Activation of glycosyl methylpropiolates by TfOH

Activation of glycosyl methylpropiolates by TfOH was investigated. Armed and superarmed glycosyl donors can be activated by use of 0.2 equivalent TfOH whereas 1.0 equivalent of TfOH was required for the activation of the disarmed glycosyl donors. All the glycosidations gave very good yields. The method is suitable for synthesis of glycosides and disaccharides and it may result in the hydrolysis of the interglycosidic bond if the sugar at the non-reducing end is armed or superarmed. These problems are not seen when gold-catalyzed activation procedures are invoked for the activation of glycosyl alkynoates.

Molecular forces driving protein complexation of lentil and whey proteins: Structure-function relationships of trehalose-conjugated protein complexes on protein digestibility and solubility

Plant-based proteins are often associated with a range of health benefits. Most research primarily investigates pea and soy proteins, while lentil proteins received minimal attention. This study evaluates the effect of protein complexation (using the pH-shifting technique) coupled with trehalose conjugation on lentil and whey proteins. The protein structures after the modification were analysed using spectroscopic methods: Fourier-transform infrared, ultraviolet spectra, and fluorescence spectra. The amide group I, conformation protein, and tertiary structure of the trehalose-conjugated lentil-whey protein complexes (T-LWPs) showed significant changes (P < 0.05). Moreover, the surface properties (surface hydrophobicity and charges) of T-LWPs were significantly modified (P < 0.05), from 457 to 324 a.u and from 36 to -40 mV, respectively. Due to these modifications on the protein structures, the protein digestibility (80-86%) and water solubility (90-94.5%) of T-LWPs increased significantly (P < 0.05) with the increase in the trehalose concentration, from 0 (control) to 5% (w/w), respectively. This study suggested that coupling protein complexation and trehalose conjugation can enhance the overall properties of lentil-based protein complexes. With this enhancement, more opportunities in the utilisation of lentils are to be expected.

Discrimination of Disaccharide Isomers of Different Glycosidic Linkages Using a Modified MspA Nanopore

Disaccharides are composed of two monosaccharide subunits joined by a glycosidic linkage in an α or β configuration. Different combinations of isomeric monosaccharide subunits and different glycosidic linkages result in different isomeric disaccharide products. Thus, direct discrimination of these disaccharide isomers from a mixture is extremely difficult. In this paper, a hetero-octameric Mycobacterium smegmatis porin A (MspA) nanopore conjugated with a phenylboronic acid (PBA) adapter was applied for disaccharide sensing, with which three most widely known disaccharides in nature, including sucrose, lactose and maltose, were clearly discriminated. Besides, all six isomeric α-D-glucopyranosyl-D-fructoses, differing only in their glycosidic linkages, were also well resolved. Assisted by a custom machine learning algorithm, a 0.99 discrimination accuracy is achieved. Nanopore discrimination of disaccharide isomers with different glycosidic linkages, which has never been previously demonstrated, is inspiring for nanopore saccharide sequencing. This sensing capacity was also applied in direct identification of isomaltulose additives in a commercial sucrose-free yogurt, from which isomaltulose, lactose and L-lactic acid were simultaneously detected.

Differences in organic nitrogen transformation during chicken manure composting with the addition of different disaccharides

The effect of different carbon sources on nitrogen (N) transformation and N loss through nitrogenous gas volatilization during composting of manure is not clear. Disaccharides had moderate degradation stability compared to monosaccharides and polysaccharides. Therefore, we investigated the effect of adding sucrose (nonreducing sugar) and maltose (reducing sugar) as carbon sources on volatile N loss and hydrolysable organic nitrogen (HON) transformation. HON is composed of bioavailable organic nitrogen (BON) and hydrolysable unknown nitrogen (HUN). Three laboratory-scale experimental groups were conducted with control (CK), 5 % sucrose (SS), and 5 % maltose (MS) addition. Our findings indicated that, while excluding leaching and surface runoff, adding sucrose and maltose decreased the N loss through gas volatilization by 15.78 % and 9.77 %, respectively. The addition of maltose significantly increased the BON content (P < 0.05), which was 6.35 % higher than in CK. The addition of sucrose led to an increase in HUN content (P < 0.05), which was 22.89 % higher than that in CK. In addition, the core microbial communities associated with HON changed after the addition of disaccharides. The transformation of the HON fractions was facilitated by the succession of microbial communities. Ultimately, variation partition analysis (VPA) and structural equation modeling (SEM) verified that the core microbial communities were the major contributors to promoting HON transformation. In summary, adding disaccharides could promote the different transformations of organic nitrogen (ON) and reduce the volatilization of nitrogenous gases by changing the succession of the core microbial communities during composting. This study provided theoretical and technical support for reducing volatile N loss and promoting ON fraction sequestration during composting. Furthermore, the effect of carbon source addition on the nitrogen cycle was also explored.

Influence of disaccharide and monosaccharide on the rheological behavior of dry-heated alocasia starch under high pressure assisted treatment

High viscous products made with starch are of great scientific interest in the food, pharmaceutical, and cosmetic industries because they can be used to make creams and gels, as well as functional foods and nutritional products. But, obtaining a good quality highly viscous materials represent a technological challenge. In this present study, the effect of high-pressure treatment at 120 psi for different time interval on the mixture of dry-heated alocasia starch in presence of monosaccharide and disaccharide was studied. A flow measurement test on the samples revealed their shear-thinning behavior. With 15 min of high-pressure processing time, the dry-heated starch and saccharide mixtures displayed the highest viscosity. The dynamic viscoelasticity measurement showed that the storage and loss modulus was enhanced significantly after high-pressure treatment, and all pressure-treated samples showed a gel-like structure (G/>G//). In temperature sweep measurement, the rheological profile of storage modulus, loss modulus, and complex viscosity exhibited a two-stage pattern, i.e., first increased, then decreased, and their values were enhanced significantly after pressure treatment. The resultant highly viscous dry-heated starch and saccharide system have various functionalities in diverse food and pharmaceutical products.

Relationships of Intestinal Lactase and the Small Intestinal Microbiome with Symptoms of Lactose Intolerance and Intake in Adults

BACKGROUND

Approximately two-thirds of adults are genetically predisposed to decreased lactase activity after weaning, putting them at risk of lactose intolerance. However, symptoms are a poor marker of lactose maldigestion.

AIMS

We assessed association between self-reported lactose intolerance and intestinal lactase, lactose intake, and the small intestinal microbiome.

METHODS

Patients 18-75 years presenting for upper endoscopy were recruited prospectively. Observational study participants completed a lactose intolerance symptom questionnaire and reported lactose intake. Post-bulbar biopsies were obtained to measure lactase activity and assess the small intestinal mucosal microbiome. We compared intestinal lactase between patients with and without lactose intolerance. We assessed associations between lactose intolerance symptoms and lactase and lactose intake. We examined associations of small bowel microbial composition with self-reported lactose intolerance and symptoms.

RESULTS

Among 34 patients, 23 (68%) reported lactose intolerance. Those with lactose intolerance had higher total symptom scores, more frequent bowel urgency, and more bowel movements after consuming dairy. The proportion of individuals with abnormal lactase activity did not differ by lactose intolerance status. Median lactase levels were correlated with total lactose intolerance symptom scores (p = 0.038) and frequency of bowel urgency (p = 0.012). Daily lactose intake did not differ between groups. In 19 patients, we observed significant associations of small intestinal microbiome beta diversity with stool consistency after consuming dairy (p = 0.03).

CONCLUSIONS

Intestinal lactase is associated with lactose intolerance symptoms and bowel urgency in adults but does not distinguish the clinical phenotype entirely. Studying other contributing factors (microbiota, diet) may further clarify the pathophysiology of lactose intolerance.

Effect of oximation reagents on gas chromatographic separation of eight different kinds of mono- and di-saccharides

The objective of this study was to investigate the effect of oximation reagents in simultaneous analysis of mono and di-saccharides using gas chromatography. Sugar oximation with O-ethylhydroxylamine separated all the mono- and di-saccharides while hydroxylamine and O-benzylhydroxylamine could make most of the saccharides separable except for xylose and arabinose. Resolution of xylose: arabinose, galactose: glucose, and fructose: galactose oximated by O-ethylhydroxylamine in DB-1ms column were 1.66, 2.15, and 6.19, respectively, which were above 1.5 and were officially acceptable for quantitative analysis according to the AOAC guideline. The applied method was then verified by the method validation parameters; LOD (0.011-0.02 mg/100 g), LOQ (0.032-0.061 mg/100 g), linearity (R² = 0.9991-1.0000) and precision (repeatability RSD: 1.4-3.3%, reproducibility RSD: 1.7-7.6%). The greatest amounts of xylose (19.03 ± 0.38 mg/100 g), maltose (6,274.48 ± 173.59 mg/100 g) were found in the oyster sauce, and the contents of glucose (10,565.00 ± 125.31 mg/100 g), galactose (170.40 ± 4.62 mg/100 g) were greatest in soybean paste.

Comprehensive analysis of heparinase derived heparin-products using two-dimensional liquid chromatography coupled with mass spectrometry

Heparin is a linear sulfated polysaccharide. It is composed of a repeating disaccharide unit with different sulfo patterns. The compositional analysis after heparin was decomposed to disaccharides and enzyme resistant domains is an important way to delve into its structure. Strong anion exchange (SAX) chromatography is commonly used for the compositional analysis due to its high resolution, stability and capability of quantitation. However, nonvolatile salt in mobile phase is not compatible with MS, then the structural domains cannot be identified without standards. Here, a new two-dimensional liquid chromatography system, multiple heart cut (MHC), was developed and linked to mass spectrometry (MS) directly to provide a comprehensive analysis of enzyme digested heparin. SAX was applied as the first dimensional chromatography, in which 17 peaks were observed and integrated in the digested heparin. Size-exclusion chromatography (SEC) was used as the second dimensional chromatography to desalt efficiently. Structural information of each component was then obtained with MS, including eight common disaccharides, eight enzyme resistant tetrasaccharides and a heparin-core protein linkage domain. The comparison of enzyme digested heparins obtained from different vendors using this system suggested their similar major structure and activity, but slightly different production processes.

The FOCCUS study: a prospective evaluation of the frequency, severity and treatable causes of gastrointestinal symptoms during and after chemotherapy

BACKGROUND

The underlying mechanisms of chemotherapy-induced gastrointestinal (GI) symptoms are poorly researched. This study characterised the nature, frequency, severity and treatable causes for GI symptoms prospectively in patients undergoing chemotherapy for GI malignancy.

METHODS

Patients receiving chemotherapy for a GI malignancy were assessed pre-chemotherapy, then monthly for 1 year using the Gastrointestinal Symptom Rating Scale, a validated patient-reported outcome measure. Patients with new, troublesome GI symptoms were offered investigations to diagnose the cause(s). Their oncologist was alerted when investigations were abnormal.

RESULTS

A total of 241 patients, 60% male, median age 63 years (range 30-88), were enrolled; 122 patients were withdrawn, 93%, because of progressive disease or death. During the study, > 20% patients reported chronic faecal incontinence and > 10% reported moderate or severe problems with taste, dysphagia, belching, heartburn, early satiety, appetite, nausea, abdominal cramps, peri-rectal pain, rectal flatulence, borborygmi, urgency of defecation or tenesmus. Thirty percent reported continuing passage of hard stools and 30% on-going diarrhoea. Moderate or severe fatigue affected 40% participants at its peak and persisted in 15% at 1 year. Toxicity dictated change in chemotherapy for 13-29% patients/month. Common Terminology Criteria for Adverse Events underestimated gastrointestinal morbidity. Pre-chemotherapy screening identified previously undiagnosed pathology: exocrine pancreatic insufficiency (9%), vitamin B12 deficiency (12%) and thyroid dysfunction (20%). Patients often refused investigations to diagnose their chemotherapy-induced symptoms; however, for every three investigations performed, one treatable cause was diagnosed: particularly small intestinal bacterial overgrowth (54%), bile acid malabsorption (43%), previously not described after chemotherapy, and unsuspected urinary tract infection (17%).

CONCLUSIONS

Patients undergoing chemotherapy for GI malignancy commonly have difficult GI symptoms requiring active management which does not occur routinely. The underlying causes for these symptoms are often treatable or curable. Randomised trials are urgently needed to show whether timely investigation and treatment of symptoms improve quality of life and survival.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT02121626.

Indium-mediated allylation of disaccharides

The indium-mediated allylation followed by ozonolysis has been applied for the elongation of different disaccharides such as cellobiose, lactose and maltose. This reaction sequence and per-O-acetylation produced the expected mixture of α/β-pyranoid as well as α/β-furanoid isomers. The main product in all cases adopted the β-pyranose form and could be isolated and fully characterized with the help of NMR-spin simulations. Thorough investigation of the side products throughout optimization of the conditions for the ozonolysis resulted in the discovery of a novel 12 membered bridged disaccharide.

Formation of protein-bound Nε-carboxymethyllysine and Nε-carboxyethyllysine in ground pork during commercial sterilization as affected by the type and concentration of sugars

This research was aimed to investigate the formation of protein-bound N^ε-carboxymethyllysine (CML) and N^ε-carboxyethyllysine (CEL) in ground pork at 121 °C (5-30 min) as affected by sugars (1-9% w/w, glucose, fructose, lactose, and sucrose).The addition of reducing sugar significantly (P < 0.05) increased the levels of CML and CEL in heat treated pork samples. Even adding 1% of glucose in pork could lead to 3.8 and 4.0 times increase in the formation rate constant (zero-order) of CML and CEL, respectively. In a typical commercial sterilization process (121 °C, 30 min), adding glucose, fructose or lactose in pork resulted in an average increase of 224-581%, 26-276%, and 8-189% CML, and 217-720%, 213%-15.8 times, and 20-150% CEL, respectively, depending on the sugar concentration. Sucrose did not promote the formation of CML and CEL in pork during heating.

Computerized Molecular Modeling of Carbohydrates

Computerized molecular modeling continues to increase in capability and applicability to carbohydrates. This chapter covers nomenclature and conformational aspects of carbohydrates, perhaps of greater use to computational chemists who do not have a strong background in carbohydrates, and its comments on various methods and studies might be of more use to carbohydrate chemists who are inexperienced with computation. Work on the intrinsic variability of glucose, an overall theme, is described. Other areas of the authors' emphasis, including evaluation of hydrogen bonding by the atoms-in-molecules approach, and validation of modeling methods with crystallographic results are also presented.

Trehalose alleviates oxidative stress-mediated liver injury and Mallor-Denk body formation via activating autophagy in mice

Autophagy is a degradation pathway for long-lived cytoplasmic proteins or damaged organelles and also for many aggregate-prone and disease-causing proteins. Endoplasmic reticulum (ER) stress and oxidative stress are associated with the pathophysiology of various liver diseases. These stresses induce the accumulation of abnormal proteins, Mallory-Denk body (MDB) formation and apoptosis in hepatocytes. A disaccharide trehalose had been reported to induce autophagy and decrease aggregate-prone proteins and cytotoxicity in neurodegenerative disease models. But the effects of trehalose in hepatocytes have not been fully understood. We examined the effect of trehalose on autophagy, ER stress and oxidative stress-mediated cytotoxicity and MDB formation in hepatocytes using mice model with 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC) treatment for 3 months. We administered trehalose by intraperitoneal injection of water containing 10% trehalose (0.02 mg/g body weight) every other day for 3 months. Our results demonstrated that trehalose induced autophagy and reduced ER stress, oxidative stress, MDB formation and apoptosis in hepatocytes of DDC-fed mice by Western blotting and immunostaining analyses. Electron microscopy revealed that trehalose induced autolysosome formation, which located is close to the MDBs. Thus, our findings suggest that trehalose can become a therapeutic agent for oxidative stress-related liver diseases via activating autophagy.

Trehalose intake and exercise upregulate a glucose transporter, GLUT8, in the brain

Physical exercise influences cognitive function through a cascade of cellular processes that promote angiogenesis and neurogenesis. Autophagy is a cellular degradation system that is capable of producing energy in response to various conditions such as starvation, physical exercise and several treatments. Our previous report demonstrated that a disaccharide, trehalose, induced autophagy in the brain and reduced the levels of potentially toxic proteins. To achieve more efficient induction of autophagy in the brain, in this study, we examined the effect of disaccharide intake combined with exercise on autophagy in vivo. Consistent with the results of previous studies, our biochemical analyses demonstrated that trehalose increased the level of lipidated LC3 (LC3II) in the brain and liver of adult mice. However, contrary to our expectation, treadmill exercise reduced the level of LC3II in the brain and liver. Interestingly, glycogen storage was preserved in the liver of trehalose-intake mice even after exercise. Moreover, the trehalose transporter GLUT8 was increased in the liver by trehalose or in the brain by trehalose together with exercise. In contrast, the level of GLUT4 remained stable in the liver and brain even after exercise. These findings suggest that trehalose and GLUT8 coordinately contribute to energy supply in the brain.

Genistein Enhances or Reduces Glycosaminoglycan Quantity in a Cell Type-Specific Manner

BACKGROUND/AIMS

Genistein is a natural isoflavone enriched in soybeans. It has beneficial effects for patients with mucopolysaccharidose type III through inhibiting glycosaminoglycan biosynthesis. However, other studies indicate that genistein does not always inhibit glycosaminoglycan biosynthesis.

METHODS

To understand the underlying molecular mechanisms, CHOK1, CHO3.1, CHO3.3, and HCT116 cells were treated with genistein and the monosaccharide compositions and quantity of all glycans from the cell lysate were measured after thorough acid hydrolysis followed by HPLC analysis. In addition, the glycosaminoglycan disaccharide compositions were obtained by stable isotope labeling coupled with LC/MS analysis.

RESULTS

Genistein treatment reduced the amount of glycans but increased the amount of glycosaminoglycans in HCT116 cells. In contrast, genistein treatment reduced both glycan and glycosaminoglycan quantities in CHOK1, CHO3.1, and CHO3.3 cells in addition to differential changes in glycosaminoglycan disaccharide compositions.

CONCLUSION

Genistein treatment reduced overall glycan quantity but glycosaminoglycan quantities were either increased or decreased in a cell type-dependent manner.

Osteogenic differentiation enhances the MC3T3-E1 secretion of glycosaminoglycans with an affinity for basic fibroblast growth factor and bone morphogenetic protein-2

Introduction

It is generally recognized that a wide variety of morphogens and growth factors bind to the glycosaminoglycans (GAG) of proteoglycans (PG) to affect their bioavailability to ligands. Many growth factors involving in osteogenic differentiation require the GAG side chains to facilitate their interaction to the cell surface receptors and the biosynthesis of osteogenic proteins. The objective of this study is to investigate the secretion of GAG from MC3T3-E1 pre-osteoblasts of a murine bone calvaria during the osteogenic differentiation.

Methods

When MC3T3-E1 cells were cultured in the differentiation medium (DM) containing bone morphogenetic protein (BMP)-2, the alkaline phosphatase activity, calcium content and the amount of basic fibroblast growth factor (bFGF)- or BMP-2-bound sulfated GAG were determined. Moreover, the disaccharide analysis of the GAG was performed.

Results

When MC3T3-E1 cells were cultured in the differentiation medium (DM) containing bone morphogenetic protein (BMP)-2, the alkaline phosphatase activity and calcium content were significantly enhanced compared with those of the BMP-2-free DM and normal medium with or without BMP-2. Significantly higher amount of GAG secreted was detected for cells cultured in the DM containing BMP-2, in contrast to other culture conditions. The GAG secreted had an affinity for BMP-2 and basic fibroblast growth factor (bFGF). The disaccharide analysis of GAG demonstrated that the percentage of ΔHexA α1,4GlcNSO₃ and ΔHexA (2-OSO₃) α1,4GlcNSO₃ increased, but that of ΔHexA α1,4GlcNSO₃(6-OSO₃) decreased (ΔHexA: unsaturated uronic acid residue, GlcNSO₃: N-sulfated glucosamine, ΔHexA (2-OSO₃): unsaturated uronic acid 2-sulfate residue, GlcNSO₃(6-OSO₃): N-sulfated glucosamine 6-sulfated).

Conclusion

It was found that the osteogenic differentiation allowed cells to enhance the secretion of GAG with an affinity for BMP-2 and bFGF.

Quantification of Soluble Sugars and Sugar Alcohols by LC-MS/MS

Sugars are simple carbohydrates composed primarily of carbon, hydrogen, and oxygen. They play a central role in metabolism as sources of energy and as building blocks for synthesis of structural and nonstructural polymers. Many different techniques have been used to measure sugars, including refractometry, colorimetric and enzymatic assays, gas chromatography, high-performance liquid chromatography, and nuclear magnetic resonance spectroscopy. In this chapter we describe a method that combines an initial separation of sugars by high-performance anion-exchange chromatography (HPAEC) with detection and quantification by tandem mass spectrometry (MS/MS). This combination of techniques provides exquisite specificity, allowing measurement of a diverse range of high- and low-abundance sugars in biological samples. This method can also be used for isotopomer analysis in stable-isotope labeling experiments to measure metabolic fluxes.

Physicochemical Aspects of the Biological Functions of Trehalose and Group 3 LEA Proteins as Desiccation Protectants

In this review, we first focus on the mechanism by which the larva of the sleeping chironomid, Polypedilum vanderplanki, survives an extremely dehydrated state and describe how trehalose and probably late embryogenesis abundant (LEA) proteins work as desiccation protectants. Second, we summarize the solid-state and solution properties of trehalose and discuss why trehalose works better than other disaccharides as a desiccation protectant. Third, we describe the structure and function of two model peptides based on group 3 LEA proteins after a short introduction of native LEA proteins themselves. Finally, we present our conclusions and a perspective on the application of trehalose and LEA model peptides to the long-term storage of biological materials.

Glycan structure of Gc Protein-derived Macrophage Activating Factor as revealed by mass spectrometry

Disagreement exists regarding the O-glycan structure attached to human vitamin D binding protein (DBP). Previously reported evidence indicated that the O-glycan of the Gc1S allele product is the linear core 1 NeuNAc-Gal-GalNAc-Thr trisaccharide. Here, glycan structural evidence is provided from glycan linkage analysis and over 30 serial glycosidase-digestion experiments which were followed by analysis of the intact protein by electrospray ionization mass spectrometry (ESI-MS). Results demonstrate that the O-glycan from the Gc1F protein is the same linear trisaccharide found on the Gc1S protein and that the hexose residue is galactose. In addition, the putative anti-cancer derivative of DBP known as Gc Protein-derived Macrophage Activating Factor (GcMAF, which is formed by the combined action of β-galactosidase and neuraminidase upon DBP) was analyzed intact by ESI-MS, revealing that the activating E. coli β-galactosidase cleaves nothing from the protein-leaving the glycan structure of active GcMAF as a Gal-GalNAc-Thr disaccharide, regardless of the order in which β-galactosidase and neuraminidase are applied. Moreover, glycosidase digestion results show that α-N-Acetylgalactosamindase (nagalase) lacks endoglycosidic function and only cleaves the DBP O-glycan once it has been trimmed down to a GalNAc-Thr monosaccharide-precluding the possibility of this enzyme removing the O-glycan trisaccharide from cancer-patient DBP in vivo.

Identification of core active disaccharides in heparin for HGF-inducing activity

Objectives:

To ascertain the positions of sulfated groups for HGF-inducing activity using differently sulfated heparin disaccharides and to investigate whether the heparin disaccharide elevates HGF levels in plasma in vivo and exerts protective effects on acute liver injury.

Materials and Methods:

The heparin disaccharides ΔUA-GlcNS, ΔUA (2S)-GlcN, ΔUA-GlcNAc (6S), ΔUA-GlcNS (6S), ΔUA (2S)-GlcNS, ΔUA (2S)-GlcNAc (6S), ΔUA-GlcNAc and ΔUA (2S)-GlcNS (6S) were added to MRC-9 fibroblasts and HGF concentrations in culture media were determined by enzyme-linked immunosorbent assay. Furthermore, ΔUA-GlcNS (100 μg/head) was injected into C57BL/6 mice and plasma levels of HGF measured at 12 h. After acute hepatitis was induced by CCl₄ (15 mg/kg) in mice, liver specimens were stained with hematoxylin and eosin (H and E). Levels of aspartate aminotransferase and alanine aminotransferase were measured at 24 h.

Results:

Among the disaccharides investigated, ΔUA-GlcNS, ΔUA-GlcNAc (6S) and ΔUA-GlcNS (6S) stimulated HGF production in MRC-9 fibroblasts. However, none of the 2-O-sulfated disaccharides [ΔUA (2S)-GlcNS, ΔUA (2S)-GlcNAc (6S) and ΔUA (2S)-GlcNS (6S)] showed any activity despite the presence of N-sulfated and/or 6-O-sulfated disaccharides. Thus, 2-O-sulfation of hexuronic acid has an inhibitory effect. Moreover, ΔUA-GlcNS administration increased plasma levels of HGF in normal mice and prevented CCl₄-induced liver injury in mice.

Conclusions:

N-sulfation and/or 6-O-sulfation of glucosamine with nonsulfated hexuronic acid provides a structural basis for the HGF-inducing activity of disaccharides. ΔUA-GlcNS increases plasma levels of HGF and protects against CCl₄-induced acute liver injury.

Crystal structures of β-primeverosidase in complex with disaccharide amidine inhibitors

β-Primeverosidase (PD) is a disaccharide-specific β-glycosidase in tea leaves. This enzyme is involved in aroma formation during the manufacturing process of oolong tea and black tea. PD hydrolyzes β-primeveroside (6-O-β-d-xylopyranosyl-β-d-glucopyranoside) at the β-glycosidic bond of primeverose to aglycone, and releases aromatic alcoholic volatiles of aglycones. PD only accepts primeverose as the glycone substrate, but broadly accepts various aglycones, including 2-phenylethanol, benzyl alcohol, linalool, and geraniol. We determined the crystal structure of PD complexes using highly specific disaccharide amidine inhibitors, N-β-primeverosylamidines, and revealed the architecture of the active site responsible for substrate specificity. We identified three subsites in the active site: subsite -2 specific for 6-O-β-d-xylopyranosyl, subsite -1 well conserved among β-glucosidases and specific for β-d-glucopyranosyl, and wide subsite +1 for hydrophobic aglycone. Glu-470, Ser-473, and Gln-477 act as the specific hydrogen bond donors for 6-O-β-d-xylopyranosyl in subsite -2. On the other hand, subsite +1 was a large hydrophobic cavity that accommodates various aromatic aglycones. Compared with aglycone-specific β-glucosidases of the glycoside hydrolase family 1, PD lacks the Trp crucial for aglycone recognition, and the resultant large cavity accepts aglycone and 6-O-β-d-xylopyranosyl together. PD recognizes the β-primeverosides in subsites -1 and -2 by hydrogen bonds, whereas the large subsite +1 loosely accommodates various aglycones. The glycone-specific activity of PD for broad aglycone substrates results in selective and multiple release of temporally stored alcoholic volatile aglycones of β-primeveroside.

Synthesis of 4-methylumbelliferyl α-d-mannopyranosyl-(1→6)-β-d-mannopyranoside and development of a coupled fluorescent assay for GH125 exo-α-1,6-mannosidases

Certain bacterial pathogens possess a repertoire of carbohydrate processing enzymes that process host N-linked glycans and many of these enzymes are required for full virulence of harmful human pathogens such as Clostridium perfringens and Streptococcus pneumoniae. One bacterial carbohydrate processing enzyme that has been studied is the pneumococcal virulence factor SpGH125 from S. pneumoniae and its homologue, CpGH125, from C. perfringens. These exo-α-1,6-mannosidases from glycoside hydrolase family 125 show poor activity toward aryl α-mannopyranosides. To circumvent this problem, we describe a convenient synthesis of the fluorogenic disaccharide substrate 4-methylumbelliferone α-d-mannopyranosyl-(1→6)-β-d-mannopyranoside. We show this substrate can be used in a coupled fluorescent assay by using β-mannosidases from either Cellulomonas fimi or Helix pomatia as the coupling enzyme. We find that this disaccharide substrate is processed much more efficiently than aryl α-mannopyranosides by CpGH125, most likely because inclusion of the second mannose residue makes this substrate more like the natural host glycan substrates of this enzyme, which enables it to bind better. Using this sensitive coupled assay, the detailed characterization of these metal-independent exo-α-mannosidases GH125 enzymes should be possible, as should screening chemical libraries for inhibitors of these virulence factors.

Differentiation of glucose-containing disaccharides isomers by fragmentation of the deprotonated non-covalent dimers using negative electrospray ionization tandem mass spectrometry

In this work, the glucose-containing disaccharide isomers were studied using negative electrospray ionization tandem mass spectrometry (ESI-MS/MS). Interestingly, the full-scan mass spectra of the disaccharides revealed that the deprotonated dimers were the predominant gas phase ions during ionization process. Importantly, several diagnostic fragment ions relative to linkage positions and anomeric configurations, arising from the covalent bond dissociation of dimers without breakdown of the non-covalent complexes, can be detected in the tandem mass spectra. Based on the scarce fragmentation characteristic, an original and simple approach for structural discrimination of disaccharide isomers was put forward. In addition, density functional theory (DFT) was employed to find out the reason why several fragmentations of intramolecular sugar bonds had preceded breakdown of the non-covalent complexes.