Molecular basis of the globoside-deficient P(k) blood group phenotype. Identification of four inactivating mutations in the UDP-N-acetylgalactosamine: globotriaosylceramide 3-beta-N-acetylgalactosaminyltransferase gene

Globoside and the mucosal pH mediate parvovirus B19 entry through the epithelial barrier

Parvovirus B19 (B19V) is transmitted primarily via the respiratory route, however, the mechanism involved remains unknown. B19V targets a restricted receptor expressed in erythroid progenitor cells in the bone marrow. However, B19V shifts the receptor under acidic conditions and targets the widely expressed globoside. The pH-dependent interaction with globoside may allow virus entry through the naturally acidic nasal mucosa. To test this hypothesis, MDCK II cells and well-differentiated human airway epithelial cell (hAEC) cultures were grown on porous membranes and used as models to study the interaction of B19V with the epithelial barrier. Globoside expression was detected in polarized MDCK II cells and the ciliated cell population of well-differentiated hAEC cultures. Under the acidic conditions of the nasal mucosa, virus attachment and transcytosis occurred without productive infection. Neither virus attachment nor transcytosis was observed under neutral pH conditions or in globoside knockout cells, demonstrating the concerted role of globoside and acidic pH in the transcellular transport of B19V. Globoside-dependent virus uptake involved VP2 and occurred by a clathrin-independent pathway that is cholesterol and dynamin-dependent. This study provides mechanistic insight into the transmission of B19V through the respiratory route and reveals novel vulnerability factors of the epithelial barrier to viruses.

Comparative analysis of antigen coding genes in 15 red cell blood group systems of Yunnan Yi nationality in China: A cross-sectional study

Introduction

There are few analyses of the 15 red blood group system antigen coding genes found in the Yunnan Yi nationality. This has caused many poteintial dangers relating to clinical blood transfusion. In this report, the coding genes and distribution of 15 blood group antigens system in the Yi nationality were tested and compared with those of Han nationality and other ethnic minorities.

Methods

The samples came from the healthy subjects in the first people's Hospital of Qujing, Yunnan Province. Two hundred and three Yunnan Yi and 197 Han nationality individuals were included. Thirty-three blood group antigens with a low frequency from the 15 blood group systems of Yunnan Yi blood donors were genotyped and analyzed by PCR-SSP. Sanger sequencing was used to detect A4GALT from the Yunnan Yi nationality. The χ 2 test was used to analyze observed and expected values of gene distribution to verify conformation to the Hardy-Weinberg equilibrium law. Fisher's exact test was used to analyze gene frequency distribution, and the statistical significance was set at p < 0.05.

Results

The ABO blood group examination results for the Yi nationality and the local Han nationality in Qujing City, Yunnan Province, showed the majority were type A and type O, while the least prevalent was type AB. RhD+ accounts for more than 98% of the Yi and Han populations. There was a significant difference in ABO blood group antigen distribution between these two nationalities (p < 0.05), but there was no significant difference in the composition ratio of D antigen in the Rh blood group system (p > 0.05). Compared with Tibetan (Tibet), Zhuang (Nanning), and Dong (Guangxi), the gene distribution frequencies of Rh blood group system phenotype CC were significantly lower in the Yunnan Yi nationality (p < 0.05). There were significant differences in six erythrocyte phenotypic antigens in the Yi nationality in Yunnan compared with Han nationality, such as LW(a-b-), JK(a-b+), MMSs, Di(a-b+), Wr(a-b-), and Kp(a-b+) (p < 0.05). There were gene phenotypes with a low frequency in the four rare blood group systems: LW, MNS, Wright, and Colton. Several different mutation types occurred in the P1PK blood group system's A4GALT gene.

Conclusion

Yunnan Yi nationality has a unique genetic background. There are some significantly different distributions of blood group system genes with a low frequency in different regions and groups in China. Multiple mutations in the A4GALT gene of the P1PK blood group system may be related to their environment and ethnic evolution.

Insilico Functional Analysis of Genome-Wide Dataset From 17,000 Individuals Identifies Candidate Malaria Resistance Genes Enriched in Malaria Pathogenic Pathways

Recent genome-wide association studies (GWASs) of severe malaria have identified several association variants. However, much about the underlying biological functions are yet to be discovered. Here, we systematically predicted plausible candidate genes and pathways from functional analysis of severe malaria resistance GWAS summary statistics (N = 17,000) meta-analysed across 11 populations in malaria endemic regions. We applied positional mapping, expression quantitative trait locus (eQTL), chromatin interaction mapping, and gene-based association analyses to identify candidate severe malaria resistance genes. We further applied rare variant analysis to raw GWAS datasets (N = 11,000) of three malaria endemic populations including Kenya, Malawi, and Gambia and performed various population genetic structures of the identified genes in the three populations and global populations. We performed network and pathway analyses to investigate their shared biological functions. Our functional mapping analysis identified 57 genes located in the known malaria genomic loci, while our gene-based GWAS analysis identified additional 125 genes across the genome. The identified genes were significantly enriched in malaria pathogenic pathways including multiple overlapping pathways in erythrocyte-related functions, blood coagulations, ion channels, adhesion molecules, membrane signalling elements, and neuronal systems. Our population genetic analysis revealed that the minor allele frequencies (MAF) of the single nucleotide polymorphisms (SNPs) residing in the identified genes are generally higher in the three malaria endemic populations compared to global populations. Overall, our results suggest that severe malaria resistance trait is attributed to multiple genes, highlighting the possibility of harnessing new malaria therapeutics that can simultaneously target multiple malaria protective host molecular pathways.

Biochemical and Functional Characterization of GALT8, an Arabidopsis GT31 β-(1,3)-Galactosyltransferase That Influences Seedling Development

Arabinogalactan-proteins (AGPs) are members of the hydroxyproline-rich glycoprotein (HRGP) superfamily, a group of highly diverse proteoglycans that are present in the cell wall, plasma membrane as well as secretions of almost all plants, with important roles in many developmental processes. The role of GALT8 (At1g22015), a Glycosyltransferase-31 (GT31) family member of the Carbohydrate-Active Enzyme database (CAZy), was examined by biochemical characterization and phenotypic analysis of a galt8 mutant line. To characterize its catalytic function, GALT8 was heterologously expressed in tobacco leaves and its enzymatic activity tested. GALT8 was shown to be a β-(1,3)-galactosyltransferase (GalT) that catalyzes the synthesis of a β-(1,3)-galactan, similar to the in vitro activity of KNS4/UPEX1 (At1g33430), a homologous GT31 member previously shown to have this activity. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) confirmed the products were of 2-6 degree of polymerisation (DP). Previous reporter studies showed that GALT8 is expressed in the central and synergid cells, from whence the micropylar endosperm originates after the fertilization of the central cell of the ovule. Homozygous mutants have multiple seedling phenotypes including significantly shorter hypocotyls and smaller leaf area compared to wild type (WT) that are attributable to defects in female gametophyte and/or endosperm development. KNS4/UPEX1 was shown to partially complement the galt8 mutant phenotypes in genetic complementation assays suggesting a similar but not identical role compared to GALT8 in β-(1,3)-galactan biosynthesis. Taken together, these data add further evidence of the important roles GT31 β-(1,3)-GalTs play in elaborating type II AGs that decorate AGPs and pectins, thereby imparting functional consequences on plant growth and development.

Understanding the genetic determinant of severity in viral diseases: a case of SARS-Cov-2 infection

Background

Numerous research studies have identified specific human gene variants that affect enhanced susceptibility to viral infections. More recently is the current pandemic where the SARS-CoV-2 infection has shown a high degree of person-to-person clinical variability. A wide range of disease severity occurs in the patients' experiences, from asymptomatic cases, mild infections to serious life threatening conditions requiring admission into the intensive care unit (ICU).

Main body of the abstract

Although, it is generally reported that age and co-morbidities contribute significantly to the variations in the clinical outcome of the scourge of COVID-19, a hypothetical question of the possibility of genetic involvement in the susceptibility and severity of the disease arose when some unique severe outcomes were seen among young patients with no co-morbidity. The role human genetics play in clinical response to the viral infections is scarcely understood; however, several ongoing researches all around the world are currently focusing on possible genetic factors. This review reports the possible genetic factors that have been widely studied in defining the severity of viral infections using SARS-CoV-2 as a case study. These involve the possible involvements of ACE2, HLA, and TLR genes such as TLR7 and TLR3 in the presentation of a more severe condition.

Short conclusion

Understanding these variations could help to inform efforts to identify people at increased risk of infection outbreaks through genetic diagnosis of infections by locating disease genes or mutations that predispose patients to severe infection. This will also suggest specific targets for therapy and prophylaxis.

Common genetic variation in humans impacts in vitro susceptibility to SARS-CoV-2 infection

The host response to SARS-CoV-2, the etiologic agent of the COVID-19 pandemic, demonstrates significant inter-individual variability. In addition to showing more disease in males, the elderly, and individuals with underlying comorbidities, SARS-CoV-2 can seemingly render healthy individuals with profound clinical complications. We hypothesize that, in addition to viral load and host antibody repertoire, host genetic variants also impact vulnerability to infection. Here we apply human induced pluripotent stem cell (hiPSC)-based models and CRISPR-engineering to explore the host genetics of SARS-CoV-2. We demonstrate that a single nucleotide polymorphism (rs4702), common in the population at large, and located in the 3'UTR of the protease FURIN, impacts alveolar and neuron infection by SARS-CoV-2 in vitro. Thus, we provide a proof-of-principle finding that common genetic variation can impact viral infection, and thus contribute to clinical heterogeneity in SARS-CoV-2. Ongoing genetic studies will help to better identify high-risk individuals, predict clinical complications, and facilitate the discovery of drugs that might treat disease.

A phylogenetic view and functional annotation of the animal β1,3-glycosyltransferases of the GT31 CAZy family

The formation of β1,3-linkages on animal glycoconjugates is catalyzed by a subset of β1,3-glycosyltransferases grouped in the Carbohydrate-Active enZYmes family glycosyltransferase-31 (GT31). This family represents an extremely diverse set of β1,3-N-acetylglucosaminyltransferases [B3GNTs and Fringe β1,3-N-acetylglucosaminyltransferases], β1,3-N-acetylgalactosaminyltransferases (B3GALNTs), β1,3-galactosyltransferases [B3GALTs and core 1 β1,3-galactosyltransferases (C1GALTs)], β1,3-glucosyltransferase (B3GLCT) and β1,3-glucuronyl acid transferases (B3GLCATs or CHs). The mammalian enzymes were particularly well studied and shown to use a large variety of sugar donors and acceptor substrates leading to the formation of β1,3-linkages in various glycosylation pathways. In contrast, there are only a few studies related to other metazoan and lower vertebrates GT31 enzymes and the evolutionary relationships of these divergent sequences remain obscure. In this study, we used bioinformatics approaches to identify more than 920 of putative GT31 sequences in Metazoa, Fungi and Choanoflagellata revealing their deep ancestry. Sequence-based analysis shed light on conserved motifs and structural features that are signatures of all the GT31. We leverage pieces of evidence from gene structure, phylogenetic and sequence-based analyses to identify two major subgroups of GT31 named Fringe-related and B3GALT-related and demonstrate the existence of 10 orthologue groups in the Urmetazoa, the hypothetical last common ancestor of all animals. Finally, synteny and paralogy analysis unveiled the existence of 30 subfamilies in vertebrates, among which 5 are new and were named C1GALT2, C1GALT3, B3GALT8, B3GNT10 and B3GNT11. Altogether, these various approaches enabled us to propose the first comprehensive analysis of the metazoan GT31 disentangling their evolutionary relationships.

Emergence and significance of carbohydrate-specific antibodies

Carbohydrate-specific antibodies are widespread among all classes of immunoglobulins. Despite their broad occurrence, little is known about their formation and biological significance. Carbohydrate-specific antibodies are often classified as natural antibodies under the assumption that they arise without prior exposure to exogenous antigens. On the other hand, various carbohydrate-specific antibodies, including antibodies to ABO blood group antigens, emerge after the contact of immune cells with the intestinal microbiota, which expresses a vast diversity of carbohydrate antigens. Here we explore the development of carbohydrate-specific antibodies in humans, addressing the definition of natural antibodies and the production of carbohydrate-specific antibodies upon antigen stimulation. We focus on the significance of the intestinal microbiota in shaping carbohydrate-specific antibodies not just in the gut, but also in the blood circulation. The structural similarity between bacterial carbohydrate antigens and surface glycoconjugates of protists, fungi and animals leads to the production of carbohydrate-specific antibodies protective against a broad range of pathogens. Mimicry between bacterial and human glycoconjugates, however, can also lead to the generation of carbohydrate-specific antibodies that cross-react with human antigens, thereby contributing to the development of autoimmune disorders.

Multiple miscarriages in two sisters of Thai origin with the rare Pk phenotype caused by a novel nonsense mutation at the B3GALNT1 locus

OBJECTIVES

To determine the genetic background underlying the P^k phenotype in two Thai sisters suffering from multiple spontaneous abortions.

BACKGROUND

The P antigen is carried by globoside, an abundant glycosphingolipid in the red blood cell (RBC) membrane. Inactivating mutations in the 3-β-N-acetylgalactosaminyltransferase gene (B3GALNT1) give rise to the rare P^k phenotype, which lack the P and PX2 antigens. Consequently, naturally occurring anti-P may cause recurrent miscarriages following the cytotoxic attack of the globoside-rich fetal portion of the placenta.

METHODS/MATERIALS

P/P1/PX2/P^k antigens on RBCs and their corresponding antibodies were detected by haemagglutination and flow cytometry. The B3GALNT1 coding region was sequenced, and an allele-specific polymerase chain reaction (PCR) was developed.

RESULTS

The two sisters had suffered 8 and 11 miscarriages, most of which occurred in the first trimester. Anti-P and anti-PX2 were identified in their plasmas, and the RBCs typed as P-PX2-P^k +, i.e. had the P^k phenotype. Sequencing revealed homozygosity for a nonsense mutation, c.420T>G, in B3GALNT1. This substitution introduces a premature stop codon, p.Tyr140Ter, which is predicted to abolish enzymatic activity. Screening of 384 Thai donors indicated an allele frequency of 0·13%.

CONCLUSION

We describe a novel nonsense mutation (c.420T>G) in B3GALNT1 (GLOB*01N·13), which was added to the 12 alleles already known in the GLOB system.

ABO blood group A transferases catalyze the biosynthesis of FORS blood group FORS1 antigen upon deletion of exon 3 or 4

Evolutionarily related ABO and GBGT1 genes encode, respectively, A and B glycosyltransferases (AT and BT) and Forssman glycolipid synthase (FS), which catalyze the biosynthesis of A and B, and Forssman (FORS1) oligosaccharide antigens responsible for the ABO and FORS blood group systems. Humans are a Forssman antigen-negative species; however, rare individuals with A_pae phenotype express FORS1 on their red blood cells. We previously demonstrated that the replacement of the LeuGlyGly tripeptide sequence at codons 266 to 268 of human AT with GBGT1-encoded FS-specific GlyGlyAla enabled the enzyme to produce FORS1 antigen, although the FS activity was weak. We searched for additional molecular mechanisms that might allow human AT to express FORS1. A variety of derivative expression constructs of human AT were prepared. DNA was transfected into COS1 (B3GALNT1) cells, and cell-surface expression of FORS1 was immunologically monitored. To our surprise, the deletion of exon 3 or 4, but not of exon 2 or 5, of human AT transcripts bestowed moderate FS activity, indicating that the A allele is inherently capable of producing a protein with FS activity. Because RNA splicing is frequently altered in cancer, this mechanism may explain, at least partially, the appearance of FORS1 in human cancer. Furthermore, strong FS activity was attained, in addition to AT and BT activities, by cointroducing 1 of those deletions and the GlyGlyAla substitution, possibly by the synergistic effects of altered intra-Golgi localization/conformation by the former and modified enzyme specificity by the latter.

Human Genetic Determinants of Viral Diseases

Much progress has been made in the identification of specific human gene variants that contribute to enhanced susceptibility or resistance to viral diseases. Herein we review multiple discoveries made with genome-wide or candidate gene approaches that have revealed significant insights into virus-host interactions. Genetic factors that have been identified include genes encoding virus receptors, receptor-modifying enzymes, and a wide variety of innate and adaptive immunity-related proteins. We discuss a range of pathogenic viruses, including influenza virus, respiratory syncytial virus, human immunodeficiency virus, human T cell leukemia virus, human papilloma virus, hepatitis B and C viruses, herpes simplex virus, norovirus, rotavirus, parvovirus, and Epstein-Barr virus. Understanding the genetic underpinnings that affect infectious disease outcomes should allow tailored treatment and prevention approaches in the future.

Identification of the Molecular and Genetic Basis of PX2, a Glycosphingolipid Blood Group Antigen Lacking on Globoside-deficient Erythrocytes

The x2 glycosphingolipid is expressed on erythrocytes from individuals of all common blood group phenotypes and elevated on cells of the rare P/P1/P(k)-negative p blood group phenotype. Globoside or P antigen is synthesized by UDP-N-acetylgalactosamine:globotriaosyl-ceramide 3-β-N-acetylgalactosaminyltransferase encoded by B3GALNT1. It is the most abundant non-acid glycosphingolipid on erythrocytes and displays the same terminal disaccharide, GalNAcβ3Gal, as x2. We encountered a patient with mutations in B3GALNT1 causing the rare P-deficient P1 (k) phenotype and whose pretransfusion plasma was unexpectedly incompatible with p erythrocytes. The same phenomenon was also noted in seven other unrelated P-deficient individuals. Thin-layer chromatography, mass spectrometry, and flow cytometry were used to show that the naturally occurring antibodies made by p individuals recognize x2 and sialylated forms of x2, whereas x2 is lacking on P-deficient erythrocytes. Overexpression of B3GALNT1 resulted in synthesis of both P and x2. Knockdown experiments with siRNA against B3GALNT1 diminished x2 levels. We conclude that x2 fulfills blood group criteria and is synthesized by UDP-N-acetylgalactosamine: globotriaosylceramide 3-β-N-acetylgalactosaminyltransferase. Based on this linkage, we proposed that x2 joins P in the GLOB blood group system (ISBT 028) and is renamed PX2 (GLOB2). Thus, in the absence of a functional P synthase, neither P nor PX2 are formed. As a consequence, naturally occurring anti-P and anti-PX2 can be made. Until the clinical significance of anti-PX2 is known, we also recommend that rare P1 (k) or P2 (k) erythrocyte units are preferentially selected for transfusion to P(k) patients because p erythrocytes may pose a risk for hemolytic transfusion reactions due to their elevated PX2 levels.

Human genetic disorders of sphingolipid biosynthesis

Monogenic defects of sphingolipid biosynthesis have been recently identified in human patients. These enzyme deficiencies affect the synthesis of sphingolipid precursors, ceramides or complex glycosphingolipids. They are transmitted as autosomal recessive or dominant traits, and their resulting phenotypes often replicate the abnormalities seen in murine models deficient for the corresponding enzymes. In quite good agreement with the known critical roles of sphingolipids in cells from the nervous system and the epidermis, these genetic defects clinically manifest as neurological disorders, including paraplegia, epilepsy or peripheral neuropathies, or present with ichthyosis. The present review summarizes the genetic alterations, biochemical changes and clinical symptoms of this new group of inherited metabolic disorders. Hypotheses regarding the molecular pathophysiology and potential treatments of these diseases are also discussed.

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.

Molecular genetic basis of the human Forssman glycolipid antigen negativity

Forssman heterophilic glycolipid antigen has structural similarity to the histo-blood group A antigen, and the GBGT1 gene encoding the Forssman glycolipid synthetase (FS) is evolutionarily related to the ABO gene. The antigen is present in various species, but not in others including humans. We have elucidated the molecular genetic basis of the Forssman antigen negativity in humans. In the human GBGT1 gene, we identified two common inactivating missense mutations (c.688G>A [p.Gly230Ser] and c.887A>G [p.Gln296Arg]). The reversion of the two mutations fully restored the glycosyltransferase activity to synthesize the Forssman antigen in vitro. These glycine and glutamine residues are conserved among functional GBGT1 genes in Forssman-positive species. Furthermore, the glycine and serine residues represent those at the corresponding position of the human blood group A and B transferases with GalNAc and galactose specificity, respectively, implicating the crucial role the glycine residue may play in the FS α1,3-GalNAc transferase activity.

Blood groups and susceptibility to virus infection: new developments

PURPOSE OF REVIEW

Histo-blood group antigens belonging to the P1PK and GLOB blood group systems are involved in bacterial infections, but a substantial body of evidence is emerging that some of these glycosphingolipids play a role in HIV infection. These recent findings have raised additional questions regarding the possible role of the P/Gb3 histo-blood group antigen in HIV-1 infection.

RECENT FINDINGS

Early studies implicated a number of glycosphingolipids able to interact with HIV envelope glycoprotein 120. It has been recently reported that cellular or soluble P/Gb3 histo-blood group antigen provides protection from HIV-1 infection. This resistance mechanism appears to be mediated through inhibition of fusion of the HIV-1 envelope to the cell target membrane. Protection has been shown to be provided to both HIV-1 X4 and R5 tropic strains. Indeed, an inverse correlation has been documented between the expression of P/Gb3 on the cellular membrane and susceptibility to HIV infection. Moreover, soluble P/Gb3 analogues have been shown to inhibit HIV infection.

SUMMARY

The P/Gb3 histo-blood group antigen is the first described cell surface expressed natural resistance factor for prevention of HIV infection. Increased expression of P/Gb3 correlates to decreased HIV infection, whereas decreased or absent P/Gb3 increases HIV susceptibility. Soluble P/Gb3 analogues can inhibit HIV by two mechanisms: direct inhibition of the free virus and inhibition of viral entry. Future development of soluble P/Gb3 analogues, pharmacologic means of increasing cell surface expression of P/Gb3 on HIV susceptible target cells or both may result in novel therapeutic modalities for the prevention and eradication of HIV/AIDS.

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.

The human Pk histo-blood group antigen provides protection against HIV-1 infection

Several human histo-blood groups are glycosphingolipids, including P/P1/Pk. Glycosphingolipids are implicated in HIV-host-cell-fusion and some bind to HIV-gp120 in vitro. Based on our previous studies on Fabry disease, where Pk accumulates and reduces infection, and a soluble Pk analog that inhibits infection, we investigated cell surface–expressed Pk in HIV infection. HIV-1 infection of peripheral blood–derived mononuclear cells (PBMCs) from otherwise healthy persons, with blood group P1k, where Pk is overexpressed, or blood group p, that completely lacks Pk, were compared with draw date–matched controls. Fluorescence-activated cell sorter analysis and/or thin layer chromatography were used to verify Pk levels. P1k PBMCs were highly resistant to R5 and X4 HIV-1 infection. In contrast, p PBMCs showed 10- to 1000-fold increased susceptibility to HIV-1 infection. Surface and total cell expression of Pk, but not CD4 or chemokine coreceptor expression, correlated with infection. Pk liposome–fused cells and CD4+ HeLa cells manipulated to express high or low Pk levels confirmed a protective effect of Pk. We conclude that Pk expression strongly influences susceptibility to HIV-1 infection, which implicates Pk as a new endogenous cell-surface factor that may provide protection against HIV-1 infection.

Identification of a novel group of putative Arabidopsis thaliana beta-(1,3)-galactosyltransferases

To begin biochemical and molecular studies on the biosynthesis of the type II arabinogalactan chains on arabinogalactan-proteins (AGPs), we adopted a bioinformatic approach to identify and systematically characterise the putative galactosyltransferases (GalTs) responsible for synthesizing the beta-(1,3)-Gal linkage from CAZy GT-family-31 from Arabidopsis thaliana. These analyses confirmed that 20 members of the GT-31 family contained domains/motifs typical of biochemically characterised beta-(1,3)-GTs from mammalian systems. Microarray data confirm that members of this family are expressed throughout all tissues making them likely candidates for the assembly of the ubiquitously found AGPs. One member, At1g77810, was selected for further analysis including location studies that confirmed its presence in the Golgi and preliminary enzyme substrate specificity studies that demonstrated beta-(1,3)-GalT activity. This bioinformatic/molecular study of CAZy GT-family-31 was validated by the recent report of Strasser et al. (Plant Cell 19:2278-2292, 2007) that another member of this family (At1g26810; GALT1) encodes a beta-(1,3)-GalT involved in the biosynthesis of the Lewis a epitope of N-glycans in Arabidopsis thaliana.

Sequence variation in the 5' untranslated region of the human A4GALT gene is associated with, but does not define, the P1 blood-group polymorphism

BACKGROUND AND OBJECTIVE

The gene responsible for the P1 polymorphism of the P blood-group system remains unidentified, although the A4GALT gene, whose product is responsible for the production of P(k), has been implicated. No coding differences in A4GALT account for the P1 polymorphism, but homozygosity for two polymorphisms (-551_-550insC and -160A>G) in the 5' untranslated region of the gene has been reported to be unique to Japanese P1- individuals. This study aimed to confirm this correlation in a larger number of British individuals.

MATERIALS AND METHODS

Serologically confirmed P1+ (n = 35) and P1- (n = 15) individuals were genotyped for polymorphisms in the 5' untranslated region of A4GALT.

RESULTS

In addition to those previously reported, a further polymorphism, -164C>T, was identified. All P1- individuals were homozygous for -551_-550insC and -160G as compared with 10 of 35 (29%) P1+ individuals (P = 0.000003, two-tailed Fisher's exact test). Allele frequencies for all polymorphisms and estimated haplotype frequencies across the region differed significantly between P1+ and P1- groups.

CONCLUSIONS

Homozygosity for the A4GALT-551_-550insC and -160G allele is significantly associated with, but not restricted to, the P1- phenotype. No single A4GALT genotype or haplotype was unique to P1- individuals. Thus, A4GALT cannot be unequivocally confirmed as the gene responsible for the P1 phenotype.

Chemoenzymatic synthesis of glycan libraries

The expanding interest for carbohydrates and glycoconjugates in cell communication has led to an increased demand of these structures for biological studies. Complicated chemical strategies in glycan synthesis are now more frequently replaced by regio- and stereo-specific enzymes. The exploration of microbial resources and improved production of mammalian enzymes have established glycosyltransferases as an efficient complementary tool for glycan synthesis. In this chapter, we demonstrate the feasibility of preparative enzymatic synthesis of different categories of glycans, such as blood group and tumor-associated poly-N-acetyllactosamines antigens, ganglio-oligosaccharides, N- and O-glycans. The enzymatic approach has generated over 100 novel oligosaccharides in amounts allowing milligram to gram distribution to many researchers in the field. Our diverse library has also formed the foundation for the successful developments of both the noncovalent enzyme-linked immunosorbent assay glycan array and the covalent printed glycan microarray.

Two previously proposed P1/P2-differentiating and nine novel polymorphisms at the A4GALT (Pk) locus do not correlate with the presence of the P1 blood group antigen

Background

The molecular genetics of the P blood group system and the absence of P1 antigen in the p phenotype are still enigmatic. One theory proposes that the same gene encodes for both the P1 and P^k glycosyltransferases, but no polymorphisms in the coding region of the P^k gene explain the P₁/P₂ phenotypes. We investigated the potential regulatory regions up- and downstream of the A4GALT (P^k) gene exons.

Results

P₁ (n = 18) and P₂ (n = 9) samples from donors of mainly Swedish descent were analysed by direct sequencing of PCR-amplified 5'- and 3'-fragments surrounding the P^k coding region. Seventy-eight P₁ and P₂ samples were investigated with PCR using allele-specific primers (ASP) for two polymorphisms previously proposed as P₂-related genetic markers (-551_-550insC, -160A>G). Haplotype analysis of single nucleotide polymorphisms was also performed with PCR-ASP. In ~1.5 kbp of the 3'-untranslated region one new insertion and four new substitutions compared to a GenBank sequence (AL049757) were found. In addition to the polymorphisms at positions -550 and -160, one insertion, two deletions and one substitution were found in ~1.0 kbp of the 5'-upstream region. All 20 P₂ samples investigated with PCR-ASP were homozygous for -550insC. However, so were 18 of the 58 P₁ samples investigated. Both the 20 P₂ and the 18 P₁ samples were also homozygous for -160G.

Conclusion

The proposed P₂-specific polymorphisms, -551_-550insC and -160G, found in P₂ samples in a Japanese study were found here in homozygous form in both P₁ and P₂ donors. Since P² is the null allele in the P blood group system it is difficult to envision how these mutations would cause the P₂ phenotype. None of the novel polymorphisms reported in this study correlated with P₁/P₂ status and the P1/p mystery remains unsolved.

Human blood group genes 2004: chromosomal locations and cloning strategies

Of the 29 human blood group system genes, 27 have been localized to 14 autosomes and 2 have been assigned to the X chromosome. It is remarkable that 28 of the 29 system genes have now been localized to a single cytogenetic band on a specific chromosome. In this review, we summarize the chromosomal locations and cloning strategies used for those genes encoding blood group systems. We highlight such information about the 3 most recently defined blood group systems (I, GLOB, and GIL). In addition, we provide new information about 2 older blood group systems (SC and RAPH) whose polymorphisms have been defined in cloned genes.

Genetic heterogeneity at the glycosyltransferase loci underlying the GLOB blood group system and collection*

The aim of this study was to further explore the molecular genetic bases of the clinically important but rare blood group phenotypes p, P(1) (k) and P(2) (k) by analysis of the 4-alpha-galactosyltransferase (P(k)) and 3-beta-N-acetylgalactosaminyltransferase (P) genes responsible for synthesis of the related P(k) (Gb(3)) and P (Gb(4)) antigens respectively. Lack of these glycolipid moieties is associated with severe transfusion reactions and recurrent spontaneous abortions but also offers immunity against certain infectious agents. Blood samples from 20 p and 11 P(1) (k) or P(2) (k) individuals of different geographic and ethnic origin were investigated. DNA sequencing by capillary electrophoresis was performed following amplification of the coding regions in the P(k) or P genes. In the P(k) gene, nine novel and five previously described mutations were detected. One of the newly found mutations introduced an immediate stop, five shifted the reading frame introducing premature stop codons and three were missense mutations causing amino acid substitutions in conserved regions of the transferase. Four new and two previously described mutations in the P gene were found. Three of the novel alleles reported here carried nonsense mutations whilst the fourth allele had a missense mutation. The finding of 13 novel mutations in 14 alleles emphasizes further the genetic heterogeneity at the glycosyltransferase loci underlying the GLOB blood group system and collection.

Additional molecular bases of the clinically important p blood group phenotype

BACKGROUND

The purpose of this study was to explore the molecular basis of the p phenotype by analysis of the recently cloned 4-alpha-galactosyltransferase gene responsible for synthesis of Pk (Gb3) antigen.

STUDY DESIGN AND METHODS

Forty samples from individuals of eight different nationalities were investigated by serologic methods and DNA sequencing of the Pk gene.

RESULTS

Ten different Pk-null alleles, of which 6 are novel, were encountered. The 29 Swedes were homozygous for M183K or G187D, with the former as the predominant allele. Three Israelis were homozygous for a single-nucleotide deletion at codon 219 that shifts and truncates the reading frame by 5 amino acids. Two Italians were homozygous for a triplet deletion causing F81del, while an English donor was heterozygous for F81del but also carried another allele with a combined deletion and insertion. A Pole was heterozygous for alleles with either a single-base deletion at codon 257 or a mutation causing S97L. A Norwegian person and a Japanese person were homozygous for single-base insertions causing a premature stop at codon 282 or extension of the protein by 92 residues, respectively. In 2 samples no mutations were detected.

CONCLUSION

The genetic heterogeneity underlying the p phenotype is further emphasized by this study. To date, 11 p-specific mutations have been found in 14 distinct alleles.

Drosophila egghead encodes a beta 1,4-mannosyltransferase predicted to form the immediate precursor glycosphingolipid substrate for brainiac

The neurogenic Drosophila genes brainiac and egghead are essential for epithelial development in the embryo and in oogenesis. Analysis of egghead and brainiac mutants has led to the suggestion that the two genes function in a common signaling pathway. Recently, brainiac was shown to encode a UDP-N-acetylglucosamine:beta Man beta 1,3-N-acetylglucosaminyltransferase (beta 3GlcNAc-transferase) tentatively assigned a key role in biosynthesis of arthroseries glycosphingolipids and forming the trihexosylceramide, GlcNAc beta 1-3Man beta 1-4Glc beta 1-1Cer. In the present study we demonstrate that egghead encodes a Golgi-located GDP-mannose:beta Glc beta 1,4-mannosyltransferase tentatively assigned a biosynthetic role to form the precursor arthroseries glycosphingolipid substrate for Brainiac, Man beta 1-4Glc beta 1-1Cer. Egghead is unique among eukaryotic glycosyltransferase genes in that homologous genes are limited to invertebrates, which correlates with the exclusive existence of arthroseries glycolipids in invertebrates. We propose that brainiac and egghead function in a common biosynthetic pathway and that inactivating mutations in either lead to sufficiently early termination of glycolipid biosynthesis to inactivate essential functions mediated by glycosphingolipids.

The Drosophila gene brainiac encodes a glycosyltransferase putatively involved in glycosphingolipid synthesis

The Drosophila genes fringe and brainiac exhibit sequence similarities to glycosyltransferases. Drosophila and mammalian fringe homologs encode UDP-N-acetylglucosamine:fucose-O-Ser beta1,3-N-acetylglucosaminyltransferases that modulate the function of Notch family receptors. The biological function of brainiac is less well understood. brainiac is a member of a large homologous mammalian beta3-glycosyltransferase family with diverse functions. Eleven distinct mammalian homologs have been demonstrated to encode functional enzymes forming beta1-3 glycosidic linkages with different UDP donor sugars and acceptor sugars. The putative mammalian homologs with highest sequence similarity to brainiac encode UDP-N-acetylglucosamine:beta1,3-N-acetylglucosaminyltransferases (beta3GlcNAc-transferases), and in the present study we show that brainiac also encodes a beta3GlcNAc-transferase that uses beta-linked mannose as well as beta-linked galactose as acceptor sugars. The inner disaccharide core structures of glycosphingolipids in mammals (Galbeta1-4Glcbeta1-Cer) and insects (Manbeta1-4Glcbeta1-Cer) are different. Both disaccharide glycolipids served as substrates for brainiac, but glycolipids of insect cells have so far only been found to be based on the GlcNAcbeta1-3Manbeta1-4Glcbeta1-Cer core structure. Infection of High Five(TM) cells with baculovirus containing full coding brainiac cDNA markedly increased the ratio of GlcNAcbeta1-3Manbeta1-4Glcbeta1-Cer glycolipids compared with Galbeta1-4Manbeta1-4Glcbeta1-Cer found in wild type cells. We suggest that brainiac exerts its biological functions by regulating biosynthesis of glycosphingolipids.