Isolation and characterization of deaminated neuraminic acid-rich glycoprotein (KDN-gp-OF) in the ovarian fluid of rainbow trout (Salmo gairdneri)

Identification and characterization of a deaminoneuraminic acid (Kdn)-specific aldolase from Sphingobacterium species

Sialic acid (Sia) is a group of acidic sugars with a 9-carbon backbone, and classified into 3 species based on the substituent group at C5 position: N-acetylneuraminic acid (Neu5Ac), N-glycolylneuraminic acid (Neu5Gc), and deaminoneuraminic acid (Kdn). In Escherichia coli, the sialate aldolase or N-acetylneuraminate aldolase (NanA) is known to catabolize these Sia species into pyruvate and the corresponding 6-carbon mannose derivatives. However, in bacteria, very little is known about the catabolism of Kdn, compared with Neu5Ac. In this study, we found a novel Kdn-specific aldolase (Kdn-aldolase), which can exclusively degrade Kdn, but not Neu5Ac or Neu5Gc, from Sphingobacterium sp., which was previously isolated from a Kdn-assimilating bacterium. Kdn-aldolase had the optimal pH and temperature at 7.0-8.0 and 50 °C, respectively. It also had the synthetic activity of Kdn from pyruvate and mannose. Site-specific mutagenesis revealed that N50 residue was important for the Kdn-specific reaction. Existence of the Kdn-aldolase suggests that Kdn-specific metabolism may play a specialized role in some bacteria.

The Aspergillus fumigatus Sialidase (Kdnase) Contributes to Cell Wall Integrity and Virulence in Amphotericin B-Treated Mice

Aspergillus fumigatus is a filamentous fungus that can cause a life-threatening invasive pulmonary aspergillosis (IPA) in immunocompromised individuals. We previously characterized an exo-sialidase from A. fumigatus that prefers the sialic acid substrate, 2-keto-3-deoxy-D-glycero-D-galacto-nononic acid (Kdn); hence it is a Kdnase. Sialidases are known virulence factors in other pathogens; therefore, the goal of our study was to evaluate the importance of Kdnase in A. fumigatus. A kdnase knockout strain (Δkdnase) was unable to grow on medium containing Kdn and displayed reduced growth and abnormal morphology. Δkdnase was more sensitive than wild type to hyperosmotic conditions and the antifungal agent, amphotericin B. In contrast, Δkdnase had increased resistance to nikkomycin, Congo Red and Calcofluor White indicating activation of compensatory cell wall chitin deposition. Increased cell wall thickness and chitin content in Δkdnase were confirmed by electron and immunofluorescence microscopy. In a neutropenic mouse model of invasive aspergillosis, the Δkdnase strain had attenuated virulence and a significantly lower lung fungal burden but only in animals that received liposomal amphotericin B after spore exposure. Macrophage numbers were almost twofold higher in lung sections from mice that received the Δkdnase strain, possibly related to higher survival of macrophages that internalized the Δkdnase conidia. Thus, A. fumigatus Kdnase is important for fungal cell wall integrity and virulence, and because Kdnase is not present in the host, it may represent a potential target for the development of novel antifungal agents.

Extensive enrichment of N-glycolylneuraminic acid in extracellular sialoglycoproteins abundantly synthesized and secreted by human cancer cells

N-Glycolylneuraminic acid (Neu5Gc) is the second most populous sialic acid (Sia). The only known biosynthetic pathway of Neu5Gc is the hydroxylation of cytidine-5'-monophosphate-N-acetylneuraminic acid (CMP-Neu5Ac), catalyzed by CMP-Neu5Ac hydroxylase (CMAH). Neu5Gc is abundantly found in mammals except for human, in which CMAH is inactivated due to mutation in the CMAH gene. Evidence has accumulated to show occurrence of Neu5Gc-containing glycoconjugates in sera of cancer patients, human cancerous tissues and cultured human cell lines. Recently, occurrence of natural antibodies against Neu5Gc was shown in healthy humans and is a serious problem for clinical xenotransplantation and stem cell therapies. Studying human occurrence of Neu5Gc is of importance and interest in a broad area of medical sciences. In this study, using a fluorometric high performance liquid chromatography method, we performed quantitative analyses of Sias both inside and in the external environment of the cell and found that (i) incorporation of Neu5Gc was most prominent in soluble glycoproteins found both in the extracellular space and inside the cell as the major Sia compounds. (ii) Of the total Neu5Gc in the Sia compounds that the cells synthesized, 90% was found in the secreted sialoglycoproteins, whereas for Neu5Ac, 70% was found in the secreted sialoglycoproteins. (iii) The Neu5Gc ratio was higher in the secreted sialoglycoproteins (as high as 40% of total Sias) than in intracellular sialoglycoproteins. (iv) The majority of the secreted sialoglycoproteins was anchored on the culture dishes and solubilized by brief trypsin treatment. Based on these findings, a new idea on the mechanism of accumulation of Neu5Gc in cancer cells was proposed.

A 1H STD NMR spectroscopic investigation of sialylnucleoside mimetics as probes of CMP-Kdn synthetase

CMP-Kdn synthetase catalyses the reaction of sialic acids (Sia) and CTP to the corresponding activated sugar nucleotide CMP-Sia and pyrophosphate PP( i ). Saturation Transfer Difference (STD) NMR spectroscopy has been employed to investigate the sub-structural requirements of the enzyme's binding domain. Sialylnucleoside mimetics, where the sialic acid moiety has been replaced by a carboxyl group and a hydrophobic moiety, have been used in NMR experiments, to probe the tolerance of the CMP-Kdn synthetase to such replacements. From our data it would appear that unlike another sialylnucleotide-recognising protein, the CMP-Neu5Ac transport protein, either a phosphate group or other functional groups on the sialic acid framework may play important roles in recognition by the synthetase.

KDN (Deaminated neuraminic acid): Dreamful past and exciting future of the newest member of the sialic acid family

KDN is an abbreviation for 2-keto-3-deoxy-D-glycero-D-galacto-nononic acid, and its natural occurrence was revealed in 1986 by a research group including the present authors. Since sialic acid was used as a synonym for N-acylneuraminic acid at that time, there was an argument if this deaminated neuraminic acid belongs to the family of sialic acids. In this review, we describe the 20 years history of studies on KDN (KDNology), through which KDN has established its position as a distinct member of the sialic acid family. These studies have clarified that: (1) KDN occurs widely among vertebrates and bacteria similar to the occurrence of the more common sialic acid, N-acetylneuraminic acid (Neu5Ac), but its abundant occurrence in animals is limited to lower vertebrates. (2) KDN is found in almost all types of glycoconjugates, including glycolipids, glycoproteins and capsular polysaccharides. (3) KDN residues are linked to almost all glycan structures in place of Neu5Ac. All linkage types known for Neu5Ac; alpha2,3-, alpha2,4-, alpha2,6-, and alpha2,8- are also found for KDN. (4) KDN is biosynthesized de novo using mannose as a precursor sugar, which is activated to CMP-KDN and transferred to acceptor sugar residues. These reactions are catalyzed by enzymes, some of which preferably recognize KDN, but many others prefer Neu5Ac to KDN. In addition to these basic findings, elevated expression of KDN was found in fetal human red blood cells compared with adult red blood cells, and ovarian tumor tissues compared with normal controls. KDNase, an enzyme which specifically cleaves KDN-linkages, was discovered in a bacterium and monoclonal antibodies that specifically recognize KDN residues in KDNalpha2,3-Gal- and KDNalpha2,8-KDN-linkages have been developed. These have been used for identification of KDN-containing molecules. Based on past basic studies and variety of findings, future perspective of KDNology is presented.

Probing a CMP-Kdn synthetase by 1H, 31P, and STD NMR spectroscopy

CMP-Kdn synthetase catalyses the reaction of sialic acids (Sia) and cytidine-5'-triphosphate (CTP) to the corresponding activated sugar nucleotide CMP-Sia and pyrophosphate PP(i). STD NMR experiments of a recombinant nucleotide cytidine-5'-monophosphate-3-deoxy-d-glycero-d-galacto-nonulosonic acid synthetase (CMP-Kdn synthetase) were performed to map the binding epitope of the substrate CTP and the product CMP-Neu5Ac. The STD NMR analysis clearly shows that the anomeric proton of the ribose moiety of both investigated compounds is in close proximity to the protein surface and is likely to play a key role in the binding process. The relative rates of the enzyme reaction, derived from (1)H NMR signal integrals, show that Kdn is activated at a rate 2.5 and 3.1 faster than Neu5Ac and Neu5Gc, respectively. Furthermore, proton-decoupled (31)P NMR spectroscopy was successfully used to follow the enzyme reaction and clearly confirmed the appearance of CMP-Sia and the inorganic pyrophosphate by-product.

A unique sialidase that cleaves the Neu5Gcalpha2-->5-O(glycolyl)Neu5Gc linkage: comparison of its specificity with that of three microbial sialidases toward four sialic acid dimers

We found that the hepatopancreas of oyster, Crassostrea virginica, contained a sialidase capable of releasing Neu5Gc from the novel polysialic acid chain (-->5-O(glycolyl)Neu5Gcalpha2-->)n more efficiently than from the conventional type of polysialic acid chains, (-->8Neu5Acalpha2-->)n, or (-->8Neu5Gcalpha2-->)n. We have partially purified this novel sialidase and compared its reactivity with that of microbial sialidases using four different sialic acid dimers, Neu5Gcalpha2-->5-O(glycolyl)Neu5Gc (Gg2), Neu5Acalpha2-->8Neu5Ac (A2), Neu5Gcalpha2-->8Neu5Gc (G2), and KDNalpha2-->8KDN (K2) as substrates. Hydrolysis was monitored by high performance anion-exchange chromatography with a CarboPac PA-100 column and pulsed amperometric detection, the method by which we can accurately quantitate both the substrate (sialiac acid dimers) and the product (sialic acid monomers). The oyster sialidase effectively hydrolyzed Gg2 and K2, whereas A2 and G2 were poor substrates. Neu5Ac2en but not KDN2en effectively inhibited the hydrolysis of Gg2 by the oyster sialidase. Likewise, the hydrolysis of K2 by the oyster sialidase was inhibited by a cognate inhibitor, KDN2en, but not by Neu5Ac2en. Using the new analytical method we found that Gg2 was hydrolyzed less efficiently than A2 but much more readily than G2 by Arthrobacter ureafaciens sialidase. This result was at variance with the previous report using the thiobarbituric acid method to detect the released free sialic acid [Kitazume, S., et al. (1994) Biochem. Biophys. Res. Commun. 205, 893-898]. In agreement with previous results, Gg2 was a poor substrate for Clostridium perfringens sialidase, while K2 was refractory to all microbial sialidases tested. Thus, the oyster sialidase is novel and distinct from microbial sialidases with regards to glycon- and linkage-specificity. This finding adds an example of the presence of diverse sialidases, in line with the diverse sialic acids and sialic acid linkages that exist in nature. The new sialidase should become useful for both structural and functional studies of sialoglycoconjugates.

Kdn-Containing Glycoprotein from Loach Skin Mucus

It has been widely recognized that the mucus coat of fish plays a variety of important physical, chemical, and physiological functions. One of the major constituents of the mucus coat is mucus glycoprotein. We found that sialic acids in the skin mucus of the loach, Misgurnus anguillicaudatus, consisted predominantly of KDN. Subsequently, we isolated KDN-containing glycoprotein from loach skin mucus and characterized its chemical nature and structure. Loach mucus glycoprotein was purified from the Tris-HCl buffer extract of loach skin mucus by DEAE-cellulose chromatography, Nuclease P1 treatment, and Sepharose CL-6B gel filtration. The purified mucus glycoprotein was found to contain 38.5 KDN, 0.5% NeuAc, 25.0% GalNAc, 3.5% Gal, 0.5% GlcNAc and 28% amino acids. Exhaustive Actinase digestion of the glycoprotein yielded a glycopeptide with a higher sugar content and higher Thr and Ser contents. The molecular size of this glycopeptide was approximately 1/12 of the intact glycoprotein. These results suggest that approximately 11 highly glycosylated polypeptide units are linked in tandem through nonglycosylated peptides to form the glycoporotein molecule. The oligosaccharide alditols liberated from the loach mucus glycoprotein by alkaline borohydride treatment were separated by Sephadex G-25 gel filtration and HPLC. The purified sugar chains were analyzed b --> 6GalNAc-ol, KDNalpha2 --> 3(GalNAcbeta1 --> 14)GalNAc-ol, KDNalpha2 --> 6(GalNAcalpha1 --> 3)GalNAc-ol, KDNalpha2 --> 6(Gal3alpha1--> 3)GalNAc-ol, and NeuAcalpha2 --> 6Gal NAc-ol. It is estimated that one loach mucus glycoprotein molecule contains more than 500 KDN-containing sugar chains that are linked to Thr and Ser residues of the protein core through GalNAc.

Biosynthesis of KDN (2-keto-3-deoxy-D-glycero-D-galacto-nononic acid). Identification and characterization of a KDN-9-phosphate synthetase activity from trout testis

Although the deaminoneuraminic acid or KDN glycotope (2-keto-3-deoxy-D-glycero-D-galacto-nononic acid) is expressed in glycoconjugates that range in evolutionary diversity from bacteria to man, there is little information as to how this novel sugar is synthesized. Accordingly, biosynthetic studies were initiated in trout testis, an organ rich in KDN, to determine how this sialic acid is formed. These studies have shown that the pathway consists of the following three sequential reactions: 1) Man + ATP --> Man-6-P + ADP; 2) Man-6-P + PEP --> KDN-9-P + P(i); 3) KDN-9-P --> KDN + P(i). Reaction 1, catalyzed by a hexokinase, is the 6-O-phosphorylation of mannose to form D-mannose 6-phosphate (Man-6-P). Reaction 2, catalyzed by KDN-9-phosphate (KDN-9-P) synthetase, condenses Man-6-P and phosphoenolpyruvate (PEP) to form KDN-9-P. Reaction 3, catalyzed by a phosphatase, is the dephosphorylation of KDN-9-P to yield free KDN. It is not known if a kinase specific for Man (Reaction 1) and a phosphatase specific for KDN-9-P (Reaction 3) may exist in tissues actively synthesizing KDN. In this study, the KDN-9-P synthetase, an enzyme that has not been previously described, was identified as at least one key enzyme that is specific for the KDN biosynthetic pathway. This enzyme was purified 50-fold from rainbow trout testis and characterized. The molecular weight of the enzyme was estimated to be about 80,000, and activity was maximum at neutral pH in the presence of Mn(2+). N-Acetylneuraminic acid 9-phosphate (Neu5Ac-9-P) synthetase, which catalyzes the condensation of N-acetyl-D-mannosamine 6-phosphate and phosphoenol-pyruvate to produce Neu5Ac-9-P, was co-purified with the KDN-9-P synthetase. Substrate competition experiments revealed, however, that syntheses of KDN-9-P and Neu5Ac-9-P were catalyzed by two separate synthetase activities. The significance of these studies takes on added importance with the recent discovery that the level of free KDN is elevated in human fetal cord but not matched adult red blood cells and in ovarian cancer cells (Inoue, S., Lin, S-L., Chang, T., Wu, S-H., Yao, C-W., Chu, T-Y., Troy, F. A., II, and Inoue, Y. (1998) J. Biol. Chem. 273, 27199-27204). This unexpected finding emphasizes the need to understand more fully the role that free KDN and KDN-glycoconjugates may play in normal hematopoiesis and malignancy.

Induction of KDNase Sm, a deaminoneuraminic acid (KDN) residue-specific sialidase from Sphingobacterium multivorum, using synthetic KDN-glycosides

Various aryl and alkyl alpha-glycosides of KDN were synthesized and tested as substrates for their susceptibility to a deaminoneuraminic acid (KDN)-specific sialidase from Sphingobacterium multivorum, designated KDNase Sm. The synthetic KDN-glycosides were all hydrolyzed by the action of KDNase Sm. A hydroxyl group at C-5 position of KDN was required for the recognition by the enzyme, and was shown not to be replaced by an amino- or an acylamino group for the enzymatic recognition. These synthetic KDN-glycosides were also examined for their inducing activity of KDNase in S. multivorum and were shown to induce the KDNase activity effectively when the bacterium was cultured minimum salt medium containing both 0.1% glucose and 0.1% various KDN-glycosides. No KDNase activity was induced by the KDN-glycosides without 0.1% glucose. This is the first case of using synthetic KDN-glycosides as inducers of KDNase Sm.

High-performance capillary electrophoretic characterization of different types of oligo- and polysialic acid chains

We have carried out comparative structural analysis of novel oligo- and polysialic acid chains from diverse sources. Controlled acid hydrolysates of (a) colominic acid, alpha2-->8-linked homopolymer of N-acetylneuraminic acid (Neu5Ac), (b) alpha2-->8-linked oligo/polyNeu5Gc chains present in rainbow trout egg polysialoglycoprotein, and (c) alpha2-->8-linked oligomers of deaminoneuraminic acid (KDN) residues of KDN-rich glycoprotein derived from rainbow trout vitelline envelope were analyzed by high-performance capillary electrophoresis (HPCE). The results showed that three different types of alpha2-->8-linked oligosialic acids having same degree of polymerization can be separated by HPCE. A partial hydrolysate of colominic acid with mild acid was shown by CE to form intramolecular esters during the controlled hydrolysis and the subsequent workup procedure. In contrast, lactonization of (-->5-Oglycolyl-Neu5Gcalpha2-->)n, alpha2-->5-Oglycolyl-linked homopolymer of N-glycolylneuraminic acid (Neu5Gc) present in the egg jelly coat of sea urchin, did not take place as readily as in (-->8Neu5Acalpha2-->)n.

Identification of 2-keto-3-deoxy-D-glycero--galactonononic acid (KDN, deaminoneuraminic acid) residues in mammalian tissues and human lung carcinoma cells. Chemical evidence of the occurrence of KDN glycoconjugates in mammals

Since the discovery of KDN glycoprotein in 1986, the occurrence of KDN (= 2-keto-3-deoxy-D-glycero-D-galactonononic acid) glycan chains has been reported for different organisms ranging from bacteria to lower vertebrates, including amphibians and fish. Recently, the presence of alpha2-->8-linked oligo/polyKDN groups in mammalian tissues was shown by immunohistochemical and immunoblotting methods. In this communication we report the detection and quantitation of the KDN residues in glycoprotein and glycolipid fractions of rat tissues and human lung cancer cell lines by a highly sensitive fluorometric high-performance liquid chromatography (HPLC) method. We now provide unequivocal chemical proof of the occurrence of KDN in mammals by isolation of KDN from pig submaxillary gland and by structural assignment using chemical methods including fast atom bombardment-mass spectrometry, fluorescence-assisted HPLC analysis, gas-liquid chromatography, and 1H NMR spectroscopy.

Poly (alpha 2,8-deaminoneuraminic acid) is expressed in lung on a single 150-kDa glycoprotein and is an oncodevelopmental antigen

Homopolymers of alpha 2,8-linked N-acetylneuraminic acid [poly(alpha 2,8-Neu5Ac)] of the neural cell adhesion molecule NCAM have been shown to be temporally expressed during lung development and represent a marker for small cell lung carcinoma. We report the presence of a further polysialic acid in lung that consists of oligo/polymers of alpha 2,8-linked deaminoneuraminic acid residues [poly (alpha 2,8-KDN)], as detected with a monoclonal antibody in conjunction with a specific sialidase. Although the various cell types forming the bronchi, alveolar septs, and blood vessels were positive for poly (alpha 2,8-KDN) by immunohistochemistry, this polysialic acid was found on a single 150-kDa glycoprotein by immunoblot analysis. The poly(alpha 2,8-KDN)-bearing glycoprotein was not related to an NCAM protein based on immunochemical criteria. The expression of the poly (alpha 2,8-KDN) was developmentally regulated as evidenced by its gradual disappearance in the rat lung parenchyma commencing 1 week after birth. In adult lung the blood vessel endothelia and the smooth muscle fibers of both blood vessels and bronchi were positive but not the bronchial and alveolar epithelium. The poly (alpha 2,8-KDN)-bearing 150-kDa glycoprotein became reexpressed in various histological types of lung carcinomas and cell lines derived from them and represents a new oncodevelopmental antigen in lung.

Occurrence of poly(alpha2,8-deaminoneuraminic acid) in mammalian tissues: widespread and developmentally regulated but highly selective expression on glycoproteins

In tissues of higher organisms homopolymers of alpha2,8-linked N-acetylneuraminic acid can be found as a posttranslational modification on selected proteins. We report here the discovery of homopolymers of alpha2,8-linked deaminoneuraminic acid [poly(alpha2,8-KDN)] in various tissues derived from all three germ layers in vertebrates including mammals. The monoclonal antibody kdn8kdn in conjunction with a bacterial KDNase permitted the detection of poly(alpha2,8-KDN) by immunohistochemistry and immunoblotting. Further evidence for the existence of poly(alpha2,8-KDN) was obtained by gas/liquid chromatography. The poly(alpha2,8-KDN) glycan was detectable in all tissues studied with the exception of mucus-producing cells present in various organs, the extracellular matrix, and basement membranes. However, in certain organs such as muscle, kidney, lung, and brain its expression was developmentally regulated. Despite its widespread tissue distribution, the poly(alpha2,8-KDN) glycan was detected on a single 150-kDa glycoprotein except for a single >350-kDa glycoprotein in kidney, which makes it most distinctive among polysialic acids. The ubiquitous yet selective expression may be indicative of a general function of the poly(alpha2,8-KDN)-bearing glycoproteins.

Substrate specificity of rainbow trout testis CMP-3-deoxy-D-glycero-D-galacto-nonulosonic acid (CMP-Kdn) synthetase: kinetic studies of the reaction of natural and synthetic analogues of nonulosonic acid catalyzed by CMP-Kdn synthetase

In this report we present kinetic data of the activation reaction of several synthetic 3-deoxy-D-glycero-D-galacto-nonulosonic acid (Kdn) and N-acetylneuraminic acid (Neu5Ac) analogues catalyzed by the rainbow trout testis CMP-Kdn synthetase. This enzyme showed broad substrate specificity in terms of substitutions at C4 or C5 position of Kdn and Neu5Ac. In contrast, calf brain CMP-N-acylneuraminic acid synthetase had narrow substrate specificity, being active only on various N-acyl analogues of Neu5Ac and only slightly active on Kdn derivatives. Usefulness of the trout testis enzyme for synthesis of various CMP-sialate analogues, which could be donor substrates for sialyltransferases, was demonstrated.

Induction, localization, and purification of a novel sialidase, deaminoneuraminidase (KDNase), from Sphingobacterium multivorum

Recently, we reported the discovery of a new type of sialidase, KDNase, which specifically hydrolyzes the ketosidic linkages of 2-keto-3-deoxy-D-glycero-D-galacto-nononic acid (KDN), but not N-acylneuraminyl linkages. We now report that this enzyme, designated KDNase SM, is an inducible enzyme that is localized in the periplasm of Sphingobacterium multivorum. Growth of S. multivorum in the presence of KDN-containing oligosaccharide alditols, KDNalpha2-->3Galbeta1-->3GalNAc alpha1-->3[KDNalpha2--> (8KDN alpha2-->)n-->6]GalNAcol, as a sole carbon source induced KDNase SM activity 15 40-fold, compared with growth in the absence of inducer. KDN, Neu5Ac, or Neu5Ac oligomers were ineffective as inducers. The enzyme was released from the periplasm of induced cells by cold osmotic shock and purified 700-fold to homogeneity. The specific activity of the pure enzyme was 82,100 units/mg of protein. KDNase SM activity resided in a single polypeptide chain with an estimated molecular weight of approximately 47,500. Enzyme activity was maximal at near neutral pH. The availability of pure KDNase will now make it possible to study the structure and functional role of KDN-glycoconjugates and to determine the molecular mechanism whereby the enzyme can discriminate between KDN and N-acylneuraminic acid.

Characterization of the antigenic specificity of four different anti-(alpha 2-->8-linked polysialic acid) antibodies using lipid-conjugated oligo/polysialic acids

A rapid, sensitive, and facile method for screening and characterizing anti-polysialic acid (polySia) antibodies using lipid-conjugated oligo/polysialic acids (oligo/polySia) was developed, which is based on an enzyme-linked immunosorbent assay. Homooligo/polymers of alpha 2-->8-linked N-acetylneuraminic acid (Neu5Ac), N-glycoly-neuraminic acid, and 2-keto-3-deoxy-D-galacto-nononic acid (KDN) were conjugated with phosphatidylethanolamine dipalmitoyl (PE) by reductive amination to prepare neo-oligo/polysialoglycolipids (oligo/polySia-PE). Using this method, the anti-polySia equine antibody, H.46, bound to (-->8Neu5Ac alpha 2-->)n-PE, where n = 9 or more residues, a result in confirmation of previous binding studies using radiolabeled oligo/polyNeu5Ac. The antigenic specificity and sensitivity of two monoclonal anti-poly/oligoNeu5Ac antibodies (mAb.12E3 and mAb.5A5) and one anti-oligoKDN antibody (mAb.kdn8kdn), were also determined. mAb.12E3 could detect as little as 25 pg/well of oligo/polyNeu5Ac-PE, while 0.4 ng/well of oligo/polyNeu5Ac-PE to be detected. mAb.kdn8kdn detected as little as 12 ng/well of oligoKDN-PE. Using a series of oligo/polySia-PE with defined degrees of polymerization (DP), the minimum chain length for immunoreactivity of the anti-polySia antibodies was determined to be: DP 5 for mAb.12E3; DP 3 for mAb.5A5; DP 2 for mAb.kdn8kdn; and DP 8 for H.46. Thus, mAb.12E3 and mAb.5A5 recognize shorter oligomers of Neu5Ac than H.46, a finding that is of practical value for identifying shorter oligoSia chains in glycoconjugates. Because mAb.12E3 and mAb.5A5 also recognize extended polySia chains, these antibodies cannot be used, however, to differentiate between short and long chains of polySia when both are expressed on the same molecule.

Identification, characterization, and developmental expression of a novel alpha 2-->8-KDN-transferase which terminates elongation of alpha 2-->8-linked oligo-polysialic acid chain synthesis in trout egg polysialoglycoproteins

A novel glycosyltransferase which catalyses transfer of deaminated neuraminic acid, KDN (2-keto-3-deoxy-D-glycero-D-galacto-nononic acid) from CMP-KDN to the non-reducing termini of oligo-polysialyl chains of polysialoglycoprotein (PSGP), was discovered in the ovary of rainbow trout (Oncorhynchus mykiss). The KDN-transferase activity was optimal at neutral pH, and stimulated 2 to 2.5-fold by 2-5 mM Mg2+ or Mn2+. Expression of KDN-transferase was developmentally regulated in parallel with expression of the alpha 2-->8-polysialyltransferase, which catalyses synthesis of the oligo-polysialyl chains in PSGP. Incorporation of the KDN residues into the oligo-polysialyl chains prevented their further elongation, resulting in 'capping' of the oligo-polysialyl chains. This is the first example of a glycosyltransferase that catalyses termination of alpha 2-->8-polysialylation in glycoproteins.

Isolation, structural determination, and calcium-binding properties of the major glycoprotein present in Bufo japonicus japonicus egg jelly

Although the previous studies showed that the jelly coat is essential in anuran fertilization under natural conditions, identification and structural studies of the macromolecules that play functional roles have remained to be elucidated. In the present study we isolated acidic glycoproteins (JGP) from the solubilized egg jelly of Bufo japonicus japonicus, and showed that they were the major non-dialyzable macromolecular components of the jelly coat. JGP was a typical mucin-type glycoprotein, and it showed high degree of polydispersity in molecular masses ranging over 100-4000 kDa, but both amino acid and carbohydrate compositions were practically identical among fractions, suggesting that JGP was composed of a repeating glycoprotein unit. Four types of short O-glycan chains were isolated from JGP by reductive beta-elimination and their structures were determined as: Gal beta 1-->3[NeuAc alpha 2-->6]GalNAcol (= N-acetylgalactosaminitol), Fuc alpha 1-->2Gal beta 1-->3 [NeuAc alpha 2-->6]GalNAcol, Fuc alpha 1-->2Gal beta 1-->3[GlcNAc beta 1-->6]GalNAcol, and Fuc alpha 1-->2Gal beta 1-->3-GalNAcol. These carbohydrate units (about 80% of the mass of JGP) were linked to nearly all the serine and threonine residues which accounted for 55% of total amino acid residues. The Ca(2+)-binding property of JGP was studied by equilibrium dialysis. The high Ca(2+)-binding capacity of JGP was abolished by its desialylation of JGP and was highly dependent on the JGP concentration. When the low JGP concentrations as in the hydrated Bufo jelly were used, a 50% increment of both n (the number of binding sites) and Kd (the dissociation constant of JGP-Ca2+) values was observed. This property of JGP is suited to retaining Ca2+ and keeping its concentration at that just necessary for fertilizing sperm.

Monoclonal antibody specific for alpha 2-->8-linked oligo deaminated neuraminic acid (KDN) sequences in glycoproteins. Preparation and characterization of a monoclonal antibody and its application in immunohistochemistry

Two particular types of sialoglycoproteins have been detected in fish: polysialoglycoproteins containing alpha 2-->8-linked polysialic acid (-->8Neu5Gc alpha 2-->)n present in unfertilized Salmonidae fish eggs, and glycoproteins bearing oligo/polymers of deaminated neuraminic acids (KDN) found in the vitelline envelope of the eggs and ovarian fluid. We report the preparation and characterization of a monoclonal antibody specifically recognizing oligo/polymers of KDN sequences in glycoproteins and its application in immunohistochemistry. Fusion of spleen cells from a BALB/c mouse immunized with a KDN-rich glycoprotein (KDN-gp) containing (-->8KDN alpha 2-->)n-->6(KDN alpha 2-->3Gal beta 1-->3G alpha lNA-c alpha 1-->3) GalNAc alpha 1-->residues, with mouse myeloma cells yielded a hybrid cell line producing a monoclonal antibody that bound to KDN-gp, but not to KDN-gp depleted of KDN residues. The specificity of the monoclonal antibody, designated mAb.kdn8kdn, was determined by an enzyme-linked immunosorbent assay using KDN-gp samples that varied in KDN content. These antigens were prepared by the selective removal of KDN residues from the native KDN-gp. The mAb.kdn8kdn reacted most strongly with the intact KDN-gp and less strongly with KDN-gp samples containing decreased numbers of KDN residues.(ABSTRACT TRUNCATED AT 250 WORDS)

Polysialic acids

1. Polysialic acids are linear homopolymers of N-acetylneuraminic acid (Neu5Ac), N-glycolylneuraminic acid (Neu5Gc) and deaminated neuraminic acid (KDN) residues joined by alpha 2,8, alpha 2-9 or alpha 2,8/alpha 2,9 ketosidic linkages. 2. They occur in glycoproteins of embryonic neural membranes (playing a role of neural cell adhesion molecules), in non-neural tissues (postnatal kidney), tumours, (neuroectodermal tumours), fish eggs and in the capsule of certain bacteria such as Neisseria meningitidis group B. 3. These polymers are synthesized through reactions which involve (a) the synthesis of sialic acid; (b) its activation to a cytidine monophosphate sugar nucleotide and (c) the polymerization of the different residues by a polysialyl-transferase complex. 4. Polysialic acids are involved in organogenesis and in cell growth. In several tissues they act as oncodevelopmental antigens, and in bacteria are also virulent determinants.

1H-and 13C-n.m.r. spectroscopy of 2-oxo-3-deoxy-D-glycero-D- galactononulosonic acid-containing oligosaccharide-alditols bearing Lewis X, Lewis Y and A-Lewis Y determinants isolated from the jelly coat of Pleurodeles waltl eggs

Three acidic oligosaccharide-alditols carrying Lewis X, Lewis Y and A-Lewis Y determinants were isolated from the jelly coat of Pleurodeles waltl eggs. These compounds possess the following structures. Gal beta 1-4(Fuc alpha 1-3)GlcNAc beta 1-3[2-oxo-3-deoxy-D- glycero-D-galactononulosonic acid (KDN)alpha 2-6] GalNAc-ol; Fuc alpha 1-2Gal beta 1-4(Fuc alpha 1-3)GlcNAc beta 1-3(KDN alpha 2-6) GalNAc-ol and Fuc alpha 1-2(GalNAc alpha 1-3)Gal beta 1-4(Fuc alpha 1-3)GlcNAc beta 1-3(KDN alpha 2-6)GalNAc-ol. The complete 1H-n.m.r.-spectrum assignment for the three compounds and the 13C-n.m.r. analysis of the A-Lewis Y determinant-containing heptasaccharide are reported.

Analytical methods for identifying and quantitating deamidated sialic acid (2-keto-3-deoxy-D-glycero-D-galactonononic acid) and alpha 2----8-linked poly(oligo)nonulosonate residues in glycoconjugates

In 1986 we reported the natural occurrence of deaminated neuraminic acid (2-keto-3-deoxy-D-glycero-D-galactonononic acid, KDN) in fish egg glycoprotein. Subsequently, we have shown that many types of sialic acid as well as KDN occur in polymeric chains, poly(oligo)-Sia and poly(oligo)KDN in nature. In this study we demonstrate that the conventional colorimetric and gas-liquid chromatographic methods used in the analysis of sialic acid can be applied to analysis of these new nonulosonate and poly(oligo)nonulosonates. We report that the thiobarbituric acid reaction can be used to analyze both free and bound KDN, but gives lower extinction values when applied to poly(oligo)KDN without prior hydrolysis. Further, the published hydrolytic and/or methanolytic procedures are suitable to release the terminal sialic acid residues, but are not appropriate for quantitative release of the nonulosonic acids from poly(oligo)nonulosonates. A new gas-liquid chromatographic procedure for the identification-quantitation of nonulosonates in poly(oligo)meric forms is described.

Detection, isolation, and characterization of oligo/poly(sialic acid) and oligo/poly(deaminoneuraminic acid) units in glycoconjugates

We have evaluated methods for separation, preparation, and characterization of alpha-2----8-linked oligomers of sialic acids (Neu5Ac and Neu5Gc) and deaminated neuraminic acid (KDN; 2-keto-3-deoxy-D-glycero-D-galacto-nononic acid) recently found as a naturally occurring novel type of sialic acid analogue. (A) We examined preparative anion-exchange chromatography for fractionation and preparation of oligo(Neu5Ac), oligo(Neu5Gc), and oligo(KDN). (B) We also examined the TLC method for separation and differentiation of the partial acid hydrolysates of colominic acid, as well as polysialoglycoproteins (PSGP) and poly(KDN)-glycoproteins (KDN-gp) isolated from rainbow trout eggs, and for discrimination of lower oligomers of Neu5Ac, Neu5Gc, and KDN. (C) We developed the high-performance adsorption-partition chromatographic method for (a) separation of monomers and oligomers of three nonulosonates according to the difference in substituents at C-5 and the presence or absence of 9-O-acetyl groups in oligo(KDN) and (b) separation of three homologous series of lower oligomers according to the degree of polymerization. (D) We examined and compared high-performance anion-exchange chromatographic separation of 3H-labeled oligo(Neu5Ac), oligo(Neu5Gc), and oligo(KDN) alditols by using Mono-Q HR 5/5 resin. (E) We examined a method of selective and quantitative microprecipitation for separation and purification of oligomers and polymers of Neu5Ac by treating them with cetylpyridinium chloride. We also used PSGP and KDN-gp to test both the sensitivity and the selectivity of this method.