Nanomedical Relevance of the Intermolecular Interaction Dynamics-Examples from Lysozymes and Insulins

Insulin and lysozyme share the common features of being prone to aggregate and having biomedical importance. Encapsulating lysozyme and insulin in micellar nanoparticles probably would prevent aggregation and facilitate oral drug delivery. Despite the vivid structural knowledge of lysozyme and insulin, the environment-dependent oligomerization (dimer, trimer, and multimer) and associated structural dynamics remain elusive. The knowledge of the intra- and intermolecular interaction profiles has cardinal importance for the design of encapsulation protocols. We have employed various biophysical methods such as NMR spectroscopy, X-ray crystallography, Thioflavin T fluorescence, and atomic force microscopy in conjugation with molecular modeling to improve the understanding of interaction dynamics during homo-oligomerization of lysozyme (human and hen egg) and insulin (porcine, human, and glargine). The results obtained depict the atomistic intra- and intermolecular interaction details of the homo-oligomerization and confirm the propensity to form fibrils. Taken together, the data accumulated and knowledge gained will further facilitate nanoparticle design and production with insulin or lysozyme-related protein encapsulation.

Exploration of the Sialic Acid World

Sialic acids are cytoprotectors, mainly localized on the surface of cell membranes with multiple and outstanding cell biological functions. The history of their structural analysis, occurrence, and functions is fascinating and described in this review. Reports from different researchers on apparently similar substances from a variety of biological materials led to the identification of a 9-carbon monosaccharide, which in 1957 was designated "sialic acid." The most frequently occurring member of the sialic acid family is N-acetylneuraminic acid, followed by N-glycolylneuraminic acid and O-acetylated derivatives, and up to now over about 80 neuraminic acid derivatives have been described. They appeared first in the animal kingdom, ranging from echinoderms up to higher animals, in many microorganisms, and are also expressed in insects, but are absent in higher plants. Sialic acids are masks and ligands and play as such dual roles in biology. Their involvement in immunology and tumor biology, as well as in hereditary diseases, cannot be underestimated. N-Glycolylneuraminic acid is very special, as this sugar cannot be expressed by humans, but is a xenoantigen with pathogenetic potential. Sialidases (neuraminidases), which liberate sialic acids from cellular compounds, had been known from very early on from studies with influenza viruses. Sialyltransferases, which are responsible for the sialylation of glycans and elongation of polysialic acids, are studied because of their significance in development and, for instance, in cancer. As more information about the functions in health and disease is acquired, the use of sialic acids in the treatment of diseases is also envisaged.

Structure-Function Relationships of Antimicrobial Peptides and Proteins with Respect to Contact Molecules on Pathogen Surfaces

The Antimicrobial peptides (e.g. defensins, hevein-like molecules and food-protecting peptides like nisin) are able to interact specifically with contact structures on pathogen surfaces. Besides protein receptors, important recognition points for such contacts are provided by pathogen glycan chains or surface lipids. Therefore, structural data concerning surface exposed glycans and lipids are of the highest clinical interest since these recognition functions play a key role when optimising anti-infection therapies. Approaches in nanomedicine and nanopharmacology in which various biophysical techniques such as NMR (Nuclear Magnetic Resonance), AFM (Atomic Force Microscopy), SPR (Surface Plasmon Resonance) and X-ray crystallography can be combined with biochemical and cell-biological methods will lead to improved antimicrobial peptides by this rational drug design approach. Such a strategy is extremely well suited to support clinical studies focussing on an effective fight against multiresistant pathogens. The data sets which are described here can be considered as universal for the design of various antimicrobial drugs against certain pathogens (bacteria, viruses and fungi) which cause severe diseases in humans and animals. Furthermore, these insights are also helpful for progressing developments in the field of food conservation and food preservation. A detailed analysis of the structure-function relationships between antimicrobial peptides and contact molecules on pathogen surfaces at the sub-molecular level will lead to a higher degree of specificity of antimicrobial peptides.

Molecular Basis of the Receptor Interactions of Polysialic Acid (polySia), polySia Mimetics, and Sulfated Polysaccharides

Polysialic acid (polySia) and polySia glycomimetic molecules support nerve cell regeneration, differentiation, and neuronal plasticity. With a combination of biophysical and biochemical methods, as well as data mining and molecular modeling techniques, it is possible to correlate specific ligand-receptor interactions with biochemical processes and in vivo studies that focus on the potential therapeutic impact of polySia, polySia glycomimetics, and sulfated polysaccharides in neuronal diseases. With this strategy, the receptor interactions of polySia and polySia mimetics can be understood on a submolecular level. As the HNK-1 glycan also enhances neuronal functions, we tested whether similar sulfated oligo- and polysaccharides from seaweed could be suitable, in addition to polySia, for finding potential new routes into patient care focusing on an improved cure for various neuronal diseases. The knowledge obtained here on the structural interplay between polySia or sulfated polysaccharides and their receptors can be exploited to develop new drugs and application routes for the treatment of neurological diseases and dysfunctions.

Sialic acid metabolic engineering: a potential strategy for the neuroblastoma therapy

Background

Sialic acids (Sia) represent negative-charged terminal sugars on most glycoproteins and glycolipids on the cell surface of vertebrates. Aberrant expression of tumor associated sialylated carbohydrate epitopes significantly increases during onset of cancer. Since Sia contribute towards cell migration ( =  metastasis) and to chemo- and radiation resistance. Modulation of cellular Sia concentration and composition poses a challenge especially for neuroblastoma therapy, due to the high heterogeneity and therapeutic resistance of these cells. Here we propose that Metabolic Sia Engineering (MSE) is an effective strategy to reduce neuroblastoma progression and metastasis.

Methods

Human neuroblastoma SH-SY5Y cells were treated with synthetic Sia precursors N-propanoyl mannosamine (ManNProp) or N-pentanoyl mannosamine (ManNPent). Total and Polysialic acids (PolySia) were investigated by high performance liquid chromatography. Cell surface polySia were examined by flow-cytometry. Sia precursors treated cells were examined for the migration, invasion and sensitivity towards anticancer drugs and radiation treatment.

Results

Treatment of SH-SY5Y cells with ManNProp or ManNPent (referred as MSE) reduced their cell surface sialylation significantly. We found complete absence of polysialylation after treatment of SH-SY5Y cells with ManNPent. Loss of polysialylation results in a reduction of migration and invasion ability of these cells. Furthermore, radiation of Sia-engineered cells completely abolished their migration. In addition, MSE increases the cytotoxicity of anti-cancer drugs, such as 5-fluorouracil or cisplatin.

Conclusions

Metabolic Sia Engineering (MSE) of neuroblastoma cells using modified Sia precursors reduces their sialylation, metastatic potential and increases their sensitivity towards radiation or chemotherapeutics. Therefore, MSE may serve as an effective method to treat neuroblastoma.

New insights on the sialidase protein family revealed by a phylogenetic analysis in metazoa

Sialidases are glycohydrolytic enzymes present from virus to mammals that remove sialic acid from oligosaccharide chains. Four different sialidase forms are known in vertebrates: the lysosomal NEU1, the cytosolic NEU2 and the membrane-associated NEU3 and NEU4. These enzymes modulate the cell sialic acid content and are involved in several cellular processes and pathological conditions. Molecular defects in NEU1 are responsible for sialidosis, an inherited disease characterized by lysosomal storage disorder and neurodegeneration. The studies on the biology of sialic acids and sialyltransferases, the anabolic counterparts of sialidases, have revealed a complex picture with more than 50 sialic acid variants selectively present in the different branches of the tree of life. The gain/loss of specific sialoconjugates have been proposed as key events in the evolution of deuterostomes and Homo sapiens, as well as in the host-pathogen interactions. To date, less attention has been paid to the evolution of sialidases. Thus we have conducted a survey on the state of the sialidase family in metazoan. Using an in silico approach, we identified and characterized sialidase orthologs from 21 different organisms distributed among the evolutionary tree: Metazoa relative (Monosiga brevicollis), early Deuterostomia, precursor of Chordata and Vertebrata (teleost fishes, amphibians, reptiles, avians and early and recent mammals). We were able to reconstruct the evolution of the sialidase protein family from the ancestral sialidase NEU1 and identify a new form of the enzyme, NEU5, representing an intermediate step in the evolution leading to the modern NEU3, NEU4 and NEU2. Our study provides new insights on the mechanisms that shaped the substrate specificity and other peculiar properties of the modern mammalian sialidases. Moreover, we further confirm findings on the catalytic residues and identified enzyme loop portions that behave as rapidly diverging regions and may be involved in the evolution of specific properties of sialidases.

The human Cas1 protein: a sialic acid-specific O-acetyltransferase?

Sialic acids are important sugars at the reducing end of glycoproteins and glycolipids. They are among many other functions involved in cell-cell interactions, host-pathogen recognition and the regulation of serum half-life of glycoproteins. An important modification of sialic acids is O-acetylation, which can alter or mask the biological properties of the parent sialic acid molecule. The nature of mammalian sialate-O-acetyltransferases (EC 2.3.1.45) involved in their biosynthesis is still unknown. We have identified the human CasD1 (capsule structure1 domain containing 1) gene as a candidate to encode the elusive enzyme. The human CasD1 gene encodes a protein with a serine-glycine-asparagine-histidine hydrolase domain and a hydrophobic transmembrane domain. Expression of the Cas1 protein tagged with enhanced green fluorescent protein in mammalian and insect cells directed the protein to the medial and trans-cisternae of the Golgi. Overexpression of the Cas1 protein in combination with α-N-acetyl-neuraminide α-2,8-sialyltransferase 1 (GD3 synthase) resulted in an up to 40% increased biosynthesis of 7-O-acetylated ganglioside GD3. By quantitative real-time polymerase chain reaction, we found up to 5-fold increase in CasD1 mRNA in tumor cells overexpressing O-Ac-GD3. CasD1-specific small interfering RNA reduced O-acetylation in tumor cells. These results suggest that the human Cas1 protein is directly involved in O-acetylation of α2-8-linked sialic acids.

Differentially regulated expression of 9-O-acetyl GD3 (CD60b) and 7-O-acetyl-GD3 (CD60c) during differentiation and maturation of human T and B lymphocytes

GD3 (CD60a) and its 9-O-acetylated variant (CD60b) are intracellular regulators of apoptosis in T lymphocytes. Surface expressed 9-O-acetyl- and 7-O-acetyl-GD3 (CD60b and CD60c) may have a functional impact on activated T and B cells. In order to investigate the balance between surface and intracellular expression and synthesis and degradation of these glycosphingolipids in human lymphocytes of various differentiation stages, we analyzed (i) expression of GD3 molecules on native T and B cells and thymocytes by flow cytometry and (ii) activity and regulation of possible key enzymes for CD60a,b,c synthesis and degradation at the transcriptional level. Both, surface and cytoplasmic expression of CD60a and CD60c was highest in tonsillar T cells. In thymocytes, CD60c outweighs the other CD60 variants and was mainly found in the cytoplasm. All lymphocyte preparations contained sialate O-acetyltransferase activity producing 7-O-acetyl-GD3. Sialidase activity was highest in peripheral blood lymphocytes followed by thymocytes and tonsillar T and B cells. Transcription of GD3 synthase (ST8SiaI), the key enzyme for GD3 synthesis, was highest in tonsillar T cells, whereas transcriptional levels of sialidase NEU3 and O-acetylesterase H-Lse were lowest in activated T cells. This balance between enzymes of sialic acid metabolism may explain the strong overall staining intensity for all GD3 forms in T cells. Both CASD1, presumably encoding a sialic acid-specific O-acetyltransferase, and H-Lse showed highest transcription in peripheral B lymphocytes corresponding to the low expression of CD60b and c in these cells. Our data point to regulatory functions of these anabolic and catabolic key enzymes for the expression of GD3 and its O-acetylated variants in lymphocytes at a given differentiation stage.

WITHDRAWN: Corrigendum to "A lectin from the Chinese bird-hunting spider binds sialic acids"

The Publisher regrets that this article is an accidental duplication of an article that has already been published, doi: 10.1016/j.carres.2010.01.003. The duplicate article has therefore been withdrawn.

Assays of sialate-O-acetyltransferases and sialate-O-acetylesterases

The O-acetylation of sialic acids is one of the most frequent modifications of these monosaccharides and modulates many cell biological and pathological events. Sialic acid-specific O-acetyltransferases and O-acetylesterases are responsible for the metabolism of esterified sialic acids. Assays were developed for the analysis of the activities and specificities of these enzymes. The methods had to be varied in dependence on the substrate assayed, the kind of biological source, and the state of enzyme purity. With the new techniques the primary site of O-acetyl incorporation at C-7, catalyzed by the animal sialate-O-acetyltransferases studied, was ascertained. Correspondingly, this enzyme, for example from bovine submandibular gland, can be denominated as AcCoA:sialate-7-O-acetyltransferase (EC 2.3.1.45). Methods for assaying the activity of esterases de-O-acetylating sialic acids and their metabolic cooperation with the O-acetyltransferases are presented.

Sialic acids as regulators of molecular and cellular interactions

The wide occurrence of sialic acids (Sia) in various chemical forms linked as monomers or polymers in an outstanding position in a multitude of complex carbohydrates of animals and microorganisms renders them as most versatile function modulators in cell biology and pathology. A survey is presented of recent advances in the study of the influences that Sias have as bulky hydrophilic and electronegatively charged monosaccharides on animal cells and on their interaction with microorganisms. Some highlights are: sialylation leads to increased anti-inflammatory activity of IgG antibodies, facilitates the escape of microorganisms from the host's immune system, and in polymeric form is involved in the regulation of embryogenesis and neuronal growth and function. The role of siglecs in immunoregulation, the dynamics of lymphocyte binding to selectins and the interactions of toxins, viruses, and other microorganisms with the host's Sia are now better understood. N-Glycolylneuraminic acid from food is antigenic in man and seems to have pathogenic potential. Sia O-acetylation mediated by various eukaryotic and prokaryotic O-acetyltransferases modulates the affinity of these monosaccharides to mammalian and microbial receptors and hinders apoptosis. The functionally versatile O-acetylated ganglioside GD3 is an onco-fetal antigen.

Low incidence of N-glycolylneuraminic acid in birds and reptiles and its absence in the platypus

The sialic acids of the platypus, birds, and reptiles were investigated with regard to the occurrence of N-glycolylneuraminic (Neu5Gc) acid. They were released from tissues, eggs, or salivary mucin samples by acid hydrolysis, and purified and analyzed by thin-layer chromatography, high-performance liquid chromatography, and mass spectrometry. In muscle and liver of the platypus only N-acetylneuraminic (Neu5Ac) acid was found. The nine bird species studied also did not express N-glycolylneuraminic acid with the exception of an egg, but not tissues, from the budgerigar and traces in poultry. Among nine reptiles, including one turtle, N-glycolylneuraminic acid was only found in the egg and an adult basilisk, but not in a freshly hatched animal. BLAST analysis of the genomes of the platypus, the chicken, and zebra finch against the CMP-N-acetylneuraminic acid hydroxylase did not reveal the existence of a similar protein structure. Apparently monotremes (platypus) and sauropsids (birds and reptiles) cannot synthesize Neu5Gc. The few animals where Neu5Gc was found, especially in eggs, may have acquired this from the diet or by an alternative pathway. Since Neu5Gc is antigenic to man, the observation that this monosaccharide does not or at least only rarely occur in birds and reptiles, may be of nutritional and clinical significance.

High level of sialate-O-acetyltransferase activity in lymphoblasts of childhood acute lymphoblastic leukaemia (ALL): enzyme characterization and correlation with disease status

Previous studies had established an over-expression of 9-O-acetylated sialoglycoproteins (Neu5,9Ac(2)-GPs) on lymphoblasts of childhood acute lymphoblastic leukaemia (ALL). Here, we report the discovery and characterization of sialate-O-acetyltransferase enzyme in ALL-cell lines and lymphoblasts from bone marrow of children diagnosed with B- and T-ALL. We observed a positive correlation between the enhanced sialate-O-acetyltransferase activity and the enhanced expression of Neu5,9Ac(2)-GPs in these lymphoblasts. Sialate-O-acetyltransferase activity in cell lysates or microsomal fractions of lymphoblasts of patients was always higher than that in healthy donors reaching up to 22-fold in microsomes. Additionally, the V (max) of this enzymatic reaction with AcCoA was over threefold higher in microsomal fractions of lymphoblasts. The enzyme bound to the microsomal fractions showed high activity with CMP-N-acetylneuraminic acid, ganglioside GD3 and endogenous sialic acid as substrates. N-acetyl-7-O-acetylneuraminic acid was the main reaction product, as detected by radio-thin-layer chromatography and fluorimetrically coupled radio-high-performance liquid chromatography. CMP and coenzyme A inhibited the microsomal enzyme. Sialate-O-acetyltransferase activity increased at the diagnosis of leukaemia, decreased with clinical remission and sharply increased again in relapsed patients as determined by radiometric-assay. A newly-developed non-radioactive ELISA can quickly detect sialate-O-acetyltransferase, and thus, may become a suitable tool for ALL-monitoring in larger scale. This is the first report on sialate-O-acetyltransferase in ALL being one of the few descriptions of an enzyme of this type in human.

Truncated E2 of bovine viral diarrhea virus (BVDV) expressed in Drosophila melanogaster cells: a candidate antigen for a BVDV ELISA

A simple and reliable indirect enzyme-linked immunosorbent assay for detection of antibodies directed against a major bovine viral diarrhea virus (BVDV) immunogen, the E2 glycoprotein (tE2-ELISA), has been developed using the recombinant C-terminal truncated E2 glycoprotein (tE2) expressed in a Drosophila melanogaster system. This strategy demonstrated that tE2 is secreted efficiently in the supernatant, no purification steps are necessary, it is easy to produce and carries out the post translational modifications necessary to preserve its native conformation. Preliminary analysis of 183 cattle serum samples using tE2-ELISA showed a 98% specificity and a 100% sensitivity compared with the standard homologous BVDV virus neutralization test. The results also showed that the tE2 is immunoreactive because the conformation and antigenicity of the original E2 are maintained to a large extent. To our knowledge this is the first study report of the recombinant tE2 of BVDV expressed in D. melanogaster system as an antigen for ELISA.

Properties and partial purification of sialate-O-acetyltransferase from bovine submandibular glands

The O-acetylation of sialic acids in various positions is a frequent modification of these residues in glycoproteins and glycolipids of higher animals and some bacteria. Sialic acid O-acetylation is involved in the regulation of many cell biological and pathophysiological events. Since the properties and the structural and molecular genetic aspects of the eukaryotic sialate O-acetyltransferases are not yet known, we attempted to isolate the enzyme from bovine submandibular glands. O-Acetyltransferase was solubilised from its microsomal location with a zwitterionic detergent and enriched by approximately 50-fold in three steps, including affinity chromatography on coenzyme A. It exhibits a molecular mass of 150-160 kDa. Evidence was obtained for the putative existence of a low-molecular-mass, dialysable enzyme activator. The enzyme showed best activity with CMP-N-acetylneuraminic acid (CMP-Neu5Ac), followed by N-acetylneuraminic acid (Neu5Ac). These compounds, as well as AcCoA, have high affinity for both the microsome-bound and the partially purified O-acetyltransferase. CoA is a strong inhibitor. N-Acetyl-9-O-acetylneuraminic acid was found to be the main reaction product. No evidence was obtained for the involvement of an isomerase that might be responsible for the migration of O-acetyl groups within the sialic acid side chain.

Localisation and distribution of O-acetylated N-acetylneuraminic acids, the endogenous substrates of the hemagglutinin-esterases of murine coronaviruses, in mouse tissue

Infections by mouse hepatitis viruses result in disease of the liver, the gastrointestinal tract, respiratory tract, and the central nervous system. Coronaviruses related to mouse hepatitis virus express a hemagglutinin-esterase surface glycoprotein, which specifically hydrolyses either 5-N-acetyl-4-O-acetyl neuraminic acid (Neu4,5Ac₂) or 5-N-acetyl-9-O-acetyl neuraminic acid (Neu5,9Ac₂). Moreover, these sialic acids represent potential cellular receptor determinants for murine coronaviruses. Until now, the distribution of these sialic acids in mouse brain was not thoroughly investigated. Particularly Neu4,5Ac₂ was not yet found in mouse brain. Using a sensitive method of gas chromatography coupled to mass spectrometry in the electron impact mode of ionization this manuscript demonstrates the occurrence of 13 different sialic acids varying in their alkyl and acyl substituents in mouse tissues including 5-N-acetyl-4-O-acetyl-9-O-lactyl-neuraminic acid (Neu4,5Ac₂9Lt), 5-N-acetyl-9-O-lactyl-neuraminic acid (Neu5Ac9Lt), 5-N-acetyl-8-O-methyl-neuraminic acid (Neu5Ac8Me) and the 1,7-lactone (Neu5Ac1,7L) of neuraminic acid. Neu4,5Ac₂, relatively abundant in the gut, was present as a minor compound in all tissues, including liver, olfactory lobe, telencephalon, metencephalon and hippocampus. Neu5,9Ac₂ was also found in these tissues, except in the liver. It is suggested that these sialic acids represent the endogenous substrate and receptor determinants for murine coronaviruses.

Nonradioactive trans-sialidase screening assay

Trans-sialidase (TS; E.C. 3.2.1.18) catalyzes the transfer of preferably alpha2,3-linked sialic acid to another glycan or glycoconjugate, forming a new alpha2,3-linkage to galactose or N-acetylgalactosamine. In the absence of an appropriate acceptor, TS acts as a sialidase, hydrolytically releasing glycosidically linked sialic acid. Interest in TS has increased rapidly in recent years owing to its great relevance to the pathogenicity of trypanosomes and its possible application in the regiospecific synthesis of sialylated carbohydrates and glycoconjugates. Recently, the authors described a newly developed nonradioactive screening test for monitoring TS activity (1). In this highly sensitive and specific assay, 4-methylumbelliferyl-beta-D-galactoside is used as acceptor substrate and sialyllactose as donor to fluorimetrically detect enzyme activity in the low mU range (approximately 0.1-1 mU/mL possible). The test can be applied to screen a large number of samples quickly and reliably during enzyme purification, for testing inhibitors, and for monitoring TS activity during the production of monoclonal antibodies (2). This chapter focuses on the main steps of this assay and gives detailed instructions for performing a nonradioactive TS 96-well-plate fluorescence test. In addition, it describes the controls necessary when starting to monitor an unknown TS and facts to be considered when testing new substrates and inhibitors.

Identification of 9-O-acetyl-N-acetylneuraminic acid in normal canine pre-ocular tear film secreted mucins and its depletion in Keratoconjunctivitis sicca

O-Acetylated sialic acids have been reported in many sialoglycoproteins where they mediate a variety of immune and other biological events. We have previously demonstrated that the protective mucus barrier on the surface of the canine eye contains sialoglycoproteins. We have also investigated the occurrence of O-acetylated sialic acids in these ocular mucins. Mucus aspirated from the surface of normal dog eyes and those with keratoconjunctivitis sicca (KCS) was fractionated into three pools by density gradient centrifugation. Sialic acids comprised 0.6-0.9% of the dry weight of the mucins isolated. The sialic acid profile in these pools was examined using HPLC. O-Acetylated sialic acids, mainly Neu5,9Ac2, were detected in normal animals and made up 10-30% of the total sialic acids detected. A doubling of the sialic acid content was found in KCS mucins, but the level of 9-O-acetylated sialic acid was reduced below 4% of total. Histological analysis of conjunctival tissue from normal and KCS dogs showed the presence of sialic acids, detected with the alpha(2-6) sialic acid-specific lectin Sambucus nigra, in the goblet cells and corresponding to the staining pattern for MUC5AC, the major ocular-secreted mucin gene product. In KCS animals a disruption of the normal pattern of conjunctival goblet cells was seen with preservation of the pattern of lectin binding observed in normal animals. Thus the data demonstrate the presence of mono-O-Acetylated sialic acids in normal canine ocular mucins and a loss of this population of sialic acids in dry eye disease in spite of a significant increase in total sialic acids in KCS mucin.

Analysis of monosaccharides, fatty constituents and rare O-acetylated sialic acids from gonads of the starfish Asterias rubens

A previous study (Bergwerff et al., Biochimie 74 (1992) 25-37) reported that sialic acids present in Asterias rubens gonads were essentially composed of 8-methyl-N-glycolylneuraminic acid (Neu5Gc8Me), a large part of it being acetylated in position 9. Using GC/MS of heptafluorobutyrate derivatives (Zanetta et al., Glycobiology 11 (2001) 663-676) on the chloroform/methanol soluble and insoluble fractions, we showed that most sialic acids were found in the latter and demonstrated that all sialic acids were derived from N-glycolylneuraminic acid, most of them being 8-methylated, but that the majority were also acetylated in position 4 or 7 (or both positions). GC/MS analyses of the constituents liberated using acid-catalysed methanolysis verified that major glycoprotein-bound glycans were N-linked and of the gluco-oligomannosidic type. Major fatty acids were poly-unsaturated (especially C20:4) and long-chain bases were C22:1 phytosphingosine and C22:2 6-hydroxysphingenine. Major monosaccharides found in the chloroform/methanol extract (quinovose and fucose) were derived from steroidal saponins.

Sialic acids: fascinating sugars in higher animals and man

Sialic acids are acidic monosaccharides, which are among the most important molecules of higher animals, and occur in some microorganisms. They are bound to complex carbohydrates and occupy prominent positions, especially in cell membranes. Their structural diversity is high and, correspondingly, the mechanisms for their biosynthesis are complex. Sialic acid substituents strongly influence the activity of catabolic enzymes, in particular the sialidases, and thus the turnover rate of glycoconjugates. These sugars are involved in manifold cell functions. Due to the surface location of the acidic molecules they shield macromolecules and cells from enzymatic and immunological attacks. But they also represent recognition sites for various physiological receptors as well as for toxins and microorganisms, and thus allow their colonization. Many viruses use sialic acids for the infection of cells. As sialic acids also play a decisive role in tumor biology they prove to be rather versatile molecules that modulate cell biological events in a sensitive way. It is discussed that their evolvement may have stimulated evolution and rendered organisms less vulnerable to environmental attacks. However, disturbance of their metabolism may cause diseases.

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

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.

Effects of Pringle manoeuvre and ischaemic preconditioning on haemodynamic stability in patients undergoing elective hepatectomy: a randomized trial

BACKGROUND

The Pringle manoeuvre and ischaemic preconditioning are applied to prevent blood loss and ischaemia-reperfusion injury, respectively, during liver surgery. In this prospective clinical trial we report on the intraoperative haemodynamic effects of the Pringle manoeuvre alone or in combination with ischaemic preconditioning.

METHODS

Patients (n=68) were assigned randomly to three groups: (i) resection with the Pringle manoeuvre; (ii) with ischaemic preconditioning before the Pringle manoeuvre for resection; (iii) without pedicle clamping.

RESULTS

Following the Pringle manoeuvre the mean arterial pressure increased transiently, but significantly decreased after unclamping as a result of peripheral vasodilation. Ischaemic preconditioning improved cardiovascular stability by lowering the need for catecholamines after liver reperfusion without affecting the blood sparing benefits of the Pringle manoeuvre. In addition, ischaemic preconditioning protected against reperfusion-induced tissue injury.

CONCLUSIONS

Ischaemic preconditioning provides both better intraoperative haemodynamic stability and anti-ischaemic effects thereby allowing us to take full advantage of blood loss reduction by the Pringle manoeuvre.

Purification and characterization of 9-O-acetylated sialoglycoproteins from leukemic cells and their potential as immunological tool for monitoring childhood acute lymphoblastic leukemia

Sialic acids as terminal residues of oligosaccharide chains play crucial roles in several cellular recognition events. Exploiting the selective affinity of Achatinin-H toward N-acetyl-9-O-acetylneuraminic acid-alpha2-6-GalNAc, we have demonstrated the presence of 9-O-acetylated sialoglycoproteins (Neu5,9Ac(2)-GPs) on lymphoblasts of 70 children with acute lymphoblastic leukemia (ALL) and on leukemic cell lines by fluorimetric HPLC and flow cytometric analysis. This study aims to assess the structural aspect of the glycotope of Neu5,9Ac(2)-GPs(ALL) and to evaluate whether these disease-specific molecules can be used to monitor the clinical outcome of ALL. The Neu5,9Ac(2)-GPs(ALL) were affinity-purified, and three distinct leukemia-specific molecular determinants (135, 120, and 90 kDa) were demonstrated by SDS-PAGE, western blotting, and isoelectric focusing. The carbohydrate epitope of Neu5,9Ac(2)-GPs(ALL) was confirmed by using synthetic sialic acid analogs. The enhanced presence of anti-Neu5,9Ac(2)-GP(ALL) antibody in ALL patients prompted us to develop an antigen-ELISA using purified Neu5,9Ac(2)-GPs(ALL) as coating antigens. Purified antigen was able to detect leukemia-specific antibodies at presentation of disease, which gradually decreased with treatment. Longitudinal monitoring of 18 patients revealed that in the early phase of the treatment patients with lower anti-Neu5,9Ac(2)-GPs showed a better prognosis. Minimal cross-reactivity was observed in other hematological disorders (n = 50) like chronic myeloid leukemia, acute myelogenous leukemia, chronic lymphocytic leukemia, and non-Hodgkin's lymphoma as well as normal healthy individuals (n = 21). This study demonstrated the potential of purified Neu5,9Ac(2)-GPs(ALL) as an alternate tool for detection of anti-Neu5,9Ac(2)-GP antibodies to be helpful for diagnosis and monitoring of childhood ALL patients.

Victor Ginsburg's influence on my research of the role of sialic acids in biological recognition

Sialic acids are monosaccharides with relatively strong acidity which belong to the most important molecules of higher animals and also occur in some microorganisms. They are bound to complex carbohydrates and occupy prominent positions, especially in cell membranes. Their structural diversity is high and, correspondingly, the mechanisms for their biosynthesis complex. Sialic acids are involved in a great number of cell functions. Due to their cell surface location these acidic molecules shield macromolecules and cells from enzymatic and immunological attacks and thus contribute to innate immunity. In contrast to this masking role, enabling, for example, blood cells and serum glycoproteins a longer life-time, sialic acids also represent recognition sites for various physiological receptors, such as the selectins and siglecs, as well as for toxins and microorganisms and thus allow their colonization. The recognition function of sialic acids can again be masked by O-acetylation, which modifies the interaction with receptors. Many viruses use sialic acids for the infection of cells. As sialic acids play also a decisive role in tumor biology, they prove to be rather versatile molecules that modulate biological and pathological cellular events in a sensitive way. Thus, they are most prominent representatives of mediators of molecular and cellular recognition.

Regulation of sialic acid O-acetylation in human colon mucosa

The expression of O-acetylated sialic acids in human colonic mucins is developmentally regulated, and a reduction of O-acetylation has been found to be associated with the early stages of colorectal cancer. Despite this, however, little is known about the enzymatic process of sialic acid O-acetylation in human colonic mucosa. Recently, we have reported on a human colon sialate-7(9)-O-acetyltransferase capable of incorporating acetyl groups into sialic acids at the nucleotide-sugar level [Shen et al., Biol. Chem. 383 (2002), 307-317]. In this report, we show that the CMP-N-acetyl-neuraminic acid (CMP-Neu5Ac) and acetyl-CoA (AcCoA) transporters are critical components for the O-acetylation of CMP-Neu5Ac in Golgi lumen, with specific inhibition of either transporter leading to a reduction in the formation of CMP-5-N-acetyl-9-O-acetyl-neuraminic acid (CMP-Neu5,9Ac2). Moreover, the finding that 5-N-acetyl-9-O-acetyl-neuraminic acid (Neu5,9Ac2 could be transferred from neo-synthesised CMP-Neu5,9Ac2 to endogenous glycoproteins in the same Golgi vesicles, together with the observation that asialofetuin and asialo-human colon mucin are much better acceptors for Neu5,9Ac2 than asialo-bovine submandibular gland mucin, suggests that a sialyltransferase exists that preferentially utilises CMP-Neu5,9Ac2 as the donor substrate, transferring Neu5,9Ac2 to terminal Galbeta1,3(4)R- residues.

O-acetylation and de-O-acetylation of sialic acids in human colorectal carcinoma

A decrease in the level of O-acetylated sialic acids observed in colorectal carcinoma may lead to an increase in the expression of sialyl Lewis(X), a tumor-associated antigen, which is related to progression of colorectal cancer to metastasis. The underlying mechanism for this reduction is, however, not fully understood. Two enzymes are thought to be primarily responsible for the turnover of O-acetyl ester groups on sialic acids; sialate-O-acetyltransferase (OAT) and sialate-O-acetylesterase (OAE). We have previously reported the characterization of OAT activity from normal colon mucosa, which efficiently O-acetylates CMP-Neu5Ac exclusively in the Golgi apparatus prior to the action of sialyltransferase. In this report we describe the identification of a lysosomal and a cytosolic OAE activity in human colonic mucosa that specifically hydrolyses 9-O-acetyl groups on sialic acid. Utilizing matched resection margin and cancer tissue from colorectal carcinoma patients we provide strong evidence suggesting that the level of O-acetylated sialic acids present in normal and diseased human colon may be dependent on the relative activities of OAT to lysosomal OAE. Furthermore, we show that the level of free cytosolic Neu5,9Ac2 in human colon is regulated by the relative activity of the cytosolic OAE.

[52-year-old patient with subcutaneous space-occupying lesion in immunosuppression]

We report the case of a 52-years-old male patient, who was diagnosed with subcutaneous alveolar echinococcosis 6 months after liver transplantation for HCV-related cirrhosis. Nether the explanted nor the transplantated liver revealed an echinococcus focus. Therefore a rare primary extrahepatic manifestation was likely. Interestingly, the echinococcal larvae had developed protoscolices. The development of mature tapeworms in human is a rarity, which could be related to the immunosuppressive therapy after liver transplantation. The patient was curatively treated by surgical removal of the subcutaneous tumor and a postoperative therapy with albendazole. Furthermore, HCV reinfection (genotype 2b) was successfully treated with interferone alpha 2b and ribavirine for 6 months.

Characterization of sialidase from an influenza A (H3N2) virus strain: kinetic parameters and substrate specificity

Neuraminidase (NA) of influenza A (H3N2) viruses was characterized after purification by gel filtration and proteolytic treatment, using the X-31 variant strain that is a reassortment between the influenza A/Victoria/3/75 (responsible for the 1975 pandemic) and the influenza A/PR/8/34 virus samples, as a model. In the purification process, NA heads, that is the spike responsible for the virus sialidase activity, were purified by filtration through a Bio-Gel polyacrylamide column. The enzyme activity was determined by periodic acid/thiobarbituric acid assay and high-performance thin-layer chromatography. The sialidase showed preference for the alpha-2,3-linkage over the alpha-2,6-linkage of sialyllactoses (K(m) of 1.8 and 5.2 x 10(-4)M, respectively) at pH 5.2. The enzyme acted on natural and synthetic substrates at different hydrolysis rates, as well as on human erythrocytes (A group, Rh+) and yeast (CANDIDA ALBICANS) cells. The active NA produced by gel filtration was characterized by different parameters of its sialidase activity, also showing to be a suitable tool for the identification of natural sialocompounds and for the screening of antisialidase drugs to treat influenza virus infections.

A nonradioactive 96-well plate assay for screening of trans-sialidase activity

Trans-sialidase (E.C. 3.2.1.18) catalyzes the transfer of preferably alpha2,3-linked sialic acid to another glycan or glycoconjugate, forming a new alpha2,3 linkage to galactose or N-acetylgalactosamine. Here, we describe a nonradioactive 96-well plate fluorescence test for monitoring trans-sialidase activity with high sensitivity, specificity, and reproducibility using sialyllactose and 4-methylumbelliferyl-beta-D-galactoside as donor and acceptor substrates, respectively. The assay conditions were optimized using the trans-sialidase from Trypanosoma congolense and its general applicability was confirmed with recombinant trans-sialidase from Trypanosoma cruzi. Using this procedure, a large number of samples can be tested quickly and reliably, for instance in monitoring trans-sialidase during enzyme purification and the production of monoclonal antibodies, for enzyme characterization, and for identifying potential substrates and inhibitors. The trans-sialidase assay reported here was capable of detecting trans-sialidase activity in the low-mU range and may be a valuable tool in the search for further trans-sialidases in various biological systems.

Trans-sialidase-like sequences from Trypanosoma congolense conserve most of the critical active site residues found in other trans-sialidases

Trypanosoma congolense is the agent of Nagana, the trypanosomiasis in African ruminants. Trypanosomes express an enzyme called trans-sialidase, which is believed to play an important role in maintaining pathogenicity of the parasites. Thus far, only two complete trans-sialidase sequences have been characterised, one from the American trypanosome T. cruzi and one from the African trypanosome T. brucei brucei. Although the crystal structure of T. cruzi trans-sialidase has recently been published [Buschiazzo et al., Mol. Cell 10 (2002), pp. 757-768], a number of questions concerning the exact transfer mechanism remain unanswered. The availability of further trans-sialidase sequences will ensure a better understanding of how transfer activity can be achieved and will provide the opportunity to develop highly specific, structure-based trans-sialidase inhibitors. Utilising a PCR-based approach two different trans-sialidase gene copies from T. congolense were identified, which share only 50% identity with each other, but show significant similarity with known viral, bacterial and trypanosomal sialidases and trans-sialidases. In both partial sequences most of the critical active site residues common to other trypanosomal sialidases and trans-sialidases are conserved. This is further illustrated by modelling the active site of the longer of the two partial gene sequences.

Reduction of CMP-N-acetylneuraminic acid hydroxylase activity in engineered Chinese hamster ovary cells using an antisense-RNA strategy

Rodent cells, widely used for the industrial production of recombinant human glycoproteins, possess CMP-N-acetylneuraminic acid hydroxylase (CMP-Neu5Ac hydroxylase; EC 1.14.13.45) which is the key enzyme in the formation of the sialic acid, N-glycolylneuraminic acid (Neu5Gc). This enzyme is not expressed in an active form in man and evidence suggests that the presence of Neu5Gc in recombinant therapeutic glycoproteins may elicit an immune response. The aim of this work was, therefore, to reduce CMP-Neu5Ac hydroxylase activity in a Chinese Hamster Ovary (CHO) cell line, and thus the Neu5Gc content of the resulting glycoconjugates, using a rational antisense RNA approach. For this purpose, the cDNA of the hamster hydroxylase was partially cloned and sequenced. Based on the sequence of the mouse and hamster cDNAs, optimal antisense RNA fragments were selected from preliminary in vitro translation tests. Compared to the parental cell line, the new strain (CHO-AsUH2), which was transfected with a 199-bp antisense fragment derived from the mouse CMP-Neu5Ac hydroxylase cDNA, showed an 80% reduction in hydroxylase activity. An analysis of the sialic acids present in the cells' own glycoconjugates revealed a decrease in the percentage of Neu5Gc residues from 4% in the parental cells to less than 1% in the CHO-AsUH2 cell line.

Solubilisation and properties of the sialate-4-O-acetyltransferase from guinea pig liver

The O-acetylation of sialic acids turns out to be one of the most important modifications that influence the diverse biological and pathophysiological properties of glycoconjugates in animals and microorganisms. To understand the functions of this esterification, knowledge of the properties, structures and regulation of expression of the enzymes involved is essential. Attempts to solubilise, purify or clone the gene of one of the sialate-O-acetyltransferases have failed so far. Here we report on the solubilisation of the sialate-4-O-acetyltransferase from guinea pig liver, the first and essential step in the purification and molecular characterisation of this enzyme, by the zwitterionic detergent CHAPS. This enzyme O-acetylates sialic acids at C-4 both free and bound to oligosaccharides, glycoproteins and glycolipids with varying activity, however, gangliosides proved to be the best substrates. Correspondingly, a rapid enzyme test was elaborated using the ganglioside GD3. The soluble O-acetyltransferase maximally operated at 30 degrees C, pH 5.6, and 50-70 mM KCl and K2HPO4 concentrations. The Km values were 3.6 microM for AcCoA and 1.2 microM for GD3. CoA inhibits the enzyme with a Ki value of 14.8 microM. A most important discovery enabling further enzyme purification is its need for an unknown low molecular mass and heat-stable cofactor that can be separated from the crude enzyme preparation by 30 kDa ultrafiltration.

Two trans-sialidase forms with different sialic acid transfer and sialidase activities from Trypanosoma congolense

Trypanosomes express an enzyme called trans-sialidase (TS), which enables the parasites to transfer sialic acids from the environment onto trypanosomal surface molecules. Here we describe the purification and characterization of two TS forms from the African trypanosome Trypanosoma congolense. The purification of the two TS forms using a combination of anion exchange chromatography, isoelectric focusing, gel filtration, and subsequently, antibody affinity chromatography resulted, in both cases, in the isolation of a 90-kDa monomer on SDS-PAGE, which was identified as trans-sialidase using micro-sequencing. Monoclonal antibody 7/23, which bound and partially inhibited TS activity, was found in both cases to bind to a 90-kDa protein. Both TS forms possessed sialidase and transfer activity, but markedly differed in their activity ratios. The TS form with a high transfer-to-sialidase activity ratio, referred to as TS-form 1, possessed a pI of pH 4-5 and a molecular mass of 350-600 kDa. In contrast, the form with a low transfer-to-sialidase activity ratio, referred to as TS-form 2, exhibited a pI of pH 5-6.5 and a molecular mass of 130-180 kDa. Both TS forms were not significantly inhibited by known sialidase inhibitors and revealed no significant differences in donor and acceptor substrate specificities; however, TS-form 1 utilized various acceptor substrates with a higher catalytic efficiency. Interestingly, glutamic acid-alanine-rich protein, the surface glycoprotein, was co-purified with TS-form 1 suggesting an association between both proteins.

Sialic acids are absent from the dermatophytes Trichophyton mentagrophytes and Trichophyton rubrum

Experiments were performed to determine whether sialic acids are expressed in two dermatophytes: Trichophyton rubrum and T. mentagrophytes, similarly to other fungal pathogens. Chemical extraction of mycelia and microconidia followed by high-performance thin-layer chromatography and colorimetric assays were all negative for sialic acid. Incubation of dermatophytes in the presence of Limax flavus agglutinin, specific for sialic acid, was negative in a fluorescence staining test. We have also used other lectins that bind to sialic acid and/or other sugar residues, and these ligands coupled to fluorescein strongly stained these fungi. Such fluorescence staining was not abolished or reduced when fungi were pretreated with sialidase. Different strains of influenza virus which recognize sialic acid residues were also used, but no agglutination of the dermatophytes was observed. Based on these methods, which successfully revealed the presence of sialic acids in other fungal pathogens, we show that these monosaccharides do not occur in both dermatophyte species. Thus, sialic acids do not seem to play a role in the pathogenicity of these fungi.

Identification and characterization of adsorbed serum sialoglycans on Leishmania donovani promastigotes

Sialic acids as terminal residues of oligosaccharide chains play a crucial role in several cellular recognition events. The presence of sialic acid on promastigotes of Leishmania donovani, the causative organism of Indian visceral leishmaniasis, was demonstrated by fluorimetric high-performance liquid chromatography showing Neu5Ac and, to a minor extent, Neu5,9Ac2. The presence of Neu5Ac was confirmed by GC/MS analysis. Furthermore, binding with sialic acid-binding lectins Sambucus nigra agglutinin (SNA), Maackia amurensis agglutinin (MAA), and Siglecs showed the presence of both alpha2,3- and alpha2,6-linked sialic acids. No endogenous biosynthetic machinery for Neu5Ac could be demonstrated in the parasite. Concomitant western blotting of parasite membranes and culture medium with SNA demonstrated the presence of common sialoglyconjugates (123, 90, and 70 kDa). Similarly, binding of MAA with parasite membrane and culture medium showed three analogous sialoglycans corresponding to 130, 117, and 70 kDa, indicating that alpha2,3- and alpha2,6-linked sialoglycans are adsorbed from the fetal calf serum present in the culture medium. L. donovani promastigotes also reacted with Achatinin-H, a lectin that preferentially identifies 9-O-acetylated sialic acid in alpha2-->6 GalNAc linkage. This determinant was evidenced on parasite cell surfaces by cell agglutination, ELISA, and flow cytometry, where its binding was abolished by pretreatment of cells with a recombinant 9-O-acetylesterase derived from the HE1 region of the influenza C esterase gene. Additionally, binding of CD60b, a 9-O-acetyl GD3-specific monoclonal antibody, corroborated the presence of terminal 9-O-acetylated disialoglycans. Our results indicate that sialic acids (alpha2-->6 and alpha2-->3 linked) and 9-O-acetyl derivatives constitute components of the parasite cell surface.

Regulation of N-glycolylneuraminic acid biosynthesis in developing pig small intestine

N -Glycolylneuraminic acid (Neu5Gc), an abundant sialic acid in animal glycoconjugates, is formed by the enzyme CMP-N-acetylneuraminic acid (CMP-Neu5Ac) hydroxylase. The amount of Neu5Gc relative to other sialic acids is highly dependent on the species, tissue and developmental stage. Although the activity of the hydroxylase is a key factor in controlling Neu5Gc incorporation in adult animals, little is known about the regulation of hydroxylase expression and the role of this enzyme in determining changes in Neu5Gc during development. Using pig small intestine as a model system, the appearance of total sialic acid and the regulation of Neu5Gc biosynthesis during development were studied in various regions of this tissue. The amount of total sialic acid and Neu5Gc declined markedly in 2 weeks after birth. Although in subsequent developmental phases there were no positional differences in total sialic acid, a significant proximal-to-distal increase in Neu5Gc was detected. In all cases, a good correlation between the amount of Neu5Gc, the activity of the hydroxylase and the level of hydroxylase mRNA was observed. However, Western-blot analysis revealed considerable accumulation of less active enzyme in the post partum period, which persisted until adulthood. No evidence for cytosolic factors influencing the hydroxylase activity or for the formation of truncated enzyme was found, raising the possibility that other regulatory mechanisms are involved. The relevance of these results in the formation of Neu5Gc as a receptor for certain pig enteric pathogens is also discussed.

Early variations of the disialoganglioside GD3 in chicken embryonic brain support its role in cell migration

In the present study a primary culture system of chicken embryo brain neurons was used in the early period of chicken brain development from day 6 until day 8, which was shown to be a suitable model of neuritogenesis, cell migration and reaggregation. Dissociated chicken optic tectum cells from embryonic stage 31 were cultured on polylysine-coated dishes under serum-free conditions up to 3 days. Freshly dissociated neurons developed short processes, which contacted one another and formed fasciculated bundles. Cell somata migrated along the neurite bundles, similar to migrating neurons in vivo, forming three-dimensional tissue-like clusters. This system was used to study the possible functions of the disialoganglioside GD3 for these neuronal differentiation steps. GD3 represents the predominant ganglioside of embryonic neurons before neuritogenesis in vitro and in vivo. Its biosynthesis is followed during day 6 until day 8 of embryonic brain development. Incubation of dissociated neurons with the monoclonal antibody R-24, recognising the GD3 on the cell surface, led to a total blocking of neurite outgrowth. Accordingly, neither cell migration nor reaggregation could be found. These results indicate that the disialoganglioside GD3 plays a central role in neuronal differentiation and development in the embryonic chicken brain.

Biological properties of N-acyl and N-haloacetyl neuraminic acids: processing by enzymes of sialic acid metabolism, and interaction with influenza virus

Several unnatural N-acyl neuraminic acids (N-propionyl, N-hexanoyl, N-benzoyl, N-trifluoroacetyl, N-chloroacetyl, N-difluoroacetyl) were prepared enzymatically using immobilised sialic acid aldolase. N-Trifluoroacetyl-, N-chloroacetyl- and N-difluoroacetyl neuraminic acids were shown to enhance up to 10-fold the rate of association of influenza virus A to a sialoglycolipid neomembrane by surface plasmon resonance, and were found to act as weak inhibitors (K(iapp) 0.45-2.0 mM) of influenza virus neuraminidase. The N-propionyl, N-chloroacetyl- and N-difluoroacetyl neuraminic acids were found to be substrates for recombinant Escherichia coli CMP sialate synthase, to give the corresponding CMP-N-acyl-neuraminic acids. CMP-N-propionyl neuraminic acid was found not to be a substrate for CMP-N-acetyl neuraminic acid hydroxylase from pig submandibular gland.