Identification of a UDP-Gal:beta-galactoside beta 1----3-galactosyltransferase in the albumen gland of the snail Lymnaea stagnalis

Tandem Exploitation ofHelix pomatia Glycosyltransferases: Facile Syntheses of H-Antigen-Bearing Oligosaccharides

Snails from the family Helicidae produce in their albumen glands a highly branched galactan, which consists almost exclusively of D- and L-galactose. The D-Gal residues are glycosydically beta(1-->6)- or beta(1-->3)-linked, whereas the L-Gal moieties are attached alpha(1-->2). Up until the present time, two beta(1-->6)-D-galactosyl transferases and one alpha(1-->2)-L-galactosyl transferase have been identified in a membrane preparation of these glands. These were used to synthesise various oligosaccharides by successive addition of the NDP-activated (NDP=nucleoside-5'-diphosphate) D-Gal or L-Fuc moieties, up to a heptasaccharide by starting from the disaccharide D-Gal-beta(1-->3)-D-Gal-beta(1-->OMe. Even larger oligosaccharides up to a tridecasaccharide were obtained by starting with the hexasaccharide D-Gal-[beta(1-->3)-D-Gal]4-beta(1-->4)-D-Glc as an acceptor substrate. This tandem exploitation process has high potential for the easy introduction of D-Gal and L-Fuc residues into a great variety of oligosaccharides, which can be used in ligand/acceptor studies.

The expression of β-1,3 galactosyltransferase and β-1,4 galactosyltransferase enzymatic activities in the mammary gland of the tammar wallaby (Macropus eugenii) during early lactation

The regulation of beta-1,3 galactosyltransferase (3betaGalT) and beta-1,4 galactosyltransferase enzymatic (4betaGalT) activities in the mammary gland of the tammar wallaby (Macropus eugenii) have been characterised. These two beta-galactosyltransferases are active at different times during the lactation cycle and play a central role in regulating the carbohydrate composition in tammar milk, which changes progressively throughout lactation to assist the physiological development of the altrical young. The 4betaGalT activity was present at parturition and increased 3-fold by day 10 of lactation (d10L), whereas 3betaGalT activity was barely detectable at day d5L and then increased 6-fold by d10L. This increase in activity of both enzymes was sucking dependent. While 3betaGalT activity was not observed in the mammary gland prior to d7L, this activity was found in mammary explants from late pregnant tammar cultured with insulin, hydrocortisone and prolactin (IFP) and was further stimulated by the addition of tri-iodothyronine (T) and 17beta-oestradiol (E). The activity of 4betaGalT in these explants was stimulated maximally with IFP. These data suggest the temporal activity of both 3betaGalT and 4betaGalT is most likely regulated by both endocrine stimuli and factors intrinsic to the mammary gland.

In vitro biosynthesis of galactans by membrane-bound galactosyltransferase from radish ( Raphanus sativus L.) seedlings

We investigated a galactosyltransferase (GalT) involved in the synthesis of the carbohydrate portion of arabinogalactan-proteins (AGPs), which consist of a beta-(1-->3)-galactan backbone from which consecutive (1-->6)-linked beta-Gal p residues branch off. A membrane preparation from 6-day-old primary roots of radish ( Raphanus sativus L.) transferred [(14)C]Gal from UDP-[(14)C]Gal onto a beta-(1-->3)-galactan exogenous acceptor. The reaction occurred maximally at pH 5.9-6.3 and 30 degrees C in the presence of 15 mM Mn(2+) and 0.75% Triton X-100. The apparent K(m) and V(max) values for UDP-Gal were 0.41 mM and 1,000 pmol min(-1) (mg protein)(-1), respectively. The reaction with beta-(1-->3)-galactan showed a bi-phasic kinetic character with K(m) values of 0.43 and 2.8 mg ml(-1). beta-(1-->3)-Galactooligomers were good acceptors and enzyme activity increased with increasing polymerization of Gal residues. In contrast, the enzyme was less efficient on beta-(1-->6)-oligomers. The transfer reaction for an AGP from radish mature roots was negligible but could be increased by prior enzymatic or chemical removal of alpha- l-arabinofuranose (alpha- l-Ara f) residues or both alpha- l-Ara f residues and (1-->6)-linked beta-Gal side chains. Digestion of radiolabeled products formed from beta-(1-->3)-galactan and the modified AGP with exo-beta-(1-->3)-galactanase released mainly radioactive beta-(1-->6)-galactobiose, indicating that the transfer of [(14)C]Gal occurred preferentially onto consecutive (1-->3)-linked beta-Gal chains through beta-(1-->6)-linkages, resulting in the formation of single branching points. The enzyme produced mainly a branched tetrasaccharide, Galbeta(1-->3)[Galbeta(1-->6)] Galbeta(1-->3)Gal, from beta-(1-->3)-galactotriose by incubation with UDP-Gal, confirming the preferential formation of the branching linkage. Localization of the GalT in the Golgi apparatus was revealed on a sucrose density gradient. The membrane preparation also incorporated [(14)C]Gal into beta-(1-->4)-galactan, indicating that the membranes contained different types of GalT isoform catalyzing the synthesis of different types of galactosidic linkage.

Cloning of a human UDP-galactose:2-acetamido-2-deoxy-D-glucose 3beta-galactosyltransferase catalyzing the formation of type 1 chains

Biochemical evidence suggests that the galactosyltransferase activity synthesizing type 1 carbohydrate chains is separate from the well characterized enzyme that is responsible for the synthesis of type 2 chains. This was recently confirmed by the cloning, from melanoma cells, of an enzyme capable of synthesizing type 1 chains, which was shown to have no homology to other galactosyltransferases. We report here the molecular cloning and functional expression of a second human beta3-galactosyltransferase distinct from the melanoma enzyme. The new beta3-galactosyltransferase has homology to the melanoma enzyme in the putative catalytic domain, but has longer cytoplasmic and stem regions and a carboxyl-terminal extension. Northern blots showed that the new gene is present primarily in brain and heart. When transfected into mammalian cells, this gene directs the synthesis of type 1 chains as determined by a monoclonal antibody specific for sialyl Lewisa. A soluble version of the cloned enzyme was expressed in insect cells and purified. The soluble enzyme readily catalyzes the transfer of galactose to GlcNAc to form Gal(beta1-3)GlcNAc. It also has a minor but distinct transfer activity toward Gal, LacNAc, and lactose, but is inactive toward GalNAc.

Purification, properties, and immunological characterization of GalT-3 (UDP-galactose: GM2 ganglioside, beta 1-3 galactosyltransferase) from embryonic chicken brain

A beta 1-3 galactosyltransferase (GalT-3; UDP-Gal; GM2 beta 1-3 galactosyltransferase) was purified over 5100-fold from 19-day-old embryonic chicken brain homogenate employing detergent solubilization, alpha-lactalbumin Sepharose, Q-Sepharose, UDP-hexanolamine Sepharose, and GalNAc beta 1-4Gal beta-Synsorb column chromatography. The purified enzyme was resolved into two bands on reducing gels with apparent molecular weights of 62 kDa and 65 kDa, respectively. GalT-3 activity was also localized in the same regions by activity gel analysis and sucrose-density gradient centrifugation of a detergent-solubilized extract of 19-day-old embryonic chicken brain. Purified GalT-3 exhibited apparent Kms of 33 microM, and 14.4 mM with respect to the substrates GM2, UDP-galactose, and MnCl2, respectively. Substrate specificity studies with the purified enzyme and a variety of glycosphingolipids, glycoproteins, and synthetic substrates revealed that the enzyme was highly specific only for the glycosphingolipid acceptors, GM2 and GgOse3Cer (asialo-GM2). Ovine-asialo-agalacto submaxillary mucin inhibited the transfer of galactose to GM2 but did not act as an acceptor in the range of concentrations tested. Polyclonal antibodies raised against purified GalT-3 inhibited GalT-3 activity in vitro and Western-immunoblot analysis of purified GalT-3 showed immunopositive bands at 62 and 65 kDa.

Biosynthesis of the storage polysaccharide from the snail Biomphalaria glabrata, identification and specificity of a branching beta 1-->6 galactosyltransferase

Adult snails synthesize in their albumen glands a storage polysaccharide called galactan which is utilized by the developing embryos. With [6-3H]-uridine 5'diphosphogalactose the incorporation of labelled D-galactose into the polysaccharide can be traced in freshly removed glands maintained in a bathing buffer. After centrifugation of homogenized glands, galactosyltransferase activity is only found in the insoluble fraction. Chaps extracts of this material retain almost all of their activity and can be used for comparison of the incorporation rates into different native galactans or in various oligosaccharides. A highly efficient beta-(1-->6) galactosyltransferase was detected when methyl 3-O-(beta-D-galactopyranosyl)-beta-D-galactopyranoside was offered as acceptor. The substitution at the penultimate residue resulted in a branched trisaccharide as demonstrated by 1H-NMR-spectroscopy and permethylation analysis of the reaction product. Comparable results were obtained with various oligosaccharides containing an internal galactose unit glycosidically linked beta 1-->3. Attempts to separate and purify the various enzymes involved resulted in the isolation of a fraction which is able to transfer D-Gal exclusively to native galactan, but not to oligosaccharides. A further fraction was obtained from a different resin with activity for native galactan and 6-O-(beta-D-galactopyranosyl)-D-galactopyranose, but without any for methyl-3-O-(beta-D-galactopyranosyl)-beta-D-galactopyranose. It is thus concluded that at least three different enzymes are involved in the biosynthesis of this snail galactan.

Identification of a novel UDP-GalNAc:GlcNAc beta-R beta 1-4 N-acetylgalactosaminyltransferase from the albumen gland and connective tissue of the snail Lymnaea stagnalis

Both the albumen gland, one of the female accessory sex glands, and connective tissue of the freshwater snail Lymnaea stagnalis contain N-acetylgalactosaminyltransferase activity, capable of transferring GalNAc from UDP-GalNAc in beta 1-4 linkage to the terminal GlcNAc residue of GlcNAc beta-R. The albumin gland enzyme was partially purified by affinity chromatography on UDP-hexanolamine-Sepharose 4B. Using GlcNAc beta 1-2Man alpha 1-6(GlcNAc beta 1-2Man alpha 1-3)Man beta 1-4GlcNAc beta 1-4GlcNAc or GlcNAc beta 1-OMe as substrates, the enzyme showed an absolute requirement for Mn2+ with an optimum concentration of 12.5-50 mM. The optimal pH was approximately pH 7.0. The enzyme activity was independent of the Triton X-100 concentration in the range 0.25-2.5%, and no activation effect was found. The more labile connective tissue microsomal enzyme, subjected to the same optimization procedure, gave comparable results. Both enzyme activities have similar substrate specificities towards GlcNAc or GlcNAc beta 1-OMe, and towards oligosaccharides or glycopeptides with a non-reducing terminal beta-GlcNAc unit, but cannot act on GlcNAc alpha 1-OMe. Saccharides with non-reducing terminal Gal or GalNAc residues, and free GalNAc, Gal or Glc residues are not acceptors. Product analysis was carried out for albumen gland N-acetylgalactosaminyltransferase and four acceptors having GlcNAc beta 1-R as the terminal non-reducing unit, and for connective tissue N-acetylgalactosaminyltransferase with GlcNAc beta 1-OMe as acceptor. In all instances, products with GalNAc beta 1-4-linked to GlcNAc were obtained, showing that the connective tissue and the albumen gland activities are probably from one enzyme. This enzyme activity can be identified as UDP-GalNAc:GlcNAc beta-R beta 1-4 N-acetylgalactosaminyltransferase, and is probably involved in the biosynthesis of N,N'-diacetyllactosediamine-containing glycoproteins, like hemocyanin, in the snail L. stagnalis.

Identification of a novel UDP-Gal:GalNAc beta 1-4GlcNAc-R beta 1-3-galactosyltransferase in the connective tissue of the snail Lymnaea stagnalis

Connective tissue of the freshwater pulmonate Lymnaea stagnalis was shown to contain galactosyltransferase activity capable of transferring Gal from UDP-Gal in beta 1-3 linkage to terminal GalNAc of GalNAc beta 1-4GlcNAc-R [R = beta 1-2Man alpha 1-O(CH2)8COOMe, beta 1-OMe, or alpha,beta 1-OH]. Using GalNAc beta 1-4GlcNAc beta 1-2Man alpha-1-O(CH2)8COOMe as substrate, the enzyme showed an absolute requirement for Mn2+ with an optimum Mn2+ concentration between 12.5 mM and 25 mM. The divalent cations Mg2+, Ca2+, Ba2+ and Cd2+ at 12.5 mM could not substitute for Mn2+. The galactosyltransferase activity was independent of the concentration of Triton X-100, and no activation effect was found. The enzyme was active with GalNAc beta 1-4GlcNAc beta 1-2Man alpha 1-O(CH2)8COOMe (Vmax 140 nmol.h-1.mg protein-1; Km 1.02 mM), GalNAc beta 1-4GlcNAc (Vmax 105 nmol.h-1.mg protein-1; Km 0.99 mM), and GalNAc beta 1-4GlcNAc beta 1-OMe (Vmax 108 nmol.h-1.mg protein-1; Km 1.33 mM). The products formed from GalNAc beta 1-4GlcNAc beta 1-2Man alpha 1-O(CH2)8COOMe and GalNAc beta 1-4GlcNAc beta 1-OMe were purified by high performance liquid chromatography, and identified by 500-MHz 1H-NMR spectroscopy to be Gal beta 1-3GalNAc beta 1-4GlcNAc 1-OMe, respectively. The enzyme was inactive towards GlcNAc, GalNac beta 1-3 GalNAc alpha 1-OC6H5, GalNAc alpha 1--ovine-submaxillary-mucin, lactose and N-acetyllactosamine. This novel UDP-Gal:GalNAc beta 1-4GlcNAc-R beta 1-3-galactosyltransferase is believed to be involved in the biosynthesis of the hemocyanin glycans of L. stagnalis.

Biosynthesis of marsupial milk oligosaccharides: characterization and developmental changes of two galactosyltransferases in lactating mammary glands of the tammar wallaby, Macropus eugenii

Tammar wallaby (Macropus eugenii) mammary glands contain two galactosyltransferases of which the first, 4 beta GalT, is a UDP-galactose:N-acetylglucosaminyl beta 1----4-galactosyltransferase equivalent to the A protein of the lactose synthase of eutherian mammals. The second enzyme, 3 beta GalT, is a UDP-galactose:lactose beta 1----3-galactosyltransferase, not previously identified in mammary glands of any species, which catalyses the formation of Gal beta 1----3 Gal beta 1----4 Glc from lactose. The two enzyme activities, as well as the lactose synthase activity, have been characterised with respect to the effects of pH, apparent Km values, effects of bovine and tammar alpha-lactalbumins, heat sensitivity and identity of products. Studies on the substrate specificity and heat sensitivity of the 3 beta GalT activity suggest that this enzyme may catalyse the beta-galactosylation of Gal beta 1----3Gal beta 1----4Glc as well as of lactose. The activity of the 3 beta GalT, unlike that of the 4 beta GalT, changes dramatically during the course of lactation in parallel with similar changes in the carbohydrate content of tammar milk.

Alpha 1----3-galactosyltransferase: the use of recombinant enzyme for the synthesis of alpha-galactosylated glycoconjugates

We have reported the isolation and characterization of a bovine cDNA clone containing the complete coding sequence for UDP-Gal:Gal beta 1----4GlcNAc alpha 1----3-galactosyltransferase [Joziasse, D. H., Shaper, J. H., Van den Eijnden, D. H., Van Tunen, A. J. & Shaper, N. L. (1989) J. Biol. Chem. 264, 14290-14297]. Insertion of this cDNA clone into the genome of Autographa californica nuclear polyhedrosis virus (AcNPV) and subsequent infection of Spodoptera frugiperda (Sf9) insect cells with recombinant virus, resulted in high-level expression of enzymatically active alpha 1----3-galactosyltransferase. The expressed enzyme accounted for about 2% of the cellular protein; the corresponding specific enzyme activity was 1000-fold higher than observed in calf thymus, the tissue with the highest specific enzyme activity reported to date. The recombinant alpha 1----3-galactosyltransferase could be readily detergent-solubilized and subsequently purified by affinity chromatography on UDP-hexanolamine-Sepharose. The recombinant alpha 1----3-galactosyltransferase showed the expected preference for the acceptor substrate N-acetyllactosamine (Gal beta 1----4GlcNAc), and demonstrated enzyme kinetics identical to those previously reported for affinity-purified calf thymus alpha 1----3-galactosyltransferase [Blanken, W. M. & Van den Eijnden, D. H. (1985) J. Biol. Chem. 260, 12927-12934]. In pilot studies, the recombinant enzyme was examined for the ability to synthesize alpha 1----3-galactosylated oligosaccharides, glycolipids and glycoproteins. By a combination of 1H-NMR, methylation analysis, HPLC, and exoglycosidase digestion it was established that, for each of the model compounds, the product of galactose transfer had the anticipated terminal structure, Gal alpha 1----3Gal beta 1----4-R. Our results demonstrate that catalysis by recombinant alpha 1----3-galactosyltransferase can be used to obtain preparative quantities of various alpha 1----3-galactosylated glycoconjugates. Therefore, enzymatic synthesis using the recombinant enzyme is an effective alternative to the chemical synthesis of these biologically relevant compounds.

Biosynthesis of galactogen: identification of a beta-(1----6)-D-galactosyltransferase in Helix pomatia albumen glands

A beta-(1----6)-D-galactosyltransferase has been purified over 2000-fold by affinity chromatography on UDP-p-aminophenyl-Sepharose. The enzyme, from a pellet fraction (8000 x g) of Helix pomatia albumen gland, catalyzes transfer of D-galactose from UDP-galactose to a (1----6) linkage on acceptor H. pomatia galactogen. Three other polymers served as acceptors: beef lung galactan, Lymnaea stagnalis galactogen and arabinogalactan from larch wood. To determine the linkage specificity of the enzyme, it was incubated with UDP-D-galactose and acceptor galactogen that had been tritiated previously by treatment with galactose oxidase and [3H]KBH4. The [3H]galactogen reaction product was recovered, methylated, hydrolyzed and acetylated; tritiated derivatives were identified by mass spectroscopy of effluent fractions separated by gas chromatography. This analysis revealed that (1----6)-linked galactosyl groups had been added to the enzyme-treated acceptor galactogen. Also identified was a hydrolytic enzyme that removed terminal alpha 1,2-linked L-galactosyl residues from H. pomatia galactogen.