ISPD produces CDP-ribitol used by FKTN and FKRP to transfer ribitol phosphate onto α-dystroglycan.

Mutations in genes required for the glycosylation of α-dystroglycan lead to muscle and brain diseases known as dystroglycanopathies. However, the precise structure and biogenesis of the assembled glycan are not completely understood. Here we report that three enzymes mutated in dystroglycanopathies can collaborate to attach ribitol phosphate onto α-dystroglycan. Specifically, we demonstrate that isoprenoid synthase domain-containing protein (ISPD) synthesizes CDP-ribitol, present in muscle, and that both recombinant fukutin (FKTN) and fukutin-related protein (FKRP) can transfer a ribitol phosphate group from CDP-ribitol to α-dystroglycan. We also show that ISPD and FKTN are essential for the incorporation of ribitol into α-dystroglycan in HEK293 cells. Glycosylation of α-dystroglycan in fibroblasts from patients with hypomorphic ISPD mutations is reduced. We observe that in some cases glycosylation can be partially restored by addition of ribitol to the culture medium, suggesting that dietary supplementation with ribitol should be evaluated as a therapy for patients with ISPD mutations.

A novel mutation on the transferrin gene abolishes one N-glycosylation site and alters the pattern of transferrin isoforms, mimicking that observed after excessive alcohol consumption.

OBJECTIVES: In the process of obtaining a driver's license, a healthy 28year old man presented increased levels of disialo-transferrin (TF) (approx. 20%, ref. value<2) by HPLC analysis of TF isoforms (%CDT), while other markers of excessive alcohol consumption (PEth, MCV and γ-GT) were in the normal range. The objective of this study was to determine the cause of the increased %CDT levels. DESIGN AND METHODS: Serum TF isoforms were re-analyzed by LC-MS. All coding exons of the TF gene were Sanger sequenced. RESULTS: Analysis of TF isoforms by LC-MS confirmed the presence of increased disialo-TF and revealed a discrepancy in the mass difference between disialo-TF and tetrasialo-TF which suggested the presence of a genetic TF isoform with one abolished N-glycosylation site. Sanger sequencing of the TF gene revealed the presence of two missense mutations in heterozygous form: c.1295A>G (p.N432S) and c.1765C>T (p.P589S). p.N432S is a novel mutation that abolishes one N-glycosylation site of TF, while p.P589S is the polymorphism that defines the C2 isoform of TF. The sum of mass shifts caused by both amino acid substitutions agrees with the mass shift observed by LC-MS, which indicates that both variants are located in cis. CONCLUSIONS: An individual initially suspected of alcohol abuse based on elevated %CDT was shown to be carrier of a novel mutation in the TF gene that abolishes the N-glycosylation site at position p.N432. The presence of this genetic variant has to be kept in mind when interpreting TF isoform patterns.

In vitro assessment of platelet concentrates with multiple electrode aggregometry.

Storage impairs platelet function. It was hypothesized that multiple electrode aggregometry in vitro could be used to follow aggregability in platelet concentrates over time and that the results predict the efficacy of platelet transfusion in an ex vivo transfusion model. In vitro platelet aggregability was assessed in apheresis and pooled buffy coat platelet concentrates (BCs) (n = 13 each) using multiple electrode aggregometry with different agonists 1, 3, 5 and 7 days after preparation. In the ex vivo transfusion model, whole blood samples from nine healthy volunteers were collected every second day. The samples were supplemented with stored platelets (+146 × 10(9) × l(-1)) from the same unit 1, 3, 5 and 7 days after preparation. Platelet aggregability was assessed in the concentrate and in the whole blood samples before and after platelet supplementation. There was a continuous reduction in in vitro platelet aggregability over time in both apheresis and pooled BCs. The same pattern was observed after ex vivo addition of apheresis and pooled BCs to whole blood samples. The best correlation between in vitro aggregability and changes in aggregation after addition was achieved with collagen as agonist (r = 0.67, p < 0.001). In conclusion, multiple electrode aggregometry can be used to follow aggregability in platelet concentrates in vitro, and the results predict with moderate accuracy changes in aggregation after addition of platelet concentrate to whole blood samples.

Mutations in GMPPA cause a glycosylation disorder characterized by intellectual disability and autonomic dysfunction.

In guanosine diphosphate (GDP)-mannose pyrophosphorylase A (GMPPA), we identified a homozygous nonsense mutation that segregated with achalasia and alacrima, delayed developmental milestones, and gait abnormalities in a consanguineous Pakistani pedigree. Mutations in GMPPA were subsequently found in ten additional individuals from eight independent families affected by the combination of achalasia, alacrima, and neurological deficits. This autosomal-recessive disorder shows many similarities with triple A syndrome, which is characterized by achalasia, alacrima, and variable neurological deficits in combination with adrenal insufficiency. GMPPA is a largely uncharacterized homolog of GMPPB. GMPPB catalyzes the formation of GDP-mannose, which is an essential precursor of glycan moieties of glycoproteins and glycolipids and is associated with congenital and limb-girdle muscular dystrophies with hypoglycosylation of α-dystroglycan. Surprisingly, GDP-mannose pyrophosphorylase activity was unchanged and GDP-mannose levels were strongly increased in lymphoblasts of individuals with GMPPA mutations. This suggests that GMPPA might serve as a GMPPB regulatory subunit mediating feedback inhibition of GMPPB instead of displaying catalytic enzyme activity itself. Thus, a triple-A-like syndrome can be added to the growing list of congenital disorders of glycosylation, in which dysregulation rather than mere enzyme deficiency is the basal pathophysiological mechanism.

Targeting the glycoproteome.

Despite numerous original publications describing the structural complexity of N- and O-linked glycans on glycoproteins, only very few answer the basic question of which particular glycans are linked to which amino acid residues along the polypeptide chain. Such structural information is of fundamental importance for understanding the biological roles of complex glycosylations as well as deciphering their non-template driven biosynthesis. This review focuses on presenting and commenting on recent strategies, specifically aimed at identifying the glycoproteome of cultured cells and biological samples, using targeted and global enrichment procedures and utilizing the high resolution power, high through-put capacity and complementary fragmentation techniques of tandem mass spectrometry. The goal is to give an update of this emerging field of protein and glyco-sciences and suggest routes to bridge the data gap between the two aspects of glycoprotein characteristics, i.e. glycan structures and their attachment sites.

O-Mannose and O-N-acetyl galactosamine glycosylation of mammalian α-dystroglycan is conserved in a region-specific manner.

Defects in the O-linked glycosylation of the peripheral membrane protein α-dystroglycan (α-DG) are the main cause of several forms of congenital muscular dystrophies and thus the characterization of the glycosylation of α-DG is of great medical importance. A detailed investigation of the glycosylation pattern of the native α-DG protein is essential for the understanding of the biological processes related to human disease in which the protein is involved. To date, several studies have reported novel O-glycans and attachment sites on the mucin-like domain of mammalian α-DG with both similar and contradicting glycosylation patterns, indicating the species-specific O-glycosylation of mammalian α-DG. By applying a standardized purification scheme and subsequent glycoproteomic analysis of native α-DG from rabbit and human skeletal muscle biopsies and from cultured mouse C2C12 myotubes, we show that the O-glycosylation patterns of the mucin-like domain of native α-DG are conserved among mammalians in a region-specific manner.

O-linked N,N'-diacetyllactosamine (LacdiNAc)-modified glycans in extracellular matrix glycoproteins are specifically phosphorylated at subterminal N-acetylglucosamine.

The terminal modification of glycans by ß4 addition of N-acetylgalactosamine to N-acetylglucosamine with formation of the N,N-diacetyllactosediamine (LacdiNAc) moiety has been well documented for a number of N-linked glycoproteins and peptides, like neurohormones. Much less is known about O-glycoproteins in this regard because only human zona pellucida glycoprotein 3 (ZP3) and bovine proopiomelanocortin were reported to be LacdiNAc-modified. In searching for mammalian proteins modified with O-linked LacdiNAc we identified six positive species among nine endogenous and recombinant O-glycoproteins, which were extracellular matrix, or matrix-related proteins. These are ZP3 and the five novel LacdiNAc-positive species ECM1, AMACO, nidogen-1, α-dystroglycan, and neurofascin. The mass spectrometric analyses revealed a core 2-based tetrasaccharide as the common structural basis of O-linked LacdiNAc that could be further modified, similar to the type 2 LacNAc termini, with fucose, sialic acid, or sulfate. Here, we provide structural evidence for a novel type of mucin-type O-glycans that is strictly specific for LacdiNAc termini: sugar phosphorylation with formation of GalNAcß1-4(phospho-)GlcNAc. The structural details of the phosphatase-labile compound were elucidated by MS(2) analysis of tetralysine complexes and by MS(n) measurements of the permethylated glycan alditols. Phospho-LacdiNAc was detected in human HEK-293 as well as in mouse myoblast cells and in bovine brain tissue.

The N-terminal domain of α-dystroglycan, released as a 38 kDa protein, is increased in cerebrospinal fluid in patients with Lyme neuroborreliosis.

α-Dystroglycan is an extracellular adhesion protein that is known to interact with different ligands. The interaction is thought to stabilize the integrity of the plasma membrane. The N-terminal part of α-dystroglycan may be proteolytically processed to generate a small 38 kDa protein (α-DG-N). The physiological significance of α-DG-N is unclear but has been suggested to be involved in nerve regeneration and myelination and to function as a potential biomarker for neurodegenerative and neuromuscular diseases. In this report we show that α-DG-N is released into different body fluids, such as lachrimal fluid, cerebrospinal fluid (CSF), urine and plasma. To investigate the significance of α-DG-N in CSF we examined the levels of α-DG-N and known neurodegenerative markers in CSF from patients diagnosed with Lyme neuroborreliosis (LNB) and healthy controls. In untreated acute phase LNB patients, 67% showed a significant increase of CSF α-DG-N compared to healthy controls. After treatment with antibiotics the CSF α-DG-N levels were normalized in the LNB patients.

Human antibody responses to bovine (Newbury-2) norovirus (GIII.2) and association to histo-blood group antigens.

Serum antibodies to bovine norovirus have been found recently in about 22% of humans. Whether this prevalence reflects limited virulence properties of the virus or that inherited host factors provide protection against bovine norovirus infection in humans remains to be established. To investigate whether histo-blood group antigens correlate with the presence of bovine norovirus (GIII.2) antibody, plasma (n = 105) from Swedish blood donors, genotyped and phenotyped for secretor, Lewis and ABO, were tested and compared for the frequency of IgG antibody and antibody titer to Bo/Newbury2/76/UK. In total, 26.7% (28/105) of Swedish blood donors were antibody-positive. Two non-secretors (2/21, 9.5%) were antibody-positive compared with 26/84 (31%) secretors (P = 0.047). While no statistically significant correlation was found between the frequency of antibodies to bovine norovirus and different ABO blood groups, individuals with blood type B presented the highest frequency of antibodies (37.5%) compared with 0-30% among other blood groups. Individuals with Le(a-b+) had not only higher frequency of antibodies (31.3%) compared with Le(a+b-) (11%) (P = 0.068) but also higher antibody titer (P = 0.085) although this was not significant statistically. No detectable cross-reaction between bovine GIII.2 and human GII.3 NoV VLP was found with human and animal sera. The results of this study suggest that bovine norovirus infections occur in Sweden and that secretor status but not ABO blood groups is a possible risk factor for infection.

Characterization of site-specific O-glycan structures within the mucin-like domain of alpha-dystroglycan from human skeletal muscle.

The glycosylation of the extracellular protein alpha-dystroglycan is important for its ligand-binding activity, and altered or blocked glycosylation is associated with several forms of congenital muscular dystrophies. By immunoprecipitation and sialic acid capture-and-release enrichment strategies, we isolated tryptic glycopeptides of alpha-dystroglycan from human skeletal muscle. Nano-liquid chromatography tandem mass spectrometry was used to identify both glycopeptides and peptides corresponding to the mucin-like and C-terminal domain of alpha-dystroglycan. The O-glycans found had either Hex-O-Thr or HexNAc-O-Ser/Thr anchored structures, which were often elongated and frequently, but not always, terminated with sialic acid. The HexNAc-O-Ser/Thr, but not Hex-O-Thr glycopeptides, displayed heterogeneity regarding glycan core structures and level of glycosylation site occupancy. We demonstrate for the first time glycan attachment sites of the NeuAcHexHexNAcHex-O structure corresponding to the anticipated Neu5Acalpha3Galbeta4GlcNAcbeta2Man-O-glycan (sLacNAc-Man), within the mucin-like domain of human alpha-dystroglycan from human skeletal muscle. Twenty-five glycopeptides were characterized from human alpha-dystroglycan, which provide insight to the complex in vivo O-glycosylation of alpha-dystroglycan.

The G428A nonsense mutation in FUT2 provides strong but not absolute protection against symptomatic GII.4 Norovirus infection.

In November 2004, 116 individuals in an elderly nursing home in El Grao de Castellón, Spain were symptomatically infected with genogroup II.4 (GII.4) norovirus. The global attack rate was 54.2%. Genotyping of 34 symptomatic individuals regarding the FUT2 gene revealed that one patient was, surprisingly, a non-secretor, hence indicating secretor-independent infection. Lewis genotyping revealed that Lewis-positive and negative individuals were susceptible to symptomatic norovirus infection indicating that Lewis status did not predict susceptibility. Saliva based ELISA assays were used to determine binding of the outbreak virus to saliva samples. Saliva from a secretor-negative individual bound the authentic outbreak GII.4 Valencia/2004/Es virus, but did not in contrast to secretor-positive saliva bind VLP of other strains including the GII.4 Dijon strain. Amino acid comparison of antigenic A and B sites located on the external loops of the P2 domain revealed distinct differences between the Valencia/2004/Es and Dijon strains. All three aa in each antigenic site as well as 10/11 recently identified evolutionary hot spots, were unique in the Valencia/2004/Es strain compared to the Dijon strain. To the best of our knowledge, this is the first example of symptomatic GII.4 norovirus infection of a Le(a+b-) individual homozygous for the G428A nonsense mutation in FUT2. Taken together, our study provides new insights into the host genetic susceptibility to norovirus infections and evolution of the globally dominating GII.4 viruses.

Genetic susceptibility to symptomatic norovirus infection in Nicaragua.

Host genetic resistance to Norovirus (NoV) has been observed in challenge and outbreak studies in populations from Europe, Asia, and USA. In this study, we have investigated if histo-blood group antigens can predict susceptibility to diarrhea caused by NoV in Nicaragua, Central America, and if this can be reflected in antibody-prevalence and titer to NoV among individuals with different histo-blood group antigen phenotypes. Investigation of 28 individuals infected with NoV and 131 population controls revealed 6% of non-secretors in the population and nil non-secretors among patients infected with NoV, suggesting that non-secretors may be protected against NoV disease in Nicaragua. Surprisingly, 25% of the population was Lewis negative (Le(a-b-)). NoV infections with genogroup I (GI) and GII occurred irrespective of Lewis genotype, but none of the Lewis a positive (Le(a + b-)) were infected. The globally dominating GII.4 virus infected individuals of all blood groups except AB (n = 5), while the GI viruses (n = 4) infected only blood type O individuals. Furthermore, O blood types were susceptible to infections with GI.4, GII.4, GII.7, GII.17, and GII.18-Nica viruses, suggesting that secretors with blood type O are susceptible (OR = 1.52) and non-secretors resistant. The overall antibody-prevalence to NoV GII.3 VLP was 62% with the highest prevalence among blood type B carriers (70%) followed by A (68%) and O (62%). All four investigated individuals carrying blood type AB were antibody-negative. Among secretors, 63% were antibody-positive compared to 33% among non-secretors (P = 0.151). This study extends previous knowledge about the histo-blood group antigens role in NoV disease in a population with different genetic background than North American and European.

Virus-induced transcriptional activation of host FUT genes associated with neo-expression of Ley in cytomegalovirus-infected and sialyl-Lex in varicella-zoster virus-infected diploid human cells.

Cell surface carbohydrate structures including sialyl-Lewis X (sLe(x)) and Lewis Y (Le(y)) are important ligands in normal and malignant tissues. The aim here was to determine the possible influence on the expression of such antigens by two viruses varicella-zoster virus (VZV) and cytomegalovirus (CMV) involved in persistent infections of humans. We found that infection of human diploid fibroblasts with both viruses resulted in transcriptional activation of several fucosyltransferase (FUT) genes that were either dormant or expressed at low levels in uninfected cells. Both viruses induced FUT3, FUT5, and FUT6, encoding alpha1,3- and/or alpha1,4-specific fucosyltransferases. CMV, but not VZV, induced transcription of FUT1 (encoding an alpha1,2-specific fucosyltransferase), FUT7, and FUT9. The changes in transcription of FUT genes were expectedly associated with expression of Le(y) in CMV-infected cells and sLe(x) in the VZV-infected fibroblasts although no expression of these antigens was observed in uninfected cells. One major explanation for this difference between CMV- and VZV-infected cells was that CMV, but not VZV, induced expression of FUT1, necessary for Le(y) expression. The induced carbohydrate antigens in CMV- and VZV-infected cells could be of significance for virus spread and possible escape from immune responses.

Antibody prevalence and titer to norovirus (genogroup II) correlate with secretor (FUT2) but not with ABO phenotype or Lewis (FUT3) genotype.

BACKGROUND: Histo-blood group antigens and secretor status have been associated with susceptibility to Norovirus infections, which suggests that antibody prevalence and titer might correlate with these phenotypes. METHODS: Plasma samples (n = 105) from Swedish blood donors that had been genotyped for secretor (FUT2) and Lewis (Le; FUT3) genotypes and phenotyped for ABO and Le blood groups were analyzed for immunoglobulin G antibody prevalence and titers to norovirus genogroup (GG) II.4. RESULTS: The results showed that nonsecretors (se4128se428) and Lea+b- individuals not only had significantly lower antibody titers than did secretors (P < .0001) and Lea-b+ individuals (P < .0002) but were also significantly more often antibody negative (P < .05). Antibody titers in secretors were not significantly different between individuals of different Le (FUT3) genotypes or different ABO phenotypes. CONCLUSIONS: Nonsecretors and Lea+b- individuals are significantly less prone to be infected with GGII noroviruses. This new information extends previous knowledge and supports the hypothesis that nonsecretors are relatively but not absolutely resistant to norovirus infections.

A homozygous nonsense mutation (428G-->A) in the human secretor (FUT2) gene provides resistance to symptomatic norovirus (GGII) infections.

Noroviruses (formerly Norwalk-like viruses) are a major cause of acute gastroenteritis worldwide and are associated with a significant number of nosocomial and food-borne outbreaks. In this study we show that the human secretor FUT2 gene, which codes for an alpha(1,2)-fucosyltransferase synthesizing the H-type 1 antigen in saliva and mucosa, is associated with susceptibility to norovirus infections. Allelic polymorphism characterization at nucleotide 428 for symptomatic (n = 53) and asymptomatic (n = 62) individuals associated with nosocomial and sporadic norovirus outbreaks revealed that homozygous nonsense mutation (428G-->A) in FUT2 segregated with complete resistance for the disease. Of all symptomatic individuals, 49% were homozygous (SeSe) and 51% heterozygous (Sese428) secretors, and none were secretor negative (se428se428), in contrast to 20% nonsecretors (se428se428) among Swedish blood donors (n = 104) (P < 0.0002) and 29% for asymptomatic individuals associated with nosocomial outbreaks (P < 0.00001). Furthermore, saliva from secretor-positive and symptomatic patients but not from secretor-negative and asymptomatic individuals bound the norovirus strain responsible for that particular outbreak. This is the first report showing that the FUT2 nonsecretor (se428se428) genotype is associated with resistance to nosocomial and sporadic outbreaks with norovirus.

Identification of seven new alpha2,3-sialyltransferase III, ST3Gal III, transcripts from human foetal brain.

We have recently cloned and sequenced 19 human ST3Gal III gene isotranscripts from peripheral blood leukocytes and identified very complex patterns of isotranscripts of this gene in neuronal tissues. We have now cloned and sequenced additionally seven new isotranscripts from foetal brain. These novel isotranscripts showed losses of complete exons along the whole length of the coding sequence. None of the new isotranscripts coded for proteins with the two (L- and S-) sialylmotifs intact. One of the isotranscripts belonged to the isoform ST3Gal III -B, five to the ST3Gal III -C isoform and one to ST3Gal III -D isoform of isotranscripts, which lacks exon 3, exons 3 and 4 and exon 4 respectively. Two of the C series isotranscripts, ST3Gal III C4 and C11 had both lost exons 12 and 13 containing the S-motif but had otherwise the L- and the VS-motifs intact. Three isotranscripts, ST3Gal III C5, C12 and D5, were similar in the 3'-end coding for an identical amino acid sequence unrelated to the original enzyme. Isotranscripts ST3Gal III C9 and B10 were distinctly different from all other forms identified so far. The splice variants reported here are unlikely to express enzymatic activities but may other biological functions.

Real time PCR for monitoring regulation of host gene expression in herpes simplex virus type 1-infected human diploid cells.

Herpes simplex virus type 1 (HSV-1) induces prominent shifts in the rates of transcription of host cellular genes of relevance for the outcome of the viral infection. The quantitative analysis of transcription may be obscured by virus-induced alterations in the levels of RNA encoded by cellular housekeeping genes that are used commonly for normalisation of real time reverse transcription PCR (RT-qPCR). In the present study, we analysed beta-actin, GAPDH and 18S rRNA for their usefulness in normalisation of RT-qPCR analysis of the transcription of the HSV-1 gamma gB-1 gene and FUT5, a cellular gene induced by viral infection. The transcription of these genes was monitored in a TaqMan-based real time RT-PCR system over a 24h interval of virus infection of human embryonic lung fibroblasts. The levels of gB-1 and FUT5 RNA were normalised via difference in the threshold cycle (deltaC(t)) values relative to each and one of the housekeeping genes or calculated in relation to the number of infected cells without any further normalisation. The levels of RNA encoded by beta-actin or GAPDH were found to vary by several orders of magnitude during HSV-1 infection, introducing large errors in the estimation of the gB-1 and FUT5 RNA levels. In contrast, the variation of C(t) values for 18S rRNA was less than one cycle during 24h period of HSV-1 infection. The FUT5 and gB-1 RNA figures obtained by DeltaC(t) normalisation relative 18S rRNA were identical to those calculated in relation to the number of infected cells. These data recommend 18S rRNA for normalisation in HSV-1-infected human cells but discourage the use of beta-actin and GAPDH RNA for this purpose. By applying these procedures, it was shown that the transcription of FUT5 was increased by 50-fold 5-24h after HSV-1 infection and 200-fold by the inhibition of viral DNA replication in HSV-infected cells.

Cloning and sequencing of nineteen transcript isoforms of the human alpha2,3-sialyltransferase gene, ST3Gal III; its genomic organisation and expression in human tissues.

The recruitment of human peripheral blood leukocytes (PBL) to sites of infection and inflammation requires the surface expression of Sialyl Lewis x glycoconjugates (SLe(x)) on white blood cells and their interaction with E- and P-selectins on activated endothelial cells. E-selectin has additionally been shown to interact with the sialyl Lewis a (SLe(a)) epitope. Human ST3Gal III codes for an alpha2,3-sialyltransferase involved in the biosynthesis of both SLe(a) and SLe(x) epitopes, although the latter with a lower efficiency. We have cloned and sequenced human ST3Gal III gene transcripts from human peripheral blood leukocytes, covering the coding region of this gene. Within our clones we isolated 19 different transcripts with a wide variety of deletions from 45 to 896 nucleotides, and insertions of 26 to 173 nucleotides. Among the insertions we identified two new exons (E3, E6). In order to map and characterise the ST3Gal III gene we used the GenBank database and "computer-cloned" and characterised the genomic organisation of the ST3Gal III gene. The coding sequences of the ST3Gal III gene stretch over a gene sequence of approximately 223 Kb comprised of 15 exons. RT-PCR and laser-induced fluorescent capillary electrophoresis (LIF-CE) were used to examine the expression of this gene in twenty-one human tissues, which showed a highly specific tissue expression pattern. Neural and muscular tissues showed the most complex patterns and were distinctly different from all other tissues examined.