Cloning and expression of human sialic acid pathway genes to generate CMP-sialic acids in insect cells.

The addition of sialic acid residues to glycoproteins can affect important protein properties including biological activity and in vivo circulatory half-life. For sialylation to occur, the donor sugar nucleotide cytidine monophospho-sialic acid (CMP-SA) must be generated and enzymatically transferred to an acceptor oligosaccharide. However, examination of insect cells grown in serum-free medium revealed negligible native levels of the most common sialic acid nucleotide, CMP-N-acetylneuraminic acid (CMP-Neu5Ac). To increase substrate levels, the enzymes of the metabolic pathway for CMP-SA synthesis have been engineered into insect cells using the baculovirus expression system. In this study, a human CMP-sialic acid synthase cDNA was identified and found to encode a protein with 94% identity to the murine homologue. The human CMP-sialic acid synthase (Cmp-Sas) is ubiquitously expressed in human cells from multiple tissues. When expressed in insect cells using the baculovirus vector, the encoded protein is functional and localizes to the nucleus as in mammalian cells. In addition, co-expression of Cmp-Sas with the recently cloned sialic acid phosphate synthase with N-acetylmannosamine feeding yields intracellular CMP-Neu5Ac levels 30 times higher than those observed in unsupplemented CHO cells. The absence of any one of these three components abolishes CMP-Neu5Ac production in vivo. However, when N-acetylmannosamine feeding is omitted, the sugar nucleotide form of deaminated Neu5Ac, CMP-2-keto-3-deoxy-D-glycero-D-galacto-nononic acid (CMP-KDN), is produced instead, indicating that alternative sialic acid glycoforms may eventually be possible in insect cells. The human CMP-SAS enzyme is also capable of CMP-N-glycolylneuraminic acid (CMP-Neu5Gc) synthesis when provided with the proper substrate. Engineering the CMP-SA metabolic pathway may be beneficial in various cell lines in which CMP-Neu5Ac production limits sialylation of glycoproteins or other glycans.

Determination of nucleotides and sugar nucleotides involved in protein glycosylation by high-performance anion-exchange chromatography: sugar nucleotide contents in cultured insect cells and mammalian cells.

We have developed a simple and highly sensitive HPLC method for determination of cellular levels of sugar nucleotides and related nucleotides in cultured cells. Separation of 9 sugar nucleotides (CMP-Neu5Ac, CMP-Neu5Gc, CMP-KDN, UDP-Gal, UDP-Glc, UDP-GalNAc, UDP-GlcNAc, GDP-Fuc, GDP-Man) and 12 nucleotides (AMP, ADP, ATP, CMP, CDP, CTP, GMP, GDP, GTP, UMP, UDP, and UTP) was examined by reversed-phase HPLC and high-performance anion-exchange chromatography (HPAEC). Although the reversed-phase HPLC, using an ion-pairing reagent, gave a good separation of the 12 nucleotides, it did not separate sufficiently the sugar nucleotides for quantification. On the other hand, the HPAEC method gave an excellent and reproducible separation of all nucleotides and sugar nucleotides with high sensitivity and reproducibility. We applied the HPAEC method to determine the intracellular sugar nucleotide levels of cultured Spodoptera frugiperda (Sf9) and Trichoplusia ni (High Five, BTN-TN-5B1-4) insect cells, and compared them with those in Chinese hamster ovary (CHO-K1) cells. Sf9 and High Five cells showed concentrations of UDP-GlcNAc, UDP-Gal, UDP-Glc, GDP-Fuc, and GDP-Man equal to or higher than those in CHO cells. CMP-Neu5Ac was detected in CHO cells, but it was not detected in Sf9 and High Five cells. In conclusion, the newly developed HPAEC method could provide valuable information necessary for generating sialylated complex-type N-glycans in insect or other cells, either native or genetically manipulated.

Crocus sativus lectin recognizes Man3GlcNAc in the N-glycan core structure.

Crocus sativus lectin (CSL) is one of the truly mannose-specific plant lectins that has a unique binding specificity that sets it apart from others. We studied sugar-binding specificity of CSL in detail by a solution phase method (fluorescence polarization) and three solid phase methods (flow injection, surface plasmon resonance, and microtiter plate), using a number of different glycopeptides and oligosaccharides. CSL binds the branched mannotriose structure in the N-glycan core. Substitution of the terminal Man in the Manalpha(1-3)Man branch with GlcNAc drastically decreases binding affinity much more than masking of the terminal Man in the Manalpha(1-6)Man branch. Most interestingly, the beta-Man-linked GlcNAc in N-glycan core structure contributes greatly to the binding. The effect of this GlcNAc is so strong that it can substantially offset the negative effect of substitution on the nonreducing terminal Man residues. On the other hand, the GlcNAc that is usually attached to Asn in N-glycans and the l-Fuc linked at the 6-position of the GlcNAc are irrelevant to the binding. A bisecting GlcNAc neither contributes to nor interferes with the binding. This unique binding specificity of CSL offers many possibilities of its use in analytical and preparative applications.

Contribution of component monosaccharides to the coordinates of neutral and sialyl pyridylaminated N-glycans on a two-dimensional sugar map.

High-performance liquid chromatography elution data on an amide-adsorption and a reverse-phase column, expressed in glucose units, of pyridylamino N-glycans have been analyzed with a new approach using multiple regression to obtain parameters for the contribution ascribable to each of 54 monosaccharide units. Our calculation was based on the 417 different N-glycan structures determined empirically. Depending on the increase in the amount of elution data, we got good correlation (r = 0.9998 for amide-silica and r = 0.9974 for octadecylsilica) and agreement between the observed and the calculated N-glycan elution coordinate values which correspond to the sum of the unit contribution of the component monosaccharides. These calculated values of unit contribution are useful in predicting glycan structure from an observed glucose unit on the map as well as to assume a glucose unit from a given structure. As an example of the application of the unit contribution values to the estimate of a sialyl N-glycan structure, the case of trisialyl triantennary N-glycans is described.

Synthetic studies on selectin ligands/inhibitors. Synthesis and biological evaluation of sulfated and phosphorylated beta-D-galacto- and lactopyranosides containing fatty-alkyl residues of different carbon chain lengths.

To investigate the biological selectin-ligand interactions, fourteen sulfated and eight phosphorylated beta-D-galacto- and lactopyranosides containing branched fatty-alkyl residues in place of the ceramide have been synthesized. Regioselective sulfation of the parent glycolipids through the dibutylstannylene acetal with a certain amount of sulfur trioxide-trimethylamine complex produced the target sulfated glycolipids, while stepwise phosphorylation by treatment of the properly protected diol with dibenzyloxy(diisopropylamino)phosphine gave the phosphorylated glycolipids. The synthetic glycolipids showed an interesting mode of inhibition of the binding of HL-60 cells to immobilized P-, L- and E-selectins during in vitro experiments. In addition, using computer modeling techniques, we examined the molecular basis for the ligand-selectin complex formation. These glycolipids may be useful as therapeutic agents against selectin-dependent inflammation.

A novel biologically active eel calcitonin analogue with carboxyl terminal Hse32-amide: carboxyl terminal Pro32-amide in calcitonin is not essential for biological activity.

Eel calcitonin (CT) analogues having C-terminal homoserine (Hse)-amide at position 31, 32, or 33 were synthesized, and in vivo hypocalcemic activity of the analogues were determined. The present study showed that: (i) An eel CT analogue having Hse-amide at position 32 was more active than native eel CT, and the duration of hypocalcemic action of the analogue was equivalent to that of native eel CT. (ii) Either curtailment or elongation of [Hse32-amide]-eel CT peptide chain by one amino acid resulted in a great loss of hypocalcemic activity. The results of the present study indicate that Pro-amide at the C-terminus of CT is not essential for its biological activity in vivo. Replacement of C-terminal Pro32-amide by Hse32-amide in eel CT molecule produced an analogue with a hypocalcemic activity greater than that of native eel CT.

Three-dimensional elution mapping of pyridylaminated N-linked neutral and sialyl oligosaccharides.

We propose a three-dimensional (3-D) sugar-mapping technique for pyridylaminated (PA) neutral and sialyl oligosaccharides as a powerful structural characterization of N-linked oligosaccharides using only picomoles of samples. The new map consists of the elution data from 42 different sialyl oligosaccharides, 26 of which are mono-, 7 of which are di-, 7 of which are tri-, and 2 of which are tetra-sialylated oligosaccharides. The 20 standard sialyl oligosaccharides were released from human serum and calf fetuin by digestion with glycoamidase A. The other 22 standard sialyl oligosaccharides were obtained by subsequent digestion of the above 20 sialyl oligosaccharides with beta-galactosidase, beta-N-acetylhexosaminidase, alpha-fucosidase, and alpha 2-->3 specific sialidase. The present 3-D mapping method involves the following four steps: First, a neutral and sialyl PA-oligosaccharide mixture is separated by HPLC on the diethylaminoethyl (DEAE) column according to the sialic acid content, and the elution data are considered as one of the three dimensions (Z-axis). Then, neutral, mono-, di-, tri-, and tetra-sialyl oligosaccharides are individually separated on the octadecylsilyl (ODS)-silica (X-axis) and amide-silica (Y-axis) columns. The fourth step is to plot the coordinates on a two-dimensional (2-D) map. Thus, for each of the groups separated on the DEAE column, a 2-D map can be achieved. By repeating the whole process for each group of different sialylation, the layers of the 2-D map lined up on the Z-axis form a 3-D map.(ABSTRACT TRUNCATED AT 250 WORDS)

Two-dimensional elution map of GalNAc-containing N-linked oligosaccharides.

We have previously published a two-dimensional (2-D) mapping technique for N-linked oligosaccharides using pyridylaminated derivatives (PA-oligosaccharides) (N. Tomiya et al. Anal. Biochem. 171, 73-90, 1988). We now report an extension of this method to GalNAc-containing N-linked oligosaccharides. The new 2-D map was prepared from the elution data of 40 different GalNAc-containing oligosaccharides, 16 of which were obtained directly from human urinary kallidinogenase by digestion with glycopeptidase A. The other 24 oligosaccharides were derived by subsequent digestion of the 16 original oligosaccharides with beta-galactosidase or alpha-fucosidase. Each of the 40 oligosaccharide derivatives was separated by high-performance liquid chromatography using ODS-silica and amide-silica columns. The 2-D map constructed by plotting elution position of each oligosaccharide (expressed in terms of glucose units) can be useful as such in delineating the structure of an unknown oligosaccharide by direct placement of its elution positions in the 2-D map. Multiple regression analysis of the data as performed previously yielded parameters related to the contribution of each component monosaccharide unit to the elution profile. The best results were obtained when the GalNAc-containing PA-oligosaccharides were classified into an F-series (those containing Fuc alpha 6GlcNAc-PA) and a Z-series (all others), based on our previous classification method. These calculated values are useful in predicting oligosaccharide structure from known elution values as well as to predict elution volumn from a known structure. The structure of a minor GalNAc-containing oligosaccharide in human urinary kallidinogenase was elucidated using these newly calculated values.

Structural elucidation of a variety of GalNAc-containing N-linked oligosaccharides from human urinary kallidinogenase.

Fifteen different structures of terminal GalNAc-containing N-linked oligosaccharides from human urinary kallidinogenase have been identified. These N-linked oligosaccharides were mostly neutral, because sialic acid content was lower than 0.13 mol of sialic acid/mol of sugar chain, and sulfate was not detected. The oligosaccharides were released from pepsin-digested protein by glycoamidase A (from almond) digestion. The reducing ends of the oligosaccharide chains were aminated with a fluorescent reagent, 2-aminopyridine. The resulting mixture of pyridylamino derivatives of the oligosaccharides were separated by high performance liquid chromatography on an ODS-silica column, and 15 oligosaccharides were isolated. The structure of each oligosaccharide fraction was analyzed by two-dimensional sugar mapping, component sugar analysis, high resolution proton nuclear magnetic resonance and methylation analysis. It was found that each N-linked oligosaccharide associated with human urinary kallidinogenase contains unsubstituted GalNAc residues at the nonreducing terminal. These 15 oligosaccharides include 5 biantennary, 7 triantennary, and 3 tetraantennary oligosaccharides.

Determination of monosaccharides and sugar alcohols in tissues from diabetic rats by high-performance liquid chromatography with pulsed amperometric detection.

A sensitive and simple high-performance liquid chromatographic method has been developed to determine the concentration of monosaccharides and sugar alcohols in animal tissues. Five neutral monosaccharides (D-glucose, D-galactose, D-mannose, D-fructose, and D-ribose) and three neutral sugar alcohols (myo-inositol, glycerol, and D-sorbitol) predominate in the renal cortices and sciatic nerves of rats. These monosaccharides and sugar alcohols were extracted with distilled water, purified by deproteinization with ethanol, a Sep-Pak C18 cartridge, and columns of Dowex 50W-X8 and Amberlite CG-400, then separated on Ca2+ and Pb2+ cation-exchange columns, eluted with deionized distilled water at 80 degrees C, and detected using integrated pulsed amperometry. About 10 pmol of each sugar was detectable with a signal-to-noise ratio of 10:1. D-Glucose, D-fructose, D-sorbitol, and D-mannose were higher in both the renal and sciatic tissues of diabetic rats than in those of normal animals. D-Ribose and glycerol were higher in the renal cortex of diabetic animals.

Calculated two-dimensional sugar map of pyridylaminated oligosaccharides: elucidation of the jack bean alpha-mannosidase digestion pathway of Man9GlcNAc2.

We have developed a two-dimensional (2-D) mapping of pyridylaminated oligosaccharides as an aid to structural determination of glycoprotein-derived oligosaccharides. Using the available data of reverse-phase HPLC of pyridylamino-oligosaccharides, this was further extended to parameterization of unit contribution by each sugar component, which allows the prediction of possible structures from the elution volume. We have extended this approach to the data obtained with amide-silica HPLC column to obtain a calculated 2-D mapping technique for the oligomannose-type oligosaccharides (M-series). In this method, the elution volumes of all possible pyridylamino-oligosaccharides up to the size of Glc1Man9GlcNAc2 (50 in total) are calculated from the established UC values to construct a 2-D map. To test the validity of the calculated 2-D map, the structures of intermediate PA-oligosaccharides generated during the alpha-mannosidase (jack bean) digestion of Man9GlcNAc2 (porcine thyroglobulin) were analyzed to establish the digestion pathway. The validity of this approach is substantiated by an independent deduction of the intermediate structures based on structural relationships and the coincidence of elution volumes. Our results agree well with the recently published digestion pathway of Man5GlcNAc2 by the same enzyme and that of Man9GlcNAc2 by lysosomal alpha-mannosidase.

Parameterization of contribution of sugar units to elution volumes in reverse-phase HPLC of 2-pyridylaminated oligosaccharides.

The reverse-phase high-performance liquid chromatography elution data, expressed in glucose units, of 2-pyridylaminated oligosaccharides (PA-oligosaccharides) originated from N-glycosides of glycoproteins have been analyzed with multiple regression to obtain parameters of contribution ascribable to each monosaccharide unit. For the best results, the known PA-oligosaccharides were classified into M-series (the "high mannose" type), X-series (those containing xylose), F-series (those containing L-Fuc alpha (1,6)GlcNAc-PA), and Z-series (all others). Within each series, a variable ("unit contribution") is assigned to every sugar component in the oligosaccharide, and the elution value of a given oligosaccharide was assumed to be the sum total of the unit contributions. The unit contribution obtained from such multiple regression calculations led to a set of elution values for oligosaccharides in each series, which showed very good agreement with the observed elution values. These unit contribution values are useful in predicting the elution value when the exact structure is known, and they also aid in predicting the structure from the known elution value.

Structural analyses of asparagine-linked oligosaccharides of porcine pancreatic kallikrein.

The structures of asparagine-linked oligosaccharides of porcine pancreatic beta-kallikrein are reported. Asparagine-linked neutral oligosaccharides were released by N-oligosaccharide glycopeptidase digestion, and the reducing ends of the oligosaccharides were derivatized with a fluorescent reagent, 2-aminopyridine. The mixture of pyridylamino oligosaccharides was separated by reverse-phase and amide-adsorption high-performance liquid chromatography. The pyridylamino oligosaccharides were separated into more than 50 kinds of oligosaccharides. The structures of 5 kinds of triantennary and 12 kinds of tetraantennary oligosaccharides were determined by the use of high-resolution proton nuclear magnetic resonance spectroscopy and methylation analysis. Furthermore, the structures of five kinds of oligomannose-type oligosaccharides were elucidated by a combination of exoglycosidase digestion and high-performance liquid chromatography. 1H NMR data for 14 out of the 17 kinds of N-acetyllactosamine-type oligosaccharides reported here have not previously been described in the literature. (1) It has been shown that fucose containing tri- and tetraantennary oligosaccharides is predominant in porcine pancreatic beta-kallikrein B. (2) It has also been shown that the heterogeneity of the structure in these types of oligosaccharides is derived from the variety of the positions of galactose residues linked to outer N-acetylglucosamine residues. (3) The distribution of oligosaccharides into two glycosylation sites, asparagine-95 and asparagine-239, of beta-kallikrein B was determined. It has been found that oligomannose-type oligosaccharides are exclusively present at asparagine-239, although N-acetyllactosamine-type oligosaccharides occur at both glycosylation sites.(ABSTRACT TRUNCATED AT 250 WORDS)

Analyses of N-linked oligosaccharides using a two-dimensional mapping technique.

We propose a two-dimensional sugar map method for the simple, reproducible, and sensitive analysis of the structures of N-linked oligosaccharides. The structure of an unknown oligosaccharide can be characterized from its position on the map. The data base for the sugar map is prepared by the use of 113 kinds of standard oligosaccharides, 58 of whose structures have been confirmed by 1H NMR spectroscopy. The present method involves six steps, (i) preparation of oligosaccharides from glycopeptides by N-oligosaccharide glycopeptidase (almond) digestion, (ii) derivatization of the reducing ends of oligosaccharides with a fluorescent reagent, 2-amino-pyridine, by using sodium cyanoborohydride, (iii) separation of oligosaccharide derivatives by high-performance liquid chromatography with an ODS-silica column, (iv) analysis of the size of each separated oligosaccharide on an amide-silica column, (v) plotting of the elution position of a sample on the two-dimensional sugar map obtained for the standard oligosaccharides, and (vi) structural analysis of the oligosaccharides by a combination of sequential exoglycosidase digestion and the steps (iii-v). The present method was applied to the identification of the structures of oligosaccharides in hen ovalbumin. It was found that two unusual oligosaccharides that have not yet been reported exist in ovalbumin.

Structural analysis of N-linked oligosaccharides by a combination of glycopeptidase, exoglycosidases, and high-performance liquid chromatography.

A simple, sensitive, and rapid method for the analysis of structures of N-linked carbohydrates is reported. The method involves four steps: preparation of carbohydrate chains from glycopeptides by N-oligosaccharide glycopeptidase digestion; derivatization of the reducing ends of carbohydrate chains with a fluorescent reagent, 2-aminopyridine, by using sodium cyanoborohydride; separation of oligosaccharide derivatives by reverse-phase high-performance liquid chromatography; and structural analysis of oligosaccharides by sequential exoglycosidase digestion. The elution positions of 50 standard oligosaccharide derivatives were determined by HPLC. The structure of an unknown oligosaccharide can be characterized by comparison of its elution position with those of the standard compounds. The method was applied to elucidate the structures of oligosaccharides in the myeloma IgG protein, Yot.

Modification of acyl-plasmin-streptokinase complex with polyethylene glycol. Reduction of sensitivity to neutralizing antibody.

Acyl-plasmin-streptokinase complex has advantages as a 'site' directed fibrinolytic agent with the active site protected from the plasma protease inhibitors. But, in clinical use, the fibrinolytic potential of this acyl-enzyme complex is modified or abolished by the presence of streptokinase antibodies in the patients. Therefore, better therapeutic agents are required. In this work, chemical modification of the acyl-plasmin-streptokinase complex with polyethylene glycol was found to result in marked resistance to neutralization with streptokinase antibodies.

Hydrolysis of sugar nucleotides in chicken egg white in response to embryonic development.

The egg white of newly laid chicken egg was found to contain about 45 mumol of UDP-N-acetylgalactosamine 4-sulfate, 34 mumole of GDP-mannose, 6 mumol of UDP-N-acetylhexosamine, and 1 mumol of UDP-N-acetylgalactosamine 4,6-bissulfate per liter. There was no significant difference between infertile and fertile eggs in the initial levels of the sugar nucleotides. During incubation for 4 days, the nucleotide levels in infertile eggs showed little change while those in fertile eggs fell continuously until the complete disappearance of the nucleotides on the fourth day. Initial removal of the blastoderm from fertile eggs resulted in cessation of the reduction in nucleotide levels in the 2- to 4-day period after the operation. The decrease of UDP-N-acetylgalactosamine 4-sulfate was followed by an increase of 1-phospho-N-acetylgalactosamine 4-sulfate then N-acetylgalactosamine 4-sulfate in the egg white. When UDP-N-acetylgalactosamine 4-[35S]sulfate or GDP-[14C]mannose was injected into the egg white of a fertile egg, the main feature of the metabolism of the labeled compounds was the successive hydrolysis of their pyrophosphate and phosphate bonds, with the formation of sugar 1-phosphate and sugar. A significant activity of nucleotide pyrophosphatase was detected in the egg white in newly laid eggs (0-day egg). However, no such activity could be detected in egg-white specimens from 1-, 2-, and 3-day eggs. The results suggest that although the decrease of sugar nucleotides in the first day could be ascribed to the hydrolytic action of the enzyme originally present in the egg white, the decrease in the subsequent 3 days results from a more complex process in which the hydrolysis of the sugar nucleotides is related to the development of the embryo.