Purification of the Lewis blood-group gene associated alpha-3/4-fucosyltransferase from human milk: an enzyme transferring fucose primarily to type 1 and lactose-based oligosaccharide chains

Associations between human milk oligosaccharides and infant growth in a Bangladeshi mother-infant cohort

BACKGROUND

We aimed to estimate associations between human milk oligosaccharides (HMOs) and infant growth (length-for-age (LAZ) and weight-for-length (WLZ) z-scores) at 12 months postnatal age.

METHODS

In this secondary analysis of data from a maternal vitamin D trial in Dhaka, Bangladesh (N = 192), absolute concentrations of HMOs were measured in 13 ± 1 week(s) postpartum milk samples, infant anthropometric measurements were obtained soon after birth and at 12 months postpartum, and infant feeding was classified during 6 months postpartum. Associations between individual HMOs or HMO groups and LAZ or WLZ were estimated by multivariable linear regression adjusting for infant feeding pattern, maternal secretor status, and other potential confounders.

RESULTS

The concentrations of 6'sialyllactose, lacto-N-neotetraose, and the non-fucosylated non-sialylated HMOs were inversely associated with LAZ at 12 months of age, whereas the fucosylated non-sialylated HMO concentration was positively associated with LAZ at 12 months. These associations were robust in analyses restricted to infants who were primarily exclusively/predominantly fed human milk during the first 3 (or 6) months.

CONCLUSIONS

Since HMOs are both positively and negatively associated with postnatal growth, there is a need for randomized trials to estimate the causal benefits and risks of exogenously administered HMOs on infant growth and other health outcomes.

IMPACT

6'sialyllactose, lacto-N-neotetraose, and the non-fucosylated non-sialylated human milk oligosaccharides (HMOs) were inversely associated with length-for-age z-scores (LAZ) at 12 months, whereas the fucosylated non-sialylated HMO concentration was positively associated with LAZ at 12 months among Bangladeshi infants. Associations between individual and grouped HMOs with infant length growth at 12 months were as strong or stronger in analyses restricted to infants who were exclusively or predominantly fed human milk up to 3 (or 6) months. Randomized trials are needed to characterize the effects of specific HMOs on infant growth, particularly in countries where postnatal linear growth faltering is common.

Evolutionary bridges: how factors present in amniotic fluid and human milk help mature the gut

Necrotizing enterocolitis (NEC) continues to be a leading cause of morbidity and mortality in preterm infants. As modern medicine significantly improves the survival of extremely premature infants, the persistence of NEC underscores our limited understanding of its pathogenesis. Due to early delivery, a preterm infant's exposure to amniotic fluid (AF) is abruptly truncated. Replete with bioactive molecules, AF plays an important role in fetal intestinal maturation and preparation for contact with the environment, thus its absence during development of the intestine may contribute to increased susceptibility to NEC. Human milk (HM), particularly during the initial phases of lactation, is a cornerstone of neonatal intestinal defense. The concentrations and activities of several bioactive factors in HM parallel those of AF, suggesting continuity of protection. In this review, we discuss the predominant overlapping bioactive components of HM and AF, with an emphasis on those associated with intestinal growth or reduction of NEC.

Human Milk Oligosaccharides and Respiratory Syncytial Virus Infection in Infants

In infants worldwide, respiratory syncytial virus (RSV) is the leading cause of lower respiratory infections, including bronchiolitis, which is a major source of infant mortality. Bronchiolitis is the most common lower respiratory infection and the major cause of hospitalization in the first 6 mo of life. Infant responses to RSV infection are highly diverse, with symptoms varying from asymptomatic or mild to so severe as to require mechanical ventilation. Breastfed infants present a lower incidence and less severe forms of RSV lower respiratory infections. Among the multitude of human milk bioactive compounds, human milk oligosaccharides (hMOSs) are strong candidates for having a protective effect against RSV. hMOS reduces the viral load and the inflammatory signaling in cultured RSV-infected respiratory human cells. In addition to this direct effect, indirect mechanisms, notably gut microbiota composition and metabolism, have been proposed to mediate the protective effect of hMOS. Intake of infant formula containing synthetic hMOS has been shown to increase Bifidobacterium abundance and that of its metabolites, especially acetate, in infant feces and to reduce lower respiratory tract infections during the first year of life. Breastfeeding and the use of hMOS are promising approaches to protect against and treat RSV disease. Here, we review current evidence on the role of hMOS with regard to RSV infection and disease, attending to knowledge gaps and future research directions.

Multifunctional Benefits of Prevalent HMOs: Implications for Infant Health

Breastfeeding is the best source of nutrition during infancy and is associated with a broad range of health benefits. However, there remains a significant and persistent need for innovations in infant formula that will allow infants to access a wider spectrum of benefits available to breastfed infants. The addition of human milk oligosaccharides (HMOs) to infant formulas represents the most significant innovation in infant nutrition in recent years. Although not a direct source of calories in milk, HMOs serve as potent prebiotics, versatile anti-infective agents, and key support for neurocognitive development. Continuing improvements in food science will facilitate production of a wide range of HMO structures in the years to come. In this review, we evaluate the relationship between HMO structure and functional benefits. We propose that infant formula fortification strategies should aim to recapitulate a broad range of benefits to support digestive health, immunity, and cognitive development associated with HMOs in breastmilk. We conclude that acetylated, fucosylated, and sialylated HMOs likely confer important health benefits through multiple complementary mechanisms of action.

Gold standard for nutrition: a review of human milk oligosaccharide and its effects on infant gut microbiota

Human milk is the gold standard for nutrition of infant growth, whose nutritional value is mainly attributed to human milk oligosaccharides (HMOs). HMOs, the third most abundant component of human milk after lactose and lipids, are complex sugars with unique structural diversity which are indigestible by the infant. Acting as prebiotics, multiple beneficial functions of HMO are believed to be exerted through interactions with the gut microbiota either directly or indirectly, such as supporting beneficial bacteria growth, anti-pathogenic effects, and modulation of intestinal epithelial cell response. Recent studies have highlighted that HMOs can boost infants health and reduce disease risk, revealing potential of HMOs in food additive and therapeutics. The present paper discusses recent research in respect to the impact of HMO on the infant gut microbiome, with emphasis on the molecular basis of mechanism underlying beneficial effects of HMOs.

Bio-therapeutics from human milk: prospects and perspectives

Human milk is elixir for neonates and is a rich source of nutrients and beneficial microbiota required for infant growth and development. Its benefits prompted research into probing the milk components and their use as prophylactic or therapeutic agents. Culture-independent estimation of milk microbiome and high-resolution identification of milk components provide information, but a holistic purview of these research domains is lacking. Here, we review the current research on bio-therapeutic components of milk and simplified future directions for its efficient usage. Publicly available databases such as PubMed and Google scholar were searched for keywords such as probiotics and prebiotics related to human milk, microbiome and milk oligosaccharides. This was further manually curated for inclusion and exclusion criteria relevant to human milk and clinical efficacy. The literature was classified into subgroups and then discussed in detail to facilitate understanding. Although milk research is still in infancy, it is clear that human milk has many functions including protection of infants by passive immunization through secreted antibodies, and transfer of immune regulators, cytokines and bioactive peptides. Unbiased estimates show that the human milk carries a complex community of microbiota which serves as the initial inoculum for establishment of infant gut. Our search effectively screened for evidence that shows that milk also harbours many types of prebiotics such as human milk oligosaccharides which encourage growth of beneficial probiotics. The milk also trains the naive immune system of the infant by supplying immune cells and stimulatory factors, thereby strengthening mucosal and systemic immune system. Our systematic review would improve understanding of human milk and the inherent complexity and diversity of human milk. The interrelated functional role of human milk components especially the oligosaccharides and microbiome has been discussed which plays important role in human health.

Gut microbiota comparison of vaginally and cesarean born infants exclusively breastfed by mothers secreting α1-2 fucosylated oligosaccharides in breast milk

BACKGROUND

Exclusive breastfeeding promotes beneficial modifications on the microbiota of cesarean born infants, but little is known about the role of specific breast milk components in this modulation. Women with an active FUT2 gene (called secretors) secrete α1-2 fucosylated human milk oligosaccharides (HMOs), which promote Bifidobacterium in the infant's gut and may modulate the microbiota of cesarean born infants.

OBJECTIVE

To compare the microbiota composition of cesarean and vaginally born infants breastfed by secretor mothers.

METHODS

Maternal secretor status was determined by the occurrence of 4 different α1-2 fucosylated HMOs in breast milk by LC-MS. The fecal microbiota composition from cesarean and vaginally born infants was analyzed by 16S rRNA gene sequencing and qPCR, stratified by the maternal secretor status, and compared.

RESULTS

Alpha and beta diversity were not significantly different in cesarean born, secretor-fed infants (CSe+) compared to vaginally born, secretor-fed infants (VSe+). There were no significant differences in the fecal relative abundance of Bifidobacterium between CSe+ and VSe+ infants, but the prevalence of the species B. longum was lower in CSe+. The fecal relative abundance of Bacteroides was also lower, while Akkermansia and Kluyvera were higher in CSe+ infants.

CONCLUSION

Cesarean and vaginally born infants fed with breast milk containing the α1-2 fucosylated HMOs fraction present similar amounts of Bifidobacterium in the feces, but differences are observed in other members of the microbiota.

Effects of Human Milk Oligosaccharides on the Adult Gut Microbiota and Barrier Function

Human milk oligosaccharides (HMOs) shape the gut microbiota in infants by selectively stimulating the growth of bifidobacteria. Here, we investigated the impact of HMOs on adult gut microbiota and gut barrier function using the Simulator of the Human Intestinal Microbial Ecosystem (SHIME®), Caco2 cell lines, and human intestinal gut organoid-on-chips. We showed that fermentation of 2'-O-fucosyllactose (2'FL), lacto-N-neotetraose (LNnT), and combinations thereof (MIX) led to an increase of bifidobacteria, accompanied by an increase of short chain fatty acid (SCFA), in particular butyrate with 2'FL. A significant reduction in paracellular permeability of FITC-dextran probe was observed using Caco2 cell monolayers with fermented 2'FL and MIX, which was accompanied by an increase in claudin-8 gene expression as shown by qPCR, and a reduction in IL-6 as determined by multiplex ELISA. Using gut-on-chips generated from human organoids derived from proximal, transverse, and distal colon biopsies (Colon Intestine Chips), we showed that claudin-5 was significantly upregulated across all three gut-on-chips following treatment with fermented 2'FL under microfluidic conditions. Taken together, these data show that, in addition to their bifidogenic activity, HMOs have the capacity to modulate immune function and the gut barrier, supporting the potential of HMOs to provide health benefits in adults.

Targeted LC-ESI-MS2 characterization of human milk oligosaccharide diversity at 6 to 16 weeks post-partum reveals clear staging effects and distinctive milk groups

Many molecular components in human milk (HM), such as human milk oligosaccharides (HMOs), assist in the healthy development of infants. It has been hypothesized that the functional benefits of HM may be highly dependent on the abundance and individual fine structures of contained HMOs and that distinctive HM groups can be defined by their HMO profiles. However, the structural diversity and abundances of individual HMOs may also vary between milk donors and at different stages of lactations. Improvements in efficiency and selectivity of quantitative HMO analysis are essential to further expand our understanding about the impact of HMO variations on healthy early life development. Hence, we applied here a targeted, highly selective, and semi-quantitative LC-ESI-MS² approach by analyzing 2 × 30 mature human milk samples collected at 6 and 16 weeks post-partum. The analytical approach covered the most abundant HMOs up to hexasaccharides and, for the first time, also assigned blood group A and B tetrasaccharides. Principal component analysis (PCA) was employed and allowed for automatic grouping and assignment of human milk samples to four human milk groups which are related to the maternal Secretor (Se) and Lewis (Le) genotypes. We found that HMO diversity varied significantly between these four HM groups. Variations were driven by HMOs being either dependent or independent of maternal genetic Se and Le status. We found preliminary evidence for an additional HM subgroup within the Se- and Le-positive HM group I. Furthermore, the abundances of 6 distinct HMO structures (including 6'-SL and 3-FL) changed significantly with progression of lactation. Graphical abstract.

More than sugar in the milk: human milk oligosaccharides as essential bioactive molecules in breast milk and current insight in beneficial effects

Human milk is the gold standard for newborn infants. Breast milk not only provides nutrients, it also contains bioactive components that guide the development of the infant's intestinal immune system, which can have a lifelong effect. The bioactive molecules in breast milk regulate microbiota development, immune maturation and gut barrier function. Human milk oligosaccharides (hMOs) are the most abundant bioactive molecules in human milk and have multiple beneficial functions such as support of growth of beneficial bacteria, anti-pathogenic effects, immune modulating effects, and stimulation of intestine barrier functions. Here we critically review the current insight into the benefits of bioactive molecules in mother milk that contribute to neonatal development and focus on current knowledge of hMO-functions on microbiota and the gastrointestinal immune barrier. hMOs produced via genetically engineered microorganisms are now applied in infant formulas to mimic the nutritional composition of breast milk as closely as possible, and their prospects and scientific challenges are discussed in depth.

Human Milk Oligosaccharide Profile Variation Throughout Postpartum in Healthy Women in a Brazilian Cohort

Human milk oligosaccharide (HMO) composition varies throughout lactation and can be influenced by maternal characteristics. This study describes HMO variation up to three months postpartum and explores the influences of maternal sociodemographic and anthropometric characteristics in a Brazilian prospective cohort. We followed 101 subjects from 28–35 gestational weeks (baseline) and throughout lactation at 2–8 (visit 1), 28–50 (visit 2) and 88–119 days postpartum (visit 3). Milk samples were collected at visits 1, 2 and 3, and 19 HMOs were quantified usinghigh-performance liquid chromatography with fluorescence detection (HPLC-FL). Friedman post-hoc test, Spearman rank correlation for maternal characteristics and HMOs and non-negative matrix factorization (NMF) were used to define the HMO profile. Most women were secretors (89.1%) and presented high proportion of 2′-fucosyllactose (2′FL) at all three sample times, while lacto-N-tetraose (LNT, 2–8 days) and lacto-N-fucopentaose II (LNFPII, 28–50 and 88–119 days) were the most abundant HMOs in non-secretor women. Over the course of lactation, total HMO weight concentrations (g/L) decreased, but total HMO molar concentrations (mmol/L) increased, highlighting differential changes in HMO composition over time. In addition, maternal pre-pregnancy body mass index (BMI) and parity influence the HMO composition in healthy women in this Brazilian cohort.

Challenges and Pitfalls in Human Milk Oligosaccharide Analysis

Human milk oligosaccharides have been recognized as an important, functional biomolecule in mothers' milk. Moreover, these oligosaccharides have been recognized as the third most abundant component of human milk, ranging from 10-15 g/L in mature milk and up to and over 20 g/L reported in colostrum. Initially, health benefits of human milk oligosaccharides were assigned via observational studies on the differences between breastfed and bottle fed infants. Later, pools of milk oligosaccharides were isolated and used in functional studies and in recent years more specific studies into structure-function relationships have identified some advanced roles for milk oligosaccharides in the healthy development of infants. In other research, the levels, diversity, and complexity of human milk oligosaccharides have been studied, showing a wide variation in results. This review gives a critical overview of challenges in the analysis of human milk oligosaccharides. In view of the myriad functions that can be assigned, often to specific structures or classes of structures, it is very relevant to assess the levels of these structures in the human milk correctly, as well as in other biological sample materials. Ultimately, the review makes a case for a comparative, inter-laboratory study on quantitative human milk oligosaccharide analysis in all relevant biological samples.

Maternal and Infant Factors Associated with Human Milk Oligosaccharides Concentrations According to Secretor and Lewis Phenotypes

Human milk oligosaccharides (HMOs) are multifunctional carbohydrates naturally present in human milk that act as prebiotics, prevent pathogen binding and infections, modulate the immune system and may support brain development in infants. HMOs composition is very individualized and differences in HMOs concentrations may affect the infant's health. HMOs variability can be partially explained by the activity of Secretor (Se) and Lewis (Le) genes in the mother, but non-genetic maternal factors may also be involved. In this cross-sectional, observational study, 78 single human milk samples ranging from 17 to 76 days postpartum (median: 32 days, IQR: 25-46 days) were collected from breastfeeding Brazilian women, analyzed for 16 representative HMOs by liquid chromatography coupled to mass spectrometry and associations between maternal and infant factors with HMOs concentrations were investigated. HMOs concentrations presented a high variability even in women with the same SeLe phenotype and associations with maternal allergic disease, time postpartum and with infant's weight, weight gain and sex. Overall, we present unprecedented data on HMOs concentrations from breastfeeding Brazilian women and novel associations of maternal allergic disease and infant's sex with HMOs concentrations. Differences in HMOs composition attributed to maternal SeLe phenotype do not impact infant growth, but higher concentrations of specific HMOs may protect against excessive weight gain.

Human Milk Oligosaccharides and Immune System Development

Maternal milk contains compounds that may affect newborn immunity. Among these are a group of oligosaccharides that are synthesized in the mammary gland from lactose; these oligosaccharides have been termed human milk oligosaccharides (HMOs). The amount of HMOs present in human milk is greater than the amount of protein. In fact, HMOs are the third-most abundant solid component in maternal milk after lactose and lipids, and are thus considered to be key components. The importance of HMOs may be explained by their inhibitory effects on the adhesion of microorganisms to the intestinal mucosa, the growth of pathogens through the production of bacteriocins and organic acids, and the expression of genes that are involved in inflammation. This review begins with short descriptions of the basic structures of HMOs and the gut immune system, continues with the beneficial effects of HMOs shown in cell and animal studies, and it ends with the observational and randomized controlled trials carried out in humans to date, with particular emphasis on their effect on immune system development. HMOs seem to protect breastfed infants against microbial infections. The protective effect has been found to be exerted through cell signaling and cell-to-cell recognition events, enrichment of the protective gut microbiota, the modulation of microbial adhesion, and the invasion of the infant intestinal mucosa. In addition, infants fed formula supplemented with selected HMOs exhibit a pattern of inflammatory cytokines closer to that of exclusively breastfed infants. Unfortunately, the positive effects found in preclinical studies have not been substantiated in the few randomized, double-blinded, multicenter, controlled trials that are available, perhaps partly because these studies focus on aspects other than the immune response (e.g., growth, tolerance, and stool microbiota).

Non-digestible carbohydrates in infant formula as substitution for human milk oligosaccharide functions: Effects on microbiota and gut maturation

Human milk (HM) is the golden standard for nutrition of newborn infants. Human milk oligosaccharides (HMOs) are abundantly present in HM and exert multiple beneficial functions, such as support of colonization of the gut microbiota, reduction of pathogenic infections and support of immune development. HMO-composition is during lactation continuously adapted by the mother to accommodate the needs of the neonate. Unfortunately, for many valid reasons not all neonates can be fed with HM and are either totally or partly fed with cow-milk derived infant formulas, which do not contain HMOs. These cow-milk formulas are supplemented with non-digestible carbohydrates (NDCs) that have functional effects similar to that of some HMOs, since production of synthetic HMOs is challenging and still very expensive. However, NDCs cannot substitute all HMO functions. More efficacious NDCs may be developed and customized for specific groups of neonates such as pre-matures and allergy prone infants. Here current knowledge of HMO functions in the neonate in view of possible replacement of HMOs by NDCs in infant formulas is reviewed. Furthermore, methods to expedite identification of suitable NDCs and structure/function relationships are reviewed as in vivo studies in babies are impossible.

The First Microbial Colonizers of the Human Gut: Composition, Activities, and Health Implications of the Infant Gut Microbiota

The human gut microbiota is engaged in multiple interactions affecting host health during the host's entire life span. Microbes colonize the neonatal gut immediately following birth. The establishment and interactive development of this early gut microbiota are believed to be (at least partially) driven and modulated by specific compounds present in human milk. It has been shown that certain genomes of infant gut commensals, in particular those of bifidobacterial species, are genetically adapted to utilize specific glycans of this human secretory fluid, thus representing a very intriguing example of host-microbe coevolution, where both partners are believed to benefit. In recent years, various metagenomic studies have tried to dissect the composition and functionality of the infant gut microbiome and to explore the distribution across the different ecological niches of the infant gut biogeography of the corresponding microbial consortia, including those corresponding to bacteria and viruses, in healthy and ill subjects. Such analyses have linked certain features of the microbiota/microbiome, such as reduced diversity or aberrant composition, to intestinal illnesses in infants or disease states that are manifested at later stages of life, including asthma, inflammatory bowel disease, and metabolic disorders. Thus, a growing number of studies have reported on how the early human gut microbiota composition/development may affect risk factors related to adult health conditions. This concept has fueled the development of strategies to shape the infant microbiota composition based on various functional food products. In this review, we describe the infant microbiota, the mechanisms that drive its establishment and composition, and how microbial consortia may be molded by natural or artificial interventions. Finally, we discuss the relevance of key microbial players of the infant gut microbiota, in particular bifidobacteria, with respect to their role in health and disease.

The functional biology of human milk oligosaccharides

Human milk oligosaccharides (HMOs) are a group of complex sugars that are highly abundant in human milk, but currently not present in infant formula. More than a hundred different HMOs have been identified so far. The amount and composition of HMOs are highly variable between women, and each structurally defined HMO might have a distinct functionality. HMOs are not digested by the infant and serve as metabolic substrates for select microbes, contributing to shape the infant gut microbiome. HMOs act as soluble decoy receptors that block the attachment of viral, bacterial or protozoan parasite pathogens to epithelial cell surface sugars, which may help prevent infectious diseases in the gut and also the respiratory and urinary tracts. HMOs are also antimicrobials that act as bacteriostatic or bacteriocidal agents. In addition, HMOs alter host epithelial and immune cell responses with potential benefits for the neonate. The article reviews current knowledge as well as future challenges and opportunities related to the functional biology of HMOs.

Beneficial effects of human milk oligosaccharides on gut microbiota

Human milk is the gold standard for nourishment of early infants because it contains a number of bioactive components, such as human milk oligosaccharides (HMOs). The high concentration and structural diversity of HMOs are unique to humans. HMOs are a group of complex and diverse glycans that are resistant to gastrointestinal digestion and reach the infant colon as the first prebiotics. N-acetyl-glucosamine containing oligosaccharides were first identified 50 years ago as the 'bifidus factor', a selective growth substrate for intestinal bifidobacteria, thus providing a conceptual basis for HMO-specific bifidogenic activity. Bifidobacterial species are the main utilisers of HMOs in the gastrointestinal tract and represent the dominant microbiota of breast-fed infants, and they may play an important role in maintaining the general health of newborn children. Oligosaccharides are also known to directly interact with the surface of pathogenic bacteria, and various oligosaccharides in milk are believed to inhibit the binding of pathogens and toxins to host cell receptors. Furthermore, HMOs are thought to contribute to the development of infant intestine and brain. Oligosaccharides currently added to infant formula are structurally different from the oligosaccharides naturally occurring in human milk and, therefore, they are unlikely to mimic some of the structure-specific effects. In this review, we describe how HMOs can modulate gut microbiota. This article summarises information up to date about the relationship between the intestinal microbiota and HMOs, and other possible indirect effects of HMOs on intestinal environment.

Human Milk Oligosaccharides (HMOS): Structure, Function, and Enzyme-Catalyzed Synthesis

The important roles played by human milk oligosaccharides (HMOS), the third major component of human milk, in the health of breast-fed infants have been increasingly recognized, as the structures of more than 100 different HMOS have now been elucidated. Despite the recognition of the various functions of HMOS as prebiotics, antiadhesive antimicrobials, and immunomodulators, the roles and the applications of individual HMOS species are less clear. This is mainly due to the limited accessibility to large amounts of individual HMOS in their pure forms. Current advances in the development of enzymatic, chemoenzymatic, whole-cell, and living-cell systems allow for the production of a growing number of HMOS in increasing amounts. This effort will greatly facilitate the elucidation of the important roles of HMOS and allow exploration into the applications of HMOS both as individual compounds and as mixtures of defined structures with desired functions. The structures, functions, and enzyme-catalyzed synthesis of HMOS are briefly surveyed to provide a general picture about the current progress on these aspects. Future efforts should be devoted to elucidating the structures of more complex HMOS, synthesizing more complex HMOS including those with branched structures, and developing HMOS-based or HMOS-inspired prebiotics, additives, and therapeutics.

Structure-function relationships of human milk oligosaccharides

Human milk contains more than a hundred structurally distinct oligosaccharides. In this review, we provide examples of how the structural characteristics of these human milk oligosaccharides (HMO) determine functionality. Specific α1-2-fucosylated HMO have been shown to serve as antiadhesive antimicrobials to protect the breast-fed infant against infections with Campylobacter jejuni, one of the most common causes of bacterial diarrhea. In contrast, α1-2-fucosylation may abolish the beneficial effects of HMO against Entamoeba histolytica, a protozoan parasite that causes colitis, acute dysentery, or chronic diarrhea. In a different context, HMO need to be both fucosylated and sialylated to reduce selectin-mediated leukocyte rolling, adhesion, and activation, which may protect breast-fed infants from excessive immune responses. In addition, our most recent data show that a single HMO that carries not 1 but 2 sialic acids protects neonatal rats from necrotizing enterocolitis, one of the most common and often fatal intestinal disorders in preterm infants. Oligosaccharides currently added to infant formula are structurally different from the oligosaccharides naturally occurring in human milk. Thus, it appears unlikely that they can mimic some of the structure-specific effects of HMO. Recent advances in glycan synthesis and isolation have increased the availability of certain HMO tri- and tetrasaccharides for in vitro and in vivo preclinical studies. In the end, intervention studies are needed to confirm that the structure-specific effects observed at the laboratory bench translate into benefits for the human infant. Ultimately, breastfeeding remains the number one choice to nourish and nurture our infants.

Human milk oligosaccharides: every baby needs a sugar mama

Human milk oligosaccharides (HMOs) are a family of structurally diverse unconjugated glycans that are highly abundant in and unique to human milk. Originally, HMOs were discovered as a prebiotic "bifidus factor" that serves as a metabolic substrate for desired bacteria and shapes an intestinal microbiota composition with health benefits for the breast-fed neonate. Today, HMOs are known to be more than just "food for bugs". An accumulating body of evidence suggests that HMOs are antiadhesive antimicrobials that serve as soluble decoy receptors, prevent pathogen attachment to infant mucosal surfaces and lower the risk for viral, bacterial and protozoan parasite infections. In addition, HMOs may modulate epithelial and immune cell responses, reduce excessive mucosal leukocyte infiltration and activation, lower the risk for necrotizing enterocolitis and provide the infant with sialic acid as a potentially essential nutrient for brain development and cognition. Most data, however, stem from in vitro, ex vivo or animal studies and occasionally from association studies in mother-infant cohorts. Powered, randomized and controlled intervention studies will be needed to confirm relevance for human neonates. The first part of this review introduces the pioneers in HMO research, outlines HMO structural diversity and describes what is known about HMO biosynthesis in the mother's mammary gland and their metabolism in the breast-fed infant. The second part highlights the postulated beneficial effects of HMO for the breast-fed neonate, compares HMOs with oligosaccharides in the milk of other mammals and in infant formula and summarizes the current roadblocks and future opportunities for HMO research.

High-throughput mass finger printing and Lewis blood group assignment of human milk oligosaccharides

The structural diversity of human milk oligosaccharides (HMOs) strongly depends on the Lewis (Le) blood group status of the donor which allows a classification of these glycans into three different groups. Starting from 50 μL of human milk, a new high-throughput, standardized, and widely automated mass spectrometric approach has been established which can be used for correlation of HMO structures with the respective Lewis blood groups on the basis of mass profiles of the entire mixture of glycans together with selected fragment ion spectra. For this purpose, the relative abundance of diagnostically relevant compositional species, such as Hex(2)Fuc(2) and Hex(3)HexNAc(1)Fuc(2), as well as the relative intensities of characteristic fragment ions obtained thereof are of key importance. For each Lewis blood group, i.e., Le(a-b+), Le(a+b-), and Le(a-b-), specific mass profile and fragment ion patterns could be thus verified. The described statistically proven classification of the derived glycan patterns may be a valuable tool for analysis and comparison of large sets of milk samples in metabolic studies. Furthermore, the outlined protocol may be used for rapid screening in clinical studies and quality control of milk samples donated to milk banks.

Biochemical characterization of Silene alba α4-fucosyltransferase and Lewis a products

alpha1,4-Fucosylation has been recently detected in Arabidopsis thaliana [Leonard et al. (2002), Glycobiology 12: 299-306], and corresponding enzymes have also been characterized in Beta vulgaris [Bakker et al. (2001), FEBS Lett, 507: 307-312], and Lycopersicum aesculentum [Wilson (2001), Glycoconjugate J., 18: 439-447]. Here we demonstrated fucosyltransferase activity (FucT) in Silene alba cells and tissues. The Fuc linkage to GlcNAc residues of the lactosamine moiety of the Type I acceptor was confirmed by mass spectrometry experiments. Le(a)-glycoconjugates are found in the Golgi apparatus and plasma membrane of plant cells. In planta, the highest levels of activity were detected in seedlings, young roots and male flowers. The enzyme was stable up to 45( composite function)C and the optimum pH of reaction was 8.0. The enzyme required Mg(2+) or Mn(2+) for activity and was inhibited by Zn(2+) and ethylenediaminetetraacetic acid. Chemical modification of the enzyme with group-selective reagents revealed that selective modifications of arginine and lysine residues had no effect on enzyme activity. However the enzyme contains histidine and tryptophan residues that are essential for its activity. In contrast to human FUT3, the S. alba alpha4-FucT was insensitive to N-ethylmaleimide (NEM) treatment. Measurement of enzyme activity in S. alba cell fractions indicated that the enzyme is bound to microsomal membranes, furthermore a soluble isoform of the protein may be present.

Detection of four human milk groups with respect to Lewis-blood-group-dependent oligosaccharides by serologic and chromatographic analysis

Oligosaccharides from human milk samples obtained from individual donors were analyzed using high-pH anion-exchange chromatography. Three patterns of neutral oligosaccharides were detected corresponding to milk groups already described. These oligosaccharide groups correspond to the Lewis blood types Le(a-b+), Le(a+b-), and Le(a-b-). A new carbohydrate pattern was detected in a milk sample from a Le(a-b-) person in which only nonfucosylated oligosaccharides and compounds bearing alpha1,3-linked fucosyl residues were found. This finding led to the hypothesis that there exist 4 different oligosaccharide milk groups that fit well to the genetic basis of the Lewis blood group system.

Expression and characterization of recombinant human alpha-3/4-fucosyltransferase III from Spodoptera frugiperda (Sf9) and Trichoplusia ni (Tn) cells using the baculovirus expression system

The human alpha-3/4-fucosyltransferase III (Fuc-TIII) participates in the synthesis of Lewis determinants. The enzyme from human sources is scarce and heterogeneous. In this paper we describe the expression of a secreted form of Fuc-TIII (SFT3) in two insect cell lines, Spodoptera frugiperda (Sf9) and Trichoplusia ni (Tn), using the baculovirus expression system. The Sf9 cells secreted approx. 0.4 unit/l (1 mg/l) of the enzyme. The Tn cells secreted approx. 3-fold this amount. A large proportion of active protein was accumulated in the two cell lines (50 and 75% respectively for Sf9 and Tn cells, on the fourth day after infection) indicating a possible limitation not only of the folding machinery, but also a saturation of the secretory pathway. SFT3 was purified by cation-exchange chromatography followed by affinity chromatography. The enzyme from the Tn cell line had a lower global charge, possibly due to post-translational modifications, such as phosphorylation or sulphation. The two glycosylation sites from SFT3 were occupied. SFT3 secreted by Sf9 cells was completely deglycosylated by peptide-N-glycanase F, whereas 50% of SFT3 secreted by Tn cells was resistant to deglycosylation by this enzyme. The apparent kinetic parameters determined with the type I acceptor were k(cat)=0.4 s(-1) and K(m)=0.87 mM for the SFT3 secreted by Tn cells, and k(cat)=0.09 s(-1) and K(m)=0.76 mM for the SFT3 secreted by Sf9 cells, indicating that the enzymes had substrate affinities within the same order of magnitude as their mammalian counterpart. Furthermore, SFT3 secreted by either cell type showed a clear preference for type 1 carbohydrate acceptors, similarly to human Fuc-TIII.

The cytoplasmic, transmembrane, and stem regions of glycosyltransferases specify their in vivo functional sublocalization and stability in the Golgi

We provide evidence for the presence of targeting signals in the cytoplasmic, transmembrane, and stem (CTS) regions of Golgi glycosyltransferases that mediate sorting of their intracellular catalytic activity into different functional subcompartmental areas of the Golgi. We have constructed chimeras of human alpha1, 3-fucosyltransferase VI (FT6) by replacement of its CTS region with those of late and early acting Golgi glycosyltransferases and have stably coexpressed these constructs in BHK-21 cells together with the secretory reporter glycoprotein human beta-trace protein. The sialyl Lewis X:Lewis X ratios detected in beta-trace protein indicate that the CTS regions of the early acting GlcNAc-transferases I (GnT-I) and III (GnT-III) specify backward targeting of the FT6 catalytic domain, whereas the CTS region of the late acting human alpha1,3-fucosyltransferase VII (FT7) causes forward targeting of the FT6 in vivo activity in the biosynthetic glycosylation pathway. The analysis of the in vivo functional activity of nine different CTS chimeras toward beta-trace protein allowed for a mapping of the CTS donor glycosyltransferases within the Golgi/trans-Golgi network: GnT-I < (ST6Gal I, ST3Gal III) < GnT-III < ST8Sia IV < GalT-I < (FT3, FT6) < ST3Gal IV < FT7. The sensitivity or resistance of the donor glycosyltransferases toward intracellular proteolysis is transferred to the chimeric enzymes together with their CTS regions. Apparently, there are at least three different signals contained in the CTS regions of glycosyltransferases mediating: first, their Golgi retention; second, their targeting to specific in vivo functional areas; and third, their susceptibility toward intracellular proteolysis as a tool for the regulation of the intracellular turnover.

The relationship between ST6Gal I Golgi retention and its cleavage-secretion

The ST6Gal I is a sialyltransferase that modifies N-linked oligosaccharides of glycoproteins. Previous results suggested a role for luminal stem and active domain sequences in the efficiency of ST6Gal I Golgi retention. Characterization of a series of STtyr isoform deletion mutants demonstrated that the stem is sensitive to proteases and that preventing cleavage in this region leads to increased cell surface expression. A mutant lacking amino acids 32-104 (STDelta4) is not active or cleaved and secreted like the wild type STtyr, but does exhibit increased cell surface expression. It is probable that the STDelta4 mutant lacks the stem region and some amino acids of the active domain because the STDelta5 mutant lacking amino acids 86-104 is also not active but is cleaved and secreted. In contrast, deletion of stem amino acids between residues 32 and 86 in the STDelta1, STDelta2, and STDelta3 mutants does not inactive these enzyme forms, eliminate their cleavage and secretion, or increase their cell surface expression. Surprisingly, cleavage occurs even though the previously identified Asn63-Ser 64 cleavage site is missing. Further evaluation demonstrated that a cleavage site between Lys 40 and Glu 41 is used in COS cells. Mutagenesis of Lys 40 significantly decreased, but did not eliminate cleavage, suggesting that there are additional secondary sites of cleavage in the ST6Gal I stem.

Aglycone structure influences alpha-fucosyltransferase III activity using N-acetyllactosamine glycoside acceptors

We showed previously that Chinese hamster ovary cells took up and utilized a variety of N-acetylglucosaminides as primers of oligosaccharide biosynthesis (Ding et al., 1999, J. Carbohydr. Chem., 18:471-475). In this study, a library of N-acetylglucosaminides was enzymatically galactosylated in vitro to yield type 2 chain N-acetyllactosaminides bearing a variety of aglycones. Those disaccharides are potential acceptors for fucosyltransferases. As an extension of the previous study, we tested the type 2 chain disaccharyl glycosides (Galbeta1,4-GlcNAcbeta-R) for their aglycone-dependent acceptor specificity for alpha-L-fucosyltransferase III (Fuc-TIII). The enzyme activity significantly depended on the aglycone structures, suggesting that, in addition to the polar groups on the sugar moiety, the hydrophobic aglycone can substantially contribute to recognition in this reaction.

In vitro alpha1-3 or alpha1-4 fucosylation of type I and II oligosaccharides with secreted forms of recombinant human fucosyltransferases III and VI

Transgalactosylation of chitobiose and chitotriose employing beta-galactosidase from bovine testes yielded mixtures with beta1-3 linked galactose (type I) and beta1-4 linked galactose (type II) in a final ratio of 1:1 for the tri- and 1:1.4 for the tetrasaccharide. After 24 h incubations of the two purified oligosaccharide mixtures with large amounts (20-fold increase compared with standard conditions) of human alpha1,3/4-fucosyltransferase III (FucT III), the type I tri-/tetrasaccharides were completely converted to the Lewis(a) structure, whereas approximately 10% fucosylation of the type II isomers to the Lewis(x) oligosaccharides was observed in long-term incubations. Employing large amounts of human alpha1,3-fucosyltransferase VI (FucT VI), the type I trisaccharide substrate was exclusively fucosylated at the proximal O-4 substituted N-acetylglucosamine (GlcNAc) (20%) whereas almost all of the type II isomers was converted to the corresponding Lewis(x) product. 45% of the type I tetrasaccharide was fucosylated at the second GlcNAc solely by FucT VI. The type II isomer was almost completely alpha1-3 fucosylated to yield the Lewisx derivative with traces of a structure that contained an additional fucose at the reducing GlcNAc. The results obtained in the present study employing high amounts of enzyme confirmed our previous results that FucT III acts preponderantly as a beta1-4 fucosyltransferase onto GlcNAc in vitro. Human FucT VI attaches fucose exclusively in an alpha1-3 linkage to 4-substituted GlcNAc in vitro and does not modify any 3-substituted GlcNAc to yield Lewis(a) oligosaccharides. With 8-methoxycarbonyloctyl glycoside acceptors used under standard conditions, FucT III acts exclusively on the type I and FucT VI only on the type II derivative. With lacto-N-tetraose, lacto-N-fucopentraose I, or LS-tetrasaccharide as substrates, FucT III modified the 3-substituted GlcNAc and the reducing glucose; FucT VI recognized only lacto-N-neotetraose as a substrate.

Detection of four human milk groups with respect to Lewis blood group dependent oligosaccharides

Neutral oligosaccharides in human milk samples from approximately 50 women were analysed applying a recently developed high-pH anion-exchange chromatographic method. Three different oligosaccharide patterns could be detected in accordance with milk groups that had been already described. These oligosaccharide groups correspond to the Lewis blood types Le(a-b+), Le(a+b-) and Le(a-b-). In addition to these oligosaccharide patterns, a new carbohydrate pattern was detected in a milk sample from a Le(a-b-) individual. Here, only nonfucosylated oligosaccharides and compounds bearing alpha1,3 linked fucosyl residues were found, whereas structures with alpha1,2 and alpha1,4 fucosyl linkages were missing. This finding led to the hypothesis that there are four different oligosaccharide milk groups that fit well to the genetic basis of the Lewis blood group system.

Significance of individual point mutations, T202C and C314T, in the human Lewis (FUT3) gene for expression of Lewis antigens by the human alpha(1,3/1,4)-fucosyltransferase, Fuc-TIII

The Lewis alpha(1,3/1,4)-fucosyltransferase, Fuc-TIII, encoded by the FUT3 gene is responsible for the final synthesis of Lea and Leb antigens. Various point mutations have been described explaining the Lewis negative phenotype, Le(a-b-), on erythrocytes and secretions. Two of these, T202C and C314T originally described in a Swedish population, have not been found as single isolated point mutations so far. To define the relative contribution of each of these two mutations to the Lewis negative phenotype, we cloned and made chimeric FUT3 constructs separating the T202C mutation responsible for the amino acid change Trp68 --> Arg, from the C314T mutation leading to the Thr105 --> Met shift. COS-7 cells were transfected and the expression of Fuc-TIII enzyme activity and the presence of Lewis antigens were determined. There was no decrease in enzyme activity nor of immunofluorescence staining on cells transfected with the construct containing the isolated C314T mutation compared with cells transfected with a wild type FUT3 allele control. No enzyme activity nor immunoreactivity for Lewis antigens was detected in FUT3 constructs containing both mutations in combination. The T202C mutation alone decreased the enzyme activity to less than 1% of the activity of the wild type FUT3 allele. These results demonstrate, that the Trp68 --> Arg substitution in human Fuc-TIII is the capital amino acid change responsible for the appearance of the Le(a-b-) phenotype on human erythrocytes in individuals homozygous for both the T202C and C314T mutations.

Stable expression of the Golgi form and secretory variants of human fucosyltransferase III from BHK-21 cells. Purification and characterization of an engineered truncated form from the culture medium

Stable BHK-21 cell lines were constructed expressing the Golgi membrane-bound form and two secretory forms of the human alpha1, 3/4-fucosyltransferase (amino acids 35-361 and 46-361). It was found that 40% of the enzyme activity synthesized by cells transfected with the Golgi form of the fucosyltransferase was constitutively secreted into the medium. The corresponding enzyme detected by Western blot had an apparent molecular mass similar to those of the truncated secretory forms. The secretory variant (amino acids 46-361) was purified by a single affinity-chromatography step on GDP-Fractogel resin with a 20% final recovery. The purified enzyme had a unique NH2 terminus and contained N-linked endo H sensitive carbohydrate chains at its two glycosylation sites. The fucosyltransferase transferred fucose to the O-4 position of GlcNAc in small oligosaccharides, glycolipids, glycopeptides, and glycoproteins containing the type I Galbeta1-3GlcNAc motif. The acceptor oligosaccharide in bovine asialofetuin was identified as the Man-3 branched triantennary isomer with one Galbeta1-3GlcNAc. The type II motif Galbeta1-4GlcNAc in bi-, tri-, or tetraantennary neutral or alpha2-3/alpha2-6 sialylated oligosaccharides with or without N-acetyllactosamine repeats and in native glycoproteins were not modified. The soluble forms of fucosyltransferase III secreted by stably transfected cells may be used for in vitro synthesis of the Lewisa determinant on carbohydrates and glycoproteins, whereas Lewisx and sialyl-Lewisx structures cannot be synthesized.

Acceptor hydroxyl group mapping for human milk alpha 1-3 and alpha 1-3/4 fucosyltransferases

Two different fucosyltransferases (Fuc-Ts) have been isolated from human milk, an alpha 1-3 Fuc-T and an alpha 1-3/4 Fuc-T, for mapping of their acceptor binding sites. Kinetic studies employing a series of monodeoxygenated and modified Gal beta 1-->4Glc-NAc beta OR and Gal beta 1-->3GlcNAc beta OR acceptor substrates showed that modifications are tolerated at every hydroxyl group in these substrates except for 6-OH of galactose and 3- or 4-OH of N-acetylglucosamine. Deoxygenation at these positions rendered these compounds inactive as both substrates and inhibitors. These essential hydroxyl groups, which are required for recognition of the substrates, are identical to the key polar groups that have previously been reported for cloned FucTs III, IV and V.

DNA sequencing and screening for point mutations in the human Lewis (FUT3) gene enables molecular genotyping of the human Lewis blood group system

The human Lewis gene encodes an alpha(1,3/1,4)-fucosyltransferase responsible for synthesis of the Le(a) and a Le(b) antigens. To define the molecular background for non-functional Lewis genes we have sequenced PCR-amplified DNA fragments from two Le(a-b-) individuals. One was homozygously mutated at nucleotides 202(T --> C) and 314 (C --> T), altering Trp68 to Arg and Thr105 to Met, and the other was homozygously mutated at nucleotides 59 (T --> G) and 1067 (T --> A), altering Leu20 to Arg and Ile356 to Lys. Using PCR we screened for these and additionally one other mutation at nucleotide 508 (G --> A) among 40 Caucasians. Of 15 Le(a-b-) individuals, 7 typed as le59/1067le202/314, 4 as le202/314le202/314 and 1 as le59/1067le59/1067. Of 21 Le(a-b+) and 4 Le(a+b-), 17 typed as LeLe and 7 as Lele202/314. A pedigree study of 8 Lewis-positive individuals showed that the mutations at nucleotides 202 and 314 were located on the same allele.

Characterization and purification of fucosyltransferases from the cytosol of rat colon

The occurrence and baseline characteristics of fucosyltransferases (alpha-1,2, alpha-1,3 and alpha-1,4) in the cytosol (soluble) and pellet (membrane-bound) of rat colon have been studied since the fucosylation process is known to alter in colon pathology. All enzymes studied in the colon pellet had higher activity when compared to the cytosol. The colon pellet alpha-1,3 fucosyltransferase preferred desialylated alpha 1-acid glycoprotein as acceptor substrate. Both soluble and membrane-bound enzymes, alpha-1,2 and alpha-1,3 fucosyltransferases, required Mn2+, Mg2+ and Ca2+ for maximum activity but were inactivated by Cu2+ ions. Both soluble alpha-1,2 and alpha-1,3 fucosyltransferases showed optimal activity at pH 6.0, whereas the optimum for their membrane-bound activities were at pH 5.8 and 6.2, respectively. Furthermore, a soluble alpha-1,3 fucosyltransferase from rat colon was purified and during purification the co-presence of alpha-1,3/4 fucosyltransferase was detected. The acceptor of preference for the purified soluble alpha-1,3 fucosyltransferase was desialylated glycoprotein while low molecular weight substrates were poor acceptors. Both the purified fucosyltransferases were inhibited by N-ethylmaleimide. The M(r) values determined by SDS-PAGE electrophoresis of alpha-1,3/4 fucosyltransferase and of alpha-1,3 fucosyltransferase were 68,780 and 40,680 respectively. In conclusion, based on their properties, the purified soluble colon alpha-1,3 fucosyltransferase appeared to be of plasma-type (or FT-I) while the soluble alpha-1,3/4 fucosyltransferase corresponded to Lewis-type or FT-III.

Purification, properties and possible gene assignment of an alpha 1,3-fucosyltransferase expressed in human liver

alpha 1,3-Fucosyltransferase solubilized from human liver has been purified 40,000-fold to apparent homogeneity by a multistage process involving cation exchange chromatography on CM-Sephadex, hydrophobic interaction chromatography on Phenyl Sepharose, affinity chromatography on GDP-hexanolamine Sepharose and HPLC gel exclusion chromatography. The final step gave a major protein peak that co-chromatographed with alpha 1,3-fucosyltransferase activity and had a specific activity of approximately 5-6 mumol min-1 mg-1 and an M(r) approximately 44,000 deduced from SDS-PAGE and HPLC analysis. The purified enzyme readily utilized Gal beta 1-4GlcNAc, NeuAc alpha 2-3Gal beta 1-4GlcNAc and Fuc alpha 1-2Gal beta 1-4GlcNAc, with a preference for sialylated and fucosylated Type 2 acceptors. Fuc alpha 1-2Gal beta 1-4Glc and the Type 1 compound Gal beta 1-3GlcNAc were very poor acceptors and no incorporation was observed with NeuAc alpha 2-6Gal beta 1-4GlcNAc. A polyclonal antibody raised against the liver preparation reacted with the homologous enzyme and also with the blood group Lewis gene-associated alpha 1,3/1,4-fucosyltransferase purified from the human A431 epidermoid carcinoma cell line. No cross reactivity was found with alpha 1,3-fucosyltransferase(s) isolated from myeloid cells. Examination by Northern blot analysis of mRNA from normal liver and from the HepG2 cell line, together with a comparison of the specificity pattern of the purified enzyme with that reported for the enzyme expressed in mammalian cells transfected with the Fuc-TVI cDNA, suggests a provisional identification of Fuc-TVI as the major alpha 1,3-fucosyltransferase gene expressed in human liver.

Blood group antigens on human erythrocytes-distribution, structure and possible functions

Human erythrocyte blood group antigens can be broadly divided into carbohydrates and proteins. The carbohydrate-dependent antigens (e.g., ABH, Lewis, Ii, P1, P-related, T and Tn) are covalently attached to proteins and/or sphingolipids, which are also widely distributed in body fluids, normal tissues and tumors. Blood group gene-specific glycosyltransferase regulate the synthesis of these antigens. Protein-dependent blood group antigens (e.g., MNSs, Gerbich, Rh, Kell, Duffy and Cromer-related) are carried on proteins, glycoproteins and proteins with glycosylphosphatidylinositol anchor. The functions of these molecules on human erythrocytes remain unknown; some of them may be involved in maintaining the erythrocyte shape. This review describes the distribution, structures and probable biological functions of some of these antigens in normal and pathological conditions.

Use of human-milk fucosyltransferase in the chemoenzymic synthesis of analogues of the sialyl Lewis(a) and sialyl Lewis(x) tetrasaccharides modified at the C-2 position of the reducing unit

Two series of trisaccharides, having the formulas alpha-Neu5Ac-(2-->3)-beta-D-Gal-(1-->4)-beta-D-GlcZ-OR and alpha-Neu5Ac-(2-->3)-beta-D-Gal-(1-->3)-beta-D-GlcZ-OR [R = (CH2)8CO2CH3] respectively, in which the 2-deoxy substituent Z is azido, amino, propionamido, or acetamido, were prepared by chemical synthesis. Both types of modified trisaccharides are acceptors for a fucosyltransferase preparation obtained from human milk. Preparative fucosylations using this enzyme provided analogues of the sialyl Lewis(x) and sialyl Lewis(a) tetrasaccharide structures, which have been proposed to be ligands for cell-adhesion molecules. These syntheses further demonstrate the utility of glycosyltransferases in the preparation of oligosaccharide analogues.

The use of human milk fucosyltransferase in the synthesis of tumor-associated trimeric X determinants

We have studied the fucosylation of a chemically synthesized trimer of N-acetyllactosamine [(LacNAc)3-EtPhNHCOCF3] with a fucosyltransferase preparation from normal human milk, which utilizes both type-1 and type-2 structures, whether sialylated or not. When fucose residues were added enzymically to the (LacNAc)3-EtPhNHCOCF3 hexasaccharide, mono-, di-, or trifucosylated oligosaccharide species were formed, containing the Lewisx determinant (Gal beta 1-->4[Fuc alpha 1-->3]Glc-NAc beta 1-->3). With excess GDP-fucose and prolonged reaction times, the trifucosylated product was formed in almost quantitative yield. Kinetic analysis of the fucosylation reaction indicated that there is a significant difference in the rate of transfer of the first, second and third fucose residues onto the acceptor molecule. The location of the fucose residues in the monofucosylated and difucosylated intermediate products was assessed by analyzing the digests obtained after endo-beta-galactosidase treatment by HPLC and reverse-phase chromatography. In addition, the fucosylated (LacNAc)3-EtPhNHCOCF3 structures were characterized by HPLC and were identified by 400-MHz 1H-NMR spectroscopy. There is a highly preferred order in which the fucosyl residues are attached to (LacN-Ac)3-EtPhNHCOCF3. In the major pathway, the first two fucose residues are transferred with equal preference to the medial (GN3) and proximal (GN1) GlcNAc residues, whereas the third fucose is attached to the distal (GN5) GlcNAc residue. These results are of relevance in understanding the role of alpha-3-fucosyltransferase in the biosynthesis of Lewisx-related cell-surface carbohydrate structures, that function as ligands for selectin-type cell-adhesion molecules and may play a role in the invasion and metastasis of several carcinoma.

Purification and properties of the alpha-3/4-L-fucosyltransferase released into the culture medium during the growth of the human A431 epidermoid carcinoma cell line

A soluble alpha-3/4-fucosyltransferase secreted into the growth medium of the human A431 epidermoid carcinoma cell line has been purified 700,000 fold by a series of steps involving chromatography on Phenyl Sepharose 4B, CM-Sephadex C-50 and GDP-hexanolamine Sepharose 4B. The untreated spent culture medium transferred almost ten times more fucose to the subterminal N-acetylglucosamine residue in the Type 1 (Gal beta 1-3GlcNAc) disaccharide than to the subterminal sugar in the Type 2 (Gal beta 1-4GlcNAc) disaccharide; the relative activity with these two substrates remained virtually unchanged throughout the purification procedure. At no stage was any alpha-3-fucosyltransferase species acting solely on N-acetylglucosamine residues in Type 2 chains separated from the bulk of the alpha-3/4-fucosyltransferase activity. The purified enzyme preparation showed insignificant activity with glycoprotein substrates having N-linked oligosaccharide chains with terminal Type 2 sequences but transferred fucose to a mucin-type glycoprotein with O-linked oligosaccharide chains with terminal Type 1 structures. Lactose was a poor substrate but the activity of the enzyme was influenced by the presence of substituents on the terminal beta-galactosyl residue and 2'-fucosyllactose was almost as good an acceptor as the Type 1 disaccharide. The properties of the purified enzyme with regard to specificity, divalent cation requirements, pH optimum, and M(r), closely resembled those of the Lewis-blood-group gene associated alpha-3/4-fucosyltransferase isolated from human milk.

Reassessment of the acceptor specificity and general properties of the Lewis blood-group gene associated alpha-3/4-fucosyltransferase purified from human milk

The acceptor specificity and general properties of a Lewis blood-group gene associated alpha-3/4-L-fucosyltransferase isolated from human milk have been examined at the penultimate purification stage involving affinity chromatography on GDP-hexanolamine Sepharose, and after a subsequent gel filtration step on Sephacryl S-200. Both preparations transferred fucose to the O-4 position of N-acetylglucosamine in Type 1 (Gal beta 1-3GlcNAc-R) acceptors and the O-3 position of glucose in lactose-based (Gal beta 1-4Glc) oligosaccharides, and both used Type 1 sialylated compounds when the terminal N-acetylneuraminic acid was present in alpha-2,3 linkage. The striking difference between the two preparations was in their reactivity with Type 2 (Gal beta 1-4GlcNAc-R) chains; after Sephacryl S-200 chromatography the apparent KM values for the alpha-3/4- preparation with unsubstituted low-molecular-weight Type 2 oligosaccharides were considerably increased. Substitution of the terminal galactose with sialic acid in alpha-2,3 linkage decreased the KM values for low-molecular-weight oligosaccharides but no detectable incorporation of fucose was observed into N-acetyllactosamine end-groups of glycoproteins with N-linked oligosaccharide chains, irrespective of the presence of sialic acid in the terminal sequences.