Molecular cloning of pigeon UDP-galactose:beta-D-galactoside alpha1,4-galactosyltransferase and UDP-galactose:beta-D-galactoside beta1,4-galactosyltransferase, two novel enzymes catalyzing the formation of Gal alpha1-4Gal beta1-4Gal beta1-4GlcNAc sequence

Two Paralogous Gb3/CD77 Synthases in Birds Show Different Preferences for Their Glycoprotein and Glycosphingolipid Substrates

Most glycosyltransferases show remarkable gross and fine substrate specificity, which is reflected in the old one enzyme-one linkage paradigm. While human Gb3/CD77 synthase is a glycosyltransferase that synthesizes the Galα1→4Gal moiety mainly on glycosphingolipids, its pigeon homolog prefers glycoproteins as acceptors. In this study, we characterized two Gb3/CD77 synthase paralogs found in pigeons (Columba livia). We evaluated their specificities in transfected human teratocarcinoma 2102Ep cells by flow cytofluorometry, Western blotting, high-performance thin-layer chromatography, mass spectrometry and metabolic labelling with 14C-galactose. We found that the previously described pigeon Gb3/CD77 synthase (called P) can use predominately glycoproteins as acceptors, while its paralog (called M), which we serendipitously discovered while conducting this study, efficiently synthesizes Galα1→4Gal caps on both glycoproteins and glycosphingolipids. These two paralogs may underlie the difference in expression profiles of Galα1→4Gal-terminated glycoconjugates between neoavians and mammals.

Clinical consequences of the extremely rare anti-PP1Pk isoantibodies in pregnancy: a case series and review of the literature

BACKGROUND

The absence of the red cell antigens P, P1 and P^k , known as 'p', represents an extremely rare red cell phenotype. Individuals with this phenotype spontaneously form anti-PP1P^k isoantibodies, associated with severe haemolytic transfusion reactions, recurrent spontaneous abortion and haemolytic disease of the fetus and newborn (HDFN).

METHODS

We report a series of four successful pregnancies in three women with anti-PP1P^k isoantibodies, one complicated by HDFN, another by intrauterine growth restriction, all managed supportively. We also review the literature regarding the management of pregnancy involving anti-PP1P^k isoimmunization.

RESULTS

The literature surrounding anti-PP1P^k in pregnancy is limited to a very small number of case reports. The majority report management with therapeutic plasma exchange (TPE) with or without intravenous immunoglobulin. The relationship between titre and risk of pregnancy loss remains unclear, though a history of recurrent pregnancy loss appears important. Although a positive cord blood direct antiglobulin test is frequently noted, clinically significant HDFN appears uncommon, though possible.

CONCLUSION

Early initiation of TPE in high risk patients should be strongly considered. If possible, pregnancies should be managed in a high-risk obstetric or maternal fetal medicine service. The fetus should be monitored closely with interval fetal ultrasound and middle cerebral artery peak systolic volume Doppler to screen for fetal anaemia. Timely sourcing of compatible blood products is likely to be highly challenging, and both directed and autologous donation should be contemplated where appropriate. The International Red Cell Donor Panel may also provide access to compatible products.

Blood group P1 antigen-bearing glycoproteins are functional but less efficient receptors of Shiga toxin than conventional glycolipid-based receptors

Shiga toxin (STx) is a virulence factor produced by enterohemorrhagic Escherichia coli. STx is taken up by mammalian host cells by binding to the glycosphingolipid (GSL) globotriaosylceramide (Gb3; Galα1-4Galβ1-4Glc-ceramide) and causes cell death after its retrograde membrane transport. However, the contribution of the hydrophobic portion of Gb3 (ceramide) to STx transport remains unclear. In pigeons, blood group P1 glycan antigens (Galα1-4Galβ1-4GlcNAc-) are expressed on glycoproteins that are synthesized by α1,4-galactosyltransferase 2 (pA4GalT2). To examine whether these glycoproteins can also function as STx receptors, here we constructed glycan-remodeled HeLa cell variants lacking Gb3 expression but instead expressing pA4GalT2-synthesized P1 glycan antigens on glycoproteins. We compared STx binding and sensitivity of these variants with those of the parental, Gb3-expressing HeLa cells. The glycan-remodeled cells bound STx1 via N-glycans of glycoproteins and were sensitive to STx1 even without Gb3 expression, indicating that P1-containing glycoproteins also function as STx receptors. However, these variants were significantly less sensitive to STx than the parent cells. Fluorescence microscopy and correlative light EM revealed that the STx1 B subunit accumulates to lower levels in the Golgi apparatus after glycoprotein-mediated than after Gb3-mediated uptake but instead accumulates in vacuole-like structures probably derived from early endosomes. Furthermore, coexpression of Galα1-4Gal on both glycoproteins and GSLs reduced the sensitivity of cells to STx1 compared with those expressing Galα1-4Gal only on GSLs, probably because of competition for STx binding or internalization. We conclude that lipid-based receptors are much more effective in STx retrograde transport and mediate greater STx cytotoxicity than protein-based receptors.

Glycan diversity in the course of vertebrate evolution

Vertebrates are estimated to have arisen over 500 million years ago in the Cambrian Period. Species that survived the Big Five extinction events at a global scale underwent repeated adaptive radiations along with habitat expansions from the sea to the land and sky. The development of the endoskeleton and neural tube enabled more complex body shapes. At the same time, vertebrates became suitable for the invasion and proliferation of foreign organisms. Adaptive immune systems were acquired for responses to a wide variety of pathogens, and more sophisticated systems developed during the evolution of mammals and birds. Vertebrate glycans consist of common core structures and various elongated structures, such as Neu5Gc, Galα1-3Gal, Galα1-4Gal, and Galβ1-4Gal epitopes, depending on the species. During species diversification, complex glycan structures were generated, maintained or lost. Whole-genome sequencing has revealed that vertebrates harbor numerous and even redundant glycosyltransferase genes. The production of various glycan structures is controlled at the genetic level in a species-specific manner. Because cell surface glycans are often targets of bacterial and viral infections, glycan structural diversity is presumed to be protective against infections. However, the maintenance of apparently redundant glycosyltransferase genes and investment in species-specific glycan structures, even in higher vertebrates with highly developed immune systems, are not well explained. This fact suggests that glycans play important roles in unknown biological processes.

Identification of multiple isomeric core chitobiose-modified high-mannose and paucimannose N-glycans in the planarian Schmidtea mediterranea

Cell surface–associated glycans mediate many cellular processes, including adhesion, migration, signaling, and extracellular matrix organization. The galactosylation of core fucose (GalFuc epitope) in paucimannose and complex-type N-glycans is characteristic of protostome organisms, including flatworms (planarians). Although uninvestigated, the structures of these glycans may play a role in planarian regeneration. Whole-organism MALDI-MS analysis of N-linked oligosaccharides from the planarian Schmidtea mediterranea revealed the presence of multiple isomeric high-mannose and paucimannose structures with unusual mono-, di-, and polygalactosylated (n = 3–5) core fucose structures; the latter structures have not been reported in other systems. Di- and trigalactosylated core fucoses were the most dominant glycomers. N-Glycans showed extensive, yet selective, methylation patterns, ranging from non-methylated to polymethylated glycoforms. Although the majority of glycoforms were polymethylated, a small fraction also consisted of non-methylated glycans. Remarkably, monogalactosylated core fucose remained unmethylated, whereas its polygalactosylated forms were methylated, indicating structurally selective methylation. Using database searches, we identified two potential homologs of the Galβ1–4Fuc–synthesizing enzyme from nematodes (GALT-1) that were expressed in the prepharyngeal, pharyngeal, and mesenchymal regions in S. mediterranea. The presence of two GALT-1 homologs suggests different requirements for mono- and polygalactosylation of core fucose for the formation of multiple isomers. Furthermore, we observed variations in core fucose glycosylation patterns in different planarian strains, suggesting evolutionary adaptation in fucose glycosylation. The various core chitobiose modifications and methylations create >60 different glycoforms in S. mediterranea. These results contribute greatly to our understanding of N-glycan biosynthesis and suggest the presence of a GlcNAc-independent biosynthetic pathway in S. mediterranea.

Structures and developmental alterations of N-glycans of zebrafish embryos

Zebrafish is a model organism suitable for studying vertebrate development. We analyzed the N-glycan structures of zebrafish embryos and their alterations during zebrafish embryogenesis to obtain basic data for studying the roles of N-glycosylation. Multiple modes of high-performance liquid chromatography and multistage mass spectrometry were used for structural analysis of N-glycans. The N-glycans from deyolked embryos at 36 hours postfertilization, a mid-pharyngula stage, contained relatively higher amounts of complex- and hybrid-type glycans with LacNAc (Galβ1-4GlcNAc) and/or sialyl LacNAc without additional β1,4-Gal, which are commonly found in mammalian tissues, as well as abundant oligomannose-type glycans. Some of the complex- and hybrid-type glycans possessed various extended LacNAc structures, such as Galβ1-4LacNAc, LacNAc-repeat or unique (+/- dHex)-GalNAcα1-GlcNAcβ1-LacNAc. In contrast, the yolk of the embryo contains predominant oligomannose-type glycans and complex-type glycans with Galβ1-4(Siaα2-3)Galβ1-4(Fucα1-3)GlcNAc antennae. N-Glycan profiles obtained from deyolked embryos at different stages showed stage-dependent variation of complex- and hybrid-type glycans. At gastrula and early segmentation stages, complex- and hybrid-type glycans were minor components, and their antenna structures were mainly sialyl LacdiNAc (Siaα2-6GalNAcβ1-4GlcNAc). From the mid-segmentation to pharyngula stages, those with LacNAc and/or α2,6-sialyl LacNAc antenna structures increased remarkably, and those with α2,3-sialyl LacNAc antenna, core α1,6-Fuc and bisecting GlcNAc modifications increased gradually. These results suggest the presence of mechanisms for regulating the antenna structures of complex/hybrid N-glycan biosynthesis in the phylotypic stage of vertebrate development.

Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: an update for 2009-2010

This review is the sixth update of the original article published in 1999 on the application of MALDI mass spectrometry to the analysis of carbohydrates and glycoconjugates and brings coverage of the literature to the end of 2010. General aspects such as theory of the MALDI process, matrices, derivatization, MALDI imaging, arrays and fragmentation are covered in the first part of the review and applications to various structural typed constitutes the remainder. The main groups of compound that are discussed in this section are oligo and polysaccharides, glycoproteins, glycolipids, glycosides and biopharmaceuticals. Many of these applications are presented in tabular form. Also discussed are medical and industrial applications of the technique, studies of enzyme reactions and applications to chemical synthesis.

Crossroads between Bacterial and Mammalian Glycosyltransferases

Bacterial glycosyltransferases (GT) often synthesize the same glycan linkages as mammalian GT; yet, they usually have very little sequence identity. Nevertheless, enzymatic properties, folding, substrate specificities, and catalytic mechanisms of these enzyme proteins may have significant similarity. Thus, bacterial GT can be utilized for the enzymatic synthesis of both bacterial and mammalian types of complex glycan structures. A comparison is made here between mammalian and bacterial enzymes that synthesize epitopes found in mammalian glycoproteins, and those found in the O antigens of Gram-negative bacteria. These epitopes include Thomsen–Friedenreich (TF or T) antigen, blood group O, A, and B, type 1 and 2 chains, Lewis antigens, sialylated and fucosylated structures, and polysialic acids. Many different approaches can be taken to investigate the substrate binding and catalytic mechanisms of GT, including crystal structure analyses, mutations, comparison of amino acid sequences, NMR, and mass spectrometry. Knowledge of the protein structures and functions helps to design GT for specific glycan synthesis and to develop inhibitors. The goals are to develop new strategies to reduce bacterial virulence and to synthesize vaccines and other biologically active glycan structures.

P1/P2 genotyping of known and novel null alleles in the P1PK and GLOB histo-blood group systems

BACKGROUND

The rare but clinically important null phenotypes of the P1PK and GLOB blood group systems are due to alterations in A4GALT and B3GALNT1, respectively. A recently identified single-nucleotide polymorphism in Exon 2a of A4GALT predicts the common P1 and P2 phenotypes but rare variants have not been tested.

STUDY DESIGN AND METHODS

The aim of this study was to analyze 84 p, P1 (k) , and P2 (k) samples, with special emphasis on unknown alleles and the P(1) /P(2) marker. Of these, 27 samples came from individuals not previously investigated genetically and were therefore subjected to sequencing of A4GALT or B3GALNT1, and a subset was tested by flow cytometry.

RESULTS

The P(1) /P(2) genotyping linked 20 p-inducing mutations in A4GALT to P(1) or P(2) allelic background. Eight p alleles remain unlinked due to compound heterozygosity. For 23 of 25 P(k) samples, concordant results were observed: P1 (k) samples had at least one P(1) allele while P2 (k) had P(2) only. The two remaining samples typed as P1+ and P1+(w) but were genetically P(2) /P(2) . A tendency toward higher P(k) antigen expression was observed on P1 (k) cells compared to P2 (k) . In total, six previously unknown null mutations were found and characterized in A4GALT while four new changes were revealed in B3GALNT1.

CONCLUSION

For the first time, p alleles were shown to occur on both P(1) and P(2) allelic backgrounds. Furthermore, P(1) /P(2) genotyping predicted the P1 (k) versus P2 (k) phenotype in more than 90% of globoside-deficient samples. The number of GLOB-null alleles was increased by 50% and several P1PK-null alleles were identified.

Distribution of the Galβ1-4Gal epitope among birds: species-specific loss of the glycan structure in chicken and its relatives

The Galβ1-4Gal epitope is rarely found in mammals, and the natural antibody against Galβ1-4Gal is rich in human. In contrast, we have previously demonstrated the presence of Galβ1-4Gal in pigeon and ostrich, and the absence of this epitope in chicken. Here, to further investigate the expression of this glycan among birds, egg white glycoproteins and egg yolk IgG from nine species of birds, namely, chicken, duck, emu, guineafowl, ostrich, peafowl, pigeon, quail, and turkey, were analyzed by western blot using an anti-(Galβ1-4Gal) antibody. The results indicated that some egg white glycoproteins from emu, ostrich, and quail, and heavy chains of IgG from all of the birds, except chicken and quail, were stained with the antibody. The presence of Galβ1-4Gal on N-glycans of IgGs from guineafowl, peafowl, and turkey were confirmed by mass spectrometry (MS), MS/MS, and MS(n) analyses. In quail, the presence of Galβ1-4Gal was confirmed by detecting the activities of UDP-galactose: β-galactoside β1,4-galactosyltransferase (β4GalT(Gal)) in various tissues, and by detecting Galβ1-4Gal by western blotting. In contrast, bamboo partridge, which is a close relative of chicken, did not show any detectable activities of β4GalT(Gal) or Galβ1-4Gal on glycoproteins. Because quail, peafowl, turkey, chicken, and bamboo partridge belong to the same family, i.e., Phasianidae, expression of Galβ1-4Gal was most likely differentiated within this family. Considering that Galβ1-4Gal is also expressed in ostrich, emu, and pigeon, which are phylogenetically distant relatives within modern birds, Galβ1-4Gal expression appears to be widely distributed among birds, but might have been abolished in the ancestors of chicken and bamboo partridge.

Identification of putative rhamnogalacturonan-II specific glycosyltransferases in Arabidopsis using a combination of bioinformatics approaches

Rhamnogalacturonan-II (RG-II) is a complex plant cell wall polysaccharide that is composed of an α(1,4)-linked homogalacturonan backbone substituted with four side chains. It exists in the cell wall in the form of a dimer that is cross-linked by a borate di-ester. Despite its highly complex structure, RG-II is evolutionarily conserved in the plant kingdom suggesting that this polymer has fundamental functions in the primary wall organisation. In this study, we have set up a bioinformatics strategy aimed at identifying putative glycosyltransferases (GTs) involved in RG-II biosynthesis. This strategy is based on the selection of candidate genes encoding type II membrane proteins that are tightly coexpressed in both rice and Arabidopsis with previously characterised genes encoding enzymes involved in the synthesis of RG-II and exhibiting an up-regulation upon isoxaben treatment. This study results in the final selection of 26 putative Arabidopsis GTs, including 10 sequences already classified in the CAZy database. Among these CAZy sequences, the screening protocol allowed the selection of α-galacturonosyltransferases involved in the synthesis of α4-GalA oligogalacturonides present in both homogalacturonans and RG-II, and two sialyltransferase-like sequences previously proposed to be involved in the transfer of Kdo and/or Dha on the pectic backbone of RG-II. In addition, 16 non-CAZy GT sequences were retrieved in the present study. Four of them exhibited a GT-A fold. The remaining sequences harbored a GT-B like fold and a fucosyltransferase signature. Based on homologies with glycosyltransferases of known functions, putative roles in the RG-II biosynthesis are proposed for some GT candidates.

Pectin biosynthesis: GALS1 in Arabidopsis thaliana is a β-1,4-galactan β-1,4-galactosyltransferase

β-1,4-Galactans are abundant polysaccharides in plant cell walls, which are generally found as side chains of rhamnogalacturonan I. Rhamnogalacturonan I is a major component of pectin with a backbone of alternating rhamnose and galacturonic acid residues and side chains that include α-1,5-arabinans, β-1,4-galactans, and arabinogalactans. Many enzymes are required to synthesize pectin, but few have been identified. Pectin is most abundant in primary walls of expanding cells, but β-1,4-galactan is relatively abundant in secondary walls, especially in tension wood that forms in response to mechanical stress. We investigated enzymes in glycosyltransferase family GT92, which has three members in Arabidopsis thaliana, which we designated GALACTAN SYNTHASE1, (GALS1), GALS2 and GALS3. Loss-of-function mutants in the corresponding genes had a decreased β-1,4-galactan content, and overexpression of GALS1 resulted in plants with 50% higher β-1,4-galactan content. The plants did not have an obvious growth phenotype. Heterologously expressed and affinity-purified GALS1 could transfer Gal residues from UDP-Gal onto β-1,4-galactopentaose. GALS1 specifically formed β-1,4-galactosyl linkages and could add successive β-1,4-galactosyl residues to the acceptor. These observations confirm the identity of the GT92 enzyme as β-1,4-galactan synthase. The identification of this enzyme could provide an important tool for engineering plants with improved bioenergy properties.

Identification of a novel A4GALT exon reveals the genetic basis of the P1/P2 histo-blood groups

The A4GALT locus encodes a glycosyltransferase that synthesizes the terminal Galα1-4Gal of the Pk (Gb3/CD77) glycosphingolipid, important in transfusion medicine, obstetrics, and pathogen susceptibility. Critical nucleotide changes in A4GALT not only abolish Pk formation but also another Galα1-4Gal–defined antigen, P1, which belongs to the only blood group system for which the responsible locus remains undefined. Since known A4GALT polymorphisms do not explain the P1−Pk+ phenotype, P2, we set out to elucidate the genetic basis of P1/P2. Despite marked differences (P1 > P2) in A4GALT transcript levels in blood, luciferase experiments showed no difference between P1/P2-related promoter sequences. Investigation of A4GALT mRNA in cultured human bone marrow cells revealed novel transcripts containing only the noncoding exon 1 and a sequence (here termed exon 2a) from intron 1. These 5′-capped transcripts include poly-A tails and 3 polymorphic sites, one of which was P1/P2-specific among > 200 donors and opens a short reading frame in P2 alleles. We exploited these data to devise the first genotyping assays to predict P1 status. P1/P2 genotypes correlated with both transcript levels and P1/Pk expression on red cells. Thus, P1 zygosity partially explains the well-known interindividual variation in P1 strength. Future investigations need to focus on regulatory mechanisms underlying P1 synthesis.

Distinct expression profiles of UDP-galactose: β-D-galactoside α1,4-galactosyltransferase and UDP-galactose: β-D-galactoside β1,4-galactosyltransferase in pigeon, ostrich and chicken

We previously identified two novel enzymes in pigeon, α1,4- and β1,4-galactosyltransferases (GalTs), which are responsible for the biosynthesis of the Galα1-4Gal and Galβ1-4Gal sequences on glycoproteins, respectively. No such glycan structures and/or enzymes have been found in mammals, suggesting that the expression of these enzymes diverged during the course of vertebrate evolution. To compare their expression profiles among avian species, we first established a method for detecting the activities of these two GalTs based on the two-dimensional high pressure liquid chromatography mapping technique, using 2-aminopyridine-derivatized asialo-biantennary N-glycans as an acceptor substrate. When we analyzed the activities of GalTs in pigeon liver extracts in the presence of UDP-Gal, 13 different products containing Galα1-4Galβ1-4GlcNAc, Galβ1-4Galβ1-4GlcNAc and/or Galα1-4Galβ1-4Galβ1-4GlcNAc branches were identified. The newly formed glycosidic linkages of the enzymatic products were determined by nuclear magnetic resonance and methylation analysis, as well as by galactosidase digestions. The activities of both α1,4- and β1,4-GalTs were detected in various tissues in pigeon, although their relative activities were different in each tissue. In contrast, ostrich expressed β1,4-GalT, but not α1,4-GalT, in all tissues analyzed, whereas neither α1,4- nor β1,4-GalT activity was detected in chicken. These results indicate that α1,4- and β1,4-GalTs are expressed in a species-specific manner and are distributed throughout the entire body of pigeon or ostrich when the enzymes are present.