The preparation of CMP-sialic acids by using CMP-acylneuraminate synthase from frog liver immobilized on sepharose 4B

Development of a simple and efficient method for assaying cytidine monophosphate sialic acid synthetase activity using an enzymatic reduced nicotinamide adenine dinucleotide/oxidized nicotinamide adenine dinucleotide converting system

A new reliable method to assay the activity of cytidine monophosphate sialic acid (CMP-Sia) synthetase (CSS) has been developed. The activation of sialic acids (Sia) to CMP-Sia is a prerequisite for the de novo synthesis of sialoglycoconjugates. In vertebrates, CSS has been cloned from human, mouse, and rainbow trout, and the crystal structure has been resolved for the mouse enzyme. The mouse and rainbow trout enzyme have been compared with respect to substrate specificity, demonstrating that the mouse enzyme exhibits a pronounced specificity for N-acetylneuraminic acid (Neu5Ac), while the rainbow trout CSS is equally active with either of three Sia species, Neu5Ac, N-glycolylneuraminic acid (Neu5Gc), and deaminoneuraminic acid (KDN). However, molecular details that explain the pronounced substrate specificities are unknown. Understanding the catalytic mechanisms of these enzymes is of major importance, since CSSs play crucial roles in cellular sialylation patterns and thus are potential drug targets in a number of pathophysiological situations. The availability of the cDNAs and the obtained structural data enable rational approaches; however, these efforts are limited by the lack of a reliable high-throughput assay system. Here we describe a new assay system that allows product quantification in a reduced nicotinamide adenine dinucleotide (NADH)-dependent color reaction. The activation reaction catalyzed by CSS, CTP+Sia-->CMP-Sia+pyrophosphate, was evaluated by a consumption of Sia, which corresponds to that of NADH on the following two successive reactions: (i) Sia-->pyruvate+ManNAc (or Man), catalyzed by a sialic acid lyase (SAL), and (ii) pyruvate+NADH-->lactate+oxidized nicotinamide adenine dinucleotide (NAD+), catalyzed by a lactate dehydrogenase (LDH). Consumption of NADH can be photometrically monitored on a microtiter plate reader for a number of test samples at the same time. Furthermore, based on the quantification of CSS used in the SAL/LDH assay, relative activities toward Sia derivatives have been obtained. The preference of mouse CSS toward Neu5Ac and the ability of the rainbow trout enzyme to activate both KDN and Neu5Ac were confirmed. Thus, this simple and time-saving method is suitable for a systematic comparison of enzyme activity of structurally mutated enzymes based on the relative specific activity.

The use of immobilised glycosyltransferases in the synthesis of sialyloligosaccharides

The CMP-sialic acids, cytidine 5'-(5-acetamido-3,5-dideoxy-beta-D-glycero-D-galacto-2-nonulopyranosy lonic acid monophosphate) (1) and cytidine 5'-(5-acetamido-9-O-acetyl-3,5-dideoxy-beta-D-glycero-D-galacto-2- nonulopyranosylonic acid monophosphate) (2) were prepared from CMP, phosphoenolpyruvate, N-acetylneuraminic acid or its 9-acetate, and a catalytic amount of ATP in the presence of immobilised pyruvate kinase, nucleoside monophosphate kinase, inorganic pyrophosphatase, and CMP-sialic acid synthetase. CMP-NeuAc (1) was used as a donor of N-acetylneuraminic acid in the reaction catalysed by immobilised porcine liver beta-D-Galp-(1----4)-alpha-D-GlcpNAc-(2----6)-sialyltransferase, alpha-D-Neup5Ac-(2----6)-beta-D-Galp-(1----4)-beta-D-GlcpNAc-(1--- -2)-alpha-D- Man-OMe (5) was obtained on a 0.1-mmol scale by enzymic sialylation of beta-D-Galp-(1----4)-beta-D-GlcpNAc-(1----2)-alpha-D-Man-OMe (4), prepared by enzymic galactosylation of beta-D-GlcpNAc-(1----2)-alpha-D-Man-OMe (3). Likewise, using 2, alpha-D-Neup-5,9Ac2-(2----6)-beta-D-Galp-(1----4)-D-GlcpNAc (7) was obtained from N-acetyl-lactosamine (6).

Structural parameters and natural occurrence of 2-deoxy-2,3-didehydro-N-glycoloylneuraminic acid

2-Deoxy-2,3-didehydro-N-glycoloylneuraminic acid has been found to occur in porcine, bovine and equine submandibular glands as well as in the urine of pig, horse and rat. This novel, unsaturated sialic acid was isolated by gel filtration and ion-exchange chromatography. Final purification was achieved by column chromatography or by preparative thin-layer chromatography on cellulose. The structural analysis was performed by combined capillary gas-liquid chromatography/mass spectrometry. The various data were compared with those from synthetic 2-deoxy-2,3-didehydro-N-glycoloylneuraminic acid. Besides of the unsaturated N-glycoloylated sialic acid, also the corresponding N-acetylated derivative was present in the materials analyzed. The inhibitory effect of 2-deoxy-2,3-didehydro-N-glycoloylneuraminic acid on Vibrio cholerae sialidase using N-acetylneuraminyl-(alpha 2----3)-lactose as substrate is slightly higher (50% inhibition at 10 microM) when compared with 2-deoxy-2,3-didehydro-N-acetylneuraminic acid (50% inhibition at 15 microM).

New techniques for the investigation of structure and metabolism of sialic acids

Sialic acid analysis in biological material including gangliosides is often confronted with the necessity to determine trace amounts of various N,O-substituted species. Therefore, techniques of high sensitivity and resolution are required, such as capillary gas-liquid chromatography (GLC) and high performance liquid chromatography (HPLC). Both methods in combination with mass spectrometry allow structural analysis of the different neuraminic acid derivatives. Thus, the number of natural sialic acids known so far has increased to more than 30, including non only saturated, but also 2,3-unsaturated and 2,7-anhydro-sialic acids. Furthermore, HPLC has proved to be especially useful for the study of enzyme reactions, as the sialic acids of enzyme assay mixtures in most cases can be analyzed without prior extensive purification or derivatization.