Leukocyte migration in experimental inflammatory bowel disease

Emigration of leukocytes from the circulation into tissue by transendothelial migration, is mediated subsequently by adhesion molecules such as selectins, chemokines and integrins. This multistep paradigm, with multiple molecular choices at each step, provides a diversity in signals. The influx of neutrophils, monocytes and lymphocytes into inflamed tissue is important in the pathogenesis of chronic inflammatory bowel disease. The importance of each of these groups of adhesion molecules in chronic inflammatory bowel disease, either in human disease or in animal models, will be discussed below. Furthermore, the possibilities of blocking these different steps in the process of leukocyte extravasation in an attempt to prevent further tissue damage, will be taken into account.

Fucosyltransferases: structure/function studies

Alpha3-fucosyltransferases (alpha3-FucTs) catalyze the final step in the synthesis of a range of important glycoconjugates that function in cell adhesion and lymphocyte recirculation. Six members of this family of enzymes have been cloned from the human genome, and their expression pattern has been shown to be highly regulated. Each enzyme has a unique acceptor substrate binding pattern, and each generates a unique range of fucosylated products. Results from a range of studies have provided information on amino acids in the FucT sequence that contribute to the differential acceptor specificity for the FucTs, and to the binding of the nucleotide sugar donor GDP-fucose. These results, in conjunction with results obtained from the analysis of the disulfide bond pattern, have provided useful clues about the spatial distribution of amino acids that influence or directly contribute to substrate binding. This information is reviewed here, and a molecular fold prediction is presented which has been constructed based on the available information and current modeling methodology.

Alpha 1,3 galactosyltransferase: new sequences and characterization of conserved cysteine residues

Nucleotide sequences were determined for alpha1,3 galactosyltransferases (alpha1,3 GalTs) from several species (bat, mink, dog, sheep, and dolphin) and compared with those previously determined for this enzyme and members of the alpha1,3 galactosyl/N-acetylgalactosyltransferase (alpha1,3 Gal(NAc)Ts) family of enzymes. Sequence comparison of the newly characterized alpha1,3 GalT nucleotide and predicted amino acid sequences with those previously characterized for other alpha1,3GalT enzymes demonstrated a remarkable level of sequence identity at the nucleotide and amino acid level. The identity of each sequence as an alpha1,3 GalT was confirmed by expressing the encoded protein and characterizing the resulting enzyme. The alpha1,3 GalTs have a significant degree of sequence homology with A and B transferases, the alpha1,3 GalNAcT that catalyzes the synthesis of Forssman antigen, and the recently cloned iso-globotriaosylceramide synthase. Among the conserved residues, there are two Cys residues. To determine if these conserved residues are free or involved in the formation of a disulfide bond, bovine alpha1,3 GalT was characterized by chemical modification and mass spectrometry. Each peptide containing a Cys residue was chemically labeled with an alkylating reagent demonstrating that these enzymes do not contain disulfide bonds. Similar results have recently been reported for A and B transferases (Yen et al., 2000, J. Mass. Spectrom., 35, 990-1002). Thus, the highly conserved Cys residues found in these members of the alpha1,3 Gal(NAc)Ts family of enzymes are likely involved in other important aspects of enzyme structure/function within this enzyme family.

Unique disulfide bond structures found in ST8Sia IV polysialyltransferase are required for its activity

NCAM polysialylation plays a critical role in neuronal development and regeneration. Polysialylation of the neural cell adhesion molecule (NCAM) is catalyzed by two polysialyltransferases, ST8Sia II (STX) and ST8Sia IV (PST), which contain sialylmotifs L and S conserved in all members of the sialyltransferases. The members of the ST8Sia gene family, including ST8Sia II and ST8Sia IV are unique in having three cysteines in sialylmotif L, one cysteine in sialylmotif S, and one cysteine at the COOH terminus. However, structural information, including how disulfide bonds are formed, has not been determined for any of the sialyltransferases. To obtain insight into the structure/function of ST8Sia IV, we expressed human ST8Sia IV in insect cells, Trichoplusia ni, and found that the enzyme produced in the insect cells catalyzes NCAM polysialylation, although it cannot polysialylate itself ("autopolysialylation"). We also found that ST8Sia IV does not form a dimer through disulfide bonds. By using the same enzyme preparation and performing mass spectrometric analysis, we found that the first cysteine in sialylmotif L and the cysteine in sialylmotif S form a disulfide bridge, whereas the second cysteine in sialylmotif L and the cysteine at the COOH terminus form a second disulfide bridge. Site-directed mutagenesis demonstrated that mutation at cysteine residues involved in the disulfide bridges completely inactivated the enzyme. Moreover, changes in the position of the COOH-terminal cysteine abolished its activity. By contrast, the addition of green fluorescence protein at the COOH terminus of ST8Sia IV did not render the enzyme inactive. These results combined indicate that the sterical structure formed by intramolecular disulfide bonds, which bring the sialylmotifs and the COOH terminus within close proximity, is critical for the catalytic activity of ST8Sia IV.

Neighboring cysteine residues in human fucosyltransferase VII are engaged in disulfide bridges, forming small loop structures

Among alpha 3-fucosyltransferases (alpha3-FucTs) from most species, four cysteine residues appear to be highly conserved. Two of these cysteines are located at the N-terminus and two at the C-terminus of the catalytic domain. FucT VII possesses two additional cysteines in close proximity to each other located in the middle of the catalytic domain. We identified the disulfide bridges in a recombinant, soluble form of human FucT VII. Potential free cysteines were modified with a biotinylated alkylating reagent, disulfide bonds were reduced and alkylated with iodoacetamide, and the protein was digested with either trypsin or chymotrypsin, before characterization by high-performance liquid chromatography/electrospray ionization mass spectrometry. More than 98% of the amino acid sequence for the truncated enzyme (beginning at amino acid 53) was verified. Mass spectrometry analysis also demonstrated that both potential N-linked sites are occupied. All six cysteines in the FucT VII sequence were shown to be disulfide-linked. The pairing of the cysteines was determined by proteolytic cleavage of nonreduced protein and subsequent analysis by mass spectrometry. The results demonstrated that Cys(68)-Cys(76), Cys(211)-Cys(214), and Cys(318)-Cys(321) are disulfide-linked. We have used this information, together with a method of fold recognition and homology modeling, using the (alpha/beta)(8)-barrel fold of Escherichia coli dihydrodipicolinate synthase as a template to propose a model for FucT VII.

Disulfide bonds of GM2 synthase homodimers. Antiparallel orientation of the catalytic domains

GM2 synthase is a homodimer in which the subunits are joined by lumenal domain disulfide bond(s). To define the disulfide bond pattern of this enzyme, we analyzed a soluble form by chemical fragmentation, enzymatic digestion, and mass spectrometry and a full-length form by site-directed mutagenesis. All Cys residues of the lumenal domain of GM2 synthase are disulfide bonded with Cys(429) and Cys(476) forming a disulfide-bonded pair while Cys(80) and Cys(82) are disulfide bonded in combination with Cys(412) and Cys(529). Partial reduction to produce monomers converted Cys(80) and Cys(82) to free thiols while the Cys(429) to Cys(476) disulfide remained intact. CNBr cleavage at amino acid 330 produced a monomer-sized band under nonreducing conditions which was converted upon reduction to a 40-kDa fragment and a 24-kDa myc-positive fragment. Double mutation of Cys(80) and Cys(82) to Ser produced monomers but not dimers. In summary these results demonstrate that Cys(429) and Cys(476) form an intrasubunit disulfide while the intersubunit disulfides formed by both Cys(80) and Cys(82) with Cys(412) and Cys(529) are responsible for formation of the homodimer. This disulfide bond arrangement results in an antiparallel orientation of the catalytic domains of the GM2 synthase homodimer.

Human alpha 1,3/4 fucosyltransferases. Characterization of highly conserved cysteine residues and N-linked glycosylation sites

Human alpha1,3 fucosyltransferases (FucTs) contain four highly conserved cysteine (Cys) residues, in addition to a free Cys residue that lies near the binding site for GDP-fucose (Holmes, E. H., Xu, Z. , Sherwood, A. L., and Macher, B. A. (1995) J. Biol. Chem. 270, 8145-8151). The participation of the highly conserved Cys residues in disulfide bonds and their functional significance were characterized by mass spectrometry (MS) analyses and site-directed mutagenesis, respectively. Among the human FucTs is a subset of enzymes (FucT III, V, and VI) having highly homologous sequences, especially in the catalytic domain, and Cys residues in FucT III and V were characterized. The amino acid sequence of FucT III was characterized. Peptides containing the four conserved Cys residues were detected after reduction and alkylation, and found to be involved in disulfide bonds. The disulfide bond pattern was characterized by multiple stage MS analysis and the use of Glu-C protease and MS/MS analysis. Disulfide bonds in FucT III occur between Cys residues (Cys(81) to Cys(338) and Cys(91) to Cys(341)) at the N and C termini of the catalytic domain, bringing these ends close together in space. Mutagenesis of highly conserved Cys residues to Ser in FucT V resulted in proteins lacking enzymatic activity. Three of the four mutants have molecular weights similar to wild type enzyme and maintained an ability to bind GDP, whereas the other (Cys(104)) produced a series of lower molecular weight bands when characterized by Western blot analysis, and did not bind GDP. FucTs have highly conserved, potential N-linked sites, and our mass spectrometry analyses demonstrated that both N-linked sites are modified with oligosaccharides.

Characterization of cysteine residues and disulfide bonds in proteins by liquid chromatography/electrospray ionization tandem mass spectrometry

Cysteine residues and disulfide bonds are important for protein structure and function. We have developed a simple and sensitive method for determining the presence of free cysteine (Cys) residues and disulfide bonded Cys residues in proteins (<100 pmol) by liquid chromatography/electrospray ionization tandem mass spectrometry (LC/ESI-MS/MS) in combination with protein database searching using the program Sequest. Free Cys residues in a protein were labeled with PEO-maleimide biotin immediately followed by denaturation with 8 M urea. Subsequently, the protein was digested with trypsin or chymotrypsin and the resulting products were analyzed by capillary LC/ESI-MS/MS for peptides containing modified Cys and/or disulfide bonded Cys residues. Although the MS method for identifying disulfide bonds has been routinely employed, methods to prevent thiol-disulfide exchange have not been well documented. Our protocol was found to minimize the occurrence of the thiol-disulfide exchange reaction. The method was validated using well-characterized proteins such as aldolase, ovalbumin, and beta-lactoglobulin A. We also applied this method to characterize Cys residues and disulfide bonds of beta 1,4-galactosyltransferase (five Cys), and human blood group A and B glycosyltransferases (four Cys). Our results demonstrate that beta 1,4-galactosyltransferase contains one free Cys residue and two disulfide bonds, which is in contrast to work previously reported using chemical methods for the characterization of free Cys residues, but is consistent with recently published results from x-ray crystallography. In contrast to the results obtained for beta 1,4-galactosyltransferase, none of the Cys residues in A and B glycosyltransferases were found to be involved in disulfide bonds.

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.

Characterization of the substrate specificity of alpha1,3galactosyltransferase utilizing modified N-acetyllactosamine disaccharides

alpha1,3galactosyltransferase (alpha1,3GalT) catalyzes the synthesis of a range of glycoconjugates containing the Galalpha1,3Gal epitope which is recognized by the naturally occurring human antibody, anti-Gal. This enzyme may be a useful synthetic tool to produce a range of compounds to further investigate the binding site of anti-Gal and other proteins with a Galalpha1,3Gal binding site. Thus, the enzyme has been probed with a series of type 2 disaccharide-C8(Galbeta1-4GlcNAc-C8) analogs. The enzyme tolerated acceptors with modifications at C2 and C3 of the N-acetylglucosamine residue, producing a family of compounds with a nonreducing alpha1,3 linked galactose. Compounds that did not serve as acceptors were evaluated as inhibitors. Interestingly, the type 1 disaccharide-C8, Galbeta1-3GlcNAc-C8, was a good inhibitor of the enzyme (Ki = 270 microM vs. Km = 190 microM for Galbeta1-4GlcNAc-C8). A potential photoprobe, based on a modified type 2 disaccharide (octyl 3-amino-3-deoxy-3-N-(2-diazo-3, 3, 3-trifluoropropionyl-beta-D-galactopyranosyl-(1, 4)-2-acetamindo-2-deoxy-beta-D-glycopyranoside, (DTFP-LacNAc-C8)), was evaluated as an inhibitor of alpha1,3GalT. alpha1,3GalT bound DTFP-LacNAc-C8 with an affinity (Ki = 300 microM) similar to that displayed by the enzyme for LacNAc-C8. Additional studies were done to determine the enzyme's ability to transfer a range of sugars from UDP-sugar donors. The results of these experiments demonstrated that alpha1,3GalT has a strict specificity for UDP-Gal. Finally, inactivation studies with various amino acid modifiers were done to obtain information on the importance of different types of amino acids for alpha1,3GalT activity.

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.

Structure/activity studies of anti-inflammatory peptides based on a conserved peptide region of the lectin domain of E-, L- and P-selectin

Previously, it was established that the peptide YYWIGIRK-NH2 inhibits both myeloid cell adhesion to selectins in vitro and neutrophil influx into inflammatory sites in vivo (Briggs et al., 1995). Initial structure/activity studies revealed that at least one Y residue at the N-terminus of the peptide was essential for these bioactivities but that the C-terminal K residue was unnecessary for inhibitory activity. We have now synthesized a new series of peptides which contain single residue substitutions at each position of the reference peptide, YYWIGIR-NH2, and have tested these peptides for inhibitory activity in a selectin cell binding assay. In addition, peptides containing single D-amino acids at selected positions, or an all D-configured reference peptide sequence, or the retro-inverso version (rigiwyy-NH2) of the reference peptide sequence have also been analyzed for inhibitory activity in the same assays. Finally, the ability of the reference peptide and a specifically designed control sequence (YY(AIB)IGIR-NH2) to discriminate between potential synthetic saccharide ligands, including sialyl-Lewis x, Lewis x, and sialyl-N-acetyl-lactosamine, was investigated using isothermal titration calorimetry. The results of these studies demonstrate that whereas many single amino acid substitutions are tolerated in the peptide without complete loss of inhibitory activity, substitution at some positions (e.g., the W residue) results in relatively inactive compounds, clearly pointing to the importance of these residues in making critical contacts with the appropriate saccharide ligand. Titration calorimetry revealed that the reference peptide does not discriminate between Lewis x or sialyl-Lewis x in vitro, but binds these saccharides with nearly 40-fold higher affinity (KD 25 microM) than the nonfucosylated trisaccharide, sialyl-N-acetyl-lactosamine. We can infer from these studies that the presence of a sialyl group per se, is not a requisite for complex formation between the reference peptide and its saccharide ligand. Substitution of single D-amino acid residues at various positions in the reference peptide sequence reduces or eliminates all inhibitory properties. However, the all D-configured peptide or the retro-inverso peptide sequence have greater activity than the all L-configured reference peptide in the in vitro biological assays, and each was an effective inhibitor of neutrophil infiltration in a thioglycolate-induced mouse peritonitis model. These results, combined with the results of titration, allow us to conclude that binding between the reference peptide and its saccharide ligand, which affords its inhibitory properties, is mediated by the presence of a contiguous, nonpolar surface, or face, presented at the N-terminus of the reference peptide, likely encompassing the sequence YYWI. Furthermore, the W plays a critical role in binding, probably through formation of an essential hydrogen bond with a suitably juxtaposed group carried on the saccharide ligand.

Structural characterization of blood group A glycosphingolipids recognized by the antibody 3G9-A

In this study, the antibody 3G9-A was assayed for activity against human erythrocyte glycosphingolipids. The antibody was found to recognize glycosphingolipid components from blood group A erythrocytes but not glycosphingolipids from blood group B or O erythrocytes. Subsequent investigation revealed that the glycosphingolipid components recognized by the antibody were also recognized by a blood group A specific monoclonal antibody. The structures of two of the isolated active glycosphingolipid components were structurally characterized using proton nuclear magnetic resonance (1H NMR) and gas chromatography-mass spectrometry (GC-MS) techniques and were found to consist of two blood group A glycosphingolipids; the type 2 chain Ab and type 3 chain Aa glycosphingolipids. Subsequent analysis of the remaining active components by GC-MS and immunostaining techniques revealed that all of the active components were blood group A glycosphingolipids. Furthermore, structural studies of the active components suggested that the epitope of the antibody consisted of the group A trisaccharide, GalNAc alpha 1,3(Fuc alpha 1,2)Gal.

Structure-function analysis of human alpha1,3-fucosyltransferase. Amino acids involved in acceptor substrate specificity

A series of molecular biology experiments were carried out to identify the catalytic domain of two human alpha1,3/4-fucosyltransferases (fucosyltransferases (FucTs) III and V), and to identify amino acids that function in acceptor substrate binding. Sixty-one and 75 amino acids could be eliminated from the N terminus of FucTs III and V, respectively, without a significant loss of enzyme activity. In contrast, the truncation of one or more amino acids from the C terminus of FucT V resulted in a dramatic or total loss of enzyme activity. Results from the truncation experiments demonstrate that FucT III62-361 (containing amino acids 62-361) and FucT V76-374 (containing amino acids 76-374) are active, whereas shorter forms of the enzymes were inactive. The shortest, active forms of the enzymes are more than 93% identical at the predicted amino acid level, but have distinct acceptor substrate specificities. Thus, FucT III is an alpha1,4-fucosyltransferase, whereas FucT V is an alpha1,3-fucosyltransferase with disaccharide substrates. All but one of the amino acid sequence differences between the two proteins occur near their N terminus. Results obtained from domain swapping experiments demonstrated that the single amino acid sequence difference near the C terminus of these enzymes did not alter the enzyme's substrate specificity. However, swapping a region near the N terminus of the truncated form of FucT III into an homologous region in FucT V produced a protein with both alpha1,3- and alpha1,4-fucosyltransferase activity. This region contains 8 of the amino acid sequence differences that occur between the two proteins.

Methyl 3-amino-3-deoxy-beta-D-galactopyranosyl-(1-->4)-2-acetamido-2- deoxy-beta-D-glucopyranoside: an inhibitor of UDP-D-galactose: beta-D-galactopyranosyl-(1-->4)-2-acetamido-2-deoxy-D-glucose (1-->3)-alpha-D-galactopyranosyltransferase

UDP-D-galactose:beta-D-galactopyranosyl-(1-->4)-2-acetamido-2-deoxy-D- glucose alpha-(1-->3)-D-galactopyranosyltransferase [E.C. 2.4.1.151] transfers D-galactosyl-residues from the sugar nucleotide with retention of configuration. We report here that synthetic methyl 3'-amino-3'-deoxy-N-acetyllactosaminide (9), where the hydroxyl group normally undergoing galactosylation has been replaced by amino group, is an inhibitor for this enzyme with Ki = 104 microM. The mode of inhibition is not competitive, but appears to be specific, since other glycosyltransferases were not affected by 9.

Alpha 1,4galactosyltransferase activity and Gb3Cer expression in human leukaemia/lymphoma cell lines

We have used two methods to evaluate the level of expression of Gb3Cer in several human leukaemia/lymphoma cell lines representative of the myeloid (K562, KG-1, HL-60, and lymphoid (Reh, Daudi, Raji, RPMI 8226, CCRF-CEM, MOLT-4) lineages blocked at varied stages of differentiation. TLC immunostaining of glycolipid extracts with a monoclonal antibody, 12-101, and FACS analysis with the same antibody were used to demonstrate that the expression of Gb3Cer in neoplastic myeloid and lymphoid cells is both lineage and differentiation dependent. As a possible control point in the regulated expression of Gb3Cer we have investigated the first committed step in the synthesis of globo series glycosphingolipids that involves UDP-Gal:LacCer alpha (1,4)-galactosyltransferase (alpha 1,4GalT). We present the first characterization of this enzyme in a human myeloid cell line using an ELISA-based assay, which was subsequently used to measure alpha 1,4GalT activity in the human leukaemia/lymphoma cell lines. In general, there is a positive correlation between the levels of endogenous Gb3Cer and the level of the alpha 1,4 GalT activity. However, in two cases (KG-1 and CCRF-CEM) the level of enzyme activity did not correspond to the level of Gb3Cer expression.

Peptides inhibit selectin-mediated cell adhesion in vitro, and neutrophil influx into inflammatory sites in vivo

The selectins are cell adhesion molecules whose carbohydrate-binding domain (C-type lectin) is thought to be involved in leukocyte adhesion to activated vascular endothelium in the inflammatory process. A series of peptides, based on a conserved region (48YYWIGIRK55-NH2) of the lectin domain of E-, L- and P-selectins, were analysed for their ability to block selectin-mediated cell adhesion in vitro, and neutrophil infiltration into sites of inflammation in vivo. The peptides inhibited the adhesion of myeloid cells to recombinant forms of E- and P-selectin. The adhesion of myeloid cells to human endothelial cells, stimulated to express E-selectin, was also inhibited by the peptides. Finally, the peptides blocked the adhesion of lymphocytes, expressing L-selectin, to high endothelial venules in lymph nodes which contain the ligand for L-selectin. A clear structure-activity relationship was established when peptides of different amino acid chain lengths were tested in these assays. Peptides lacking tyrosine residues (e.g. WIGIR-NH2) at their amino terminus were poor inhibitors of selectin-mediated cell adhesion in vitro. The peptides that were found to be inhibitors of cell adhesion in vitro were also found to inhibit (up to 70%) neutrophil infiltration into sites of inflammation in a thioglycollate-induced peritonitis mouse model system. They also significantly reduced (> 50%) the migration of neutrophils into cytokine-treated skin. These results strongly suggest that compounds based on these tyrosine-containing, selectin-derived peptides could be used as anti-inflammatory therapeutic agents.

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

The acceptor specificity of recombinant full-length, membrane-bound fucosyltransferases, expressed in COS-7 cells, and soluble, protein-A chimeric forms of alpha 1,3-fucosyltransferase (Fuc-T) III, Fuc-TIV, and Fuc-TV was analyzed toward a broad panel of oligosaccharide, glycolipid, and glycoprotein substrates. Our results on the full-length enzymes confirm and extend previous studies. However, chimeric Fuc-Ts showed increased activity toward glycoproteins, whereas chimeric Fuc-TIII and Fuc-TV had a decreased activity with glycosphingolipids, compared to the full-length enzymes. Unexpectedly, chimeric Fuc-TV exhibited a GDP-fucose hydrolyzing activity. In substrates with multiple acceptor sites, the preferred site of fucosylation was identified. Fuc-TIII and Fuc-TV catalyzed fucose transfer exclusively to OH-3 of glucose in lacto-N-neotetraose and lacto-N-tetraose, respectively, as was demonstrated by 1H NMR spectroscopy. Thin layer chromatography immunostaining revealed that FucT-IV preferred the distal GlcNAc residue in nLc6Cer, whereas Fuc-TV preferred the proximal Gl-cNAc residue. Incubation of Fuc-TIV or Fuc-TV with VI3NeuAcnLc6Cer resulted in products with the sialyl-LewisX epitope as well as the VIM-2 structure. To identify polar groups on acceptors that function in enzyme binding, deoxygenated substrate analogs were tested as acceptors. All three Fuc-Ts had an absolute requirement for a hydroxyl at C-6 of galactose in addition to the accepting hydroxyl at C-3 or C-4 of GlcNAc.

Structure-function analysis of human alpha 1-->3fucosyltransferases. A GDP-fucose-protected, N-ethylmaleimide-sensitive site in FucT-III and FucT-V corresponds to Ser178 in FucT-IV

Human alpha 1-->3fucosyltransferases constitute a family of closely related membrane-bound enzymes distinguished by differences in acceptor specificities and inherent protein biochemical properties. One such biochemical property is sensitivity to enzyme inactivation by sulfhydral-group modifying reagents such as N-ethylmaleimide. The basis for this property has been studied using a fusion protein of FucT-III and FucT-V composed of Protein A coupled to the catalytic domain of the enzyme. The results indicate that modification of FucT-V by 5,5'-dithiobis(2-nitrobenzoic acid) resulted in efficient enzyme inactivation that could be reversed by excess thiol reagent suggesting that the free sulfhydral group on the enzyme was required for activity. Recombinant forms of both FucT-III and FucT-V were irreversibly inactivated by N-ethylmaleimide and could be effectively protected from inactivation by GDP-fucose and GDP but not by UDP-galactose, fucose, or N-acetyllactosamine. Analysis of the distribution of Cys residues in aligned sequences of cloned human alpha 1-->3fucosyltransferases indicated one site, Cys143 of FucT-III and Cys156 of FucT-V, corresponded to the highly conservative replacement of Ser178 in FucT-IV, an enzyme insensitive to N-ethylmaleimide. A site-directed mutagenesis experiment was performed to replace Ser178 of FucT-IV with a Cys residue. The mutant FucT-IV enzyme was active; however, the Km for GDP-fucose was increased about 3-fold compared to the native enzyme to 28 +/- 3 microM. This enzyme was N-ethylmaleimide sensitive and could be partially protected by GDP-fucose but not N-acetyllactosamine. These results support the importance of Ser178 of FucT-IV in donor substrate binding and strongly suggest analogous Cys residues are the GDP-fucose protectable, N-ethylmaleimide-sensitive sites present in FucT-III and -V.

Characterization of porcine kidney neutral glycosphingolipids: identification of a carbohydrate antigen recognized by human natural antibodies

We have investigated the glycosphingolipids of pig kidney with a special interest in identifying compounds which may be involved in the rejection of tissue in xenotransplantation. Nine neutral glycosphingolipids have been characterized in porcine kidney and structurally characterized by a combination of techniques including 1H-NMR, permethylation analysis and thin-layer chromatography (TLC) immunostaining with carbohydrate sequence-specific monoclonal antibodies. The major components are members of the globo family and represent the human pk and P antigens. Three other compounds were found to contain a neolacto core structure; the major neolacto compound carries a nonreducing terminal epitope (Gal alpha 1-3Gal beta 1-4GlcNAc) recognized by the naturally-occurring human antibody, anti-Gal, and a second neolacto compound carries the blood group A trisaccharide (GalNAc alpha 1-3(Fuc alpha 1-2)Gal). These results are discussed with respect to tissue transplantation.

Structural characterization of intermediates in the biosynthetic pathway of neolacto glycosphingolipids: differential expression in human leukaemia cells

The biosynthesis of neolacto glycosphingolipids is thought to proceed via reactions catalysed by the two enzymes beta 1-3-N-acetylglucosaminyltransferase (beta 1,3GlcNAcT) and beta 1-4 galactosyltransferase (beta 1,4GalT). In general, only the products of the latter enzyme have been isolated from tissues and structurally characterized. Among the GlcNAc beta 1-3-R glycosphingolipids, only lactotrioasylceramide (Lc3Cer, the initial product in the biosynthesis of neolacto glycosphingolipids) has been isolated and structurally characterized. Longer-chain glycosphingolipids with a terminal GlcNAc-beta 1-3-R structure are considered to be intermediates in the synthesis of complex neolacto glycosphingolipids. We have detected a series of GlcNAc beta 1-3-R glycosphingolipids in extracts obtained from human leukocytes isolated from patients with leukaemia using a monoclonal antibody (TE5) which specifically recognizes these compounds. The structures of three of these compounds purified from chronic myelocytic leukaemia (CML) cells have been determined using a combination of enzymatic, immunostaining and chemical methods. The compounds were found to have the following structures: GlcNAc beta 1-3Gal beta 1-4Glc beta 1-1Cer (Lc3Cer) GlcNAc beta 1-3Gal beta 1-4GlcNAc beta 1-3Gal beta 1-4Glc beta 1-1Cer (nLc5Cer) GlcNAc beta 1-3Gal beta 1-4GlcNAc beta 1-3Gal beta 1-4GlcNAc beta 1-3Gal beta 1-4Glc beta 1-1Cer (nLc7Cer) A longer-chain compound, apparently nLc9Cer, was also detected. TLC immunostaining analysis of glycosphingolipids isolated from cells obtained from patients with various leukaemias demonstrated that GlcNAc beta 1-3-R glycosphingolipids have a distribution that depends on the stage of differentiation and lineage of the cell population.(ABSTRACT TRUNCATED AT 250 WORDS)

Expression of fucosylated antigens and alpha 1,3 fucosyltransferases in human leukaemia cell lines

The expression of alpha 1,3 fucosylated type 2 antigens is generally thought to be restricted to myeloid cells among normal human haemopoietic tissue. The distribution of three fucosylated antigens [Lewis X (Le(x)), sialyl Lewis X (sLex) and VIM2] was investigated among nine human leukaemia cell lines by fluorescence activated cell sorting (FACS) analysis. As expected, all myeloid cell lines were positively stained by antibodies against these three fucosylated antigens. Unexpectedly, two T-lymphocytic cell lines (CCRF-CEM and MOLT4) were found to express Le(x) and VIM2, and the plasma, B-cell line, RPMI 8226, expressed all three fucosylated antigens. Enzymatic and RNA analyses [Northern blot and reverse transcription polymerase chain reaction (RT-PCR)] were used to evaluate possible control points in the biosynthetic pathway for Le(x) and sLex. beta 1,4 Galactosyltransferase (beta 1,4GalT, an enzyme involved in the synthesis of the core oligosaccharide of the three fucosylated antigens) activity and the corresponding mRNA were found in all of the leukaemia cell lines, regardless of whether or not they expressed the fucosylated antigens. In contrast, alpha 1,3 fucosyltransferase (GDP-fucose:beta-D-N-acetylglucosaminide 3-alpha-L-fucosyltransferase; alpha 1,3FT) activity and the corresponding mRNA were found only in those cell lines expressing fucosylated antigens. Based on RNA analysis, acceptor specificity and N-ethylmaleimide inhibition studies, it was concluded that all of the cell lines expressing fucosylated antigens contained alpha 1,3FTIV (myeloid alpha 1,3FT). This appeared to be the major alpha 1,3FT in the myeloid and T-lymphocytic cell lines. Interestingly, even though both types of cell lines expressed the same alpha 1,3FT, only the myeloid cell lines expressed sLex, whereas all of the myeloid and T-lymphocytic cell lines expressed a structural analogue of sLex (i.e. VIM2). In contrast to the myeloid and T-cell lines, RPMI 8226 cells contained more than one fucosyltransferase activity. Acceptor specificity analysis demonstrated that this cell line contains alpha 1,3 and alpha 1,4FTs. Among the fucosyltransferases expressed by RPMI 8226, alpha 1,3FTIV accounted for only a small amount of the total activity. The results of this study demonstrate that fucosylated antigens, which are generally considered to be myeloid specific antigens, are also expressed by lymphocytic leukaemia cell lines, and that the types of fucosylated antigens and fucosyltransferases expressed in these cell lines vary.

Analysis of glycosphingolipid glycosyltransferase products on TLC plates by combined storage phosphor and immunostaining techniques

Measurement of glycosyltransferase activity in whole cell extracts is often complicated by the fact that several enzymes in an homogenate are capable of using the same nucleotide sugar donor, thereby generating a range of products from both an exogenous and any endogenous acceptors. We report the use of a novel combination of techniques to simultaneously identify and quantify the products generated from a whole cell extract in a single experiment. Several radiolabeled glycosphingolipid products were generated by the addition of UDP-[14C]Gal to a reaction mixture containing an homogenate from a human leukemia cell line, THP-1. After the 14C-labeled products were separated on a TLC plate, storage phosphor technology and immunostaining (with carbohydrate sequence-specific monoclonal antibodies) were used sequentially on the same plate to simultaneously identify and quantify each of the glycosyltransferase products. This method allows product identification and quantification in the femtomole range. Thus, low levels of endogenous acceptors were easily detected. We have used a similar method with UDP-[3H]Gal to obtain glycosyltransferase product profiles from several human leukemia/lymphoma cell lines and subsequently identify two galactosyltransferase activities in these cell lines: UDP-Gal:Gal beta 1-4Glc beta 1-1Cer alpha 1,4galactosyltransferase; and UDP-Gal:GlcNAc beta 1--3Gal beta 1--4Glc beta 1--1Cer beta 1,4galactosyltransferase. In addition to product characterization, this method was used with reaction mixtures at different pH to demonstrate the usefulness of the method for characterizing multiple enzyme activities simultaneously.

Defining the minimal size of catalytically active primate alpha 1,3 galactosyltransferase: structure-function studies on the recombinant truncated enzyme

The glycosylation enzyme alpha 1,3 galactosyltransferase, which synthesizes the carbohydrate Gal alpha 1-3Gal beta 1-4GlcNAc-R, is active in non-primate mammals, prosimians and New World monkeys, but not in Old World monkeys, apes and humans. In this study, we have cloned and sequenced the enzyme expressed in a New World monkey, determined the exact size of the stem region and assessed the minimal size of catalytically active alpha 1,3 galactosyltransferase (alpha 1,3GT). Various primer sets were used in the polymerase chain reaction to generate cDNAs which coded for forms of alpha 1,3GT with deletions at the N- or C-terminal domains. The cDNA was inserted into the expression vector pPROTA which contains the coding sequence for protein A, and subsequently transfected into COS cells. The soluble chimeric products (truncated enzyme and protein A) were harvested from the cell culture medium using IgG-Sepharose beads and assayed for enzymatic activity. As many as 67 amino acids could be truncated at the amino terminal region of the luminal portion of the enzyme without affecting its catalytic activity. Truncation of 68, 69 and 74 amino acids resulted in a 50, 75 and > 95% loss in the in vitro catalytic actively, respectively. Introduction of a frameshift mutation which is characteristic of apes and human alpha 1,3GT gene resulted in the complete loss of enzyme activity. Moreover, truncation of as few as three amino acids at the carboxyl end of alpha 1,3GT resulted in complete loss of the catalytic activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Glycosphingolipids of rabbit, sheep, and pig thymus

The thymus plays a major role in the immune system and many of the processes that occur in this tissue depend on cell-cell interactions. Glycoconjugates are known to mediate cell-cell interactions and thus to understand more fully the function of this class of compounds in thymus, structural characterization and quantification of the glycosphingolipids in thymus from sheep, rabbit, and pig were performed. Qualitative and quantitative differences were found for each species. Thymus from all three species contained neolacto (Gal beta 1-4GlcNAc) glycosphingolipids; however, significant differences in the types and quantities expressed by each animal were found. An evaluation of other classes of glycosphingolipids and their quantities demonstrate that pig thymus has a much different pattern of glycosphingolipid expression than sheep and rabbit thymus. The major glycosphingolipids in pig thymus are globo-series neutral glycosphingolipids (Gb3 and Gb4) and lactosyl-series gangliosides (GM3 and GD3). In contrast, sheep and rabbit thymus express significant levels of lacto and neolacto neutral glycosphingolipids, and also lacto and neolacto gangliosides, including three previously unidentified compounds. The major difference in glycosphingolipid expression in these two species was the presence of branched-chain gangliosides in sheep thymus.

Beta 1-3-N-acetylglucosaminyltransferase in human leukocytes: properties and role in regulating neolacto glycosphingolipid biosynthesis

There are well-established differences in the expression of neolacto neutral glycosphingolipids among human leukocyte subclasses. Mature myeloid cells express several types of these compounds, whereas mature lymphoid cells are deficient in such compounds. The biochemical basis for this is unknown. Therefore, enzyme studies were done to determine whether different classes of leukocytes (represented by cell lines) contained beta 1-3-N-acetylglucosaminyltransferase activity (EC 2.4.1.149, beta 1-3GlcNAcT(i)). This enzyme participates in the synthesis of Type 2 chains in glycosphingolipids by catalyzing the following two reactions: (i) Gal beta 1-4Glc beta 1-1Cer (lactosylceramide, LacCer) + UDP-GlcNAc-->GlcNAc beta 1-3Gal beta 1-4Glc beta 1- 1Cer (lactotriaosylceramide) and (ii) Gal beta 1-4GlcNAc beta 1-3Gal beta 1-4Glc beta 1-1Cer (neolactotetraosylceramide) + UDP-GlcNAc-->GlcNAc beta 1-3Gal beta 1-4GlcNAc beta 1-3Gal beta 1-4Glc beta 1-1Cer. The first reaction may be the key step in the biosynthetic pathway of neolacto structures in human leukocytes. Therefore, extracts from several cell lines representative of both myeloid and lymphoid lineages, at varied stages of maturity, were assayed with LacCer for the presence of beta 1-3GlcNAcT(i) activity. Our results indicate that myeloid cells contain this initiating beta 1-3GlcNAcT(i) activity, whereas lymphoid cells do not. This is consistent with our thin-layer chromatography immunostain results which show that all myeloid cell lines express neutral neolacto glycosphingolipids and lymphoid cells do not. Our findings suggest that the presence of the initiating activity only in myeloid cells is a regulatory factor in the expression of neutral neolacto glycosphingolipids in human leukocytes. We also tested both myeloid and lymphoid cell lines for the presence of elongating beta 1-3GlcNAcT(i) activity (reaction (ii) above) by using neolactotetraosylceramide as an acceptor. Our results show that an elongating activity is expressed by all myeloid and lymphoid cell lines tested. Initiating (myeloid) and elongating (myeloid and lymphoid) activities were distinguished by several characteristics: metal ion activation, pH optimum, and kinetic constants. In conclusion, our results indicate the presence of two beta 1-3GlcNAcT(i) activities in human leukocytes: one that catalyzes the initial reaction and is found only in the myeloid lineage and one that catalyzes the elongating reaction and is found in both myeloid and lymphoid cells.

Specificity of fucose transfer to GlcNAc residues of extended chain neolacto-series glycolipids catalyzed by human alpha 1-->3fucosyltransferases: effect of the lipidic environment on the myeloid enzyme form

Multiple alpha 1-->3fucosyltransferases occur in the human genome of which the Lewis (FucT-III), myeloid (FucT-IV), and plasma (FucT-V) enzyme forms have received the greatest attention. In this paper, the acceptor properties of the myeloid alpha 1-->3fucosyltransferase from human promyelocytic leukemia HL-60 cells have been studied. Fucose transfer into glycolipid acceptors was activated by detergents G-3634-A or taurodeoxycholate resulting in efficient transfer to neutral acceptors but poor transfer to sialylated acceptors, characteristic of the myeloid-type enzyme. Fucose transfer to nLc6 yielded both mono- and difucosyl derivatives under both detergent conditions. The nLc6 monofucosyl products were isolated and analyzed by TLC immunostaining and fast atom bombardment-mass spectroscopy analysis. The G-3634-A monofucosyl product was found to be composed solely of V3FucnLc6, whereas that with taurodeoxycholate was determined to be a mixture of III3FucnLc6 and V3FucnLc6 in near equal amounts. Analysis of reaction products using enzyme activation by phospholipids indicated that phosphatidylethanolamine and phosphatidylinositol behaved similarly to G-3634-A. In contrast, phosphatidylglycerol yielded results similar those of taurodeoxycholate. Fucose transfer to VI3NeuAcnLc6 yielded approximately 75% of the product as the III-GlcNAc monofucosyl derivative regardless of the detergent or phospholipid condition used. Analysis of fucose transfer to nLc6 catalyzed by the Lewis enzyme from Colo 205 cells using taurodeoxycholate yielded solely the III-GlcNAc monofucosyl derivative, whereas the predominant product with G-3634-A was V-GlcNAc fucosylated. In contrast, under both conditions only the V-GlcNAc monofucosylation product was found with the enzyme from NCI-H69 cells. The results indicate that subtle intrinsic differences exist between human alpha 1-->3fucosyltransferases. Modulation of enzyme specificity via the nature of the membrane environment could participate in regulation of expression of distinct cell surface antigens.

Fucosylated glycosphingolipids of human myeloid cells

Our efforts to determine the carbohydrate binding specificity of two myeloid-specific monoclonal antibodies (VIM-1 and VIM-10) resulted in the purification of three fucosylated glycosphingolipids from human chronic myelogenous leukemia cells. After repeated high-performance liquid chromatographic separations, two forms of fucosylated glycosphingolipids were resolved. VIM-1 and VIM-10 were found to bind to the heptaosylceramide Gal beta 1-4 (Fuc alpha 1-3)GlcNAc beta 1-3Gal beta 1-4GlcNAc beta 1-3Gal beta 1-4Glc beta 1-1Cer with the Le(x) (Lewis X) epitope, but not to either the hexaosylceramide Fuc alpha 1-2Gal beta 1-4(Fuc alpha 1-3)GlcNAc beta 1-3Gal beta 1-4Glc beta 1-1-Cer or the octaosylceramide Fuc alpha 1-2Gal beta 1-4(Fuc alpha 1-3)GlcNAc beta 1-3Gal beta 1-4GlcNAc beta 1-3Gal beta 1-4Glc beta 1-1Cer, each with the Le(y) (Lewis Y) epitope. The latter two glycosphingolipids are the first Le(y) antigens to be purified from human leukocytes and structurally characterized. Binding studies with a range of glycosphingolipids from myeloid cells and other biological sources demonstrated that VIM-1 and VIM-10 bind to Le(x) glycosphingolipids with five or more sugar residues, but not to a glycosphingolipid (III3Fuc-nLc6Cer) with an internal Le(x) trisaccharide.

Molecular cloning of a human fucosyltransferase gene that determines expression of the Lewis x and VIM-2 epitopes but not ELAM-1-dependent cell adhesion

We have used the human Lewis blood group fucosyltransferase cDNA and cross-hybridization procedures to isolate a human gene that encodes a distinct fucosyltransferase. Its DNA sequence predicts a type II transmembrane protein whose sequence is identical to 133 of 231 amino acids at corresponding positions within the catalytic domain of the Lewis fucosyltransferase. When expressed by transfection in cultured cell lines, this gene determines expression of a fucosyltransferase capable of efficiently utilizing N-acetyllactosamine to form the Lewis x determinant (Gal beta 1----4[Fuc alpha 1----3]GlcNAc). By contrast, biochemical and flow cytometry analyses suggest that the enzyme cannot efficiently utilize the type II acceptor NeuNAc alpha 2----3Gal beta 1----4GlcNAc, to form the sialyl Lewis x determinant. In Chinese hamster ovary cells, however, the enzyme can determine expression of the alpha 2----3-sialylated, alpha 1----3-fucosylated structure known as VIM-2, a putative oligosaccharide ligand for ELAM-1. Cell adhesion assays using VIM-2-positive, sialyl Lewis x-negative transfected Chinese hamster ovary cells indicate that surface expression of the VIM-2 determinant is not sufficient to confer ELAM-1-dependent adhesive properties upon the cells. These results demonstrate that substantial structural similarities can exist between mammalian glycosyltransferases with closely related enzymatic properties, thus facilitating isolation of their cognate genes by cross-hybridization methods. The results further suggest that cell surface expression of the VIM-2 determinant is not necessarily sufficient to mediate ELAM-1-dependent cell adhesion.

Requirement for sialic acid on neutrophils in a GMP-140 (PADGEM) mediated adhesive interaction with activated platelets

Platelet GMP-140, along with ELAM-1 and gp90MEL, comprise the LEC-CAM family of cell-cell adhesion proteins. The three proteins demonstrate a highly related domain organization, which includes an extracellular calcium-type lectin motif. gp90MEL, a lymphocyte homing receptor, mediates lymphocyte attachment to high endothelial venules of lymph nodes through recognition of a sialylated ligand on the endothelial cells. The rosetting of neutrophils or promyelocytic HL60 cells by activated platelets is mediated by GMP-140 on the platelets. We show here that treatment of neutrophils or HL60 cells with 3 broad spectrum sialidases completely prevents rosetting. However, the Newcastle disease virus sialidase, an enzyme specific for alpha 2,3 and alpha 2,8 linkages of sialic acid does not affect rosetting of HL60 cells. These results indicate that the ligand for GMP-140 requires sialic acid and suggest that an alpha 2,6 linkage may be critical.

Regulation of the expression of Gal alpha 1-3Gal beta 1-4GlcNAc glycosphingolipids in kidney

Previous studies (Galili, U., Clark, M. R., Shohet, S. B., Buehler, J., and Macher, B. A. (1987) Proc. Natl. Acad. Sci. U. S. A. 84, 1369-1373; Galili, U., Shohet, S. B., Korbrin, E., Stults, C. L. M., and Macher, B. A. (1988) J. Biol. Chem. 263, 17755-17762) have established that there is a unique evolutionary distribution of glycoconjugates carrying the Gal alpha 1-3Gal beta 1-4GlcNAc epitope. These glycoconjugates are expressed by cells from New World monkeys and non-primate mammals, but not by cells from humans, Old World monkeys, or apes. The lack of expression of this epitope in the latter species appears to result from the suppression of gene expression for the enzyme UDP-galactose:nLc4Cer alpha 1-3-galactosyltransferase (alpha 1-3GalT) (Joziasse, D. H., Shaper, J. H., Van den Eijnden, D. H., Van Tunen, A. J., and Shaper, N. L. (1989) J. Biol. Chem. 264, 14290-14297). Although many non-primate species are known to express this carbohydrate epitope, the nature (i.e. glycoprotein or glycosphingolipid) of the glycoconjugate carrying this epitope is only known for a few tissues in a few animal species. Furthermore, it is not known whether all animal species express this epitope in the same tissues. We have investigated these questions by analyzing the glycosphingolipids in kidney from several non-primate animal species. Immunostained thin layer chromatograms of glycosphingolipids from sheep, pig, rabbit, cow, and rat kidney with the Gal alpha 1-3Gal beta 1-4GlcNAc glycosphingolipid-specific monoclonal antibody, Gal-13, demonstrated that kidney from all of these species except rat contained Gal alpha 1-3Gal beta 1-4GlcNAc neutral glycosphingolipids. A lack of expression of Gal alpha 1-3Gal beta 1-4GlcNAc glycosphingolipids in rat may be due to the lack of expression of the enzyme (alpha 1-3GalT) which catalyzes the formation of the Gal alpha 1-3Gal nonreducing terminal sequence of these compounds or to the lack of expression of glycosyltransferases which are necessary for the synthesis of the neolacto core structure of these compounds. These possibilities were evaluated in two ways. First, the three enzymes (UDP-N-acetylglucosamine:LacCer beta 1-3-N-acetyl-glucosaminyltransferase, UDP-galactose:Lc3Cer beta 1-4-galactosyltransferase, and alpha 1-3GalT) involved in the synthesis of the Gal alpha 1-3Gal beta 1-4GlcNAc glycosphingolipids were assayed using an enzyme-linked immunosorbent assay-based assay system and carbohydrate sequence-specific monoclonal antibodies. Second, TLC immunostaining was done to determine if the glycosphingolipid precursors (i.e. Lc3Cer and nLc4Cer) are expressed in rat kidney. Interestingly, rat kidney had a relatively high level of alpha 1-3GalT activity compared with the other animals tested.(ABSTRACT TRUNCATED AT 400 WORDS)

Measurement of beta-galactosyltransferase activity in cell extracts with an ELISA-based assay

An enzyme-linked immunosorbent assay (ELISA)-based glycosyltransferase assay has been used to measure UDP-Gal:N-acetylglucosamine beta-1,4-galactosyl-transferase (EC 2.4.1.38) activity in detergent extracts of chinese hamster ovary (CHO) cells. LEC11 cells (a mutant of the CHO cell line, Pro -5), which are known to express a complex array of carbohydrate structures, were used to develop the assay for use with whole cell extracts. A detergent-solubilized preparation of the enzyme from whole cells was used to convert the substrate, lactotriglycosylceramide, to the product, neolactotetraglycosylceramide. The monoclonal antibody, 1B2, which specifically binds to the Gal beta 1-4GlcNAc epitope, was used in an ELISA to identify and quantify the product. The enzyme activity in the preparations was found to be similar to that obtained by conventional radioactive assay methods. The beta-galactosyltransferase found in LEC11 cell detergent extracts exhibited an absolute requirement for the nucleotide sugar and MnCl2. The activity of the enzyme was also strictly dependent on the presence of exogenous glycolipid acceptor. When Triton X-114 was used to solubilize the LEC11 beta-galactosyltransferase, activity was found in both the hydrophilic and the hydrophobic phases, suggesting the presence of two forms of the enzyme. The ELISA-based assay was used to compare beta-1,4-galactosyltransferase activity in detergent extracts of four CHO cell lines: Pro-5, Lec1, LEC11, and LEC12 and in detergent-solubilized microsomes from human leukemia cells. The results from this study demonstrate the utility of the ELISA-based assay for measuring glycosyltransferase activity in detergent-solubilized whole cells and microsome preparations.

Distribution of VIM-2 and SSEA-1 glycoconjugate epitopes among human leukocytes and leukemia cells

Anti-SSEA-1 which binds to glycoconjugates with a Gal beta 1-4(fuc alpha 1-3)GlcNAc epitope and VIM-2 which binds to gangliosides with a NeuAc alpha 2-3GlcNAc beta-4(FUC alpha 1-3) GlcNAc beta 1-3Gal-epitope were used to determine the expression of their corresponding carbohydrate antigens in human leukocytes and leukemia cells. Expression of these antigens was evaluated by immunohistochemical staining of plastic embedded sections of bone marrow or isolated cells, and by immunostaining of isolated glycosphingolipids separated by thin layer chromatography. The expression of both antigens was restricted to normal and leukemic myeloid cells. A range of positive immunohistochemical staining was found among normal marrow myeloid precursors, with myeloblasts giving weaker staining than more mature cells (promyelocytes, myelocytes, metamyelocytes). A similar trend was observed with leukemia cell lines, in that the myeloblastic cell line KG1 was weakly stained compared to the partially differentiated cell line HL-60. Immunohistochemical staining of marrows from acute leukemia patients showed that the VIM-2 antigen is more strongly expressed than the SSEA-1 antigen. Interestingly, both antibodies stained AMMoL cells more intensely than AML cells. Granulocytes from marrows of chronic myelogenous leukemia (CML) patients were intensely stained by both antibodies, whereas lymphocytic leukemias (acute lymphocytic, chronic lymphocytic and hairy cell marrows) were negative. Thus, although both antigens are restricted to myeloid cells there are differences in the level of expression depending on the level of cell maturity. Immunostaining of glycosphingolipids isolated from myeloid cells demonstrated that the SSEA-1 epitope is carried by several neutral glycosphingolipids and that the VIM-2 epitope is carried by three or more gangliosides. Major SSEA-1 glycosphingolipids, with seven to more than ten monosaccharides, are expressed by all myeloid cells regardless of the level of maturity, although quantitative differences are apparent in different patient samples. Two strongly immunoreactive VIM-2 gangliosides with ten and twelve monosaccharides, respectively were found in myeloid cells. The ratio of these two gangliosides varied dramatically, with greater amounts of the more complex ganglioside being present in most cell samples. Normal neutrophils and CML cells had much greater quantities of the VIM-2 gangliosides than acute leukemia cells. This observation correlates with our earlier findings that: (1) acute leukemia cells have less total ganglioside than granulocytes and (2) acute leukemia cells have a predominance of short chain gangliosides (i.e. less than five monosaccharide units). Finally, both CML cells and normal neutrophils express a shorter chain VIM-2 ganglioside, which was not detected in acute myelogenous leukemia cells.

Man, apes, and Old World monkeys differ from other mammals in the expression of alpha-galactosyl epitopes on nucleated cells

The study of the expression of alpha-galactosyl epitopes on various mammalian cells is of particular interest, since as much as 1% of circulating IgG antibodies in humans interact with this carbohydrate residue. This natural antibody, designated "anti-Gal," was previously found to bind to terminal Gal alpha 1----3Gal beta 1----4GlcNAc-R on biochemically defined glycolipids (Galili, U., Macher, B. A., Buehler, J., and Shohet, S. B. (1985) J. Exp. Med. 162, 573-582; Galili, U., Buehler, J., Shohet, S. B., and Macher, B. A. (1987) J. Exp. Med. 165, 693-704). The expression of anti-Gal binding epitopes on nucleated cells from various mammalian species was studied by immunostaining with this antibody. The binding of anti-Gal to various cells was correlated with the binding of the lectin Bandeiraea (Griffonia) simplicifolia IB4 (BS lectin). The BS lectin also interacts with alpha-galactosyl residues and particularly with high affinity with Gal alpha 1----3Gal beta 1----4GlcNAc residues. We observed a striking evolutionary pattern in the expression of these epitopes on mammalian nucleated cells. Fibroblasts, epithelial cells, endothelial cells, smooth muscle cells, and lymphoid cells of nonprimate mammals, prosimians, and New World monkeys readily bound both anti-Gal and BS lectin. However, no such binding was detectable on cells of Old World monkeys, apes, and humans. Measurment of the binding of radiolabeled BS lectin to the various nucleated cells suggests that cells binding anti-Gal express 10(6) to 3.5 x 10(7) alpha-galactosyl epitopes, most of which, based on the anti-Gal specificity, seem to have the structure of Gal alpha 1----3Gal beta 1----4GlcNAc-R. The absence of these epitopes from human cells results from diminished activity of the enzyme alpha 1----3 galactosyltransferase, which catalyzes the following reaction. Gal beta 1----4GlcNAc-R + UDP-Gal(alpha 1----3-galactosyltransferase)----Gal alpha 1----3Gal beta 1----4GlcNAc-R + UDP This enzyme, which participates in the glycosylation of cell membrane glycoconjugates in nonprimate mammals, prosimians, and New World monkeys, appears to have been suppressed in Old World primates as a result of evolutionary events which occurred 20-30 million years ago. It is argued that an anomalous activity of this enzyme in man may result in initiation of autoimmune diseases because of the de novo expression of Gal alpha 1----3Gal beta 1----4GlcNAc-R epitopes recognized by anti-Gal.

Enzyme-linked immunosorbent assay (ELISA)-based quantification and identification of in vitro enzyme-catalyzed glycosphingolipid synthesis and degradation products with carbohydrate sequence-specific monoclonal antibodies

A new method has been developed to monitor glycosyltransferase and glycosylhydrolase activities. Reaction product identification and quantification are accomplished simultaneously with an enzyme-linked immunosorbent assay (ELISA) using carbohydrate sequence-specific monoclonal antibodies. beta-Galactosyltransferase and alpha-galactosidase reactions were used to illustrate the salient features of the method. These include simple product identification and quantification, no detergent requirement, consumption of small amounts of reagents, and no use of radioisotopes. Furthermore, it is possible to measure substrate disappearance or product formation with this method. Enzyme characteristics such as Km, Vmax, divalent cation requirement, and pH optimum were investigated with this new method.

A novel carbohydrate, differentiation antigen on fucogangliosides of human myeloid cells recognized by monoclonal antibody VIM-2

A mouse monoclonal antibody, VIM-2, specific for human blood cells of myelomonocytic lineage, was found to bind to a series of minor gangliosides isolated from the cells of patients with chronic myelogenous leukemia (Uemura, K., Macher, B.A., DeGregorio, M., Scudder, P., Buehler, J., Knapp, W., and Feizi, T. (1985) Biochim. Biophys. Acta 846, 26-36). TLC immunostaining studies with the VIM-2 antibody of gangliosides from normal human neutrophils, acute myeloid leukemia, and chronic myelogenous leukemia cells showed that the total amount and the ratio of the VIM-2 gangliosides varies among these different myeloid cells and appears to be related to the level of cellular differentiation. Purification of these gangliosides from chronic myelogenous leukemia cells was aided by a sensitive enzyme-linked immunosorbent assay procedure used in conjunction with high performance liquid chromatography. Structures for two of the immunoreactive gangliosides (a ceramide decasaccharide, VIII3NeuAcV3-Fuc-nLc8Cer and a ceramide dodecasaccharide X3-NeuAcVII3Fuc-nLc10Cer) are proposed from negative ion fast atom bombardment mass spectrometry of the native gangliosides, methylation analysis, and the combined use of glycosidase treatment and TLC immunostaining with carbohydrate sequence specific antibodies. The VIM-2 antigen was thus characterized as involving the sialofucooligosaccharide sequence.

Lipooligosaccharides (LOS) of Neisseria gonorrhoeae and Neisseria meningitidis have components that are immunochemically similar to precursors of human blood group antigens. Carbohydrate sequence specificity of the mouse monoclonal antibodies that recognize crossreacting antigens on LOS and human erythrocytes

We have used mouse mAbs, 3F11 and 06B4, that are specific for highly conserved epitopes of Neisseria gonorrhoeae lipooligosaccharides (LOS) to identify immunochemically similar structures on human erythrocytes. mAb 3F11 agglutinated erythrocytes from all randomly selected adult humans, while mAb 06B4 agglutinated only 80% of the same specimens. The antibodies had an activity with erythrocytes similar to human cold agglutinins in that agglutination occurred at 4 degrees C and decreased with increasing incubation temperature. Human infant erythrocytes were agglutinated less well, but enzymatic treatment of either infant or adult cells resulted in an increase in expression of the 3F11- and 06B4-defined epitopes. Both antibodies bound to a series of neutral glycosphingolipids from human erythrocytes and neutrophils that have a type 2 (Gal beta 1----4GlcNAc) or N-acetyllactosamine structure. Neither antibody bound to glycosphingolipids from human meconium, which have a type 1 (Gal beta 1----3GlcNAc) structure. The antibodies were unable to bind to N-acetyl-lactosamine glycosphingolipids with a nonreducing terminal sialic acid or a Gala1----3Gal disaccharide. Antibody binding also was blocked by the presence of fucose linked to the penultimate glucosamine residue of N-acetyllactosamine glycosphingolipids. Although both antibodies bound to linear and branched-chain N-acetyllactosamine glycosphingolipids, 3F11 had a higher affinity for branched structures than did 06B4. The activity of 3F11 with human adult and infant treated and untreated erythrocytes with N-acetyllactosamine glycosphingolipids, and with LOS was very similar, if not identical, in specificity to 1B2, an mAb prepared from mice inoculated with a linear N-acetyllactosamine glycosphingolipid.

Use of the enzyme-linked immunoadsorbent assay to monitor the purification of glycosphingolipid antigens by high-performance liquid chromatography

An enzyme-linked immunoadsorbent assay (ELISA) technique has been applied to the analysis of glycosphingolipid fractions separated by high-performance liquid chromatography. Nanogram amounts of selected fractions were placed in microtiter wells and analyzed for glycosphingolipids carrying carbohydrate epitopes recognized by monoclonal antibodies using an avidin-biotin enzyme system (ABC reagents). A large number of fractions (more than 100) can be conveniently evaluated for the presence of glycosphingolipids recognized by one or more monoclonal antibodies in a single analysis. This method is a rapid and sensitive procedure for monitoring the purification of glycosphingolipid antigens and can be used in conjunction with immunostaining of glycosphingolipids separated by thin-layer chromatography.

Lectin affinity fractionation of asparagine-linked oligosaccharides from normal human and chronic leukemic leukocytes

Asparagine-linked oligosaccharides were isolated from normal and chronic leukemic leukocytes (normal neutrophils, normal lymphocytes, chronic myeloid, chronic lymphoid and hairy cell leukemic leukocytes) and analyzed by sequential lectin affinity column chromatography. The neutral and sialylated glycopeptides ranged in size from 1,800 to 4,000 da. on gel filtration. Sequential lectin affinity analysis was then used to fractionate the Asn-oligosaccharides into major structural classes of high mannose, hybrid, and bi-, tri- and tetraantennary complex structures. Using lectins of well defined specificity, the sequential chromatography provided a satisfactory means of assessing the overall glycopeptide profiles of the different leukocyte types. Results from 10 patient samples show that alterations in leukocyte Asn-oligosaccharides occur during leukemogenesis. Most notable was an average twofold increase in the relative amount of high mannose glycopeptides compared to complex glycopeptides for the leukemic cells. High mannose glycopeptides comprised 8.6 percent of the total lectin-adherent glycopeptides from leukemics, and 4.2 percent in the normals. In addition, carbohydrate analysis has revealed that the total amount of neutral hexose was markedly decreased in all leukemic samples. Leukemics ranged from 10.5 to 18.8, while normals ranged from 24.2 to 49.2 nanomole of hexose per 100 micrograms protein. The sialic acid content of the leukemic glycopeptides was relatively unchanged from that of normals, resulting in an apparent increase in the sialic acid: hexose ratio for all leukemic glycopeptides. The results suggest that in the leukemic cells, high mannose structures constitute a larger proportion of the total Asn-linked oligosaccharides, while the overall level of protein glycosylation is decreased. Complex multiantennary glycopeptides, when synthesized, tended to be more fully sialylated than their normal counterparts.

Identification of erythrocyte Gal alpha 1-3Gal glycosphingolipids with a mouse monoclonal antibody, Gal-13

The Gal alpha 1-3Gal structural determinant has been found to have a unique distribution in mammals. Although this determinant is abundantly expressed by erythrocytes and nucleated cells of many mammals, it has not been detected in human cells. However, our previous studies (Galili, U., Rachmilewitz, E. A., Peleg, A., and Flechner, I. (1984) J. Exp. Med. 160, 1519-1531; Galili, U., Clark, M. R., and Shohet, S. B. (1986) J. Clin. Invest. 77, 27-33) have suggested that this epitope is present in small amounts and may be involved in immune-mediated destruction of senescent human erythrocytes. To have a means for exploring this possibility and for studying the species and tissue distribution of this epitope we have raised a monoclonal antibody (Gal-13) which specifically binds to glycoconjugates with a nonreducing terminal Gal alpha 1-3Gal disaccharide. Mice were immunized with rabbit erythrocytes, which express an abundance of glycoconjugates with Gal alpha 1-3Gal epitopes. Clones were screened with a solid-phase binding assay (enzyme-linked immunosorbent assay) for antibodies which bound to ceramide pentahexoside (Gal alpha 1-3Gal beta 1-4GlcNAc beta 1-3-Gal beta Gal beta 1-4Glc1-1Cer) but not to ceramide trihexoside (Gal alpha 1-4Gal beta 1-4Glc1-1Cer). Gal-13 bound to a number of neutral glycosphingolipids from rabbit and bovine erythrocytes. These glycosphingolipids have previously been shown to be a family of linear and branched polylactosamine structures, which have non-reducing terminal Gal alpha 1-3Gal epitopes. The antibody did not bind to the human blood group B glycolipid, Gal alpha 1-3(Fuc alpha 1-2)Gal beta 1-4GlcNAc beta 1-3Gal beta 1-4Glc1-1Cer, and, therefore, branching at the penultimate galactose blocks Gal-13 binding. However, after removal of the fucose from the B antigen Gal-13 recognized the resulting derivative. Other Gal alpha 1-3Gal glycosphingolipids with an isogloboside or globoside core structure were not recognized by Gal-13 suggesting that the antibody binds to Gal alpha 1-3Gal carried by a lactosamine core structure. Gal-13 has been used to demonstrate that the Gal alpha 1-3Gal ceramide pentahexoside has been evolutionarily conserved in red cells of animals up to the stage of New World monkeys but is not found in Old World monkey red cells.(ABSTRACT TRUNCATED AT 400 WORDS)

Evolutionary relationship between the natural anti-Gal antibody and the Gal alpha 1----3Gal epitope in primates

Anti-Gal is a natural antibody, which constitutes as much as 1% of circulating IgG in humans and displays a distinct specificity for the structure Gal alpha 1----3Gal. This glycosidic structure has been found on various tissues of many nonprimate mammals. A comparative study of the occurrence of anti-Gal versus the expression of the Gal alpha 1----3Gal epitope was performed in primates, and a distinct evolutionary pattern was observed. Whereas anti-Gal was found to be present in Old World monkeys and apes in titers comparable to those in humans, its corresponding antigenic epitope is abundantly expressed on erythrocytes of New World monkeys. Immunostaining with anti-Gal of glycolipids from New World monkey erythrocytes indicated that the molecules to which anti-Gal binds are similar to those found in rabbit and bovine erythrocytes. These findings indicate that there is an evolutionary reciprocity between New World and Old World primates in the production of the Gal alpha 1----3Gal structure and the antibody that recognizes it. The expression of the Gal alpha 1----3Gal epitope was evolutionarily conserved in New World monkeys, but it was suppressed in ancestral lineages of Old World primates. The suppression of this epitope was accompanied by the production of anti-Gal. The observed in vivo binding of anti-Gal to human normal senescent and some pathologic erythrocytes implies that the Gal alpha 1----3Gal epitope is present in man in a cryptic form.

The human natural anti-Gal IgG. III. The subtlety of immune tolerance in man as demonstrated by crossreactivity between natural anti-Gal and anti-B antibodies

A well-defined antigen/antibody system was used to evaluate the effect of immune tolerance on the spectrum of specificities of natural antibodies. The antibody used in this study, anti-Gal, is a naturally occurring, polyclonal IgG that constitutes 1% of the circulating IgG in humans. We have previously shown that anti-Gal, purified from AB sera, specifically interacts with glycosphingolipids bearing a Gal alpha 1----3Gal epitope, but not with the closely related B antigen in which the penultimate galactose of the Gal alpha 1----3Gal epitope is fucosylated Gal alpha 1----3(Fuc alpha 1----2)Gal. This narrow specificity was assumed to be the result of an effective immune tolerance mechanism that prevents the expression of antibody clones that can recognize both the Gal alpha 1----3Gal and the self B epitopes. If the assumption that immune tolerance determines the range of anti-Gal specificity is correct, then anti-Gal from individuals lacking the B antigen (A and O blood types) would be expected to interact with both Gal alpha 1----3Gal and Gal alpha 1----3(Fuc alpha 1----2)Gal epitopes. In this study, anti-Gal from the serum of individuals of various blood types was purified by affinity chromatography on Gal alpha 1----3Gal adsorbent and tested for its reaction with the B antigen. Whereas anti-Gal from AB and B individuals only reacted with Gal alpha 1----3Gal epitopes, anti-Gal from A and O individuals reacted with both Gal alpha 1----3Gal and B epitopes. Furthermore, it was determined that the majority of anti-B reactivity in A and O individuals is in fact anti-Gal antibodies capable of recognizing both Gal alpha 1----3Gal and B epitopes. It can be concluded from these results that immune tolerance accurately controls the spectrum of natural antibody specificities by preventing the production of antibody clones that can interact with self antigens.

Glycosphingolipid immunostaining: detection of antibody binding with an avidin-biotin enzyme system

Glycosphingolipids carrying carbohydrate sequences recognized by antibodies and lectins can be detected on thin layer chromatograms using an avidin-biotin enzyme system (ABC reagents). This same method can be used to detect glycosphingolipids blot-transferred from thin layer chromatograms to nitrocellulose. This method has certain advantages over the original radioimmunoassay method, including development of positive bands in minutes after incubation with the substrate, avoidance of handling hazardous radioactive materials and stability of reagents. We have demonstrated the usefulness of this method for immunostaining glycosphingolipids with both monoclonal and polyclonal anti-carbohydrate antibodies. These reagents have previously been used to detect carbohydrate antigens in tissues and isolated cells and now it is possible to use the same reagents for the detection of glycosphingolipid antigens on chromatograms.