N-glycoproteomic analyses of human intestinal enteroids, varying in histo-blood group geno- and phenotypes, reveal a wide repertoire of fucosylated glycoproteins

Human noroviruses, globally the main cause of viral gastroenteritis, show strain specific affinity for histo-blood group antigens (HBGA) and can successfully be propagated ex vivo in human intestinal enteroids (HIEs). HIEs established from jejunal stem cells of individuals with different ABO, Lewis and secretor geno- and phenotypes, show varying susceptibility to such infections. Using bottom-up glycoproteomic approaches we have defined and compared the N-linked glycans of glycoproteins of seven jejunal HIEs. Membrane proteins were extracted, trypsin digested, and glycopeptides enriched by hydrophilic interaction liquid chromatography and analyzed by nanoLC-MS/MS. The Byonic software was used for glycopeptide identification followed by hands-on verifications and interpretations. Glycan structures and attachment sites were identified from MS2 spectra obtained by higher-energy collision dissociation through analysis of diagnostic saccharide oxonium ions (B-ions), stepwise glycosidic fragmentation of the glycans (Y-ions), and peptide sequence ions (b- and y-ions). Altogether 694 unique glycopeptides from 93 glycoproteins were identified. The N-glycans encompassed pauci- and oligomannose, hybrid- and complex-type structures. Notably, polyfucosylated HBGA-containing glycopeptides of the four glycoproteins tetraspanin-8, carcinoembryonic antigen-related cell adhesion molecule 5, sucrose-isomaltase and aminopeptidase N were especially prominent and were characterized in detail and related to donor ABO, Lewis and secretor types of each HIE. Virtually no sialylated N-glycans were identified for these glycoproteins suggesting that terminal sialylation was infrequent compared to fucosylation and HBGA biosynthesis. This approach gives unique site-specific information on the structural complexity of N-linked glycans of glycoproteins of human HIEs and provides a platform for future studies on the role of host glycoproteins in gastrointestinal infectious diseases.

Novel GH109 enzymes for bioconversion of group A red blood cells to the universal donor group O

Glycoside hydrolases (GHs) have been employed for industrial and biotechnological purposes and often play an important role in new applications. The red blood cell (RBC) antigen system depends on the composition of oligosaccharides on the surface of erythrocytes, thus defining the ABO blood type classification. Incorrect blood transfusions may lead to fatal consequences, making the availability of the correct blood group critical. In this regard, it has been demonstrated that some GHs may be helpful in the conversion of groups A and B blood types to produce group O universal donor blood. GHs belonging to the GH109 family are of particular interest for this application due to their ability to convert blood from group A to group O. This work describes the biochemical characterisation of three novel GH109 enzymes (NAg68, NAg69 and NAg71) and the exploration of their ability to produce enzymatically converted RBCs (ECO-RBC). The three enzymes showed superior specificity on pNP-α-N-acetylgalactosamine compared to previously reported GH109 enzymes. These novel enzymes were able to act on purified antigen-A trisaccharides and produce ECO-RBC from human donor blood. NAg71 converted type A RBC to group O with increased efficiency in the presence of dextran compared to a commercially available GH109, previously used for this application.

ABO phenotype and SARS-CoV-2 infection: Is there any correlation?

COVID-19 is the currently evolving viral disease worldwide. It mainly targets the respiratory organs, tissues and causes illness. A plethora of studies has been performing to bring proper treatment and prevent people from the infection. Likewise, susceptibility to some infectious diseases has been associated with blood group phenotypes. The co-relationship of blood group with the occurrence of SARS-CoV-2 infection and death has been examined in numerous studies. This review explained the described studies regarding the correlation of blood group and the other essential factors with COVID-19.

Blood group antigen A on von Willebrand factor is more protective against ADAMTS13 cleavage than antigens B and H

BACKGROUND

ADAMTS13 specifically cleaves the peptide bond between Y1605 and M1606 within the VWF-A2 domain.

OBJECTIVE

The VWF contains ABO(H) blood group antigens, which may influence the susceptibility of VWF to ADAMTS13.

METHODS

Using a unique monoclonal antibody recognizing the Y1605 residue, we have developed a sandwich ELISA to analyze the generation of a VWF-DP by ADAMTS13 quantitatively.

RESULTS

Production of VWF-DP after exposure to four different degrees of high shear stress was validated in comparison to the reduction in high-molecular-weight multimers using VWF multimer analysis. In analysis of plasma from 259 healthy individuals, plasma levels of VWF antigen (VWF:Ag) were significantly lower in blood group O than in the other groups and were significantly correlated with plasma VWF-DP levels. The ratio between VWF-DP and VWF:Ag was significantly higher in blood group O than in blood groups A and AB. The ratio in blood group B was also significantly higher than those in A and AB, but did not differ from blood group O. Finally, to examine whether ABO(H) blood group antigens contributed to VWF cleavage, 82 plasma samples were exposed to high shear stress using a cone-plate shear stress inducer. The difference in the VWF-DP/VWF:Ag ratio before and after high shear stress in blood group O was significantly greater than those in groups A and AB.

CONCLUSION

These results indicate that blood group antigen A on VWF was more protective against ADAMTS13 cleavage than antigens B and H.

Conserved residues Arg188 and Asp302 are critical for active site organization and catalysis in human ABO(H) blood group A and B glycosyltransferases

Homologous glycosyltransferases GTA and GTB perform the final step in human ABO(H) blood group A and B antigen synthesis by transferring the sugar moiety from donor UDP-GalNAc/UDP-Gal to the terminal H antigen disaccharide acceptor. Like other GT-A fold family 6 glycosyltransferases, GTA and GTB undergo major conformational changes in two mobile regions, the C-terminal tail and internal loop, to achieve the closed, catalytic state. These changes are known to establish a salt bridge network among conserved active site residues Arg188, Asp211 and Asp302, which move to accommodate a series of discrete donor conformations while promoting loop ordering and formation of the closed enzyme state. However, the individual significance of these residues in linking these processes remains unclear. Here, we report the kinetics and high-resolution structures of GTA/GTB mutants of residues 188 and 302. The structural data support a conserved salt bridge network critical to mobile polypeptide loop organization and stabilization of the catalytically competent donor conformation. Consistent with the X-ray crystal structures, the kinetic data suggest that disruption of this salt bridge network has a destabilizing effect on the transition state, emphasizing the importance of Arg188 and Asp302 in the glycosyltransfer reaction mechanism. The salt bridge network observed in GTA/GTB structures during substrate binding appears to be conserved not only among other Carbohydrate Active EnZyme family 6 glycosyltransferases but also within both retaining and inverting GT-A fold glycosyltransferases. Our findings augment recently published crystal structures, which have identified a correlation between donor substrate conformational changes and mobile loop ordering.

Glycosyltransfer in mutants of putative catalytic residue Glu303 of the human ABO(H) A and B blood group glycosyltransferases GTA and GTB proceeds through a labile active site

The homologous glycosyltransferases α-1,3-N-acetylgalactosaminyltransferase (GTA) and α-1,3-galactosyltransferase (GTB) carry out the final synthetic step of the closely related human ABO(H) blood group A and B antigens. The catalytic mechanism of these model retaining enzymes remains under debate, where Glu303 has been suggested to act as a putative nucleophile in a double displacement mechanism, a local dipole stabilizing the intermediate in an orthogonal associative mechanism or a general base to stabilize the reactive oxocarbenium ion-like intermediate in an SNi-like mechanism. Kinetic analysis of GTA and GTB point mutants E303C, E303D, E303Q and E303A shows that despite the enzymes having nearly identical sequences, the corresponding mutants of GTA/GTB have up to a 13-fold difference in their residual activities relative to wild type. High-resolution single crystal X-ray diffraction studies reveal, surprisingly, that the mutated Cys, Asp and Gln functional groups are no more than 0.8 Å further from the anomeric carbon of donor substrate compared to wild type. However, complicating the analysis is the observation that Glu303 itself plays a critical role in maintaining the stability of a strained "double-turn" in the active site through several hydrogen bonds, and any mutation other than E303Q leads to significantly higher thermal motion or even disorder in the substrate recognition pockets. Thus, there is a remarkable juxtaposition of the mutants E303C and E303D, which retain significant activity despite disrupted active site architecture, with GTB/E303Q, which maintains active site architecture but exhibits zero activity. These findings indicate that nucleophilicity at position 303 is more catalytically valuable than active site stability and highlight the mechanistic elasticity of these enzymes.

Non-AUG start codons responsible for ABO weak blood group alleles on initiation mutant backgrounds

Histo-blood group ABO gene polymorphism is crucial in transfusion medicine. We studied the activity and subcellular distribution of ABO gene-encoded A glycosyltransferases with N-terminal truncation. We hypothesized that truncated enzymes starting at internal methionines drove the synthesis of oligosaccharide A antigen in those already described alleles that lack a proper translation initiation codon. Not only we tested the functionality of the mutant transferases by expressing them and assessing their capacity to drive the appearance of A antigen on the cell surface, but we also analyzed their subcellullar localization, which has not been described before. The results highlight the importance of the transmembrane domain because proteins deprived of it are not able to localize properly and deliver substantial amounts of antigen on the cell surface. Truncated proteins with their first amino acid well within the luminal domain are not properly localized and lose their enzymatic activity. Most importantly, we demonstrated that other codons than AUG might be used to start the protein synthesis rather than internal methionines in translation-initiation mutants, explaining the molecular mechanism by which transferases lacking a classical start codon are able to synthesize A/B antigens.

Crosstalk between ABO and Forssman (FORS) blood group systems: FORS1 antigen synthesis by ABO gene-encoded glycosyltransferases

A and B alleles at the ABO genetic locus specify A and B glycosyltransferases that catalyze the biosynthesis of A and B oligosaccharide antigens, respectively, of blood group ABO system which is important in transfusion and transplantation medicine. GBGT1 gene encodes Forssman glycolipid synthase (FS), another glycosyltransferase that produces Forssman antigen (FORS1). Humans are considered to be Forssman antigen-negative species without functional FS. However, rare individuals exhibiting Apae phenotype carry a dominant active GBGT1 gene and express Forssman antigen on RBCs. Accordingly, FORS system was recognized as the 31st blood group system. Mouse ABO gene encodes a cis-AB transferase capable of producing both A and B antigens. This murine enzyme contains the same GlyGlyAla tripeptide sequence as FSs at the position important for the determination of sugar specificity. We, therefore, transfected the expression construct into appropriate recipient cells and examined whether mouse cis-AB transferase may also exhibit FS activity. The result was positive, confirming the crosstalk between the ABO and FORS systems. Further experiments have revealed that the introduction of this tripeptide sequence to human A transferase conferred some, although weak, FS activity, suggesting that it is also involved in the recognition/binding of acceptor substrates, in addition to donor nucleotide-sugars.

A new chemical approach to human ABO histo-blood group type 2 antigens

A new chemical approach to synthesizing human ABO histo-blood type 2 antigenic determinants was developed. N-Phthaloyl-protected lactosaminyl thioglycoside derived from lactulose via the Heyns rearrangement was employed to obtain a type 2 core disaccharide. Use of this scheme lowered the overall number of reaction steps. Stereoselective construction of the α-galactosaminide/galactoside found in A- and B-antigens, respectively, was achieved by using a unique di-tert-butylsilylene-directed α-glycosylation method. The proposed synthetic scheme provides an alternative to existing procedures for preparing ABO blood group antigens.

Deciphering the glycan preference of bacterial lectins by glycan array and molecular docking with validation by microcalorimetry and crystallography

Recent advances in glycobiology revealed the essential role of lectins for deciphering the glycocode by specific recognition of carbohydrates. Integrated multiscale approaches are needed for characterizing lectin specificity: combining on one hand high-throughput analysis by glycan array experiments and systematic molecular docking of oligosaccharide libraries and on the other hand detailed analysis of the lectin/oligosaccharide interaction by x-ray crystallography, microcalorimetry and free energy calculations. The lectins LecB from Pseudomonas aeruginosa and BambL from Burkholderia ambifaria are part of the virulence factors used by the pathogenic bacteria to invade the targeted host. These two lectins are not related but both recognize fucosylated oligosaccharides such as the histo-blood group oligosaccharides of the ABH(O) and Lewis epitopes. The specificities were characterized using semi-quantitative data from glycan array and analyzed by molecular docking with the Glide software. Reliable prediction of protein/oligosaccharide structures could be obtained as validated by existing crystal structures of complexes. Additionally, the crystal structure of BambL/Lewis x was determined at 1.6 Å resolution, which confirms that Lewis x has to adopt a high-energy conformation so as to bind to this lectin. Free energies of binding were calculated using a procedure combining the Glide docking protocol followed by free energy rescoring with the Prime/Molecular Mechanics Generalized Born Surface Area (MM-GBSA) method. The calculated data were in reasonable agreement with experimental free energies of binding obtained by titration microcalorimetry. The established predictive protocol is proposed to rationalize large sets of data such as glycan arrays and to help in lead discovery projects based on such high throughput technology.

Bivalent carbohydrate binding is required for biological activity of Clitocybe nebularis lectin (CNL), the N,N'-diacetyllactosediamine (GalNAcβ1-4GlcNAc, LacdiNAc)-specific lectin from basidiomycete C. nebularis

Lectins are carbohydrate-binding proteins that exert their biological activity by binding to specific cell glycoreceptors. We have expressed CNL, a ricin B-like lectin from the basidiomycete Clitocybe nebularis in Escherichia coli. The recombinant lectin, rCNL, agglutinates human blood group A erythrocytes and is specific for the unique glycan N,N'-diacetyllactosediamine (GalNAcβ1-4GlcNAc, LacdiNAc) as demonstrated by glycan microarray analysis. We here describe the crystal structures of rCNL in complex with lactose and LacdiNAc, defining its interactions with the sugars. CNL is a homodimeric lectin, each of whose monomers consist of a single ricin B lectin domain with its β-trefoil fold and one carbohydrate-binding site. To study the mode of CNL action, a nonsugar-binding mutant and nondimerizing monovalent CNL mutants that retain carbohydrate-binding activity were prepared. rCNL and the mutants were examined for their biological activities against Jurkat human leukemic T cells and the hypersensitive nematode Caenorhabditis elegans mutant strain pmk-1. rCNL was toxic against both, although the mutants were inactive. Thus, the bivalent carbohydrate-binding property of homodimeric CNL is essential for its activity, providing one of the rare pieces of evidence that certain activities of lectins are associated with their multivalency.

PP13, maternal ABO blood groups and the risk assessment of pregnancy complications

BACKGROUND

Placental Protein 13 (PP13), an early biomarker of preeclampsia, is a placenta-specific galectin that binds beta-galactosides, building-blocks of ABO blood-group antigens, possibly affecting its bioavailability in blood.

METHODS AND FINDINGS

We studied PP13-binding to erythrocytes, maternal blood-group effect on serum PP13 and its performance as a predictor of preeclampsia and intrauterine growth restriction (IUGR). Datasets of maternal serum PP13 in Caucasian (n = 1078) and Hispanic (n = 242) women were analyzed according to blood groups. In vivo, in vitro and in silico PP13-binding to ABO blood-group antigens and erythrocytes were studied by PP13-immunostainings of placental tissue-microarrays, flow-cytometry of erythrocyte-bound PP13, and model-building of PP13--blood-group H antigen complex, respectively. Women with blood group AB had the lowest serum PP13 in the first trimester, while those with blood group B had the highest PP13 throughout pregnancy. In accordance, PP13-binding was the strongest to blood-group AB erythrocytes and weakest to blood-group B erythrocytes. PP13-staining of maternal and fetal erythrocytes was revealed, and a plausible molecular model of PP13 complexed with blood-group H antigen was built. Adjustment of PP13 MoMs to maternal ABO blood group improved the prediction accuracy of first trimester maternal serum PP13 MoMs for preeclampsia and IUGR.

CONCLUSIONS

ABO blood group can alter PP13-bioavailability in blood, and it may also be a key determinant for other lectins' bioavailability in the circulation. The adjustment of PP13 MoMs to ABO blood group improves the predictive accuracy of this test.

Effects of blood type and blood handling on feeding success, longevity and egg production in the body louse, Pediculus humanus humanus

The effects of feeding different types of human blood to human body lice, Pediculus humanus humanus L. (Phthiraptera: Pediculidae), on feeding success, longevity and numbers of eggs laid were investigated using an artificial blood-feeding system in the laboratory. No significant differences were found between lice fed on different human blood types for any of the parameters tested. However, when lice were fed on human blood of one blood type followed immediately by a different blood type, they took significantly smaller bloodmeals, their longevity was reduced and they laid fewer eggs per female than control lice that had been fed twice on the same human blood type. When lice were fed human blood that had been stored for 1-26 weeks, the quantity of blood taken, the proportion of lice that became fully engorged and lice longevity diminished gradually as the storage time of the blood increased, but there was no effect of storage time on the mean number of eggs laid per female. However, lice would not feed on 26-week-old blood. The type of anticoagulant used had a significant effect on the proportion fed, longevity and number of eggs laid per female. Generally, EDTA (ethylenediaminetetraacetic acid)-treated blood reduced longevity and the number of eggs laid per female to a greater degree than heparinized or citrated blood. Lice fed on rabbit blood took significantly larger amounts of blood, lived longer and laid a higher mean number of eggs per female than lice fed on human blood.

Preliminary joint neutron time-of-flight and X-ray crystallographic study of human ABO(H) blood group A glycosyltransferase

The biosyntheses of oligosaccharides and glycoconjugates are conducted by glycosyltransferases. These extraordinarily diverse and widespread enzymes catalyze the formation of glycosidic bonds through the transfer of a monosaccharide from a donor molecule to an acceptor molecule, with the stereochemistry about the anomeric carbon being either inverted or retained. Human ABO(H) blood group A α-1,3-N-acetylgalactosaminyltransferase (GTA) generates the corresponding antigen by the transfer of N-acetylgalactosamine from UDP-GalNAc to the blood group H antigen. To understand better how specific active-site-residue protons and hydrogen-bonding patterns affect substrate recognition and catalysis, neutron diffraction studies were initiated at the Protein Crystallography Station (PCS) at Los Alamos Neutron Science Center (LANSCE). A large single crystal was subjected to H/D exchange prior to data collection and time-of-flight neutron diffraction data were collected to 2.5 Å resolution at the PCS to ∼85% overall completeness, with complementary X-ray diffraction data collected from a crystal from the same drop and extending to 1.85 Å resolution. Here, the first successful neutron data collection from a glycosyltransferase is reported.

Molecular basis of cholera blood-group dependence and implications for a world characterized by climate change

Climate change has the potential to increase the threat of water-borne diseases, through rises in temperature and sea-level, and precipitation variability. Cholera poses a particular threat, and the need to develop better intervention tools is imminent. Cholera infections are particularly severe for blood group O individuals, who are less protected by the current vaccines. Here we derive a hypothesis as to the molecular origins of blood-group dependence of this disease, based on relevant epidemiological, clinical and molecular data, and give suggestions on how to plan prevention strategies, and develop novel and improved pharmaceuticals.

Antigen recognition by variable lymphocyte receptors

Variable lymphocyte receptors (VLRs) rather than antibodies play the primary role in recognition of antigens in the adaptive immune system of jawless vertebrates. Combinatorial assembly of leucine-rich repeat (LRR) gene segments achieves the required repertoire for antigen recognition. We have determined a crystal structure for a VLR-antigen complex, VLR RBC36 in complex with the H-antigen trisaccharide from human blood type O erythrocytes, at 1.67 angstrom resolution. RBC36 binds the H-trisaccharide on the concave surface of the LRR modules of the solenoid structure where three key hydrophilic residues, multiple van der Waals interactions, and the highly variable insert of the carboxyl-terminal LRR module determine antigen recognition and specificity. The concave surface assembled from the most highly variable regions of the LRRs, along with diversity in the sequence and length of the highly variable insert, can account for the recognition of diverse antigens by VLRs.

The O2 allele: questioning the phenotypic definition of an ABO allele

There are three main alleles in the ABO blood group system, A, B, and O. The former two alleles encode glycosyltransferases resulting in the wild-type A and B phenotypes, whereas the latter allele does not encode a functional enzyme owing to a frameshift polymorphism in the majority of cases. Thus the group O phenotype is the absence of A or B sugars. More than 15 years ago the O2 allele was described; this allele did not feature the usual crippling 261delG polymorphism, which up to that point was the hallmark of an allele encoding group O, but instead had several other nucleotide polymorphisms that reduced or eliminated the activity of its resulting protein. The classification of this type of allele as encoding group O has been called into question of late as some individuals with an O2 allele appear to have a weak A phenotype. Others with the same allele do not demonstrate any A antigens on their RBCs but might be involved in reverse typing discrepancies. Even within the same pedigree these alleles do not necessarily produce a consistent phenotype. This paper will summarize the detailed biochemical and population-based evidence both for and against the O2 allele's ability to create A antigens or the absence of anti-A in plasma.

The effect of heavy atoms on the conformation of the active-site polypeptide loop in human ABO(H) blood-group glycosyltransferase B

The human ABO(H) blood-group antigens are oligosaccharide structures that are expressed on erythrocyte and other cell surfaces. The terminal carbohydrate residue differs between the blood types and determines the immune reactivity of this antigen. Individuals with blood type A have a terminal N-acetylgalactosamine residue and those with blood type B have a terminal galactose residue. The attachment of these terminal carbohydrates are catalyzed by two different glycosyltransferases: an alpha(1-->3)N-acetylgalactosaminyltransferase (GTA) and an alpha(1-->3)galactosyltransferase (GTB) for blood types A and B, respectively. GTA and GTB are homologous enzymes that differ in only four of 354 amino-acid residues (Arg/Gly176, Gly/Ser235, Leu/Met266 and Gly/Ala268 in GTA and GTB, respectively). Diffraction-quality crystals of GTA and GTB have previously been grown from as little as 10 mg ml(-1) stock solutions in the presence of Hg, while diffraction-quality crystals of the native enzymes require much higher concentrations of protein. The structure of a single mutant C209A has been determined in the presence and absence of heavy atoms and reveals that when mercury is complexed with Cys209 it forces a significant level of disorder in a polypeptide loop (amino acids 179-195) that is known to cover the active site of the enzyme. The observation that the more highly disordered structure is more amenable to crystallization is surprising and the derivative provides insight into the mobility of this polypeptide loop compared with homologous enzymes.

ABO blood group and related antigens, natural antibodies and transplantation

The current success rate of transplant surgery and immunosuppression has led to a demand for organs that has outstripped the supply. This has required investigation of alternate strategies. Therefore, allotransplantation across the ABO blood group barrier has commenced, and pig-to-human xenotransplantation is under consideration. The first immunological barrier to both these types of transplantation is the prevention of the antibody-mediated rejection. This rejection is a result of natural preformed antibodies circulating in the serum of the recipient binding to either ABO (for allo) or alpha-galactose (alpha-Gal) (for xeno) antigens expressed on the donor tissue. These antibodies recognise antigens that are, in both cases, carbohydrate molecules with the characteristic feature that the nonreducing terminal carbohydrate is either a Gal or N-acetlygalactosamine residue in an alpha1,3 linkage. These epitopes are synthesised by closely related members of a single family of glycosyltransferases. This review discusses the carbohydrate antigens, the enzymes involved in their synthesis and the consequences of natural antibodies binding these antigens.

Bacterial glycosidases for the production of universal red blood cells

Enzymatic removal of blood group ABO antigens to develop universal red blood cells (RBCs) was a pioneering vision originally proposed more than 25 years ago. Although the feasibility of this approach was demonstrated in clinical trials for group B RBCs, a major obstacle in translating this technology to clinical practice has been the lack of efficient glycosidase enzymes. Here we report two bacterial glycosidase gene families that provide enzymes capable of efficient removal of A and B antigens at neutral pH with low consumption of recombinant enzymes. The crystal structure of a member of the alpha-N-acetylgalactosaminidase family reveals an unusual catalytic mechanism involving NAD+. The enzymatic conversion processes we describe hold promise for achieving the goal of producing universal RBCs, which would improve the blood supply while enhancing the safety of clinical transfusions.

Structural basis for the recognition of blood group trisaccharides by norovirus

Noroviruses are one of the major causes of nonbacterial gastroenteritis epidemics in humans. Recent studies on norovirus receptors show that different noroviruses recognize different human histo-blood group antigens (HBGAs), and eight receptor binding patterns of noroviruses have been identified. The P domain of the norovirus capsids is directly involved in this recognition. To determine the precise locations and receptor binding modes of HBGA carbohydrates on the viral capsids, a recombinant P protein of a GII-4 strain norovirus, VA387, was cocrystallized with synthetic type A or B trisaccharides. Based on complex crystal structures observed at a 2.0-A resolution, we demonstrated that the receptor binding site lies at the outermost end of the P domain and forms an extensive hydrogen-bonding network with the saccharide ligand. The A and B trisaccharides display similar binding modes, and the common fucose ring plays a key role in this interaction. The extensive interface between the two protomers in a P dimer also plays a crucial role in the formation of the receptor binding interface.

Structural Effects of Naturally Occurring Human Blood Group B Galactosyltransferase Mutations Adjacent to the DXD Motif

Human blood group A and B antigens are produced by two closely related glycosyltransferase enzymes. An N-acetylgalactosaminyltransferase (GTA) utilizes UDP-GalNAc to extend H antigen acceptors (Fuc alpha(1-2)Gal beta-OR) producing A antigens, whereas a galactosyltransferase (GTB) utilizes UDP-Gal as a donor to extend H structures producing B antigens. GTA and GTB have a characteristic (211)DVD(213) motif that coordinates to a Mn(2+) ion shown to be critical in donor binding and catalysis. Three GTB mutants, M214V, M214T, and M214R, with alterations adjacent to the (211)DVD(213) motif have been identified in blood banking laboratories. From serological phenotyping, individuals with the M214R mutation show the B(el) variant expressing very low levels of B antigens, whereas those with M214T and M214V mutations give rise to A(weak)B phenotypes. Kinetic analysis of recombinant mutant GTB enzymes revealed that M214R has a 1200-fold decrease in k(cat) compared with wild type GTB. The crystal structure of M214R showed that DVD motif coordination to Mn(2+) was disrupted by Arg-214 causing displacement of the metal by a water molecule. Kinetic characterizations of the M214T and M214V mutants revealed they both had GTA and GTB activity consistent with the serology. The crystal structure of the M214T mutant showed no change in DVD coordination to Mn(2+). Instead a critical residue, Met-266, which is responsible for determining donor specificity, had adopted alternate conformations. The conformation with the highest occupancy opens up the active site to accommodate the larger A-specific donor, UDP-GalNAc, accounting for the dual specificity.

Is there an association between maternal ABO and rhesus blood groups and the first-trimester serum markers free β-hCG and PAPP-A used for the detection of fetal aneuploidy?

OBJECTIVES

To evaluate whether first-trimester levels of PAPP-A and serum free-beta-human chorionic gonadotrophin (free beta-hCG) vary with maternal blood group and rhesus status and to assess whether this has implications for first-trimester screening for chromosomal anomalies.

METHODS

Blood group and rhesus status information was extracted from birth records for women undergoing first-trimester screening. The birth records were combined with prenatal screening records by an in-house developed record linkage software. In 2252 singleton pregnancies of normal obstetric outcome, the median weight-corrected, ethnicity-corrected and smoking-corrected MoM were compared in the various blood groups, using t-tests after log10 transformation of the marker MoM against the whole study group.

RESULTS

Only those women with a B rhesus positive blood group had statistically significant higher MoM levels of PAPP-A (0.995 v 0.937).

CONCLUSIONS

A larger study is required to establish the validity of this increase in PAPP-A in the B rhesus positive group. If this can be substantiated, the elevation in PAPP-A in this group may require correction when screening for chromosomal anomalies.

Novel glycolipid variations revealed by monoclonal antibody immunochemical analysis of weak ABO subgroups of A

BACKGROUND AND OBJECTIVES

The chemical basis of the subgroups of A is largely unknown. We used thin-layer chromatography immunochemical staining techniques together with a range of characterized monoclonal reagents to analyse glycolipids isolated from a variety of weak subgroups.

MATERIALS AND METHODS

Glycolipids isolated from red cells collected from nine genetically defined individuals of the rare subgroups of A, including a novel A(3) allele (A(2) 539G>A) not described previously, were subjected to a highly sensitive thin-layer chromatographic immunochemical analysis.

RESULTS

Semicharacterized monoclonal antibodies revealed that, in addition to the expected quantitative differences between common phenotypes and the weak subgroups, qualitative glycolipid differences (or at least an apparent qualitative basis), caused by major changes in the ratios of different structures exist. Specifically it was found that the weakest A-expressing samples (A(el) phenotype) appeared to express an unusual A structure in the 8-12 sugar region. Variable expression of several structures in one of the A weak samples were suggestive of novel blood group A structures.

CONCLUSIONS

Although no structural characterization could be undertaken, the results are clearly indicative that the variant glycosyltransferases of the rare ABO subgroups are not only inefficient, but they may potentially synthesize novel ABO structures.

Bombay phenotype is associated with reduced plasma-VWF levels and an increased susceptibility to ADAMTS13 proteolysis

ABO blood group is an important determinant of plasma von Willebrand factor antigen (VWF:Ag) levels, with lower levels in group O. Previous reports have suggested that ABO(H) sugars affect the susceptibility of VWF to ADAMTS13 (a disintegrin and metalloproteinase with thrombospondin type-1 repeats-13) cleavage. To further test this hypothesis, we collected plasma from individuals with the rare Bombay blood group. VWF:Ag levels were significantly lower in Bombay patients (median, 0.69 IU/mL) than in groups AB, A, or B (P < .05) and lower than in group O individuals (median, 0.82 IU/mL). Susceptibility of purified VWF fractions to recombinant ADAMTS13 cleavage, assessed using VWF collagen-binding assay (VWF:CB), was increased in Bombays compared with either group O or AB. Increasing urea concentration (0.5 to 2 M) increased the cleavage rate for each blood group but eliminated the differences between groups. We conclude that reduction in the number of terminal sugars on N-linked glycan increases susceptibility of globular VWF to ADAMTS13 proteolysis and is associated with reduced plasma VWF:Ag and VWF:CB levels.

Amino-acid substitution in the disordered loop of blood group B-glycosyltransferase enzyme causes weak B phenotype

BACKGROUND

Few studies have investigated the reaction kinetics and interactions with nucleotide donor and acceptor substrates of mutant human ABO glycosyltransferases. Previous work identified a B(w) allele featuring a 556G>A polymorphism giving rise to a weak B phenotype. This polymorphism is predicted to cause a M186V amino-acid mutation within a highly conserved series of 16 amino acids present both in both blood group A- and blood group B-synthesizing enzymes. These residues are known as the disordered loop because their location cannot be determined in the crystal structure of the enzyme. Another patient has been identified with a 556G>A B(w) allele and the kinetics of the resulting mutant glycosyltransferase were studied.

STUDY DESIGN AND METHODS

Serologic testing with murine and human reagents, amplification of the coding regions of exons 6 and 7, and DNA sequencing were performed with standard protocols. Enzyme kinetic studies utilized a model of human GTB M186V expressed in Escherichia coli with radiolabeled UDP-galactose and UDP-N-acetylgalactosamine as donor substrates and synthetic H-disaccharide as acceptor following standard protocols.

RESULTS

The patient's red blood cells demonstrated a weak, but not mixed-field, B phenotype. Kinetic studies on the mutant enzyme revealed diminished activity (k(cat) = 0.15 per sec with UDP-galactose compared to 5.1 per sec for wild-type GTB) and elevated K(m) values for all substrates.

CONCLUSION

This enzyme with a mutation in the disordered loop produces weak B antigen expression because of greatly decreased enzyme activity and reduced affinity for B-donor and acceptor substances.

Differential effect of the ABO blood group on von Willebrand factor collagen binding activity and ristocetin cofactor assay

Diagnosis of von Willebrand disease requires a combination of quantitative and qualitative tests including the von Willebrand factor ristocetin cofactor assay (vWF:RCo), the von Willebrand factor collagen binding assay (vWF:CB) and von Willebrand factor antigen quantification (vWF:Ag). Genetic factors, especially the ABO blood group, contribute significantly to the variation in vWF levels and function. Recent studies suggest that ethnicity may be another important modulator. We investigated the effect of the ABO blood group on these tests in 52 blood group O and 54 non-group O Chinese blood donors who were well-matched for sex and age distribution. Group O donors had significantly lower vWF:RCo, vWF:Ag and vWF:CB (P < 0.0001). Reduction in vWF:CB was greater than vWF:RCo in group O donors (53 versus 27%). This led to a lower vWF:CB/vWF:Ag ratio (P < 0.0001) in group O donors whereas the vWF:RCo/vWF:Ag ratio was unaffected (P = 0.97). These variations should be taken into consideration when interpreting these results in the Chinese.

Soluble type A substance in fresh-frozen plasma as a function of ABO and Secretor genotypes and Lewis phenotype

Soluble ABO blood group substance (SAS) in fresh-frozen plasma (FFP) and its cognate alloantibody titer reduction capacity (TRC) are not considered when prescribing this product for plasma exchange (PEX) therapy of ABO incompatible transplant recipients. SAS was quantified in 250 single FFPs using ELISA. Total and IgG class-specific anti-A TRCs of FFPs were measured using a microhemagglutination inhibition assay. SAS level depended not only on the A subtype (p < 0.0001) and the Secretor status (p < 0.0001), but also on the expression of ALe(b) in A1 secretors (p < 0.0001). The variation was as great as 137.6 arbitrary units (aU) for 14 A1 Le(a-b-) secretors and 1.2 aU for 6 A2 non-secretors. Homozygous expression of the A1, A2 and Secretor alleles did not increase SAS levels. Only total anti-A TRC, but not IgG class-specific TRC depended on the detected SAS level (r = 0.566, p = 0.0003).

Solution Syntheses of Protected Type II Lewis Blood Group Oligosaccharides: Study for Automated Synthesis

Glycosyl phosphate and trichloroacetimidate monosaccharide building blocks were used in a stepwise solution-phase synthesis of three Lewis blood group oligosaccharides. The syntheses were conducted to establish general routes for the automated assembly of the oligosaccharide portion of biologically important glycolipids. The H-type II pentasaccharide, Le(x) pentasaccharide, and Le(y) hexasaccharide were prepared in high yield. These syntheses served to evaluate the utility and limitations of the 2-(azidomethyl)benzoate ester (AZMB) for the construction of complex carbohydrates. Development of a glucosamine building block containing a N-trichloroacetamide group to mask the C2 amine improved coupling yields and was key for completion of the Le(x) and Le(y) structures.

Design of the blood group AB glycotope

Although the nature of the blood groups A and B has been comprehensively studied for a long time, it is still unclear as to what exactly is the epitope that is recognized by antibodies having AB specificity, i.e. monoclonal and polyclonal antibodies which are capable of interacting equally well with the antigens GalNAcalpha 1-3(Fucalpha 1-2)Gal (A trisaccharide) and Galalpha 1-3(Fucalpha 1-2)Gal (B trisaccharide), but do not react with their common fragment Fucalpha 1-2Gal. We have supposed that besides Fucalpha 1-2Gal, A and B antigens have one more shared epitope. The trisaccharides A and B are practically identical from the conformational point of view, the only difference being situated at position 2 of Galalpha residue, i.e. trisaccharide A has a NHAc group, whereas trisaccharide B has a hydroxyl group (see formulas). We have hypothesized that the AB-epitope should be situated in the part of the molecule that is opposite to the NHAc group of GalNAc residue. In order to test this hypothesis we have synthesized a polymeric conjugate in such a way that de-N-acetylated A-trisaccharide is attached to a polymer via the nitrogen in position C-2 of the galactosamine residue. In this conjugate the supposed AB-epitope should be maximally accessible for antibodies from the solution, whereas the discrimination site of antigens A and B by the antibodies should be maximally hidden due to the close proximity of the polymer. Interaction with several anti-AB monoclonal antibodies revealed that a part of them really interacted with the synthetic AB-glycotope, thus confirming our hypothesis. Moreover, similar antibodies were revealed in the blood of healthy blood group 0 donors. Analysis of spatial models was performed in addition to identify the hydroxyl groups of Fuc, Galalpha, and Galbeta residues, which are particularly involved in the composition of the AB-glycotope.

Effects of polyvalency of glycotopes and natural modifications of human blood group ABH/Lewis sugars at the Galbeta1-terminated core saccharides on the binding of domain-I of recombinant tandem-repeat-type galectin-4 from rat gastrointestinal tract (G4-N)

In our recent publication, we defined core aspects of the carbohydrate specificity of domain-I of recombinant tandem-repeat-type galectin-4 from rat gastrointestinal tract (G4-N), especially its potent interaction with the linear tetrasaccharide Galbeta1-3GlcNAcbeta1-3Galbeta1-4Glc (Ibeta1-3L). The assumed role of galectin-4 as a microvillar raft stabilizer/organizer and as a malignancy-associated factor in hepatocellular and gastrointestinal carcinomas called for further refinement of its binding specificity. Thus, the effects of polyvalency of glycotopes and natural modifications of human blood group ABH/Lewis sugars at the terminal Galbeta1-core saccharides were thoroughly examined by the enzyme-linked lectinosorbent and lectin-glycan inhibition assays. The results indicate that (a) a high-density of polyvalent Galbeta1-3/4GlcNAc (I/II), Galbeta1-3GalNAc (T) and/or GalNAcalpha1-Ser/Thr (Tn) strongly favors G4-N/glycoform binding. These glycans were up to 2.3 x 10(6), 1.4 x 10(6), 8.8 x 10(5), and 1.4 x 10(5) more active than Gal, GalNAc, monomeric I/II and T, respectively; (b) while lFuc is a poor inhibitor, its presence as alpha1-2 linked to terminal Galbeta1-containing oligosaccharides, such as H active Ibeta1-3L, markedly enhances the reactivities of these ligands; (c) when blood group A (GalNAcalpha1-) or B (Galalpha1-) determinants are attached to terminal Galbeta1-3/4GlcNAc (or Glc) oligosaccharides, the reactivities are also increased; (d) with lFucalpha1-3/4 linked to sub-terminal GlcNAc, the reactivities of these haptens are reduced; and (e) short chain Le(a)/Le(x)/Le(y) and the short chains of sialyl Le(a)/Le(x) are poor inhibitors. These distinct binding features of G4-N establish the important concept of affinity enhancement by high density polyvalencies of glycotopes (vs. multi-antennary I/II) and by introduction of an ABH key sugar to Galbeta1-terminated core glycotopes. The polyvalent ligand binding properties of G4-N may help our understanding of its crucial role for cell membrane raft stability and provide salient information for the optimal design of blocking substances such as anti-tumoral glycodendrimers.

Purification and Characterization of Liver Lectins from a Lizard,Sceloporus spinosus

This study discusses the purification of soluble beta-galactose lectins obtained from the lizard liver of Sceloporus spinosus. The first lectin named lizard hepatic lectin-1 (LHL-1) presented a molecular weight of 31,750, with an isoelectric point of 4.25. The highest specific hemagglutinating activity was achieved using human blood type A1: N-acetylgalactosamine (GalNAc)-galactose (Gal)-fucose (Fuc). Carbohydrate inhibition assays indicated a higher lectin specificity for GalNAc. For LHL-2 the molecular weight obtained was 23,850 with an isoelectric point of 3.25. The highest carbohydrate specificity was observed for Gal. These lizard hepatic lectins are similar to the mammal hepatic lectins previously reported. However, it is different from the alligator hepatic lectin (AHL). The homology analyses of LHL-1 resulted in 100% identity with the Steroidogenic acute regulatory protein (StAR), while LHL-2 was similar to adenylate kinase (75% identity). We suggest that these liver lectins are related to the inherent functions of liver previously reported.

Structural basis for the inactivity of human blood group O2 glycosyltransferase

The human ABO(H) blood group antigens are carbohydrate structures generated by glycosyltransferase enzymes. Glycosyltransferase A (GTA) uses UDP-GalNAc as a donor to transfer a monosaccharide residue to Fuc alpha1-2Gal beta-R (H)-terminating acceptors. Similarly, glycosyltransferase B (GTB) catalyzes the transfer of a monosaccharide residue from UDP-Gal to the same acceptors. These are highly homologous enzymes differing in only four of 354 amino acids, Arg/Gly-176, Gly/Ser-235, Leu/Met-266, and Gly/Ala-268. Blood group O usually stems from the expression of truncated inactive forms of GTA or GTB. Recently, an O(2) enzyme was discovered that was a full-length form of GTA with three mutations, P74S, R176G, and G268R. We showed previously that the R176G mutation increased catalytic activity with minor effects on substrate binding. Enzyme kinetics and high resolution structural studies of mutant enzymes based on the O(2) blood group transferase reveal that whereas the P74S mutation in the stem region of the protein does not appear to play a role in enzyme inactivation, the G268R mutation completely blocks the donor GalNAc-binding site leaving the acceptor binding site unaffected.

Blood group B degrading activity of Ruminococcus gnavus alpha-galactosidase

Ruminococcus gnavus is a Gram positive, nonspore-forming obligate anaerobe normally found in the human alimentary tract. In culture, this organism constitutively produces a 1-3 alpha-galactosidase. We fractionated and characterized this enzyme demonstrating hydrolysis of the B epitope on erythrocyte membranes and seroconversion to H epitope (blood type O). Since the enzyme yield was low, cell suspension studies could not be performed. Instead, hydrolysis of the B membrane epitope was studied with an ELISA. A highly purified enzyme product was analyzed for characteristics such as pH, ionic strength, and temperature optimum. Activity in red cell preservative solutions and in the presence of type B plasma was also demonstrated. Ruminococcus gnavus a 1-3 alpha-galactosidase has potential application in the enzymatic conversion of type B to O packed red blood cell units.

Ability of blood group A-active glycosphingolipids to act as Escherichia coli heat-labile enterotoxin receptors in HT-29 cells

We examined the ability of blood group A-active glycoconjugates to act as receptors for Escherichia coli heat-labile type I enterotoxin (LT-I) in HT-29 cells. These cells contained ~4 times more specific binding sites for LT-I than for cholera toxin (CT). Binding of LT-I could not be blocked by the B subunit of CT (CT-B), indicating the existence of LT-I receptors in addition to the glycosphingolipid GM1. LT-I was able to increase levels of cyclic adenosine monophosphate (AMP), even in the presence of CT-B. Helix pomatia and anti-blood group A antibody caused a dose-dependent inhibition of binding of LT-I to cells and production of cyclic AMP. LT-I recognized several complex blood group A-active glycosphingolipids from cells, and this interaction was also interfered with by H. pomatia. Treatment of cells with D,L-threo-1-phenyl-2-hexadecanoylamino-3-morpholino-1-propanol diminished surface expression of blood group A-active glycosphingolipids and binding of LT-I to non-GM1 receptors. These observations suggest that blood group A-active glycosphingolipids can function as alternative receptors for LT-I in HT-29 cells.

The third chains of living organisms—a trail of glycobiology that started from the third floor of building 4 in NIH

Application of a finger-printing method to the analysis of human milk oligosaccharides led to the finding that several oligosaccharides were missing in the milk of non-secretor or Lewis-negative individuals. This finding helped us in opening the door of elucidating the enzymatic basis of blood types in human. Based on these successful studies, a strategy to establish reliable techniques to elucidate the structures and functions of the N-linked sugar chains of glycoproteins was devised. It was to contrive enzymatic and chemical means to release quantitatively the N-linked sugar chains as oligosaccharides, and finger-print them by using appropriate methods to demonstrate the sugar pattern of a glycoprotein. These methods enabled us to determine that the N-linked sugar chains of glycoproteins can be classified into three subgroups: high mannose-type, complex-type, and hybrid-type. By comparative studies of the sugar patterns of a glycoprotein produced by different organs and different animals, occurrences of organ- and species-specific glycosylation were found in many glycoproteins. By comparative studies of the glycosylation patterns of the subunits constructing human chorionic gonadotropin and other glycoproteins, occurrence of site-directed N-glycosylation was also found, indicating that the processing and maturation of the N-linked sugar chains of a glycoprotein might be controlled by the structure of polypeptide moiety. Furthermore, these methods enabled us to elucidate the structural alteration of the sugar chains of a glycoprotein induced by diseased state of the producing cells, such as rheumatoid arthritis and malignancy. Recent studies of glycoproteins in the brain-nervous system through aging revealed that N-glycosylation of P(0) in the rat spinal cord is induced by aging. Therefore, glycobiology is expanding tremendously into fields such as pathological and gerontological research.

Molecular modeling of glycosyltransferases involved in the biosynthesis of blood group A, blood group B, Forssman, and iGb3 antigens and their interaction with substrates

A terminal alpha1-3 linked Gal or GalNAc sugar residue is the common structure found in several oligosaccharide antigens, such as blood groups A and B, the xeno-antigen, the Forssman antigen, and the isogloboside 3 (iGb3) glycolipid. The enzymes involved in the addition of this residue display strong amino acid sequence similarities, suggesting a common fold. From a recently solved crystal structure of the bovine alpha3-galactosyltransferase complexed with UDP, homology modeling methods were used to build the four other enzymes of this family in their locked conformation. Nucleotide-sugars, the Mn2+ ion, and oligosaccharide acceptors were docked in the models. Nine different amino acid regions are involved in the substrate binding sites. After geometry optimization of the complexes and analysis of the predicted structures, the basis of the specificities can be rationalized. In the nucleotide-sugar binding site, the specificity between Gal or GalNAc transferase activity is due to the relative size of two clue amino acids. In the acceptor site, the presence of up to three tryptophan residues define the complexity of the oligosaccharide that can be specifically recognized. The modeling study helps in rationalizing the crystallographic data obtained in this family and provides insights on the basis of substrate and donor recognition.

Micromolar A and B blood group active trisaccharides abolish human complement haemolytic activity assayed by erythrocytes

BACKGROUND

At present, there is really no satisfactory treatment of severe haemolytic transfusion reactions involving the ABO system other than the use of steroids that at best are palliative in their effects. In contrast, the use of micromolar concentrations of A or B blood group active trisaccharides that are inexpensive and readily available may prevent lysis by generating soluble immune complexes (ICs) that consume complement. The purpose of this study was to determine the total lytic activity of human serum and to estimate the extent to which trisaccharides can exhaust this capacity.

METHODS

We measured complement consumption by (ICs) formed between anti-blood group antibodies and A or B blood group active sugars on erythrocytes (solid phase) or soluble components carrying trisaccharides (fluid phase) in AB serum. A direct complement-mediated lysis (DCL) assay measured the solid-phase reaction and an indirect complement consumption assay (CCA) allowed determination of the fluid-phase reaction. In CCA, the residual lytic activity of AB serum was measured following preincubation with various ICs.

RESULTS

Based on over 4000 data points a new mathematical model of complement consumption was formulated. Its predictions deviated by less than 6% in DCL and 9% in CCA when compared with the experimentally accessible data. The new model describes the dynamics of complement consumption including the soluble phase of the reaction.

CONCLUSIONS

The mathematical model extrapolation predicts that: (1) in undiluted human serum up to 40% of the physiological erythrocyte concentration could be lysed (when antibodies did not limit lysis); and (2) a 40 microM (or less) concentration of blood group active trisaccharides per patient is sufficient to block the haemolytic complement activity.

Diversity of the human erythrocyte membrane sialic acids in relation with blood groups

The composition of the human erythrocyte membrane (RBC) glycoprotein- and glycolipid-bound sialic acids of A, B, AB and O type donors was studied using a new method (Zanetta et al., Glycobiology 11 (2001) 663-676). In addition to Neu5Ac as the major compound, Kdn, Neu5,9Ac(2), Neu5,7Ac(2), Neu (de-N-acetylated-Neu5Ac), Neu5Ac8Me, Neu5Ac9Lt, Neu4,5Ac(2), Neu5,8Ac(2)9Lt and Neu5Ac8S were characterised. Among these different compounds, Neu5Ac8Me, Neu5Ac9Lt, Neu4,5Ac(2), Neu5,8Ac(2)9Lt and Neu5Ac8S have never been described and quantitatively determined before in human tissues or cells. Neu5Gc and its O-alkylated or O-acylated derivatives were not detected.

Defects in degradation of blood group A and B glycosphingolipids in Schindler and Fabry diseases

Skin fibroblast cultures from patients with inherited lysosomal enzymopathies, alpha-N-acetylgalactosaminidase (alpha-NAGA) and alpha-galactosidase A deficiencies (Schindler and Fabry disease, respectively), and from normal controls were used to study in situ degradation of blood group A and B glycosphingolipids. Glycosphingolipids A-6-2 (GalNAc (alpha 1-->3)[Fuc alpha 1-->2]Gal(beta1-->4)GlcNAc(beta 1-->3)Gal(beta 1--> 4)Glc (beta 1-->1')Cer, IV(2)-alpha-fucosyl-IV(3)-alpha-N-acetylgalactosaminylneolactotetraosylceramide), B-6-2 (Gal(alpha 1-->3)[Fuc alpha 1--> 2] Gal (beta 1-->4)GlcNAc(beta 1-->3)Gal(beta 1-->4)Glc(beta 1-->1')Cer, IV(2)- alpha-fucosyl-IV(3)-alpha-galactosylneolactotetraosylceramide), and globoside (GalNAc(beta 1-->3)Gal(alpha 1-->4)Gal(beta 1-->4)Glc(beta 1-->1') Cer, globotetraosylceramide) were tritium labeled in their ceramide moiety and used as natural substrates. The degradation rate of glycolipid A-6-2 was very low in fibroblasts of all the alpha-NAGA-deficient patients (less than 7% of controls), despite very heterogeneous clinical pictures, ruling out different residual enzyme activities as an explanation for the clinical heterogeneity. Strongly elevated urinary excretion of blood group A glycolipids was detected in one patient with blood group A, secretor status (five times higher than upper limit of controls), in support of the notion that blood group A-active glycolipids may contribute as storage compounds in blood group A patients. When glycolipid B-6-2 was fed to alpha-galactosidase A-deficient cells, the degradation rate was surprisingly high (50% of controls), while that of globotriaosylceramide was reduced to less than 15% of control average, presumably reflecting differences in the lysosomal enzymology of polar glycolipids versus less-polar ones. Relatively high-degree degradation of substrates with alpha-D-Galactosyl moieties hints at a possible contribution of other enzymes.

Conformational studies of blood group A and blood group B oligosaccharides using NMR residual dipolar couplings

The conformations of two synthetic trisaccharides of blood group A and B (alpha-L-Fucp-(1-->2)-[alpha-D-GalpNAc-(1-->3)]-alpha-D-Galp and alpha-L-Fucp-(1-->2)-[alpha-D-Galp-(1-->3)]-alpha-D-Galp, respectively) and of a type A tetrasaccharide alditol, Fucp-(1-->2)-[alpha-D-GalpNAc-(1-->3)]-beta-D-Galp-(1-->3)-GalNAc-ol, were studied by NMR measurements of one-bond C-H residual dipolar couplings in partially oriented liquid crystal solutions. The conformations of the three oligosaccharides were analyzed by generating thousands of structures using a Monte-Carlo method. Two different strategies were applied to calculate theoretical dipolar couplings for these structures. In the first method, the orientation of the molecule was calculated from the optimal fit of the molecular model to the experimental data, while in the second method the orientation tensor was calculated directly from the moment of inertia of the molecular model. Both methods of analysis give similar results but with slightly better agreement with experiment for the former one. The analysis of the results implies a single unique conformation for both blood group epitopes in solution in disagreement with theoretical models suggesting the existence of two conformers in solution.

Linear synthesis of a protected H-type II pentasaccharide using glycosyl phosphate building blocks

A linear synthesis of a fully protected H-type II blood group determinant pentasaccharide utilizing glycosyl phosphate and glycosyl trichloroacetimidate building blocks is reported. Envisioning an automated solid-phase synthesis of blood group determinants, the utility of glycosyl phosphates in the stepwise construction of complex oligosaccharides, such as the H-type II antigen, is demonstrated. Installation of the central glucosamine building block required the screening of a variety of nitrogen protecting groups to ensure good glucosamine donor reactivity and protecting group compatibility. The challenge to differentiate C2 of the terminal galactose in the presence of other hydroxyl and amine protecting groups prompted us to introduce the 2-(azidomethyl)benzoyl group as a novel mode of protection for carbohydrate synthesis. The compatibility of this group with traditionally employed protecting groups was examined, as well as its use as a C2 stereodirecting group in glycosylations. The application of the 2-(azidomethyl)benzoyl group along with a systematic evaluation of glycosyl donors allowed for the completion of the pentasaccharide and provides a synthetic strategy that is expected to be generally amenable to the solid support synthesis of blood group determinants.

Modified blood group A trisaccharide probes: synthesis and interaction with antibodies

Three derivatives modified at the acetamide fragment of blood group trisaccharide A, GalNAcalpha1-3(Fucalpha1-2)Galbeta-O-spacer were synthesised. In the first compound the amide oxygen was substituted for the sulfur atom. In the second compound the methyl group was replaced with the trifluoromethyl moiety, and in the third compound the methyl group was replaced with the hydrogen atom. The interaction of these probes with anti-A monoclonal antibodies gives the information about significance of trisaccharide methyl and carbonyl groups for the formation of protein-carbohydrates complex.

The relationship between ABO histo-blood group, factor VIII and von Willebrand factor

ABO histo-blood group is a major determinant of plasma levels of factor VIII (FVIII) and von Willebrand factor (vWF). Blood group O individuals have significantly (approximately 25%) lower plasma levels of both glycoproteins. This association is of clinical significance. Low plasma levels of either FVIII or vWF have long been established as causes of excess bleeding. Conversely, there is accumulating evidence that elevated FVIII-vWF levels may represent an important risk factor for ischaemic heart disease and venous thromboembolic disease. In spite of the well-documented association between ABO blood group and FVIII-vWF levels, the underlying mechanism remains unknown. However, it has been established that the ABO effect is primarily mediated through a direct functional effect of the ABO locus on plasma vWF levels. Theoretically, ABO blood group may alter the rate of vWF synthesis or secretion within endothelial cells. Alternatively, ABO group may affect vWF plasma clearance rates. ABH antigenic determinants have been identified on the N-linked oligosaccharide chains of circulating vWF and FVIII, according to the blood group of the individual. It remains unclear whether these carbohydrate structures are responsible for mediating the effect of ABO blood group on plasma vWF levels.

ABH and Lewis histo-blood group antigens, a model for the meaning of oligosaccharide diversity in the face of a changing world

Antigens of the ABH and Lewis histo-blood group family have been known for a long time. Yet their biological meaning is still largely obscure. Based on the available knowledge about the genes involved in their biosynthesis and about their tissue distribution in humans and other mammals, we discuss here the selective forces that may maintain or propagate these oligosaccharide antigens. The ABO, alpha 1,2fucosyltransferase and alpha 1,3fucosyltransferase enzyme families have been generated by gene duplications. Members of these families contribute to biosynthesis of the antigens through epistatic interactions. We suggest that the highly polymorphic genes of each family provide intraspecies diversity that allows coping with diverse and rapidly evolving pathogens. In contrast, the genes of low frequency polymorphism are expected to play roles at the cellular level, although they may be dispensable at the individual level. In addition, some members of these three gene families are expected to be functionally redundant and may either provide a reservoir for additional diversity in the future or become inactivated. We also discuss the role of the ABH and Lewis histo-blood group antigens in pathologies such as cancer and cardiovascular diseases, but argue that it is merely incidental and devoid of evolutionary impact.