completed GAG core structures. Less than 10% of the products within the Golgi are the expected core structures containing a second Gal residue or, in addition, GlcUA. The amount of the sialylated products is only partially decreased if the chase is omitted or if the chase is done in the absence of added CMP-Sia, suggesting a pool of previously transported CMP-Sia drives synthesis of the major products. Conversely, when detergent permeabilized vesicles are provided with high concentration of the same sugar nucleotides, the ratio of sialylated products is reduced and replaced by an increase in GAG-like products. These results argue that GAG core-specific Ga1 transferase I and II are not extensively co-localized within the same Golgi compartment. By contrast, glycosaminoglycan core Gal transferase I is substantially co-localized with an alpha-2,3-sialyltransferase and an alpha-2,8-sialyltransferase. Incubating intact Golgi vesicles with exogenous diffusible acceptors offers a novel method to assess the functional co-localization of glycosyltransferases of multiple pathways within the Golgi compartments.

Differential localization of two epitopes of Escherichia coli ribosomal protein L2 on the large ribosomal subunit by immune electron microscopy using monoclonal antibodies

Two monoclonal antibodies (mAb), directed toward different epitopes of Escherichia coli ribosomal protein L2, have been used as probes in immune electron microscopy. mAb 5-186 recognizes an epitope within residues 5-186 of protein L2; it is seen to bind to 50 S subunits at or near the peptidyl transferase center, beside the subunit head on the L1 shoulder. mAb 187-272 recognizes an epitope within residues 187-272. This antibody binds to the face of the 50 S subunit, below the head and slightly toward the side with the stalk; this site is near the translocation domain. Both antibodies can bind simultaneously to single subunits. This indicates that protein L2 is elongated, reaching from the peptidyl transferase center to below the subunit head and approaching the translocational domain. The different locations of the two epitopes are consistent with previous biochemical results with the two antibodies (Nag, B., Tewari, D. S., Etchison, J. R., Sommer, A., and Traut, R. R. (1986) J. Biol. Chem. 261, 13892-13897).

A rapid, quantitative assay for titration of bovine virus diarrhoea-mucosal disease virus

An end point dilution microtitration assay is described that can be used for the titration of both cytopathic and non-cytopathic isolates of bovine virus diarrhoea-mucosal disease virus. Indirect immunofluorescence is used to detect infected MDBK cells in the wells of Terasaki plates. The virus titre is derived from the number of uninfected wells, using the Poisson distribution. The assay is simple, fast and economical. Titres of cytopathic virus determined by the microtitration assay and standard plaque assay are equivalent.

Monoclonal antibody-aided characterization of cellular p220 in uninfected and poliovirus-infected HeLa cells: subcellular distribution and identification of conformers

A monoclonal antibody directed against the Mr-220,000 subunit (p220) of the mRNA cap-binding complex has been prepared and used to analyze the sucrose gradient sedimentation and subcellular location of p220 and its poliovirus-induced cleavage products. The antibody reacted with p220 on immunoblots of cell lysates from uninfected cells, but only with several smaller polypeptides, the p220 cleavage products, in cell lysates from poliovirus-infected cells. The sedimentation of p220 antigens from uninfected or infected cells was analyzed by immunoblot and by enzyme-linked immunosorbent assay (ELISA) of sucrose gradient fractions. The results indicate that antibody reactivity was partially influenced by antigen conformation. Major forms of intact p220 and cleaved p220 were identified by immunoblot, and these had similar sedimentation properties. ELISA analysis of the same gradient fractions detected only uncleaved p220; p220 cleavage products were not recognized. Furthermore, the antibody recognized two forms of native uncleaved p220, one of which appeared to bind antibody with greater affinity. This result suggested the existence of conformational variants of p220. The differential reactivity of the antibody for cleaved versus uncleaved p220 served as a useful control during indirect immunofluorescence analysis to determine the subcellular distribution of p220 antigens. The distribution of p220 in uninfected cells was mainly cytoplasmic, but some nuclear antigens were also apparent. After poliovirus infection only the nuclear pattern remained. Disappearance of the cytoplasmic pattern confirmed the inability of the antibody to react with native p220 cleavage products. The cytoplasmic pattern also disappeared after human rhinovirus 14 infection, but not after mengovirus infection, results which correlated with the ability of human rhinovirus 14 and the inability of mengovirus to induce the cleavage of p220. The results demonstrate that p220 is not likely to be associated with the cytoskeleton and hint at the possibility of a partially nuclear location.

Two monoclonal antibodies against Escherichia coli ribosomal protein L2 distinguish different locations for their respective epitopes in intact ribosomes

Two monoclonal antibodies raised against intact Escherichia coli ribosomal protein L2 were isolated, affinity-purified, and characterized. One of the antibodies (Ab 5-186) recognizes an epitope within residues 5-186, and the other (Ab 187-272) recognizes an epitope within residues 182-272. Both antibodies strongly inhibit in vitro polyphenylalanine synthesis when they are first allowed to bind to 50 S subunits prior addition of 30 S subunits. However, only Ab 187-272 is inhibitory when added to preformed 70 S ribosomes. Ab 5-186 binds to 50 S subunits but not to 70 S ribosomes. Ab 187-272 does not cause dissociation of 70 S ribosomes under the ionic conditions of the assay for polyphenylalanine synthesis (15 mM magnesium), although at 10 mM magnesium it does cause dissociation. Both antibodies inhibit the reassociation of 50 S with 30 S subunits. Both antibodies strongly inhibit peptidyltransferase activity. The two antibodies differ in their effects on interactions with elongation factors Tu (EF-Tu) and G (EF-G). Neither antibody significantly inhibits EF-G-dependent GTPase activity, nor the binding of EF-G when the antibodies are incubated with 50 S subunits; however, Ab 187-272 causes a decrease in the binding of EF-Tu X aminoacyl-tRNA X GTP ternary complex and of EF-Tu-dependent GTPase when it is incubated with 70 S ribosomes. The Fab fragments of both antibodies had effects similar to the intact antibodies. The results show that monoclonal antibodies can be used to discriminate different regions of L2 and that EF-Tu and EF-G do not have identical ribosomal binding sites.

An immunohistochemical characterization of rhesus monkey respiratory secretions using monoclonal antibodies

A series of 12 monoclonal antibodies was made against mucous and serous components of rhesus monkey trachea. These antibodies were used to localize secretory products in the respiratory epithelium by immunohistochemical methods. Mucous cells of the tracheal surface epithelium and submucosal glands were shown by histochemical methods to be a homogeneous population containing periodate-reactive sulfated glycoconjugates. Immunohistochemical staining using the monoclonal antibodies on glycol methacrylate sections serial to those stained histochemically revealed a more antigenically heterogeneous population of secretory cells. Four distinct staining patterns were observed with the 12 monoclonal antibodies. Eight antibodies reacted with most, but not all, mucous and serous cells. Two antibodies recognized subpopulations of secretory cells. One antibody stained tracheal mucous cells with a concentration of reaction product on the luminal border, and one antibody stained only serous cells within the glands. Ten of the 12 antibodies were shown to react in an ELISA with the high molecular weight void volume containing mucous glycoproteins separated on a Sepharose CL-4B gel filtration column. None of the antibodies recognized blood group antigens. We conclude: (1) that production of a large panel of monoclonal antibodies to respiratory tract mucins from primates is feasible, (2) that the monoclonal antibodies will recognize epitopes on biochemically identifiable glycoproteins, and (3) that the intracellular mucous products of tracheal secretory cells exhibit greater heterogeneity than is detectable by conventional histochemistry.

Preparation and characterization of two monoclonal antibodies against different epitopes in Escherichia coli ribosomal protein L7/L12

Two monoclonal antibodies with specificities for Escherichia coli 50 S ribosomal subunit protein L7/L12 were isolated. The antibodies and Fab fragments thereof were purified by affinity chromatography using solid-phase coupled L7/L12 protein as the immunoadsorbent. The two antibodies were shown to recognize different epitopes; one in the N-terminal and the other in the C-terminal domain of protein L7/L12. Both intact antibodies strongly inhibited polyuridylic acid-directed polyphenylalanine synthesis, ribosome-dependent GTPase activity, and the binding of elongation factor EF-G to the ribosome. Ratios of antibody to ribosome of 4:1 or less were effective in inhibiting these activities. Neither antibody prevented the association of ribosomal subunits to form 70 S ribosomes. The Fab fragments showed similar effects.

An immunocytochemical/histochemical approach to tracheobronchial mucus characterization in the rabbit

Monoclonal antibodies have been made against components of rabbit respiratory mucous secretions, and these were used to localize secretory products in the respiratory epithelium by immunocytochemical methods. The antigen recognized by one antibody was localized within granules of mucous cells containing sulfated glycoprotein. This antibody also reacted with the ciliated surface layer of upper respiratory airways and mucous cells of colonic epithelium. However, only a subset of respiratory mucous cells containing sulfated glycoprotein, as determined by histochemistry, reacted with this monoclonal antibody. Other antibodies also recognized antigens on the ciliated surface of the rabbit respiratory tree but not in intracellular mucus. Thus, a library of monoclonal antibodies made against respiratory mucous secretions should represent an effective approach to defining the mucous lining of normal and diseased respiratory airways.

Presence of a nonlysosomal endo-beta-N-acetylglucosaminidase in the cellular slime mold Dictyostelium discoideum

Vegetative cells of the cellular slime mold Dictyostelium discoideum have been found to contain an endo-beta-N-acetylglucosaminidase (EC 3.2.1.96) activity which hydrolyzes the di-N-acetylchitobiosyl linkage found in asparagine-linked oligosaccharides. In contrast to other previously characterized glycosyl hydrolases of Dictyostelium, this endoglycosidase is not secreted during vegetative growth or development nor is it developmentally regulated. Cellular fractionation studies showed that the endoglycosidase activity is not associated with lysosomes and remains soluble after centrifugation at 180,000g for 1 h. The enzyme has been partially purified (350-fold) from cell lysates, and its substrate specificity has been examined by its ability to hydrolyze several glycopeptides prepared from ovalbumin and from slime mold lysosomal enzymes. These preliminary studies revealed that the enzyme, called endoglycosidase S, has a substrate specificity similar to that of endo-beta-N-acetylglucosaminidase CII secreted by Clostridium perfringens.

Carbohydrate cytochemistry of tracheobronchial airway epithelium of the rabbit

Three types of nonciliated secretory epithelial cells contribute to the mucous lining of pulmonary airways: mucous cells, serous cells, and Clara cells. Contrary to observations in other species, airways of the rabbit have very few mucous cells. In the rabbit, the predominant secretory cell throughout the entire airway tree, including the trachea, appears to be one cell type, the Clara cell. While these cells share the same ultrastructural features throughout the tree, the nature of their contribution to the mucous blanket is not clear. This study was designed to characterize the carbohydrate components of secretory granules in tracheal Clara cells, and to compare that carbohydrate with that of tracheal mucous (goblet) cells and with Clara cells of more distal airway generations. Trachea and lungs of six adult male rabbits were fixed by airway infusion, the conducting airways of the right cranial lobe dissected and tissue selected from the trachea and five distal airway generations. For light microscopy (LM), sections of paraffin-embedded tissues were stained with Alcian blue-periodic acid-Schiff (AB/PAS), dialyzed iron (DI), and high iron diamine-Alcian blue (HID-AB). For electron microscopy (EM), fixed tissues were incubated with DI, HID, MgCl2, or buffer, postosmicated, embedded in epoxy resin, and thin sections stained with periodic acid-thiocarbohydrazide-silver proteinate (PA-TCH-SP). By LM, most Clara cells did not react with PAS, AB, HID, or DI. A few in trachea and bronchi had PAS-positive apical margins. Mucous goblet cells were positive with PAS, AB, and HID, indicating sulfated glycoproteins. By EM, a small number of Clara cells had PA-TCH-SP-positive luminal granules, a few luminal granules had DI-positive rims. Almost all Clara cell granules were negative with PA-TCH-SP, HID, and DI. The granules of mucous goblet cells had a finely granular core surrounded by a meshwork of variable density. The meshwork was positive with PA-TCH-SP, DI, and HID. The cores were not. We concluded that: 1) the Clara cell does not contribute carbohydrates to the airway mucous lining; 2) mucous goblet cells secrete predominantly sulfated glycoprotein; and 3) the contribution to mucous carbohydrates by Clara cells does not vary with the airway level in which they are located.

Comparison of the oligosaccharide structure of the glycoprotein of vesicular stomatitis virus and a thermolabile mutant (tl-17)

As a means of examining the extent to which the polypeptide structure of a virus glycoprotein contributes to the overall structure and composition of the carbohydrate moieties, we have made a detailed comparison of the structure of the oligosaccharide moieties of wild-type vesicular stomatitis virus (VSV) glycoprotein with those of a glycoprotein-defective mutant of VSV, tl-17 (VSV). Characterization of the oligosaccharides by ion-exchange and gel filtration chromatography after sequential enzymic degradation reveals similar structures in the wt and mutant glycoproteins. However, the altered polypeptide structure of the tl-17 glycoprotein affects the extent of addition of sialic acid and fucose, both of which are added late in the maturation of the glycoprotein.

Host cell-dependent differences in the oligosaccharide moieties of the VSV G protein

The oligosaccharide moieties of vesicular stomatitis virus glycoprotein from virus grown in four different cell lines have been characterized by sequential enzymic degradation followed by ion-exchange chromatography and analytical gel filtration. Whilst the same two peptide sites are glycosylated in all cell lines, the extent of sialylation of the oligosaccharides is, however, a function of the cell line in which the virus is produced. Using specific purified glycosidases for sequential degradation of glycopeptides obtained after Pronase digestion, the oligosaccharide structures from the different host cell lines appear similar. However, differential sensitivity of the glycopeptides to treatment with a partially purified mixture of endo- and exoglycosidases indicates that the oligosaccharide structures are not identical.

Oligosaccharide chains of avian RNA tumor virus glycoproteins contain heterogeneous oligomannosyl cores

Chicken embryo fibroblasts (C/E phenotype) infected with subgroups B and C of the Prague strain of Rous sarcoma virus were radiolabeled with either [6-(3)H]-glucosamine or [2-(3)H]mannose, and virus was purified from the growth medium. The large envelope glycoprotein, gp85, was the only major radiolabeled component of purified virus. Pronase-digested glycopeptides from purified virus were analyzed by a combination of (i) gel filtration with columns of Sephadex G15/G50 and Bio-Gel P4 and (ii) enzymatic digestion of the oligosaccharide chains with specific exoglycosidases and endo-beta-N-acetylglucosaminidases. The rather broad molecular weight distribution (approximately 2,000 to 4,000) for glycopeptides in these studies and previous studies in other laboratories was shown to represent actual heterogeneity in the carbohydrate moieties: (i) the glycopeptides contained both mannose-rich, neutral chains and complex, acidic chains with terminal sialic acid; and (ii) both classes of asparagine-linked carbohydrate structures exhibited heterogeneity in the size of the oligomannosyl core (a mixture of approximately 5 to 9 mannose units for the neutral structures, and 3 or 5 mannose units for the acidic structures). With the [2-(3)H]mannose-labeled glycopeptides from Rous sarcoma virus, Prague strain subgroup C, most of the oligosaccharide chains were high-molecular-weight, acidic structures, with similar numbers of 3-mannose and 5-mannose core structures.

Specific changes in the oligosaccharide moieties of VSV grown in different lectin-resistnat CHO cells

The carbohydrate moieties of the G glycoprotein of vesicular stomatitis virus (VSV) grown in three distinct lectin-resistant (LecR) Chinese hamster ovary (CHO) cell lines have been compared by fine structural analysis of radiolabeled glycopeptides. The mutant WgaRIII, selected for resistance to wheat germ agglutinin (WGA), produces VSV containing G glycoprotein specifically lacking in sialic acid. The mutant PhaRI, selected for resistance to phytohemagglutinin (PHA) and previously shown to lack a particular glycoprotein N-acetyl-glucosaminyl-transferase activity, produces VSV containing G glycoprotein specifically lacking terminal N-acetylglucosamine-galactose-sialic acid sequences and possessing an increased number of mannose residues in the "core" region of its carbohydrate moieties. The mutant PhaRIConARII, a "double" mutant selected from PhaRI cells for resistance to concanavalin A (ConA), produces VSV containing G glycoprotein with a further alteration in the mannose residues of the "core" oligosaccharide region. We discuss the relevance of these findings to the mechanisms of glycoprotein biosynthesis in mammalian cells and to the biochemical bases of lectin resistance in CHO cells.

Oligosaccharide chains are trimmed during synthesis of the envelope glycoprotein of vesicular stomatitis virus

The biosynthesis and maturation of the oligosaccharide moieties of the envelope glycoprotein of vesicular stomatitis virus were investigated in virus-infected HeLa and BHK21 cells after pulse labeling with [2-3H]mannose. Two major forms of the virus glycoprotein were detected by polyacrylamide gel electrophoresis, which appear to correspond to the viral glycoprotein with either "precursor" or "mature" oligosaccharide chains. The precursor chains in both HeLa and BHK21 cells infected with vesicular stomatitis virus obtained after a 30-min pulse were large oligomannose structures containing approximately 7--9 mannose residues as estimated by gel filtration analysis. The size of the oligomannose structures initially transferred to the protein may have been even larger. Mature, virus-size oligosaccharide chains, which could be detected after a 20- to 30-min delay, contained only three mannose residues and, in addition, contained branch structures terminating in sialic acid. A precursor--product relationship of these two forms of oligosaccharide chains was demonstrated by pulse--chase labeling of virus-infected HeLa cells. These studies indicated that the large oligomannosyl core structures initially added to the glycoprotein were being "trimmed" by the removal of mannose residues prior to (and/or during) the addition of the branch chains terminating in sialic acid.

Glycosylation sites of vesicular stomatitis virus glycoprotein

Detailed analysis on DEAE-Sephadex of the tryptic digestion products of the glycoprotein from vesicular stomatitis virus grown in HeLa suspension cultures revealed the presence of two major and several minor sugar-labeled species. The minor tryptic glycopeptides were converted to one of the two major glycopeptide species by treatment with neuraminidase. Thus, vesicular stomatitis virus glycoprotein contains only two oligosaccharide side chains that are heterogeneous in their sialic acid content.

Carbohydrate composition of the membrane glycoprotein of vesicular stomatitis virus grown in four mammalian cell lines

The carbohydrate composition of the membrane glycoprotein of vesicular stomatitis virus has been determined for virus grown in four different mammalian cell lines. The glycoprotein contains mannose, galactose, N-acetylglucosamine, and neuraminic acid as the major carbohydrate components, whereas N-acetyl-galactosamine and fucose are present in lesser amounts. The glycoprotein contains approximately 9-10% carbohydrate regardless of the host cell in which it is synthesized. Small quantitative differences are evident in the composition of the component sugars of the glycoprotein when the virus is grown in different host cells, and the glycoprotein of virus grown in a mouse fibroblast line (L cells) lacks fucose. The major oligosaccharide moieties of the virus glycoprotein from all cells are approximately the same size (3000-3400 daltons). The data presented here, in conjunction with previous data, indicate that the viral glycoprotein contains two major oligosaccharide constituents regardless of the host cell in which it is synthesized.