Publisher Summary This chapter discusses the chemistry, metabolism, and biological functions of sialic acids. Interest in the sialic acids has rapidly increased in recent years, especially because of the reorganization of their involvement in the regulation of a great variety of biological phenomena. The occurrence of sialic acids in plants has never unequivocally been established, although some positive reports exist. The acylneuraminic acids can be released from their glycosidic linkages either by dilute (aqueous or methanolic) acids or sialidases. The unequivocal determination of sialic acids occurring in low concentrations in many biological materials is rather difficult, and this explains the many errors that have been made in this field. The biosynthesis of N-acetylneuraminic acid (Neu5Ac) is briefly reported in this chapter and more attention is given to the enzyme reactions modifying this compound. Little information is available about the role of the modifications of sialic acid resulting in a species- and tissue-specific distribution of different N,O-acylated and O-methylated sialic acids.

Chemistry, Metabolism, and Biological Functions of Sialic Acids

The elderberry (Sambucus nigra L.) bark lectin recognizes the Neu5Ac(alpha 2-6)Gal/GalNAc sequence.

Publisher Summary This chapter discusses structure and procedure for isolation, and analysis of gangliosides. Most widely used procedure for isolation is based on the ability of gangliosides to partition from the chloroform-methanol phase in which they are extracted into the upper water-enriched phase, leaving behind the bulk of other lipids. There is also a procedure based on DEAE-Sephadex. This method employs an anion-exchange resin to separate gangliosides first, along with other acidic lipids, from the much larger quantity of neutral and zwitterionic lipids that do not bind to the resin. The subsequent steps of base treatment, dialysis, and silicic acid chromatography are designed to remove the other acidic lipids and any acidic low molecular weight contaminants that accompany the gangliosides. Other types of chromatography is used for resolution. Quantitative estimation of gangliosides is usually based on the sialic acid moiety. Various procedures are outlined, along with a gas-liquid chromatographic method that has the attributes, of specificity and sensitivity.

Gangliosides: structure, isolation, and analysis.

2 – Isolation, Physicochemical Characterization, and Carbohydrate-Binding Specificity of Lectins

Historical background It is now more than 50 years since N-acetyl-neuraminic acid was first discovered and subsequently characterized by several groups (reviewed in Roseman, 1970; Gottschalk, 1972; Rosenberg and Schengrund, 1976; Schauer, 1982; Faillard, 1989). Relatively soon after its discovery, it became apparent that this molecule was actually the major member of a family of compounds related to neuraminic acid that were christened the 'sialic acids' (Blix etai, 1957). Early studies paid close attention to the different types of sialic acids and the interrelationships between them. However, interest in these complexities subsequently waned and unpublished 'folk-lore' had it that modified sialic acids were species-specific curiosities found only in a few tissues, such as erythrocytes and submaxillary glands. In fact, many investigators in the 1970s and 80s used the terms W-acetyl-neuraminic acid' and 'sialic acid' synonymously. Thus, for example, when structural or biological changes were noted following treatments with a sialidase (neuraminidase), it was often assumed that the sialic acid released was A^-acetyl-neuraminic acid. It is now clear tjiat the different types of sialic acids are much more widely distributed than previously thought. This review attempts to briefly summarize current knowledge concerning the occurrence, structure, biochemistry and biological significance of this diversity in the sialic acids. Particular attention is given to the two most common and better studied modifications: the addition of 0-acetyl esters to the hydroxyl groups at the 4-, 7-, 8- and 9-positions, and the conversion of the 7V-acetyl group to an /V-glycolyl group. Given the breadth of the review, the bibliography is only representative, and tends to emphasize more recent studies.

/pdf/diversity-in-the-sialic-acids-2cnnxmsk42.pdf

Diversity in the sialic acids

Neuraminic acid-specific modification and tritium labelling of gangliosides.

Ganglioside fractions were isolated from brains of man, cow, horse, pig, sheep, cat, rabbit, rat, chicken and codfish. The acylneuraminic acid residues, liberated from these gangliosides by treatment with dilute aqueous acid or neuraminidase, were analysed by the thin-layer chromatography and combined gas-liquid chromatography/mass spectrometry. Small amounts (up to 20%) of 9-O-acetyl-N-acetylneuraminic acid, and in bovine and porcine brain gangliosides also traces of N-glycoloylneuraminic acid, were found in addition to N-acetylneuraminic acid.

/pdf/demonstration-of-9-o-acetyl-n-acetylneuraminic-acid-in-brain-50387aqnth.pdf

Demonstration of 9-O-acetyl-N-acetylneuraminic acid in brain gangliosides from various vertebrates including man

Lipid vesicles containing derivatives of GM3 ganglioside (II3-N-acetylneuraminosyllactosyl ceramide) were used to study the specificities of two lectins (limulin and wheat germ agglutinin) towards N-acetyl neuraminic acid and N-glycoloylneuraminic acid and some of their natural and chemically modified derivatives.



The extent of the lectin binding to the gangliosides was related to the aggregation process of the lipid vesicles which was monitored as an absorbance increase.



Limulin binds specifically to lipid vesicles containing N-glycoloyl derivatives of GM3. The hydroxyl group at C-4 and the carboxyl group of neuraminic acid have to be free for the binding to limulin. The side chain of neuraminic acid is not involved in the binding site of limulin.



Wheat germ agglutinin binds to GM3 ganglioside only when the hydrophilic tail of the neuraminic group is cut off (C7 analogues). The acetamido group but not the carboxyl group is involved in the binding to wheat germ agglutinin. The wheat-germ-agglutinin-induced aggregation of vesicles containing derivatives of GM3-ganglioside is dependent on the pH, on the ionic strength and on the presence of Ca2+ ions. The dependence on ionic strength and Ca2+ is a consequence of the electrostatic repulsion of the vesicles.



The wheat-germ-agglutinin-induced aggregation process of vesicles containing any suitable GM3-ganglioside derivative was reversed by the addition of N-acetylglucosamine showing that the N-acetylneuraminic acid derivatives bind to the N-acetylglucosamine binding site.

https://febs.onlinelibrary.wiley.com/doi/pdf/10.1111/j.1432-1033.1981.tb06164.x

Specificities of limulin and wheat-germ agglutinin towards some derivatives of GM3 gangliosides.

Gangliosides have been found to contain up to five sialic acid moieties bound to galactose residues in α, 2->3 linkages either at the end of the oligosaccharide chain or within the chain, and may form di- and trisialyl groups with α,2->8 linkages (1,2). N-Acetylneuraminic acid (NeuAc) and N-glycolylneuraminic acid (NeuG1) have been identified as the commonly occurring sialic acids in gangliosides, while the O-acetylated sialic acids occur less frequently. The 9-O-acetyl-N-acetylneuraminic acid has been found in gangliosides from a variety of vertebrates including man (3), and 4-O-acetyl-N-glycolylneuraminic acid (4-OAc-NeuGl) has been isolated from horse erythrocyte hematoside (4).

Michael Sander

Papers

Neuraminic acid-specific modification and tritium labelling of gangliosides.

Demonstration of 9-O-acetyl-N-acetylneuraminic acid in brain gangliosides from various vertebrates including man

Specificities of limulin and wheat-germ agglutinin towards some derivatives of GM3 gangliosides.

“Neuraminidase-Resistant” Sialic Acid Residues of Gangliosides

Demonstration of O-Acetyl Groups in Ganglioside-Bound Sialic Acids and Their Effect on the Action of Bacterial and Mammalian Neuraminidases