Enzymatic hydrolysis of glycosphingolipids

Activated microglia release β-galactosidase that promotes inflammatory neurodegeneration

Beta (β)-galactosidase is a lysosomal enzyme that removes terminal galactose residues from glycolipids and glycoproteins. It is upregulated in, and used as a marker for, senescent cells. Microglia are brain macrophages implicated in neurodegeneration, and can upregulate β-galactosidase when senescent. We find that inflammatory activation of microglia induced by lipopolysaccharide results in translocation of β-galactosidase to the cell surface and release into the medium. Similarly, microglia in aged mouse brains appear to have more β-galactosidase on their surface. Addition of β-galactosidase to neuronal-glial cultures causes microglial activation and neuronal loss mediated by microglia. Inhibition of β-galactosidase in neuronal-glial cultures reduces inflammation and neuronal loss induced by lipopolysaccharide. Thus, activated microglia release β-galactosidase that promotes microglial-mediated neurodegeneration which is prevented by inhibition of β-galactosidase.

Preparation of Complex Glycans From Natural Sources for Functional Study

One major barrier in glycoscience is the lack of diverse and biomedically relevant complex glycans in sufficient quantities for functional study. Complex glycans from natural sources serve as an important source of these glycans and an alternative to challenging chemoenzymatic synthesis. This review discusses preparation of complex glycans from several classes of glycoconjugates using both enzymatic and chemical release approaches. Novel technologies have been developed to advance the large-scale preparation of complex glycans from natural sources. We also highlight recent approaches and methods developed in functional and fluorescent tagging and high-performance liquid chromatography (HPLC) isolation of released glycans.

Degradation of glycosphingolipids in oyster: ceramide glycanase and ceramidase in the hepatopancreas of oyster, Crassostrea virginica

The hepatopancreas of oyster, Crassostrea virginica, was found to contain two unique glycosphingolipid (GSL) cleaving enzymes, ceramide glycanase (CGase) and ceramidase. These two enzymes were found to be tightly associated together through the consecutive purification steps including gel filtration, hydrophobic interaction and cation-exchange chromatographies. They were separated only by preparatory SDS-PAGE. The purified CGase was found to have a molecular mass of 52 kDa and pH optimum of 3.2-3.3. This enzyme prefers to hydrolyze the acidic GSLs, II³SO₃LacCer and gangliosides over the neutral GSLs. Oyster ceramidase was found to have a molecular mass of 88 kDa and pH optimum of 4-4.5. Since oyster ceramidase greatly prefers ceramides with C₆ to C₈ fatty acids, C₆-ceramide (N-hexanoyl-D-sphingosine) was used as the substrate for its purification and characterization. The oyster acid ceramidase also catalyzed the synthesis of ceramide from a sphingosine and a fatty acid. For the synthesis, C₁₆ and C₁₈ fatty acids were the best precursors. The amino acid sequences of the two cyanogenbromide peptides derived from the purified ceramidase were found to have similarities to those of several neutral and alkaline ceramidases reported. The tight association of CGase and ceramidase may indicate that CGase in oyster hepatopancreas acts as a vehicle to release ceramide from GSLs for subsequent generation of sphingosines and fatty acids by ceramidase to serve as signaling factors and energy source.

Hooked on α-d-galactosidases: from biomedicine to enzymatic synthesis

α-d-Galactosidases (EC 3.2.1.22) are enzymes employed in a number of useful bio-based applications. We have depicted a comprehensive general survey of α-d-galactosidases from different origin with special emphasis on marine example(s). The structures of natural α-galactosyl containing compounds are described. In addition to 3D structures and mechanisms of action of α-d-galactosidases, different sources, natural function and genetic regulation are also covered. Finally, hydrolytic and synthetic exploitations as free or immobilized biocatalysts are reviewed. Interest in the synthetic aspects during the next years is anticipated for access to important small molecules by green technology with an emphasis on alternative selectivity of this class of enzymes from different sources.

A facile method for controlling the reaction equilibrium of sphingolipid ceramide N-deacylase for lyso-glycosphingolipid production

Lyso-glycosphingolipids (lyso-GSLs), the N-deacylated forms of glycosphingolipids (GSLs), are important synthetic intermediates for the preparation of GSL analogs. Although lyso-GSLs can be produced by hydrolyzing natural GSLs using sphingolipid ceramide N-deacylase (SCDase), the yield for this reaction is usually low because SCDase also catalyzes the reverse reaction, ultimately establishing an equilibrium between hydrolysis and synthesis. In the present study, we developed an efficient method for controlling the reaction equilibrium by introducing divalent metal cation and detergent in the enzymatic reaction system. In the presence of both Ca(2+) and taurodeoxycholate hydrate, the generated fatty acids were precipitated by the formation of insoluble stearate salts and pushing the reaction equilibrium toward hydrolysis. The yield of GM1 hydrolysis can be achieved as high as 96%, with an improvement up to 45% compared with the nonoptimized condition. In preparative scale, 75 mg of lyso-GM1 was obtained from 100 mg of GM1 with a 90% yield, which is the highest reported yield to date. The method can also be used for the efficient hydrolysis of a variety of GSLs and sphingomyelin. Thus, this method should serve as a facile, easily scalable, and general tool for lyso-GSL production to facilitate further GSL research.

Cloning of Gb3 synthase, the key enzyme in globo-series glycosphingolipid synthesis, predicts a family of alpha 1, 4-glycosyltransferases conserved in plants, insects, and mammals

We have cloned Gb(3) synthase, the key alpha1, 4-galactosyltransferase in globo-series glycosphingolipid (GSL) synthesis, via a phenotypic screen, which previously yielded iGb(3) synthase, the alpha1,3-galactosyltransferase required in isoglobo-series GSL (Keusch, J. J., Manzella, S. M., Nyame, K. A., Cummings, R. D., and Baenziger, J. U. (2000) J. Biol. Chem. 33). Both transferases act on lactosylceramide, Galbeta1,4Glcbeta1Cer (LacCer), to produce Gb(3) (Galalpha1,4LacCer) or iGb(3) (Galalpha1, 3LacCer), respectively. GalNAc can be added sequentially to either Gb(3) or iGb(3) yielding globoside and Forssman from Gb(3), and isogloboside and isoForssman from iGb(3). Gb(3) synthase is not homologous to iGb(3) synthase but shows 43% identity to a human alpha1,4GlcNAc transferase that transfers a UDP-sugar in an alpha1, 4-linkage to a beta-linked Gal found in mucin. Extensive homology (35% identity) is also present between Gb(3) synthase and genes in Drosophila melanogaster and Arabidopsis thaliana, supporting conserved expression of an alpha1,4-glycosyltransferase, possibly Gb(3) synthase, throughout evolution. The isolated Gb(3) synthase cDNA encodes a type II transmembrane glycosyltransferase of 360 amino acids. The highest tissue expression of Gb(3) synthase RNA is found in the kidney, mesenteric lymph node, spleen, and brain. Gb(3) glycolipid, also called P(k) antigen or CD77, is a known receptor for verotoxins. CHO cells that do not express Gb(3) and are resistant to verotoxin become susceptible to the toxin following transfection with Gb(3) synthase cDNA.

Determination of N-acetyl- and N-glycolylneuraminic acids in gangliosides by combination of neuraminidase hydrolysis and fluorometric high-performance liquid chromatography using a GM3 derivative as an internal standard

A highly sensitive method for quantification of sialic acids in gangliosides was developed. The sialic acids, released by hydrolysis of gangliosides, were converted to fluorescent derivatives with 1,2-diamino-4,5-(methylenedioxy)benzene (DMB) and separated on a reversed-phase C18 column with an isocratic elution. As little as 0.1-1.0 nmol of sialic acid in ganglioside was quantified. The use of acetate buffer instead of water in the mobile phase could prevent damage on the column and reduce background peaks derived from the reagents. When gangliosides were subjected to acid hydrolysis, the velocity of hydrolysis varied depending on their structures and a part of the sialic acid liberated decomposed with prolonged heating time. Therefore gangliosides were hydrolyzed by Arthrobacter ureafaciens neuraminidase in the presence of sodium cholate after addition of an internal standard. For the internal standard, GM3 with N-propionylneuraminic acid (GM3(NeuPr)) was synthesized from GM3(NeuAc) by N-deacylation followed by N-propionylation. Folch partition was used to decrease lipophilic materials included in the sample, and the sialic acids released were recovered from the upper phase. The present method has a satisfactory sensitivity in the simultaneous quantification of NeuAc and NeuGc in purified gangliosides as well as in crude lipid fractions containing a variety of gangliosides.