Acceptor specificity of different length constructs of human recombinant alpha 1,3/4-fucosyltransferases. Replacement of the stem region and the transmembrane domain of fucosyltransferase V by protein A results in an enzyme with GDP-fucose hydrolyzing activity

A GDP-fucose-protected, pyridoxal-5'-Phosphate/NaBH(4)-sensitive lys residue common to human alpha1-->3Fucosyltransferases corresponds to Lys(300) in FucT-IV

Human alpha1-->3/4fucosyltransferases (FucTs) contain a common essential pyridoxal-5'-phosphate(PLP)/NaBH(4) reactive, GDP-fucose-protectable Lys. For identification, site-directed mutants at lysines of FucT-IV and -VII were prepared and tested. Non conserved lysine mutants K119Y and K394Q were similar to wild-type FucT-IV. However, mutants of conserved lysines K228R and K300R were distinct. The specific activity of K228R was 2- to 3-fold lower but retained K(m) values for donor and acceptor substrates as wild-type FucT-IV. The specific activity of K300R was reduced over 400-fold with an apparent K(m) for GDP-fucose over 200 microM. FucT-VII mutants K169R and K240R (equivalent to K228R and K300R for FucT-IV, respectively) were inactive. No change in PLP/NaBH(4) sensitivity occurred with K119Y, K228R, and K394Q compared to wild-type FucT-IV. These and previous results (A. L. Sherwood, A. T. Nguyen, J. M. Whitaker, B. A. Macher, M. R. Stroud, and E. H. Holmes, J. Biol. Chem. 273, 25256-25260, 1998) demonstrate that of three conserved lysines in FucT-IV, two (Lys(228) and Lys(283)) are not involved in substrate binding but perhaps in catalysis. The third site, Lys(300), is involved in GDP-fucose binding and PLP/NaBH(4) inactivation.

Unravelling the biochemical basis of blood group ABO and Lewis antigenic specificity

The ABO blood-group polymorphism is still the most clinically important system in blood transfusion practice. The groups were discovered in 1900 and the genes at the ABO locus were cloned nearly a century later in 1990. To enable this goal to be reached intensive studies were carried out in the intervening years on the serology, genetics, inheritance and biochemistry of the antigens belonging to this system. This article describes biochemical genetic investigations on ABO and the related Lewis antigens starting from the time in the 1940s when serological and classical genetical studies had established the immunological basis and mode of inheritance of the antigens but practically nothing was known about their chemical structure. Essential steps were the definition of H as the product of a genetic system Hh independent of ABO, and the establishment of the precursor-product relationship of H to A and B antigens. Indirect methods gave first indications that the specificity of antigens resided in carbohydrate and revealed the immunodominant sugars in the antigenic structures. Subsequently chemical fragmentation procedures enabled the complete determinant structures to be established. Degradation experiments with glycosidases revealed how loss of one specificity by the removal of a single sugar unit exposed a new specificity and suggested that biosynthesis proceeded by a reversal of this process whereby the oligosaccharide structures were built up by the sequential addition of sugar units. Hence, the primary blood-group gene products were predicted to be glycosyltransferase enzymes that added the last sugar to complete the determinant structures. Identification of these enzymes gave new genetic markers and eventually purification of the blood-group A-gene encoded N-acetylgalactosaminyltransferase gave a probe for cloning the ABO locus. Blood-group ABO genotyping by DNA methods has now become a practical possibility.

Biochemical characterization and molecular cloning of an alpha-1,2-fucosyltransferase that catalyzes the last step of cell wall xyloglucan biosynthesis in pea

Pea microsomes contain an alpha-fucosyltransferase that incorporates fucose from GDP-fucose into xyloglucan, adding it preferentially to the 2-O-position of the galactosyl residue closest to the reducing end of the repeating subunit. This enzyme was solubilized with detergent and purified by affinity chromatography on GDP-hexanolamine-agarose followed by gel filtration. By utilizing peptide sequences obtained from the purified enzyme, a cDNA clone was isolated that encodes a 565-amino acid protein with a predicted molecular mass of 64 kDa and shows 62.3% identity to its Arabidopsis homolog. The purified transferase migrates at approximately 63 kDa by SDS-polyacrylamide gel electrophoresis but elutes from the gel filtration column as an active protein of higher molecular weight ( approximately 250 kDa), indicating that the active form is an oligomer. The enzyme is specific for xyloglucan and is inhibited by xyloglucan oligosaccharides and by the by-product GDP. The enzyme has a neutral pH optimum and does not require divalent ions. Kinetic analysis indicates that GDP-fucose and xyloglucan associate with the enzyme in a random order. N-Ethylmaleimide, a cysteine-specific modifying reagent, had little effect on activity, although several other amino acid-modifying reagents strongly inhibited activity.

Evolution of alpha 2-fucosyltransferase genes in primates: relation between an intronic Alu-Y element and red cell expression of ABH antigens

Coding sequences of the paralogous FUT1 (H), FUT2 (Se), and Sec1 alpha 2-fucosyltransferase genes were obtained from different primate species. Analysis of the primate FUT1-like and FUT2-like sequences revealed the absence of the known human inactivating mutations giving rise to the h null alleles of FUT1 and the se null alleles of FUT2. Therefore, most primate FUT1-like and FUT2-like genes potentially code for functional enzymes. The Sec1-like gene encodes for a potentially functional alpha 2-fucosyltransferase enzyme in nonprimate mammals, New World monkeys, and Old World monkeys, but it has been inactivated by a nonsense mutation at codon 325 in the ancestor of humans and African apes (gorillas, chimpanzees). Human and gorilla Sec1's have, in addition, two deletions and one insertion, respectively, 5' of the nonsense mutation leading to proteins shorter than chimpanzee Sec1. Phylogenetic analysis of the available H, Se, and Sec1 mammalian protein sequences demonstrates the existence of three clusters which correspond to the three genes. This suggests that the differentiation of the three genes is rather old and predates the great mammalian radiation. The phylogenetic analysis also suggests that Sec1 has a higher evolutionary rate than FUT2 and FUT1. Finally, we show that an Alu-Y element was inserted in intron 1 of the FUT1 ancestor of humans and apes (chimpanzees, gorillas, orangutans, and gibbons); this Alu-Y element has not been found in monkeys or nonprimate mammals, which lack ABH antigens on red cells. A potential mechanism leading to the red cell expression of the H enzyme in primates, related to the insertion of this Alu-Y sequence, is proposed.

Cloning and characterization of the alpha(1,3/4) fucosyltransferase of Helicobacter pylori

The gastric pathogen Helicobacter pylori can express the histo blood group antigens, which are on the surface of many human cells. Most H. pylori strains express the type II carbohydrates, Lewis X and Y, whereas a small population express the type I carbohydrates, Lewis A and B. The expression of Lewis A and Lewis X, as in the case of H. pylori strain UA948, requires the addition of fucose in alpha1,4 and alpha1,3 linkages to type I or type II carbohydrate backbones, respectively. This work describes the cloning and characterization of a single H. pylori fucosyltransferase (FucT) enzyme, which has the ability to transfer fucose to both of the aforementioned linkages in a manner similar to the human fucosyltransferase V (Fuc-TV). Two homologous copies of the fucT gene have been identified in each of the genomes sequenced. The characteristic adenosine and cytosine tracts in the amino terminus and repeated regions in the carboxyl terminus are present in the DNA encoding the two UA948fucT genes, but these genes also contain differences when compared with previously identified H. pylori fucTs. The UA948fucTa gene encodes an approximately 52-kDa protein containing 475 amino acids, whereas UA948fucTb does not encode a full-length FucT protein. In vitro, UA948FucTa appears to add fucose with a greater than 5-fold preference for type II chains but still retains significant activity using type I acceptors. The addition of the fucose to the type II carbohydrate acceptors, by UA948FucTa, does not appear to be affected by fucosylation at other sites on the carbohydrate acceptor, but the rate of fucose transfer is affected by terminal fucosylation of type I acceptors. Through mutational analysis we demonstrate that only FucTa is active in this H. pylori isolate and that inactivation of this enzyme eliminates expression of all Lewis antigens.

Fucose in N-glycans: from plant to man

Fucosylated oligosaccharides occur throughout nature and many of them play a variety of roles in biology, especially in a number of recognition processes. As reviewed here, much of the recent emphasis in the study of the oligosaccharides in mammals has been on their potential medical importance, particularly in inflammation and cancer. Indeed, changes in fucosylation patterns due to different levels of expression of various fucosyltransferases can be used for diagnoses of some diseases and monitoring the success of therapies. In contrast, there are generally at present only limited data on fucosylation in non-mammalian organisms. Here, the state of current knowledge on the fucosylation abilities of plants, insects, snails, lower eukaryotes and prokaryotes will be summarised.

Aglycone structure influences alpha-fucosyltransferase III activity using N-acetyllactosamine glycoside acceptors

We showed previously that Chinese hamster ovary cells took up and utilized a variety of N-acetylglucosaminides as primers of oligosaccharide biosynthesis (Ding et al., 1999, J. Carbohydr. Chem., 18:471-475). In this study, a library of N-acetylglucosaminides was enzymatically galactosylated in vitro to yield type 2 chain N-acetyllactosaminides bearing a variety of aglycones. Those disaccharides are potential acceptors for fucosyltransferases. As an extension of the previous study, we tested the type 2 chain disaccharyl glycosides (Galbeta1,4-GlcNAcbeta-R) for their aglycone-dependent acceptor specificity for alpha-L-fucosyltransferase III (Fuc-TIII). The enzyme activity significantly depended on the aglycone structures, suggesting that, in addition to the polar groups on the sugar moiety, the hydrophobic aglycone can substantially contribute to recognition in this reaction.

Sequential biosynthesis of sulfated and/or sialylated Lewis x determinants by transferases of the human bronchial mucosa

The structural determination of sulfated carbohydrate chains from a cystic fibrosis patient respiratory mucins has shown that sulfation may occur either on the C-3 of the terminal Gal, or on the C-6 of the GlcNAc residue of a terminal N -acetyllactosamine unit. The two enzymes responsible for the transfer of sulfate from PAPS to the C-3 of Gal or to the C-6 of GlcNAc residues have been characterized in human respiratory mucosa. These two enzymes, in conjunction with fucosyl- and sialyltransferases, allow the synthesis of different sulfated epitopes such as 3-sulfo Lewis x (with a 3- O -sulfated Gal), 6-sulfo Lewis x and 6-sulfo-sialyl Lewis x (with a 6- O -sulfated GlcNAc). In the present study, the sequential biosynthesis of these epitopes has been investigated using microsomal fractions from human respiratory mucosa incubated with radiolabeled nucleotide-sugars or PAPS, and oligosaccharide acceptors, mostly prepared from human respiratory mucins. The structures of the radiolabeled products have been determined by their coelution in HPAEC with known oligosaccharidic standards. In the biosynthesis of 6- O -sulfated carbohydrate chains by the human respiratory mucosa, the 6- O -sulfation of a terminal nonreducing GlcNAc residue precedes beta1-4-galactosylation, alpha2-3-sialylation (to generate 6-sulfo-sialyl- N -acetyllactosamine), and alpha1-3-fucosylation (to generate the 6-sulfo-sialyl Lewis x determinant). The 3- O -sulfation of a terminal N -acetyllactosamine may occur if this carbohydrate unit is not substituted. Once an N -acetyllactosamine unit is synthesized, alpha1-3-fucosylation of the GlcNAc residue to generate a Lewis x structure blocks any further substitution. Therefore, the present study defines the pathways for the biosynthesis of Lewis x, sialyl Lewis x, sulfo Lewis x, and 6-sulfo-sialyl Lewis x determinants in the human bronchial mucosa.

Biosynthesis of sialylated and fucosylated selectin ligands of HL-60 cells in vitro. Midchain alpha3-fucose units inhibit terminal alpha6-sialylation but not alpha3-sialylation of polylactosamines

Polylactosamines Neu5Ac alpha2-3'Lex beta1-3'Lex beta1-3'Lex and Neu5Ac alpha2-3'LNbeta1-3'Lex beta1-3'Lex [Lex, Gal beta1-4(Fuc alpha1-3)GlcNAc; LN, Gal beta1-4GlcNAc] decorate selectin counterreceptors in human HL-60 cells. Here, we show that HL-60 cell lysates catalyze distal alpha3-sialylation of LNbeta1-3'LNbeta1-3'LN and LNbeta1-3'Lex beta1-3'Lex efficiently, outlining two potential sets of biosynthetic pathways leading to the selectin ligands. In one set, alpha3-sialylation precedes internal fucosylation of the polylactosamine backbone, whereas in the other one, internal fucosylation is initiated before alpha3-sialylation. In contrast to alpha3-sialylation, LNbeta1-3'Lex beta1-3'Lex was alpha6-sialylated much less efficiently than LNbeta1-3'LNbeta1-3'LN by HL-60 cell lysates. Hence, internal fucosylation may regulate the extent of alpha6-sialylation of polylactosamines in these cells.

The acceptor substrate specificity of human beta4-galactosyltransferase V indicates its potential function in O-glycosylation

In order to assess the function of the different human UDP-Gal:GlcNAc beta4-galactosyltransferases, the cDNAs of two of them, beta4-GalT I and beta4-GalT V, were expressed in the baculovirus/insect cell expression system. The soluble recombinant enzymes produced were purified from the medium and used to determine their in vitro substrate specificities. The specific activity of the recombinant beta4-GalT V was more than 15 times lower than that of beta4-GalT I, using GlcNAc beta-S-pNP as an acceptor. Whereas beta4-GalT I efficiently acts on all substrates having a terminal beta-linked GlcNAc, beta4-GalT V appeared to be far more restricted in acceptor usage. Beta4-GalT V acts with high preference on acceptors that contain the GlcNAc beta1-->6GalNAc structural element, as found in O-linked core 2-, 4- and 6-based glycans, but not on substrates related to V-linked or blood group I-active oligosaccharides. These results suggest that beta4-GalT V may function in the synthesis of lacNAc units on O-linked chains, particularly in tissues which do not express beta4-GalT I, such as brain.

A single amino acid in the hypervariable stem domain of vertebrate alpha1,3/1,4-fucosyltransferases determines the type 1/type 2 transfer. Characterization of acceptor substrate specificity of the lewis enzyme by site-directed mutagenesis

Alignment of 15 vertebrate alpha1,3-fucosyltransferases revealed one arginine conserved in all the enzymes employing exclusively type 2 acceptor substrates. At the equivalent position, a tryptophan was found in FUT3-encoded Lewis alpha1,3/1,4-fucosyltransferase (Fuc-TIII) and FUT5-encoded alpha1,3/1,4-fucosyltransferase, the only fucosyltransferases that can also transfer fucose in alpha1, 4-linkage. The single amino acid substitution Trp111 --> Arg in Fuc-TIII was sufficient to change the specificity of fucose transfer from H-type 1 to H-type 2 acceptors. The additional mutation of Asp112 --> Glu increased the type 2 activity of the double mutant Fuc-TIII enzyme, but the single substitution of the acidic residue Asp112 in Fuc-TIII by Glu decreased the activity of the enzyme and did not interfere with H-type 1/H-type 2 specificity. In contrast, substitution of Arg115 in bovine futb-encoded alpha1, 3-fucosyltransferase (Fuc-Tb) by Trp generated a protein unable to transfer fucose either on H-type 1 or H-type 2 acceptors. However, the double mutation Arg115 --> Trp/Glu116 --> Asp of Fuc-Tb slightly increased H-type 1 activity. The acidic residue adjacent to the candidate amino acid Trp/Arg seems to modulate the relative type 1/type 2 acceptor specificity, and its presence is necessary for enzyme activity since its substitution by the corresponding amide inactivated both Fuc-TIII and Fuc-Tb enzymes.

The gain-of-function Chinese hamster ovary mutant LEC11B expresses one of two Chinese hamster FUT6 genes due to the loss of a negative regulatory factor

The LEC11 Chinese hamster ovary (CHO) gain-of-function mutant expresses an alpha(1,3)fucosyltransferase (alpha(1,3)Fuc-T) activity that generates the LeX, sialyl-LeX, and VIM-2 glycan determinants and has been extensively used for studies of E-selectin ligand specificity. In order to identify regulatory mechanisms that control alpha(1,3)Fuc-T expression in mammals, mechanisms of FUT gene expression were investigated in LEC11 cells and two new, independent mutants, LEC11A and LEC11B. Northern and ribonuclease protection analyses, using probes that span the coding region of a cloned CHO FUT gene, detected transcripts in each LEC11 mutant but not in CHO cells or other gain-of-function CHO mutants that express a different alpha(1,3)Fuc-T activity. Coding region sequence analysis and alpha(1,3)Fuc-T acceptor specificity comparisons with recombinant human Fuc-TV and Fuc-TVI showed that the cloned FUT gene is orthologous to the human FUT6 gene. Southern analyses identified two closely related FUT6 genes in the Chinese hamster, whose evolutionary relationships are discussed. The blots showed that rearrangements had occurred in LEC11A and LEC11 genomic DNA, consistent with a cis mechanism of FUT6 gene activation in these mutants. By contrast, somatic cell hybrid analyses revealed that LEC11B cells express FUT6 gene transcripts due to the loss of a trans-acting, negative regulatory factor. Sequencing of reverse transcriptase-polymerase chain reaction products identified unique 5'- and 3'-untranslated region sequences in FUT6 gene transcripts from each LEC11 mutant. Northern and Southern analyses with gene-specific probes showed that LEC11A cells express only the cgFUT6A gene (where cg is Cricetulus griseus), whereas LEC11 and LEC11B cells express only the cgFUT6B gene. In LEC11A x LEC11B hybrid cells, the cgFUT6A gene was predominantly expressed, as predicted if a trans-acting negative regulatory factor functions to suppress cgFUT6B gene expression in CHO cells. This factor is predicted to be a cell type-specific regulator of FUT6 gene expression in mammals.

Genetic engineering of recombinant glycoproteins and the glycosylation pathway in mammalian host cells

The analysis of many natural glycoproteins and their recombinant counterparts from mammalian hosts has revealed that the basic oligosaccharide structures and the site occupancy of glycosylated polypeptides are primarily dictated by the protein conformation. The equipment of many frequently used host cells (e.g. BHK-21 and CHO-cells) with glycosyltransferases, nucleotide-sugar synthases and transporters appears to be sufficient to guarantee complex-type glycosylation of recombinant proteins with a high degree of terminal alpha2-3 sialylation even under high expression conditions. Some human tissue-specific terminal carbohydrate motifs are not synthesized by these cells since they lack the proper sugar-transferring enzymes (e.g. alpha1-3/4 fucosyltransferases, alpha2-6 sialyltransferases). Glycosylation engineering of these hosts by stable transfection with genes encoding terminal human glycosyltransferases allows to obtain products with tailored (human tissue-specific) glycosylation in high yields. Using site-directed mutagenesis, unglycosylated polypeptides can be successfully converted in N- and/or O-glycoproteins by transferring glycosylation domains (consisting of 7-17 amino acids) from donor glycoproteins to different loop regions of acceptor proteins. The genetic engineering of glycoproteins and of host cell lines are considered to provide a versatile tool to obtain therapeutic glyco-products with novel/improved in-vivo properties, e.g. by introduction of specific tissue-targeting signals by a rational design of terminal glycosylation motifs.

Expression of human alpha-l-fucosyltransferase gene homologs in monkey kidney COS cells and modification of potential fucosyltransferase acceptor substrates by an endogenous glycosidase

Previous investigations on the monkey kidney COS cell line demonstrated the weak expression of fucosylated cell surface antigens and presence of endogenous fucosyltransferase activities in cell extracts. RT-PCR analyses have now revealed expression of five homologs of human fucosyltransferase genes, FUT1, FUT4, FUT5, FUT7, and FUT8, in COS cell mRNA. The enzyme in COS cell extracts acting on unsialylated Type 2 structures is closely similar in its properties to the alpha1,3-fucosyltransferase encoded by human FUT4 gene and does not resemble the product of the FUT5 gene. Although FUT1 is expressed in the COS cell mRNA, it has not been possible to demonstrate alpha1,2-fucosyltransferase activity in cell extracts but the presence of Le(y) and blood-group A antigenic determinants on the cell surface imply the formation of H-precursor structures at some stage. The most strongly expressed fucosyltransferase in the COS cells is the alpha1,6-enzyme transferring fucose to the innermost N -acetylglucosamine unit in N -glycan chains; this enzyme is similar in its properties to the product of the human FUT8 gene. The enzymes resembling the human FUT4 and FUT8 gene products both had pH optima of 7.0 and were resistant to 10 mM NEM. The incorporation of fucose into asialo-fetuin was optimal at 5.5 and was inhibited by 10 mM NEM. This result initially suggested the presence of a third fucosyltransferase expressed in the COS cells but we have now shown that triantennary N- glycans with terminal nonreducing galactose units, similar to those present in asialo-fetuin, are modified by a weak endogenous beta-galactosidase in the COS cell extracts and thereby rendered suitable substrates for the alpha1,6-fucosyltransferase.

Mouse C127 cells transfected with fucosyltransferase fuc-TIII express masked Lewisx but not Lewisx antigen

To study human alpha1,3/1,4fucosyltransferase (Fuc-TIII) as an alpha1,3 fucosyltransferase, we constructed two cell clones, C127-FT and C127-T-FT, by transfecting cDNA in parental (C127) or Polyoma T antigen expressing (C127-T) mouse cells, respectively. Both C127-FT and C127-T-FT clones express high levels of a fucosyltransferase activity kinetically similar to Fuc-TIII and an RNA that is amplified by a Fuc-TIII-specific oligonucleotide primer pair after reverse transcription. Clone C127-FT is Lewisxpositive, by flow cytometry, only after alpha-galactosidase or sialidase treatment, and releases [3H]Fuc N-glycans which efficiently bind to immobilized Griffonia simplicifolia I and Sambucus nigra lectins. Immunoblotting confirms that C127-FT glycoproteins acquire Lewisxreactivity only after specific deglycosylation, and shows that a small subset of Griffonia simplicifolia I isolectin B4reactive glycoproteins bears masked Lewisx, suggesting fine substrate recognition by Fuc-TIII. Moreover, transient transfection of H type alpha1, 2fucosyltransferase in clone C127-T-FT directs synthesis of Lewisyantigen, as detected by flow cytometry. Results indicate that Fuc-TIII expressed in C127 cells synthesizes masked Lewisxantigen while Lewisxantigen is not detectable.

In vivo specificity of human alpha1,3/4-fucosyltransferases III-VII in the biosynthesis of LewisX and Sialyl LewisX motifs on complex-type N-glycans. Coexpression studies from bhk-21 cells together with human beta-trace protein

Each of the five human alpha1,3/4-fucosyltransferases (FT3 to FT7) has been stably expressed in BHK-21 cells together with human beta-trace protein (beta-TP) as a secretory reporter glycoprotein. In order to study their in vivo properties for the transfer of peripheral Fuc onto N-linked complex-type glycans, detailed structural analysis was performed on the purified glycoprotein. All fucosyltransferases were found to peripherally fucosylate 19-52% of the diantennary beta-TP N-glycans, and all enzymes were capable of synthesizing the sialyl LewisX (sLex) motif. However, each enzyme produced its own characteristic ratio of sLex/Lex antennae as follows: FT7 (only sLex), FT3 (14:1), FT5 (3:1), FT6 (1.1:1), and FT4 (1:7). Fucose transfer onto beta-TP N-glycans was low in FT3 cells (11% of total antennae), whereas the values for FT7, FT5, FT4, and FT6 cells were 21, 25, 35, and 47%, respectively. FT3, FT4, FT5, and FT7 transfer preponderantly one Fuc per diantennary N-glycan. FT4 preferentially synthesizes di-Lex on asialo diantennary N-glycans and mono-Lex with monosialo chains. In contrast, FT6 forms mostly alpha1,3-difucosylated chains with no, one, or two NeuAc residues. FT3, FT4, and FT6 were proteolytically cleaved and released into the culture medium in significant amounts, whereas FT7 and FT5 were found to be largely resistant toward proteolysis. Studies on engineered soluble variants of FT6 indicate that these forms do not significantly contribute to the in vivo fucose transfer activity of the enzyme when expressed at activity levels comparable to those obtained for the wild-type Golgi form of FT6 in the recombinant host cells.

Expression cloning and characterization of a novel murine alpha1, 3-fucosyltransferase, mFuc-TIX, that synthesizes the Lewis x (CD15) epitope in brain and kidney

The 3-fucosyl-N-acetyllactosamine (Lewis x, CD15, SSEA-1) carbohydrate epitope is widely distributed in many tissues and is developmentally expressed in some rodent and human tissues, i.e. brain and lung, and mouse early embryo. In such tissues, the Lewis x epitope is considered to be involved in cell-cell interactions. We isolated a novel mouse alpha1,3-fucosyltransferase gene, named mFuc-TIX, from an adult mouse brain cDNA library using the expression cloning method. On flow cytometric analysis, Namalwa cells transfected stably with the mFuc-TIX gene showed a marked increase in Lewis x epitopes but not sialyl Lewis x epitopes. As seen experiments involving oligosaccharides as acceptor substrates, mFuc-TIX transfers a fucose to lacto-N-neotetraose but not to either alpha2,3-sialyl lacto-N-neotetraose or lacto-N-tetraose. The substrate specificity of mFuc-TIX was similar to that of mouse myeloid-type alpha1,3-fucosyltransferase (mFuc-TIV). The deduced amino acid sequence of mFuc-TIX, consisting of 359 residues, indicated a type II membrane protein and shows low degrees of homology to the previously cloned alpha1,3-fucosyltransferases, i.e. mFuc-TIV (48.4%), mouse Fuc-TVII (39.1%), and human Fuc-TIII (43.0%), at the amino acid sequence level. A phylogenetic tree of the alpha1, 3-fucosyltransferases constructed by the neighbor-joining method showed that mFuc-TIX is quite distant from the other alpha1, 3-fucosyltransferases. Thus, mFuc-TIX does not belong to any subfamilies of known alpha1,3Fuc-Ts. The mFuc-TIX transcript was mainly detected in brain and kidney with the Northern blotting and competitive reverse transcription-polymerase chain reaction methods, whereas the mFuc-TIV transcript was not detected in brain with these methods. On in situ hybridization, the mFuc-TIX transcript was detected in neuronal cells but not in the glial cells including astrocytes. These results strongly indicated that mFuc-TIX participates in the Lewis x synthesis in neurons of the brain and may be developmentally regulated.

Detailed acceptor specificities of human alpha1,3-fucosyltransferases, Fuc-TVII and Fuc-TVI

To clarify the acceptor specificity of Fuc-TVII, its activity toward various analogs of a 2-(trimethylsilyl)ethyl alpha2,3-sialyl lacto-N-neotetraose, an acceptor for both Fuc-TVII and Fuc-TVI, was examined in comparison with that of Fuc-TVI. Fuc-TVII required three portions of alpha2,3-sialylated type-2 oligosaccharide structures (i.e., the hydroxyl group at C-4 of Gal, the hydroxyl group at C-3 of GlcNAc, and the carbonylamino group at C-2 of GlcNAc) for its acceptor recognition. Fuc-TVI required the carbonylamino group at C-2 of GlcNAc for its acceptor recognition. Fuc-TVII showed higher affinity toward two analogs, in which the hydroxyl group at C-6 of GlcNAc has been deoxygenated and the acetamide group of N-acetylneuraminic acid has been replaced with a glycolylamino group, respectively, than that toward the original compound. On the other hand, Fuc-TVI showed higher affinity toward an analog, in which the acetamide group of GlcNAc has been modified with a lauroylamino group, than that toward the original compound. Analysis involving mass spectrometry confirmed that both Fuc-TVII and Fuc-TVI could fucosylate these three analogs to yield sialyl Lewis x derivatives.

Human alpha1,3/4-fucosyltransferases. III. A Lys/Arg residue located within the alpha1,3-FucT motif is required for activity but not substrate binding

Amino acid sequence alignment of human alpha1, 3/4-fucosyltransferases (FucTs) demonstrates that three highly conserved Lys residues are present in the catalytic domain of FucTs III, IV, V, and VI. Two of these sites are conserved in FucT VII, with the third located within the alpha1,3-FucT motif as a conservative change to Arg at position 223. Site-directed mutagenesis experiments were conducted to change Lys255 of FucT V (equivalent to Arg223 of FucT VII) to either Arg255 or Ala255. Enzyme assays demonstrate that the FucT V K255R mutant has a 34-fold lower specific activity than native FucT V and that the K255A mutant is inactive. Site-directed mutagenesis of FucT VII was also conducted to change Arg223 to Lys223 for analysis of the effect on enzyme kinetic parameters. No differences in acceptor specificities or Km values for either substrate were observed between native FucT VII and the R223K mutant; however, the purified R223K mutant enzyme had a 2-fold increased specific activity compared with purified native FucT VII. No change in GDP-fucose-protectable pyridoxal-P/NaBH4 inactivation was observed for native or mutant FucT V or VII, further supporting the absence of involvement of this residue in sugar nucleotide binding. The results indicate that a basic residue in this position is required for enzyme activity, with a Lys residue providing higher intrinsic activity. The lack of influence of this site on substrate binding parameters and its location within the alpha1,3-FucT motif suggest that at least some of the residues within this motif are involved in catalysis rather than substrate binding.

Human alpha1,3/4-fucosyltransferases. II. A single amino acid at the COOH terminus of FucT III and V alters their kinetic properties

An analysis of the acceptor substrate specificity of domain swap mutants of human alpha1,3/4-fucosyltransferases (FucTs) III and V has been carried out. The results demonstrate that changing Asp336 of FucT III to Ala (as in FucT V) produced a protein (III/V1) with a reduced activity with a variety of acceptors. An analysis of the kinetic properties of FucT III and the III/V1 mutant demonstrated that III/V1 had a 40-fold reduction in its affinity for the H-type 1 acceptor substrate (Fucalpha1,2Galbeta1,3GlcNAc) and 4-fold reduction in its affinity for GDP-fucose when compared with FucT III. Further, the overall catalytic efficiency of III/V1 was approximately 100-fold lower than that of FucT III with an H-type 1 acceptor substrate. The complementary domain swap resulting from the change of Ala349 of FucT V to Asp (V/III1) produced a FucT that had higher enzyme activity with a range of acceptor substrates and had a higher affinity for an H-type 2 acceptor substrate (Fucalpha1, 2Galbeta1,4GlcNAc) with an 8-fold higher overall catalytic efficiency than that of FucT V. No significant change occurred in the Km for GDP-fucose for this protein when compared with FucT V. Kinetic parameters of two other FucT domain swaps (III8/V and V8/III), resulting in proteins that differed from FucT III and V at the NH2 terminus of their catalytic domain, were not significantly different from those of the parental enzymes when H-type 1 and H-type 2 acceptor substrates were utilized. Thus, substitution of an acidic amino acid for a nonpolar amino acid (i.e. Asp versus Ala) at the COOH terminus of FucTs produces an enzyme with enhanced enzyme activities. These results, together with the results presented in the accompanying papers (Nguyen, A. T., Holmes, E. H., Whitaker, J. M., Ho, S., Shetterly, S., and Macher, B. A. (1998) J. Biol. Chem. 273, 25244-25249; Sherwood, A. L., Nguyen, A. T., Whitaker, J. M., Macher, B. A., and Holmes, E. H. (1998) J. Biol. Chem. 273, 25256-25260), provide new insights into the structure/function relationships of human alpha1,3/4-FucT enzymes.

Human alpha1,3/4-fucosyltransferases. I. Identification of amino acids involved in acceptor substrate binding by site-directed mutagenesis

In a previous study (Xu, Z., Vo, L., and Macher, B. A. (1996) J. Biol. Chem. 271, 8818-8823), a domain swapping approach demonstrated that a region of amino acids found in human alpha1, 3/4-fucosyltransferase III (FucT III) conferred a significant increase in alpha1,4-FucT acceptor substrate specificity into alpha1, 3-fucosyltransferase V (FucT V), which, under the same assay conditions, has extremely low alpha1,4-FucT acceptor substrate specificity. In the current study, site-directed mutagenesis was utilized to identify which of the eight amino acids, associated with alpha1,4-FucT acceptor substrate specificity, is/are responsible for conferring this new property. The results demonstrate that increased alpha1,4-FucT activity with both disaccharide and glycolipid acceptors can be conferred on FucT V by modifying as few as two (Asn86 to His and Thr87 to Ile) of the eight amino acids originally swapped from FucT III into the FucT V sequence. Neither single amino acid mutant had increased alpha1,4-FucT activity relative to that of FucT V. Kinetic analyses of FucT V mutants demonstrated a reduced Km for Galbeta1,3GlcNAc (type 1) acceptor substrates compared with native FucT V. However, this was about 20-fold higher than that found for native FucT III, suggesting that other amino acids in FucT III must contribute to its overall binding site for type 1 substrates. These results demonstrate that amino acid residues near the amino terminus of the catalytic domain of FucT III contribute to its acceptor substrate specificity.

In vitro alpha1-3 or alpha1-4 fucosylation of type I and II oligosaccharides with secreted forms of recombinant human fucosyltransferases III and VI

Transgalactosylation of chitobiose and chitotriose employing beta-galactosidase from bovine testes yielded mixtures with beta1-3 linked galactose (type I) and beta1-4 linked galactose (type II) in a final ratio of 1:1 for the tri- and 1:1.4 for the tetrasaccharide. After 24 h incubations of the two purified oligosaccharide mixtures with large amounts (20-fold increase compared with standard conditions) of human alpha1,3/4-fucosyltransferase III (FucT III), the type I tri-/tetrasaccharides were completely converted to the Lewis(a) structure, whereas approximately 10% fucosylation of the type II isomers to the Lewis(x) oligosaccharides was observed in long-term incubations. Employing large amounts of human alpha1,3-fucosyltransferase VI (FucT VI), the type I trisaccharide substrate was exclusively fucosylated at the proximal O-4 substituted N-acetylglucosamine (GlcNAc) (20%) whereas almost all of the type II isomers was converted to the corresponding Lewis(x) product. 45% of the type I tetrasaccharide was fucosylated at the second GlcNAc solely by FucT VI. The type II isomer was almost completely alpha1-3 fucosylated to yield the Lewisx derivative with traces of a structure that contained an additional fucose at the reducing GlcNAc. The results obtained in the present study employing high amounts of enzyme confirmed our previous results that FucT III acts preponderantly as a beta1-4 fucosyltransferase onto GlcNAc in vitro. Human FucT VI attaches fucose exclusively in an alpha1-3 linkage to 4-substituted GlcNAc in vitro and does not modify any 3-substituted GlcNAc to yield Lewis(a) oligosaccharides. With 8-methoxycarbonyloctyl glycoside acceptors used under standard conditions, FucT III acts exclusively on the type I and FucT VI only on the type II derivative. With lacto-N-tetraose, lacto-N-fucopentraose I, or LS-tetrasaccharide as substrates, FucT III modified the 3-substituted GlcNAc and the reducing glucose; FucT VI recognized only lacto-N-neotetraose as a substrate.

Heterologous expression of an engineered truncated form of human Lewis fucosyltransferase (Fuc-TIII) by the methylotrophic yeast Pichia pastoris

A stable GS115 Pichia pastoris recombinant strain was constructed to secrete a truncated form of the human alpha(1,3/4) fucosyltransferase (amino acids 45-361). Enzyme production resulted from a secretory pathway based on the pre-pro- alpha mating factor signal sequence of the yeast Saccharomyces cerevisiae . Following its transit through the Golgi apparatus, the enzyme accumulated in the periplasmic space before its release in the culture broth (about 30 mg/l). Cell-enclosed enzyme ( approximately 0.16%) proved to be fairly stable for many freezing and thawing cycles and could be used several times as an immobilized catalyst. Soluble enzyme (>99.8%) representing the main protein of the culture broth (10%) has been characterized by Western-blotting, substrate specificities and kinetic parameters. The two forms (cell-enclosed and soluble) of recombinant enzyme may be used for in vitro synthesis of Lewisadeterminants.

alpha1,3 Fucosyltransferase, alpha-L-fucosidase, alpha-D-galactosidase, beta-D-galactosidase, and Le(x) glycoconjugates in developing rat brain

Fucosyltransferases (FTs) and various glycosidases that are involved in the biosynthesis or degradation of SSEA-1 (Le(x)) antigens and their precursors in the CNS are developmentally regulated. In forebrain and cerebellum with lactosamine (LacNAc) as acceptor the FT activity was maximal at P15-P22, but with the glycolipid substrate paragloboside (nLc4) the maximal activity in cerebellum was obtained at P10-P15. The FT activity, with these substrates, was insensitive to N-ethylmaleimide (NEM) and the glycolipid product had an alpha1,3 linkage (Fuc to GlcNAc) suggesting similarities of the investigated enzyme to the cloned human and rat FT IV. However, the observation of different patterns of FT activity in isoelectrofocused fractions (pH 3.5-10) with different types of acceptors, and the differential expression of Le(x) containing glycolipids and glycoproteins during development strongly suggest the presence of more than one type of FT during development. Data on developmental expression of the hydrolytic enzymes, alpha-L-fucosidase, beta-D-galactosidase and alpha-D-galactosidase, which can potentially hydrolyse SSEA-1 or its precursors, support the notion that SSEA-1 expression is the result of a dynamic balance between the activity of transferases and hydrolases.

Identification of an alpha3-fucosyltransferase and a novel alpha2-fucosyltransferase activity in cercariae of the schistosome Trichobilharzia ocellata: biosynthesis of the Fucalpha1-->2Fucalpha1-->3[Gal(NAc)beta1-->4]GlcNAc sequence

Fucose is a major constituent of the protein- and lipid-linked glycans of the various life-cycle stages of schistosomes. These fucosylated glycans are highly antigenic and seem to play a role in the pathology of schistosomiasis. In this article we describe the identification and characterization of two fucosyltransferases (FucTs) in cercariae of the avian schistosome Trichobilharzia ocellata, a GDP-Fuc:[Galbeta1-->4]GlcNAcbeta-R alpha1-->3-FucT and a novel GDP-Fuc:Fucalpha-R alpha1-->2-FucT. Triton X-100 extracts of cercariae were assayed for FucT activity using a variety of acceptor substrates. Type 1 chain (Galbeta1-->3GlcNAc) based compounds were poor acceptors, whereas those based on a type 2 chain (Galbeta1-->4GlcNAc), whether alpha2'-fucosylated, alpha3'-sialylated, or unsubstituted, and whether present as oligosaccharide or contained in a glycopeptide or glycoprotein, all served as acceptor substrates. In this respect the schistosomal alpha3-FucT resembles human FucT V and VI rather than other known FucTs. N-ethylmaleimide, an inhibitor of several human FucTs, had no effect on the activity of the schistosomal alpha3-FucT, whereas GDP-beta-S was strongly inhibitory. Large scale incubations were carried out with Galbeta1-->4GlcNAc, GalNAcbeta1-->4GlcNAcbeta-O -(CH2)8COOCH3 and Fucalpha1-->3GlcNAcbeta1-->2Man as acceptor substrates and the products of the incubations were isolated using a sequence of chromatographic techniques. By methylation analysis and 2D-TOCSY and ROESY1H-NMR spectroscopy the products formed were shown to be Galbeta1-->4[Fucalpha1-->2Fucalpha1-->3]GlcNAc, GalNAcbeta1-->4[Fucalpha1-->2Fucalpha1-->3]GlcNAcbe ta-O-(CH2)8COOCH3, and Fucalpha1-->2Fucalpha1-->3GlcNAcbeta1-->2Man, respectively. It is concluded that the alpha2-FucT and alpha3-FucT are involved in the biosynthesis of the (oligomeric) Lewisx sequences and the Fucalpha1-->2Fucalpha1-->3GlcNAc structural element that have been described on schistosomal glycoconjugates.

Acceptor specificity of the human leukocyte alpha3 fucosyltransferase: role of FucT-VII in the generation of selectin ligands

The alpha3 fucosyltransferase, FucT-VII, is one of the key glycosyltransferases involved in the biosynthesis of the sialyl Lewis X (sLex) antigen on human leukocytes. The sialyl Lewis X antigen (NeuAcalpha(2-3)Galbeta(1-4)[Fucalpha(1-3)]GlcNAc-R) is an essential component of the recruitment of leukocytes to sites of inflammation, mediating the primary interaction between circulating leukocytes and activated endothelium. In order to characterize the enzymatic properties of the leukocyte alpha3 fucosyltransferase FucT-VII, the enzyme has been expressed in Trichoplusia ni insect cells. The enzyme is capable of synthesizing both sLexand sialyl-dimeric-Lexstructures in vitro , from 3'-sialyl-lacNAc and VIM-2 structures, respectively, with only low levels of fucose transfer observed to neutral or 3'-sulfated acceptors. Studies using fucosylated NeuAcalpha(2-3)-(Galbeta(1-4)GlcNAc)3-Me acceptors demonstrate that FucT-VII is able to synthesize both di-fucosylated and tri-fucosylated structures from mono-fucosylated precursors, but preferentially fucosylates the distal GlcNAc within a polylactosamine chain. Furthermore, the rate of fucosylation of the internal GlcNAc residues is reduced once fucose has been added to the distal GlcNAc. These results indicate that FucT-VII is capable of generating complex selectin ligands, in vitro , however the order of fucose addition to the lactosamine chain affects the rate of selectin ligand synthesis.

Complementary acceptor and site specificities of Fuc-TIV and Fuc-TVII allow effective biosynthesis of sialyl-TriLex and related polylactosamines present on glycoprotein counterreceptors of selectins

The P-selectin counterreceptor PSGL-1 is covalently modified by mono alpha2,3-sialylated, multiply alpha1,3-fucosylated polylactosamines. These glycans are required for the adhesive interactions that allow this adhesion receptor-counterreceptor pair to facilitate leukocyte extravasation. To begin to understand the biosynthesis of these glycans, we have characterized the acceptor and site specificities of the two granulocyte alpha1,3-fucosyltransferases, Fuc-TIV and Fuc-TVII, using recombinant forms of these two enzymes and a panel of synthetic polylactosamine-based acceptors. We find that Fuc-TIV can transfer fucose effectively to all N-acetyllactosamine (LN) units in neutral polylactosamines, and to the "inner" LN units of alpha2,3-sialylated acceptors but is ineffective in transfer to the distal alpha2,3-sialylated LN unit in alpha2,3-sialylated acceptors. Fuc-TVII, by contrast, effectively fucosylates only the distal alpha2,3-sialylated LN unit in alpha2,3-sialylated acceptors and thus exhibits an acceptor site-specificity that is complementary to Fuc-TIV. Furthermore, the consecutive action of Fuc-TIV and Fuc-TVII, in vitro, can convert the long chain sialoglycan SAalpha2-3'LNbeta1-3'LNbeta1-3'LN (where SA is sialic acid) into the trifucosylated molecule SAalpha2-3'Lexbeta1-3'Lexbeta1-3'Lex (where Lex is the trisaccharide Galbeta1-4(Fucalpha1-3)GlcNAc) known to decorate PSGL-1. The complementary in vitro acceptor site-specificities of Fuc-TIV and Fuc-TVII imply that these enzymes cooperate in vivo in the biosynthesis of monosialylated, multifucosylated polylactosamine components of selectin counterreceptors on human leukocytes.

Measurement of alpha(1-3) fucosyltransferase activity using scintillation proximity

The alpha 3 fucosyltransferases are a family of glycosyltransferases involved in the addition of fucose onto glycoproteins and glycolipids. One of the best defined roles for the alpha 3 fucosyltransferases is in the biosynthesis of the carbohydrate antigen sialyl Lewis X, the minimal ligand for the selectin family of adhesion molecules. We describe here the development of a single-step assay for the measurement of alpha 3 fucosyltransferase activity based on the principle of scintillation proximity. The fucosyltransferase catalyses the transfer of [3H]fucose, from GDP-[3H]fucose, onto the sugar chains of a glycoprotein acceptor noncovalently bound to a scintillant-impregnated microsphere (SPA bead). The resultant signal can be used as a measure of enzyme activity. Due to the nature of this assay no steps are required to separate unused substrate from product. Kinetic data from the assay compare favorably with those obtained from assays currently used for the alpha 3 fucosyltransferases. This SPA-based assay appears generic for the alpha 3 fucosyltransferases and readily adaptable for other glycosyltransferases. The particular advantage of the assay is anticipated to be found in the simple, routine testing of a large number of samples.

Conserved structural features in eukaryotic and prokaryotic fucosyltransferases

Fucosyltransferases are the enzymes transferring fucose from GDP-Fuc to Gal in an alpha1,2-linkage and to GlcNAc in alpha1,3-, alpha1,4-, or alpha1,6-linkages. Since all fucosyltransferases utilize the same nucleotide sugar, their specificity will probably reside in the recognition of the acceptor and in the type of linkage formed. A search of nucleotide and protein databases yielded more than 30 sequences of fucosyltransferases originating from mammals, chicken, nematode, and bacteria. On the basis of protein sequence similarities, these enzymes can be classified into four distinct families: (1) the alpha-2-fucosyltransferases, (2) the alpha-3-fucosyltransferases, (3) the mammalian alpha-6-fucosyltransferases, and (4) the bacterial alpha-6-fucosyltransferases. Nevertheless, using the sensitive hydrophobic cluster analysis (HCA) method, conserved structural features as well as a consensus peptide motif have been clearly identified in the catalytic domains of all alpha-2 and alpha-6-fucosyltranferases, from prokaryotic and eukaryotic origin, that allowed the grouping of these enzymes into one superfamily. In addition, a few amino acids were found strictly conserved in this family, and two of these residues have been reported to be essential for enzyme activity for a human alpha-2-fucosyltransferase. The alpha-3-fucosyltransferases constitute a distinct family as they lack the consensus peptide, but some regions display similarities with the alpha-2 and alpha-6-fucosyltranferases. All these observations strongly suggest that the fucosyltransferases share some common structural and catalytic features.

Enzymatic characterization of human alpha1,3-fucosyltransferase Fuc-TVII synthesized in a B cell lymphoma cell line

The human alpha1,3-fucosyltransferase, Fuc-TVII, a key enzyme in the biosynthesis of selectin ligands, was expressed as a soluble protein-A chimeric form in a human B cell lymphoma cell line, Namalwa KJM-1, and purified using IgG-Sepharose. The enzymatic properties of recombinant soluble Fuc-TVII were then examined. Its enzyme activity was highest at pH 7.5, and the presence of 25 mM Mn2+ was required for full activity. Fuc-TVII exhibits an acceptor specificity restricted to alpha2,3-sialylated type 2 oligosaccharides, and the apparent Km values for alpha2,3-sialyl lacto-N-neotetraose and GDP-fucose were 3.08 mM and 16.4 microM, respectively. The inhibitory effects of various nucleotides on the activity of Fuc-TVII reflected its donor specificity for the nucleotide portion of GDP. Fuc-TVII was demonstrated to be useful for the synthesis of a sialyl Lewis x hexasaccharide from lacto-N-neotetraose in combination with an alpha2, 3-sialyltransferase, ST3Gal IV. Polyethylene glycols enhanced the thermal stability of Fuc-TVII, leading to increased formation of the reaction product.

Enzyme-assisted synthesis of Asn-linked diantennary oligosaccharides occurring on glycodelin A

The preparation of a series of sialylated and fucosylated N,N'-diacetyllactosediamine-type diantennary glycopeptides is reported. By sequential enzymatic action of jack bean beta-galactosidase, snail beta 4-N-acetyl-galactosaminyltransferase, bovine colostrum alpha 6-sialyltransferase and human milk alpha 3-fucosyltransferase, a diantennary glycopeptide obtained from asialo fibrinogen was converted at a 5-mumol scale to a series of structures occurring on the glycoprotein glycodelin A, which potentially inhibit human sperm-egg binding.

Evolution of fucosyltransferase genes in vertebrates

Cloning and expression of chimpanzee FUT3, FUT5, and FUT6 genes confirmed the hypothesis that the gene duplications at the origin of the present human cluster of genes occurred between: (i) the great mammalian radiation 80 million years ago and (ii) the separation of man and chimpanzee 10 million years ago. The phylogeny of fucosyltransferase genes was completed by the addition of the FUT8 family of alpha(1,6)fucosyltransferase genes, which are the oldest genes of the fucosyltransferase family. By analysis of data banks, a new FUT8 alternative splice expressed in human retina was identified, which allowed mapping the human FUT8 gene to 14q23. The results suggest that the fucosyltransferase genes have evolved by successive duplications, followed by translocations, and divergent evolution from a single ancestral gene.

Enzyme-catalyzed formation of glycosidic linkages

Significant progress has recently been achieved in the use of glycosidases and glycosyltransferases as synthetic tools. Glycosidases have been used to synthesize trisaccharides with a reasonable overall yield, as well as high-mannose neoglycoconjugates. Studies on glycosyltransferases have defined reaction mechanisms and demonstrated reasonable substrate tolerance of these enzymes. Effective methodology for the synthesis of defined glycoproteins has also been demonstrated.

Utilization of glycosyltransferases to change oligosaccharide structures

Carbohydrates on cell surfaces are important biomolecules in various biological recognition processes. Elucidation of the biological roles of complex oligosaccharides necessitates an efficient methodology to synthesize these compounds and their analogs. Enzymatic synthesis renders itself to be useful in the construction of an oligosaccharide structure owing to its mild reaction condition, high regio- and stereoselectivity. This review article focuses on the recent progress in oligosaccharide syntheses catalyzed by glycosyltransferases, namely sialyltransferase, galactosyltransferase, fucosyltransferase, and N-acetylglucosaminyltransferase. A survey of the latest patent and literature related to this field is also included.

Fucosylation of complex glycosphingolipids by recombinant fucosyltransferase-VII

Fucosyltransferase VII (FucT-VII) is one of five known alpha 1-->3fucosyltransferases capable of transferring fucose to the C-3 position of N-acetylglucosamine residues found in lactosamine based glycans. Previous studies have indicated that FucT-VII has a very restricted specificity, capable of fucosylating only terminally alpha 2-->3sialylated carbohydrate substrates, resulting in the synthesis of the sialyl Lewis x (sLe(x)) epitope. Although FucT-VII is expressed in cells of myeloid origin, the monosialylganglioside fraction of HL60 cells contains only internally and/or multiply fucosylated polylactosamine structures; no monofucosylated sLe(x) derivatives are detected. We now report that the structure of the final product formed by the action of FucT-VII on sialynorhexaosylceramide (a glycosphingolipid substrate having multiple fucosylation sites) is extended monofucosyl sLe(x) and fucosylation is restricted to the terminal GlcNAc-V. This indicates that the biosynthesis of all fucosylated monosialylated gangliosides found in HL60 cells (including the E-selectin binding fractions) involves at least one additional alpha 1-->3fucosyltransferase.

Lewis X biosynthesis in Helicobacter pylori. Molecular cloning of an alpha(1,3)-fucosyltransferase gene

The lipopolysaccharide of certain strains of Helicobacter pylori was recently shown to contain the Lewis X (Lex) trisaccharide (Galbeta-1, 4-(Fucalpha(1,3))-GlcNAc). Lex is an oncofetal antigen which appears on human gastric epithelium, and its mimicry by carbohydrate structures on the surface of H. pylori may play an important part in the interaction of this pathogen with its host. Potential roles for bacterial Lex in mucosal adhesion, immune evasion, and autoantibody induction have been proposed (Moran, A. P., Prendergast, M. M., and Appelmelk, B. J. (1996) FEMS Immunol. Med. Microbiol. 16, 105-115). In mammals, the final step of Lex biosynthesis is the alpha(1,3)-fucosylation of GlcNAc in a terminal Galbeta(1-->4)GlcNAc unit, and a corresponding GDP-fucose:N-acetylglucosaminyl alpha(1,3) fucosyltransferase (alpha(1,3)-Fuc-T) activity was recently discovered in H. pylori extracts. We used part of a human alpha(1, 3)-Fuc-T amino acid sequence to search an H. pylori genomic data base for related sequences. Using a probe based upon weakly matching data base sequences, we retrieved clones from a plasmid library of H. pylori DNA. DNA sequence analysis of the library clones revealed a gene which we have named fucT, encoding a protein with localized homology to the human alpha(1,3)-Fuc-Ts. We have demonstrated that fucT encodes an active Fuc-T enzyme by expressing the gene in Escherichia coli. The recombinant enzyme shows a strong preference for type 2 (e.g. LacNAc) over type 1 (e.g. lacto-N-biose) acceptors in vitro. Certain residues in a short segment of the H. pylori protein are completely conserved throughout the alpha(1,3)-Fuc-T family, defining an alpha(1,3)-Fuc-T motif which may be of use in identifying new fucosyltransferase genes.

Three different endogenous alpha-L-fucosyltransferases expressed in COS cells

The monkey kidney COS cell line is frequently used for the transient expression of cloned human fucosyltransferase cDNAs in the belief that negligible endogenous expression of fucosyltransferase genes occurs in these cells. In the course of transfection experiments we observed weak cell surface expression of sialyl-Lex and weak fucosyltransferase activity in extracts of control untransfected cells. Since these activities could complicate interpretation of the results with the transfected genes, a more detailed examination was undertaken that has now revealed expression of three different fucosyltransferases in the cells. One enzyme, which utilises N-acetyllactosamine as substrate, has a pH optimum of 7.0, is resistant to heat inactivation, and has been tentatively identified as an alpha1,3-fucosyltransferase. A second enzyme which acts on asialo-fetuin has a pH optimum of 5.5 and is rapidly inactivated by heat; the acceptor sugar and positional linkage of the transferred fucose are not yet established. A third enzyme that utilises asialo-agalacto-fetuin as acceptor is provisionally identified as an alpha1,6-fucosyltransferase.

Distinct substrate specificities of five human alpha-1,3-fucosyltransferases for in vivo synthesis of the sialyl Lewis x and Lewis x epitopes

Five different human alpha-1,3-fucosyltransferase genes, the Fuc-TIII, Fuc-TIV, Fuc-TV, Fuc-TVI and Fuc-TVII genes, have been cloned to date. We transfected HeLa cells and Namalwa cells with each of the five different genes, and established a series of stable cloned transformant cells. Thin-layer chromatography immunostaining analysis revealed that all five enzymes were able to synthesize sialyl Lewis x (sLe(x)) epitopes on glycolipids in HeLa cells, but each enzyme showed a different preference as to the carbohydrate chain length on glycolipids as acceptor substrates. Fuc-TIII and Fuc-TV showed very similar patterns of sLe(x) positive bands, which indicated that the enzymes have similar acceptor substrate specificities. Fuc-TVI exhibited a little different pattern from those of the former two enzymes. Fuc-TIV and Fuc-TVII showed similarity in the positive bands, however, their patterns were quite different from those of the former three enzymes. Four enzymes except for Fuc-TVII were able to synthesize the Lewis x (Le(x)) epitope on glycolipids in HeLa cells. Fuc-TV alone showed a little different pattern of Le(x) positive bands from those of the other three enzymes. Flow cytometric analysis of HeLa cells and Namalwa cells again demonstrated the similar specificities of Fuc-TIII and Fuc-TV. They exhibited similar stronger staining with FH6 (anti-sLe(x)) antibodies than that with the other enzymes. A phylogenetic tree of the five enzymes constructed using the neighbor-joining method showed good agreement with the similarities in the enzyme substrate specificity.

Do synovial fluid acute phase proteins from patients with rheumatoid arthritis originate from serum?

This study was performed in order to gain insight into the occurrence, glycosylation and the possible origin of the acute-phase proteins alpha1-acid glycoprotein (AGP) and alpha1-protease inhibitor (PI) in sera and synovial fluid from patients with rheumatoid arthritis (RA). Therefore paired sera and synovial fluid samples from patients with RA, and paired synovial fluid samples from right and left knees of patients with varying degrees of arthritis were studied. Crossed affinity immunoelectrophoresis (CAIE) was used with concanavalin A and Aleuria aurantia lectin for the detection of the degree of branching and fucosylation, respectively, and the monoclonal CSLEX-1 for the detection of Sialyl Lewis(X) (SLe(X)) groups on AGP. For PI, not only CAIE, but also high-pressure-anion-exchange chromatography with pulsed amperometric detection was used to study the glycosylation. It was established that the concentrations of AGP and PI were increased in the serum of RA patients compared to normal healthy controls, but that the concentration of both proteins, as well as albumin, was significantly lower in synovial fluid than in serum. Furthermore, the type of glycosylation of both AGP and PI found in RA was significantly different from that found in normals, with increased fucosylation, but there were no major differences in the degree of branching of AGP- or PI-glycans in RA, compared to normals. No differences in glycosylation could be established between serum and synovial fluid in RA. For PI an increased fucosylation was found, both in serum and synovial fluid, using both methods of detection, and it could be established that only the alpha1-->3- and not the alpha1-->6-fucosylation of PI was affected by RA. The increased fucosylation of AGP resulted in an increased expression of SLe(X) on AGP-glycans. Since the alpha1-->3-fucosylation of AGP was significantly increased in both serum and synovial fluid from RA patients, and this correlated with systemic but not with local disease parameters, it can be suggested that acute phase proteins in synovial fluid are most probably of hepatic origin.

Stable expression of the Golgi form and secretory variants of human fucosyltransferase III from BHK-21 cells. Purification and characterization of an engineered truncated form from the culture medium

Stable BHK-21 cell lines were constructed expressing the Golgi membrane-bound form and two secretory forms of the human alpha1, 3/4-fucosyltransferase (amino acids 35-361 and 46-361). It was found that 40% of the enzyme activity synthesized by cells transfected with the Golgi form of the fucosyltransferase was constitutively secreted into the medium. The corresponding enzyme detected by Western blot had an apparent molecular mass similar to those of the truncated secretory forms. The secretory variant (amino acids 46-361) was purified by a single affinity-chromatography step on GDP-Fractogel resin with a 20% final recovery. The purified enzyme had a unique NH2 terminus and contained N-linked endo H sensitive carbohydrate chains at its two glycosylation sites. The fucosyltransferase transferred fucose to the O-4 position of GlcNAc in small oligosaccharides, glycolipids, glycopeptides, and glycoproteins containing the type I Galbeta1-3GlcNAc motif. The acceptor oligosaccharide in bovine asialofetuin was identified as the Man-3 branched triantennary isomer with one Galbeta1-3GlcNAc. The type II motif Galbeta1-4GlcNAc in bi-, tri-, or tetraantennary neutral or alpha2-3/alpha2-6 sialylated oligosaccharides with or without N-acetyllactosamine repeats and in native glycoproteins were not modified. The soluble forms of fucosyltransferase III secreted by stably transfected cells may be used for in vitro synthesis of the Lewisa determinant on carbohydrates and glycoproteins, whereas Lewisx and sialyl-Lewisx structures cannot be synthesized.

Molecular cloning and expression of a bovine alpha(1,3)-fucosyltransferase gene homologous to a putative ancestor gene of the human FUT3-FUT5-FUT6 cluster

Only one bovine gene, corresponding to the human cluster of genes FUT3-FUT5-FUT6, was found by Southern blot analysis. The cognate bovine alpha(1,3)-fucosyltransferase shares 67.3, 69.0, and 69.3% amino acid sequence identities with human FUC-T3, FUC-T5, and FUC-T6 enzymes, respectively. As revealed by protein sequence alignment, potential sites for asparagine-linked glycosylation and conserved cysteines, the bovine enzyme is an intermediate between FUC-T3, FUC-T5, and FUC-T6 human enzymes. Transfected into COS-7 cells, the bovine gene induced the synthesis of an alpha(1, 3)-fucosyltransferase enzyme with type 2 substrate acceptor pattern specificity and induced expression of fucosylated type 2 epitopes (Lex and sialyl-Lex), but not of type 1 structures (Lea or sialyl-Lea), suggesting that it has an acceptor specificity similar to the human plasma FUC-T6. However, no enzyme activity was detected in bovine plasma. Gene transcripts are detected on tissues such as bovine liver, kidney, lung, and brain. The type 2 sialyl-Lex epitope was found in renal macula densa and biliary ducts, and Lex and Ley epitopes were detected on the brush border of epithelial cells of small and large intestine, suggesting a tissue distribution closer to human FUC-T3, but fucosylated type 1 structures (Lea, Leb, or sialyl-Lea) were not detected at all in any bovine tissue. Analysis of genetic distances on a combined phylogenetic tree of fucosyltransferase genes suggests that the bovine gene is the orthologous homologue of the ancestor of human genes constituting the present FUT3-FUT5-FUT6 cluster.

Chemical modification of an alpha 3-fucosyltransferase; definition of amino acid residues essential for enzyme activity

The biosynthesis of the carbohydrate antigen sialyl Lewis X (sLe(x)) is dependent on the activity of an alpha 3-fucosyltransferase (EC 2.4.1.152, GDP-fucose:Gal beta (1-4)GlcNAc-R alpha (1-3)fucosyltransferase). This enzyme catalyses the transfer of fucose from GDP-beta-fucose to the 3-OH of N-acetylglucosamine present in lactosamine acceptors. In this report, we have investigated the amino acids essential for the activity of a recombinant alpha 3-fucosyltransferase (FucT-VI) through chemical modification of the enzyme with group-selective reagents. FucT-VI activity was found to be particularly sensitive to the histidine-selective reagent diethylpyrocarbonate and the cysteine reagent N-ethylmaleimide, with IC50 values of less than 200 microM. Reagents selective for arginine and lysine had no effect on enzyme activity. The inclusion of GDP-beta-fucose during preincubation with NEM reduces the rate of inactivation whereas inclusion of an acceptor saccharide for the enzyme, Gal beta (1-4)GlcNAc, had no effect. No protective effect with either GDP-beta-fucose or Gal beta (1-4)GlcNAc was observed on treatment of the enzyme with diethylpyrocarbonate. These data suggest that in addition to an NEM-reactive cysteine in, or adjacent to, the substrate-binding site of the enzyme, FucT-VI possesses histidine residue(s) that are essential for enzyme activity.

Cloning of a rat alpha1,3-fucosyltransferase gene: a member of the fucosyltransferase IV family

We report the cloning of a rat alpha1,3-fucosyltransferase gene (rFuc-T), isolated from a rat genomic library by a PCR-cross-hybridization based cloning approach using primers derived from the conserved region of human alpha1,3-Fuc-T sequences. Comparison of the rFuc-T predicted amino acid sequence with those of previously cloned human and murine fucosyltransferases showed highest degree of homology to murine Fuc-TIV (87% identity) and human Fuc-TIV (78% identity), with lower homology (41-49% identity) to Fuc-TIII, V, VI, and VII. COS-1 cells transfected with the rFuc-Tgene expressed a fucosyltransferase activity with type 2 (Gal beta1-->4GlcNAc)-containing oligosaccharides and the glycolipid acceptor neolactotetraosylceramide but only low activity with sialylated substrates; the SSEA-1/Le(x) antigen was detected in transfected cells by immunocytochemistry. Based on these results, we surmise that rFuc-T is a member of the fucosyltransferase IV family. Northern blot analysis with a rFuc-T specific probe indicated a major transcript of 4.2 kb most abundantly expressed in rat spleen; minor transcripts of different sizes were detected in several tissues, including rat brain.

Expression of human H-type alpha1,2-fucosyltransferase encoding for blood group H(O) antigen in Chinese hamster ovary cells. Evidence for preferential fucosylation and truncation of polylactosamine sequences

The human H(O) blood group is specified by the structure Fucalpha1-2Galbeta1-R, but the factors regulating expression of this determinant on cell surface glycoconjugates are not well understood. To learn more about the regulation of H blood group expression, cDNA encoding the human H-type GDPFuc:beta-D-galactoside alpha1, 2-fucosyltransferase (alpha1,2FT) was stably transfected into Chinese hamster ovary (CHO) cells. The new cell line, designated CHO(alpha1,2)FT, expressed surface neoglycans containing the H antigen. The structures of the fucosylated neoglycans in CHO(alpha1, 2)FT cells and the distribution of these glycans on glycoproteins were characterized. Seventeen percent of the [3H]Gal-labeled glycopeptides from CHO(alpha1,2)FT cells bound to the immobilized H blood group-specific lectin Ulex europaeus agglutinin-I (UEA-I), whereas none from parental CHO cells bound to the lectin. The glycopeptides from CHO(alpha1,2)FT cells binding to UEA-I contained polylactosamine [3Galbeta1-4GlcNAcbeta1-]n with the terminal sequence Fucalpha1-2Galbeta1- 4GlcNAc-R. Fucosylation of the polylactosamine sequences on complex-type N-glycans in CHO(alpha1, 2)FT cells caused a decrease in both sialylation and length of polylactosamine. Unexpectedly, only small amounts of terminal fucosylation was found in diantennary complex-type N-glycans. The O-glycans and glycolipids were not fucosylated by the H-type alpha1, 2FT. Two major high molecular weight glycoproteins, one of which was shown to be the lysosome-associated membrane glycoprotein LAMP-1, preferentially contained the H-type structure and were bound by immobilized UEA-I. These results demonstrate that in CHO cells the expressed H-type alpha1,2FT does not indiscriminately fucosylate terminal galactosyl residues in complex-type N-glycans, but it favors glycans containing polylactosamine and dramatically alters their length and sialylation.

Glycobiotechnology: enzymes for the synthesis of nucleotide sugars

Complex carbohydrates, as constituting part of glycoconjugates such as glycoproteins, glycolipids, hormones, antibiotics and other secondary metabolites, play an active role in inter- and intracellular communication. The aim of "glycobiotechnology" as an upcoming interdisciplinary research field is to develop highly efficient synthesis strategies, including in vivo and in vitro approaches, in order to bring such complex molecules into analytical and therapeutic studies. The enzymatic synthesis of glycosidic bonds by Leloir-glycosyltransferases is an efficient strategy for obtaining saccharides with absolute stereo- and regioselectivity in high yields and under mild conditions. There are, however, two obstacles hindering the realization of this process on a biotechnological scale, namely the production of recombinant Leloir-glycosyltransferases and the availability of enzymes for the synthesis of nucleotide sugars (the glycosyltransferase donor substrates). The present review surveys some synthetic targets which have attracted the interest of glycobiologists as well as recombinant expression systems which give Leloir-glycosyltransferase activities in the mU and U range. The main part summarizes publications concerned with the complex pathways of primary and secondary nucleotide sugars and the availability and use of these enzymes for synthesis applications. In this context, a survey of our work will demonstrate how enzymes from different sources and pathways can be combined for the synthesis of nucleotide deoxysugars and oligosaccharides.

Elevation of an alpha(1,3)fucosyltransferase activity correlated with apoptosis in the human colon adenocarcinoma cell line, HT-29

We studied changes in the carbohydrate expression following apoptotic cell death induced by treatment with interferon (IFN)-gamma and anti-Fas antibody using human colon adenocarcinoma HT-29 cells. An apoptotic cell death of HT-29 accompanied with typical DNA fragmentation was observed when the cells, were cultured sequentially with IFN-gamma and anti-Fas antibody. In flow cytometric analyses, the expression of Le(x) and Le(y) antigen was strongly and slightly enhanced, respectively, on the cell surface in accordance with the apoptosis. When the fucosyltransferase (Fuc-T) activities of the lysates from the treated cells were examined relative to those from untreated cells, a 2.5-fold increase of alpha(1,3)-Fuc-T activities and a slight increase of alpha(1,2)-Fuc-T activities were observed, but little or no increase of alpha(1,4)-Fuc-T activity was detected. In Northern blot analyses using probes for Fuc-T III, IV, V, VI and VII genes, strong RNA messages for Fuc-T III, V and/or VI and a weak RNA message for Fuc-T IV were detected in the untreated HT-29 cells. On the other hand, in the treated cells, the messages for Fuc-T III, V and/or VI were found to almost disappear and the 2.3 kb message for Fuc-T IV was observed to elevate 2.8-fold. Therefore, we suggest that the strongly increased expression of Le(x) antigen found on the HT-29 cell surface might be involved in the process of apoptosis, and that the enhancement of the antigen expression seems to result from the increased activity of alpha(1,3)-Fuc-T encoded mainly by the Fuc-T IV gene.

Acceptor hydroxyl group mapping for human milk alpha 1-3 and alpha 1-3/4 fucosyltransferases

Two different fucosyltransferases (Fuc-Ts) have been isolated from human milk, an alpha 1-3 Fuc-T and an alpha 1-3/4 Fuc-T, for mapping of their acceptor binding sites. Kinetic studies employing a series of monodeoxygenated and modified Gal beta 1-->4Glc-NAc beta OR and Gal beta 1-->3GlcNAc beta OR acceptor substrates showed that modifications are tolerated at every hydroxyl group in these substrates except for 6-OH of galactose and 3- or 4-OH of N-acetylglucosamine. Deoxygenation at these positions rendered these compounds inactive as both substrates and inhibitors. These essential hydroxyl groups, which are required for recognition of the substrates, are identical to the key polar groups that have previously been reported for cloned FucTs III, IV and V.

Mechanism and specificity of human alpha-1,3-fucosyltransferase V

Human alpha-1,3-fucosyltransferase catalyzes the transfer of the L-fucose moiety from guanosine diphosphate-beta-L-fucose (GDP-Fuc) to acceptor sugars to form biologically important fucoglycoconjugates, including sialyl Lewis x (SLex). Evidence for a general base mechanism is supported by a pH-rate profile that revealed a catalytic residue with a pKa of 4.1. The characterized solvent kinetic isotope effect (Dv = 2.9, Dv/k = 2.1) in a proton inventory study indicates that only one-proton transfer is involved in the catalytic step leading to the formation of the transition state. Evidence for Mn2+ as an electrophilic catalyst was supported by the observation that the nonenzymatic transfer of L-fucose from GDP-Fuc to the hydroxyl group of water in the presence of 10 mM MnCl2 at 20 degrees C was accelerated from K(obs)= 3.5 x 10(-6) to 3.8 x 10(-5) min-1. Using the GDP-Fuc hydrolysis as the nonenzymatic rate, the enzymatic proficiency of FucT V, (Kcat/Ki,GDP-fuc. K(m),1.acNAc)/K(non), was estimated to be 1.2 x 10(10) M-1 with a transition-state affinity of 8.6 x 10(-11) M. The Km for Mn2+ was determined to be 6.1 mM, and alternative divalent metal cofactors were identified as Ca2+, Co2+, and Mg2+. Detailed kinetic characterization of the acceptor sugar specificity indicated that incorporation of hydrophobic functionality [e.g. -O-(CH2)5CO2CH3] to the reducing end of the acceptor sugar substantially decreased the K(m),acceptor by over 100-fold. The role of the nucleotide was investigated by studying the inhibition of nucleotides, including the guanosine series. The inhibitory potency trend (GTP approximately GDP > GMP > > guanosine) is consistent with bidentate chelation of Mn2+ by GDP-Fuc. The role of charge and distance in the synergistic inhibitory effect by the combination of GDP, an aza sugar, and the acceptor sugar was probed. A mechanism for fucosyl transfer incorporating these findings is proposed and discussed.