Branched arabino-oligosaccharides isolated from sugar beet arabinan

Structural characterization of a Chlorella heteropolysaccharide by analyzing its depolymerized product and finding an inducer of human dendritic cell maturation

Chlorella polysaccharides have been gaining increasing attention because of their high yield from dried Chlorella powder and their remarkable immunomodulatory activity. In this study, the major polysaccharide fraction, CPP-3a, in Chlorella pyrenoidosa, was isolated, and its detailed structure was investigated by analyzing the low-molecular-weight product prepared via free radical depolymerization. The results indicated that CPP-3a with a molecular weight of 195.2 kDa was formed by →2)-α-L-Araf-(1→, →2)-α-D-Rhap-(1→, →5)-α-L-Araf-(1→, →3)-β-D-Glcp-(1→, →4)-α-D-Glcp-(1→, →4)-α-D-GlcpA-(1→, →2,3)-α-D-Manp-(1→, →3,4)-α-D-Manp-(1→, →3,4)-β-D-Galp-(1→, →3,6)-β-D-Galp-(1→, and →2,3,6)-α-D-Galp-(1→ residues, branched at C2, C3, C4, or C6 of α/β-D-Galp and α-D-Manp, and terminated by α/β-L-Araf, α-L-Arap, α-D-Galp, and β-D-Glcp. Biological assays showed that CPP-3a significantly altered the dendritic morphology of immature dendritic cells (DCs). Enhanced CD80, CD86, and MHC I expression on the cell surface and decreased phagocytic ability indicated that CPP-3a could induce the maturation of DCs. Furthermore, CPP-3a-stimulated DCs not only stimulated the proliferation of allogeneic naïve CD4+ T cells and the secretion of IFN-γ, but also directly stimulated the activation and proliferation of CD8+ T cells through cross-antigen presentation. These findings indicate that CPP-3a can promote human DC maturation and T-cell stimulation and may be a novel DC maturation inducer with potential developmental value in DC immunotherapy.

Structure of KOH-soluble polysaccharides from сoniferous greens of Norway spruce (Picea abies): The pectin-xylan-AGPs complex. Part 1

Using 7 % KOH, the polysaccharide PAK has been isolated from the coniferous greens of Norway spruce. PAK was found to contain predominantly arabinoglucuronoxylan, xyloglucan and arabinan, but also pectic polysaccharides, glucomannan and arabinogalactan proteins (AGPs), as determined by 1D/2D NMR analysis. It was found that fractionation of PAK on DEAE-cellulose resulted in simultaneous elution of pectins, arabinoglucuronoxylans and AGPs. It was evident that the content of 4-OMe-α-D-GlcpA and xylose, 1,4-β-D-GlcpA, and T-β-D-GlcpA increased with an increase in NaCl concentration. However, 1,4-α-D-GalpA content was almost independent of NaCl concentration, indicating unchanged pectic polysaccharide concentration. Interestingly, pectins extracted with 0.1-0.3 M NaCl solutions were richer in rhamnogalacturonan-I (RG-I) than those extracted with water and 0.01 M NaCl. Conclusion: The content of RG-I, AGPs and arabinoglucuronoxylan rises with rising NaCl concentration. An intense signal indicating an intermolecular linkage between the xylan and RG-I domains, i.e. that part of the arabinoglucuronoxylan is covalently bound to RG-I, is observed in the HMBC spectra of the polysaccharides obtained. The discovery here of a new relationship between rhamnogalacturonan I and xylan contradicts the prevailing cell wall model.

Chromatography based profiling of feruloylated arabinans and galactans

Profiling of pectic arabinans and galactans by analysis of the released oligosaccharides after backbone cleavage provides information on the complexity of the polymer structure. In plants of the family Amaranthaceae, arabinan and galactan substitution with ferulates extends the polysaccharide complexity, changing its chemical properties. Knowledge of the ferulate environment is crucial to understand structure-function-relationships of feruloylated pectins. Here, we present an approach to separate enzymatically generated feruloylated and non-feruloylated arabino- and galactooligosaccharides, followed by deesterification and semiquantitative analysis by HPAEC-PAD using previously reported relative response factors. Application of this approach to sugar beet pectins and insoluble and soluble dietary fiber preparations of amaranth and quinoa suggests that ferulates are preferably incorporated into more complex structures, as nicely demonstrated for feruloylated galactans. Also, ferulate substitution appears to negatively affect enzymatic cleavage by using endo-enzymes. As a consequence, we were able to tentatively identify new feruloylated tri- and tetrasaccharides of galactans isolated from sugar beet pectins.

Rhamnogalacturonan I with β-(1,4)-Galactan Side Chains as an Ever-Present Component of Tertiary Cell Wall of Plant Fibers

The cellulose-enriched tertiary cell walls present in many plant fibers have specific composition, architecture, machinery of formation, and function. To better understand the mechanisms underlying their mode of action and to reveal the peculiarities of fibers from different plant species, it is necessary to more deeply characterize the major components. Next to overwhelming cellulose, rhamnogalacturonan I (RG-I) is considered to be the key polymer of the tertiary cell wall; however, it has been isolated and biochemically characterized in very few plant species. Here, we add RG-I to the list from the phloem fibers of the Phaseolus vulgaris stem that was isolated and analyzed by nuclear magnetic resonance (NMR), dynamic light scattering, and immunolabeling, both within tissue and as an isolated polymer. Additionally, fibers with tertiary cell walls from nine species of dicotyledonous plants from the orders Malphigiales, Fabales, and Rosales were labeled with RG-I-related antibodies to check the presence of the polymer and compare the in situ presentation of its backbone and side chains. The obtained results confirm that RG-I is an obligatory polymer of the tertiary cell wall. However, there are differences in the structure of this polymer from various plant sources, and these peculiarities may be taxonomically related.

Influence of Arabinan Fine Structure, Galacturonan Backbone Length, and Degree of Esterification on the Emulsifying Properties of Acid-Extracted Sugar Beet Pectins

Sugar beet pectins (SBPs) are known for their emulsifying properties, but it is yet unknown which structural elements are most important for functionality. Recent results indicated that the arabinose content has a decisive influence, but the approach applied did not allow causality to be established. In this study, a mostly intact SBP was selectively modified and the obtained pectins were analyzed for their molecular structure and their emulsifying properties. De-esterification only resulted in a moderate increase in droplet size. The length of the pectin backbone only influenced the emulsifying properties when the homogalacturonan backbone was cleaved to a higher extent. By using different arabinan-modifying enzymes, it was demonstrated that both higher portions and chain lengths of arabinans positively influence the emulsifying properties of SBPs. Therefore, we were able to refine the structure-function relationships for acid-extracted SBPs, which can be used to optimize extraction conditions.

Polysaccharides of Salsola passerina: Extraction, Structural Characterization and Antioxidant Activity

The above-ground part of the Salsola passerine was found to contain ~13% (w/w) of polysaccharides extractable with water and aqueous solutions of ammonium oxalate and sodium carbonate. The fractions extracted with aqueous sodium carbonate solutions had the highest yield. The polysaccharides of majority fractions are characterized by similar monosaccharide composition; namely, galacturonic acid and arabinose residues are the principal components of their carbohydrate chains. The present study focused on the determination of antioxidant activity of the extracted polysaccharide fractions and elucidation of the structure of polysaccharides using nuclear magnetic resonance (NMR) spectroscopy. Homogalacturonan (HG), consisting of 1,4-linked residues of α-D-galactopyranosyluronic acid (GalpA), rhamnogalacturonan-I (RG-I), which contains a diglycosyl repeating unit with a strictly alternating sequence of 1,4-linked D-GalpA and 1,2-linked L-rhamnopyranose (Rhap) residues in the backbone, and arabinan, were identified as the structural units of the obtained polysaccharides. HMBC spectra showed that arabinan consisted of alternating regions formed by 3,5-substituted and 1,5-linked arabinofuranose residues, but there was no alternation of these residues in the arabinan structure. Polysaccharide fractions scavenged the 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical at 0.2-1.8 mg/mL. The correlation analysis showed that the DPPH scavenging activity of polysaccharide fractions was associated with the content of phenolic compounds (PCs).

Bioactive polysaccharides and oligosaccharides from garlic (Allium sativum L.): Production, physicochemical and biological properties, and structure-function relationships

Garlic is a common food, and many of its biological functions are attributed to its components including functional carbohydrates. Garlic polysaccharides and oligosaccharides as main components are understudied but have future value due to the growing demand for bioactive polysaccharides/oligosaccharides from natural sources. Garlic polysaccharides have molecular weights of 1 × 10³ to 2 × 10⁶  Da, containing small amounts of pectins and fructooligosaccharides and large amounts of inulin-type fructans ((2→1)-linked β-d-Fruf backbones alone or with attached (2→6)-linked β-d-Fruf branched chains). This article provides a detailed review of research progress and identifies knowledge gaps in extraction, production, composition, molecular characteristics, structural features, physicochemical properties, bioactivities, and structure-function relationships of garlic polysaccharides/oligosaccharides. Whether the extraction processes, synthesis approaches, and modification methods established for other non-garlic polysaccharides are also effective for garlic polysaccharides/oligosaccharides (to preserve their desired molecular structures and bioactivities) requires verification. The metabolic processes of ingested garlic polysaccharides/oligosaccharides (as food ingredients/dietary supplements), their modes of action in healthy humans or populations with chronic conditions, and molecular/chain organization-bioactivity relationships remain unclear. Future research directions related to garlic polysaccharides/oligosaccharides are discussed.

Mechanism of cooperative degradation of gum arabic arabinogalactan protein by Bifidobacterium longum surface enzymes

Gum arabic is an arabinogalactan protein (AGP) that is effective as a prebiotic for the growth of bifidobacteria in the human intestine. We recently identified a key enzyme in the glycoside hydrolase (GH) family 39, 3-O-α-d-galactosyl-α-l-arabinofuranosidase (GAfase), for the assimilation of gum arabic AGP in Bifidobacterium longum subsp. longum. The enzyme released α-d-Galp-(1→3)-l-Ara and β-l-Arap-(1→3)-l-Ara from gum arabic AGP and facilitated the action of other enzymes for degrading the AGP backbone and modified sugar. In this study, we identified an α-l-arabinofuranosidase (BlArafE; encoded by BLLJ_1850), a multidomain enzyme with both GH43_22 and GH43_34 catalytic domains, as a critical enzyme for the degradation of modified α-l-arabinofuranosides in gum arabic AGP. Site-directed mutagenesis approaches revealed that the α1,3/α1,4-Araf double-substituted gum arabic AGP side chain was initially degraded by the GH43_22 domain and subsequently cleaved by the GH43_34 domain to release α1,3-Araf and α1,4-Araf residues, respectively. Furthermore, we revealed that a tetrasaccharide, α-l-Rhap-(1→4)-β-d-GlcpA-(1→6)-β-d-Galp-(1→6)-d-Gal, was a limited degradative oligosaccharide in the gum arabic AGP fermentation of B. longum subsp. longum JCM7052. The oligosaccharide was produced from gum arabic AGP by the cooperative action of the three cell surface-anchoring enzymes, GAfase, exo-β1,3-galactanase (Bl1,3Gal), and BlArafE, on B. longum subsp. longum JCM7052. Furthermore, the tetrasaccharide was utilized by the commensal bacteria.

IMPORTANCE Terminal galactose residues of the side chain of gum arabic arabinogalactan protein (AGP) are mainly substituted by α1,3/α1,4-linked Araf and β1,6-linked α-l-Rhap-(1→4)-β-d-GlcpA residues. This study found a multidomain BlArafE with GH43_22 and GH43_34 catalytic domains showing cooperative action for degrading α1,3/α1,4-linked Araf of the side chain of gum arabic AGP. In particular, the GH43_34 domain of BlArafE was a novel α-l-arabinofuranosidase for cleaving the α1,4-Araf linkage of terminal galactose. α-l-Rhap-(1→4)-β-d-GlcpA-(1→6)-β-d-Galp-(1→6)-d-Gal tetrasaccharide was released from gum arabic AGP by the cooperative action of GAfase, GH43_24 exo-β-1,3-galactanase (Bl1,3Gal), and BlArafE and remained after B. longum subsp. longum JCM7052 culture. Furthermore, in vitro assimilation test of the remaining oligosaccharide using Bacteroides species revealed that cross-feeding may occur from bifidobacteria to other taxonomic groups in the gut.

Structure of KOH-extractable polysaccharides of tree greenery of from Siberian fir Abies sibirica Ledeb

Polysaccharide AS_K was extracted with aqueous KOH from the Abies sibirica foliage. Pectin, xylan, AGPs and xyloglucan were isolated from AS_K by anion-exchange chromatography and Smith degradation, combined with enzymatic cleavage. Potential interactions between those polymers were examined. Since xylan, AGPs, RG-I and glucan were co-fractionated following complete removal of galacturonan (HG) with polygalacturonase, it can be inferred that the enzymatic cleavage of HG did not affect co-fractionation of cross-linking glycans, RG-I and AGPs. These were hypothesized to be bound via a covalent cross-link, as the removal of HG regions did not affect this complex. Given that pectin was represented solely by RG-I regions, it can be assumed that some of glucan, xylan and AGPs were associated directly with RG-I. Besides, the enzymatic hydrolysis eliminated most of xylose and rhamnose. This suggests implicitly that some of xylan was linked to RG-I.

Structure, physicochemical characterization, and antioxidant activity of the highly arabinose-branched exopolysaccharide EPS-M2 from Streptococcus thermophilus CS6

Streptococcus thermophilus CS6 could produce the high exopolysaccharide (EPS) level in optimized skimmed milk medium. However, physicochemical properties and structure of these polymers have not been fully characterized. In this study, two purified fractions (EPS-M1 and EPS-M2) exhibited good rheology, thermostability and antioxidant activity. Further monosaccharide composition, molecular weight and NMR analysis indicated EPS-M2 was composed of galactose, arabinose and glucose (5:2.5:1) with an average molecular weight of 2.22 × 10⁴ Da and its suggested repeating unit was →6)-[α-L-Araf-(1 → 3)]-β-D-Galp-(1 → 4)-β-D-Galp-(1 → 6)-[α-L-Araf-(1 → 5)-{α-L-Araf-(1 → 3)}-α-L-Araf-(1 → 3)]-β-D-Galp-(1 → 4)-β-D-Galp-(1 → 6)-[β-D-Galp-(1 → 5)-α-L-Araf-(1 → 5)-α-L-Araf-(1 → 3)]-β-D-Galp-(1 → 6)-[β-D-Galp-(1 → 5)-α-L-Araf-(1 → 5)-{α-L-Araf-(1 → 3)}-α-L-Araf-(1 → 3)]-β-D-Galp-(1→. High EPS production relied on the expression of eps gene cluster and key enzymes of nucleotide sugar metabolism. Overall, EPS-M2 from a potential functional starter S. thermophilus CS6 provided opportunities for natural thickener, stabilizer, and antioxidant agent exploration in the food industry.

Characterization of pectin-xylan-glucan-arabinogalactan proteins complex from Siberian fir Abies sibirica Ledeb

Polysaccharide AS_K was isolated from the Abies sibirica foliage by extraction with an aqueous KOH solution. AS_K was shown to contain structurally different polymers such as arabinoglucuronoxylans, xyloglucans, glucomannans, arabinogalactan-proteins (AGPs). The pectic polysaccharides were also found in the alkaline extract of AS_K and were represented by regions of homogalactorunan and rhamnogalactouronan-I whose side sugar chains were made up chiefly of highly branched 1,5-α-l-arabinan. The potential couplings between those polysaccharides were examined. Our studies showed simultaneous elution of pectin, xyloglucans, arabinoglucuronoxylans and AGPs, indicating that pectins can be covalently bound to the other cell-wall polysaccharides. NMR spectroscopy results revealed that the polysaccharides obtained by ion-exchange chromatography almost had no free reducing ends. These findings corroborate the conclusion that pectin, AGPs, glucan and xylan are bound together. The existence of the covalently bound complex of pectin-xylan-xyloglucan-AGP is suggested herein. Pectin and xylan are hypothesized to be covalently linked through RG-I regions.

Characterization of a novel strain of Aspergillus aculeatinus: From rhamnogalacturonan type I pectin degradation to improvement of fruit juice filtration

Aspergillus spp. are well-known producers of pectinases commonly used in the industry. Aspergillus aculeatinus is a recently identified species but poorly characterized. This study aimed at giving a comprehensive characterization of the enzymatic potential of the O822 strain to produce Rhamnogalacturonan type I (RGI)-degrading enzymes. Proteomic analysis identified cell wall degrading enzymes (cellulases, hemicellulases, and pectinases) that accounted for 92 % of total secreted proteins. Twelve out of fifty proteins were identified as RGI-degrading enzymes. NMR and enzymatic assays revealed high levels of arabinofuranosidase, arabinanase, galactanase, rhamnogalacturonan hydrolases and rhamnogalacturonan acetylesterase activities in aqueous extracts. Viscosity assays carried out with RGI-rich camelina mucilage confirmed the efficiency of enzymes secreted by O822 to hydrolyze RGI, by decreasing viscosity by 70 %. Apple juice trials carried out at laboratory and pilot scale showed an increase in filtration flow rate and yield, paving the way for an industrial use of enzymes derived from A. aculeatinus.

Structural elucidation of three novel oligosaccharides from Kunlun Chrysanthemum flower tea and their bioactivities

Coreopsis tinctoria is commonly called Kunlun Chrysanthemum and a plateau plant with tremendous commercial value in functional tea and medicinal applications. In folk medicine, Kunlun Chrysanthemum flower is often used as an adjunctive therapy for diabetes and Alzheimer's disease. To further explore the chemicals responsible for the health benefits of Kunlun Chrysanthemum flowers, three homogeneous oligosaccharides, CT70-1A, CT70-1B and CT70-2 were isolated, and their detailed structures were determined from chemical and spectral analyses. The three oligosaccharides were composed of glucose, mannose, galactose, and arabinose in different ratios. They showed dose-dependent α-amylase and α-glucosidase inhibitory effects. In addition, they showed NO production inhibitory activities in BV2 cells, with IC₅₀ values of 0.23, 0.24 and 0.27 mM, respectively. Taken together, these results suggested that Kunlun Chrysanthemum oligosaccharides might ameliorate hyperglycemia and neuroinflammation, which could prevent the development of diseases such as type 2 diabetes and Alzheimer's disease. This study provides chemical and bioactive perspectives that support the consumption of Kunlun Chrysanthemum flower tea for health benefits.

An efficient protocol for the preparation of linear arabino-oligosaccharides

In this study, we report the development of an efficient protocol in the preparation of linear arabino-oligosaccharides derived from sugar beet arabinan. By optimizing hydrolytic conditions and separation on tandem Bio-Gel P4 columns, we obtained arabino-oligosaccharides with various degrees of polymerization (DP) from 2 to 15. All of these α-1,5-linked arabino-oligosaccharides are highly pure (>95%) as determined by HPAEC, MALDI-TOF mass spectrometry and ¹³C NMR spectroscopy. Due to their purity, these oligosaccharides can be used as standards to identify other oligosaccharides and as substrates to characterize new arabinan-specific enzymes, as well as for the development of new functional oligosaccharides.

Structural characterization and immunostimulatory activity of polysaccharides from Pyrus sinkiangensis Yu

Two neutral polysaccharides (PSNP-1, 104.7 kDa; PSNP-2, 24.5 kDa) were isolated from the pulp of Pyrus sinkiangensis Yu. by using the combined techniques of ion-exchange and gel permeation chromatography. According to the IR, NMR spectra, monosaccharide composition, and methylation analyses, PSNP-1 was mainly composed of glucose and xylose residues, which form a typical xyloglucan. PSNP-2 contained an arabinan region composed of 1,5-linked Araf residues, a xyloglucan region that was mainly composed of t-, 1,2-linked Xylp, and 1,4-, 1,4,6-linked Glcp residues. PSNP-1 and PSNP-2 could stimulate the cell viability, NO release, and cytokine secretion (IL-6 and TNF-α) of RAW264.7 macrophages at the adosage of 250 μg/mL. It was suggested that PSNP-1 and PSNP-2 may increase macrophage-mediated immunostimulatory activity.

Structural characteristics and rheological properties of alkali-extracted arabinoxylan from dehulled barley kernel

Arabinoxylan (BIF-60) was isolated from barley water-insoluble fiber (BIF) by ethanol precipitation at 60 % (v/v). BIF-60 was composed of xylose (48.5 %) and arabinose (30.3 %). Its average molecular weight was 1360 kDa. Methylation and 1D/2D NMR analysis showed that BIF-60 possessed β-(l→4)-xylan as backbone, comprised of un-substituted (1,4-linked β-Xylp, 56.9 %), mono-substituted (1,2,4-linked and 1,3,4-linked β-Xylp, 22.1 %) and di-substituted (1,2,3,4-lin4ked β-Xylp, 18.4 %) xylose units, as well as other residues (T-Araf-(1→, T-Xylp-(1→, →5)-Araf-(1→, →2)-Araf-(1→, →3)-Araf-(1→ and →4)-Glcp-(1→). BIF-60 exhibited shear-thinning behaviour, low gel stability and weak gelling ability at high concentrations. This work provides a theoretical and experimental basis for molecular structure and properties of the alkali-extracted arabinoxylan from barley kernel, which could guide further functional research and application of barley-derived arabinoxylan.

Structural characteristics of oxalate-soluble polysaccharides from Norway spruce (Picea abies) foliage

Structurally different polymers were derived from Picea abies foliage by successive extraction with water (PA_W), HCl solution (PA_A) and (NH₄)₂C₂O₄ solution (PA_O). The P. abies foliage was found to contain basically low-methoxyl pectin extractable with an (NH₄)₂C₂O₄ solution. PA_W was shown to comprise primarily arabinogalactan-proteins (AGPs); PA_A was composed of mixed AGPs and pectic polysaccharides, with the latter prevailing; and polysaccharide PA_O isolated in the highest yield included chiefly pectic polysaccharides. The major constituents of PA_O were low-methoxyl and low-acetylated 1,4-α-d-galacturonan and partially acetylated RG-I. The sugar side chains of RG-I contained chiefly highly branched 1,5-α-l-arabinan and arabinogalactan type I as a minor constituent. RG-I whose side chains had 1,5-α-l-arabinan represented short regions alternating with non-acetylated and unmethylesterified galacturonan regions. In addition to pectins, polysaccharide PA_O contained AGPs, xylanes and glucomannans, indicating that these polysaccharides are in an intimate interaction.

Two Novel α-l-Arabinofuranosidases from Bifidobacterium longum subsp. longum Belonging to Glycoside Hydrolase Family 43 Cooperatively Degrade Arabinan

Arabinose-containing poly- or oligosaccharides are suitable carbohydrate sources for Bifidobacterium longum subsp. longum However, their degradation pathways are poorly understood. In this study, we cloned and characterized the previously uncharacterized glycoside hydrolase family 43 (GH43) enzymes B. longum subsp. longum ArafC (BlArafC; encoded by BLLJ_1852) and B. longum subsp. longum ArafB (BlArafB; encoded by BLLJ_1853) from B. longum subsp. longum JCM 1217. Both enzymes exhibited α-l-arabinofuranosidase activity toward p-nitrophenyl-α-l-arabinofuranoside but no activity toward p-nitrophenyl-β-d-xylopyranoside. The specificities of the two enzymes for l-arabinofuranosyl linkages were different. BlArafC catalyzed the hydrolysis of α1,2- and α1,3-l-arabinofuranosyl linkages found on the side chains of both arabinan and arabinoxylan. It released l-arabinose 100 times faster from arabinan than from arabinoxylan but did not act on arabinogalactan. On the other hand, BlArafB catalyzed the hydrolysis of the α1,5-l-arabinofuranosyl linkage found on the arabinan backbone. It released l-arabinose from arabinan but not from arabinoxylan or arabinogalactan. Coincubation of BlArafC and BlArafB revealed that these two enzymes are able to degrade arabinan in a synergistic manner. Both enzyme activities were suppressed with EDTA treatment, suggesting that they require divalent metal ions. The GH43 domains of BlArafC and BlArafB are classified into GH43 subfamilies 27 and 22, respectively, but show very low similarity (less than 15% identity) with other biochemically characterized members in the corresponding subfamilies. The B. longum subsp. longum strain lacking the GH43 gene cluster that includes BLLJ_1850 to BLLJ_1853 did not grow in arabinan medium, suggesting that BlArafC and BlArafB are important for assimilation of arabinan.IMPORTANCE We identified two novel α-l-arabinofuranosidases, BlArafC and BlArafB, from B. longum subsp. longum JCM 1217, both of which are predicted to be extracellular membrane-bound enzymes. The former specifically acts on α1,2/3-l-arabinofuranosyl linkages, while the latter acts on the α1,5-l-arabinofuranosyl linkage. These enzymes cooperatively degrade arabinan and are required for the efficient growth of bifidobacteria in arabinan-containing medium. The genes encoding these enzymes are located side by side in a gene cluster involved in metabolic pathways for plant-derived polysaccharides, which may confer adaptability in adult intestines.

The modular arabinanolytic enzyme Abf43A-Abf43B-Abf43C from Ruminiclostridium josui consists of three GH43 modules classified in different subfamilies

The abnA gene from Ruminiclostridium josui encodes the large modular arabinanolytic enzyme, Abf43A-Abf43B-Abf43C, consisting of an N-terminal signal peptide, a Laminin_G_3 module, a GH43_22 module, a Laminin_G_3 module, a Big_4 module, a GH43_26 module, a GH43_34 module and a dockerin module in order with a calculated molecular weight of 204,108. Three truncated enzymes were recombinantly produced in Escherichia coli and biochemically characterized, RjAbf43A consisting of the first Laminin_G_3 module and GH43_22 module, RjAbf43B consisting of the second Laminin_G_3 module, Big_4 module and GH43_26 module, and RjAbf43C consisting of the GH43_34 module. RjAbf43A showed a strong α-l-arabinofuranosidase activity toward sugar beet arabinan, highly branched arabinan but not linear arabinan, thus it acted in the removal of arabinose side chains from sugar beet arabinan. By contrast, RjAbf43B showed a strong exo-α-1,5-l-arabinofuranosidase activity toward linear arabinan and arabinooligosaccharides whereas RjAbf43C showed low activity toward these substrates. Although RjAbf43B was activated by the presence of some metal ions such as Zn²⁺, Mg²⁺ and Ni²⁺, RjAbf43A was inhibited by these ions. RjAbf43A and RjAbf43B attacked sugar beet arabinan in a synergistic manner. By comparison, RjAbf43A-Abf43B containing both GH43_22 and GH43_26 modules showed lower hydrolytic activity toward sugar beet arabinan but higher activity toward sugar beet fiber than the sum of the individual activities of RjAbf43A and RjAbf43B, suggesting that the coexistence of two distinct GH43 modules in a single polypeptide is important for the efficient hydrolysis of an insoluble and natural polysaccharide but not a soluble substrate.

Structural identification and osteogenic activity of a novel heteropolysaccharide obtained from female flowers of Humulus lupulus

The flowers and infructescences of Humulus lupulus are used worldwide in beer brewing as an essential flavoring ingredient, and are also used in traditional Chinese medicine.

Biochemistry of complex glycan depolymerisation by the human gut microbiota

The human gut microbiota (HGM) makes an important contribution to health and disease. It is a complex microbial community of trillions of microbes with a majority of its members represented within two phyla, the Bacteroidetes and Firmicutes, although it also contains species of Actinobacteria and Proteobacteria. Reflecting its importance, the HGM is sometimes referred to as an 'organ' as it performs functions analogous to systemic tissues within the human host. The major nutrients available to the HGM are host and dietary complex carbohydrates. To utilise these nutrient sources, the HGM has developed elaborate, variable and sophisticated systems for the sensing, capture and utilisation of these glycans. Understanding nutrient acquisition by the HGM can thus provide mechanistic insights into the dynamics of this ecosystem, and how it impacts human health. Dietary nutrient sources include a wide variety of simple and complex plant and animal-derived glycans most of which are not degraded by enzymes in the digestive tract of the host. Here we review how various adaptive mechanisms that operate across the major phyla of the HGM contribute to glycan utilisation, focusing on the most complex carbohydrates presented to this ecosystem.

Continuous enzymatic hydrolysis of sugar beet pectin and l-arabinose recovery within an integrated biorefinery

Sugar beet pulp (SBP) fractionated by steam explosion, released sugar beet pectin (SB-pectin) which was selectively hydrolysed using a novel α-l-arabinofuranosidase (AF), yielding monomeric l-arabinose (Ara) and a galacturonic acid rich backbone (GABB). AF was immobilised on an epoxy-functionalised resin with 70% overall immobilisation yield. Pretreatment of SB-pectin, to remove coloured compounds, improved the stability of the immobilised AF, allowing its reutilisation for up to 10 reaction cycles in a stirred tank reactor. Continuous hydrolysis of SB-pectin was subsequently performed using a packed bed reactor (PBR) with immobilised AF. Reactor performance was evaluated using a Design of Experiment approach. Pretreated SB-pectin hydrolysis was run for 7 consecutive days maintaining 73% of PBR performance. Continuous separation of Ara from GABB was achieved by tangential flow ultrafiltration with 92% Ara recovery. These results demonstrate the feasibility of establishing a continuous bioprocess to obtain Ara from the inexpensive SBP biomass.

Function of a laminin_G_3 module as a carbohydrate-binding module in an arabinofuranosidase from Ruminiclostridium josui

Laminin_G_3 modules can exist together with family-43 catalytic modules of glycoside hydrolase (GH43), but their functions are unknown. Here, a laminin_G_3 module and a GH43 module derived from a Ruminiclostridium josui modular arabinofuranosidase Abf43A-Abf43B-Abf43C were produced individually as RjLG3 and RjGH43_22, respectively, or combined as RjGH43-1 to gain insights into their activities. Isothermal calorimetry analysis showed that RjLG3 has high affinity toward 3² -α-l-arabinofuranosyl-(1,5)-α-l-arabinotriose but not for α-1,5-linked arabinooligosaccharides, which suggests that RjLG3 interacts specifically with a branched arabinofuranosyl residue of an arabinooligosaccharide but not an arabinofuranosyl residue at the end of α-1,5-linked arabinooligosaccharides. RjGH43-1 (with CBM) shows higher activity toward sugar beet arabinan than RjGH43_22 (without CBM), which suggests that the LG3 module in RjGH43-1 plays an important role in substrate hydrolysis as a carbohydrate-binding module.

Characterization of a new heteropolysaccharide from green guava and its application as an α-glucosidase inhibitor for the treatment of type II diabetes

Psidium guajava fruit is a subtropical fruit, functional food and traditional medicine for the adjuvant treatment of diabetes mellitus in China. To investigate the active components responsible for its health benefits, a novel heteropolysaccharide GP70-3 was purified by water extraction, ethanol precipitation and column chromatography. Structural characterization of GP70-3 was elucidated for the first time by monosaccharide composition assay, Fourier transform-infrared spectroscopy (FT-IR), methylation analysis, gas chromatography coupled with mass spectrometry (GC-MS) and nuclear magnetic resonance spectroscopy (NMR). The data revealed that GP70-3 contained a backbone of 1→3,6)-linked β-d-Galp, 1→5)-linked α-l-Araf, 1→6)-linked β-d-Galp and 1→3)-linked β-d-Galp, branched with 1→2,3,5)-linked α-l-Araf, 1→3)-linked α-l-Araf, 1→3)-linked α-l-Rhap, 1→3)-linked β-d-GlcpA, 1→3)-linked β-d-GalpA and terminated with →1)-linked β-d-Galp. Advanced structure studies showed GP70-3 consisted of irregular flakes with rounded-spherical pores. Moreover, GP70-3 exhibited outstanding α-glucosidase inhibitory activity in vitro, with an IC50 value of 2.539 ± 0.144 μM, which was 1867 times higher than that of the positive control acarbose (IC50 value of 4.744 ± 0.026 mM). Therefore, consumption of guava polysaccharides may be beneficial as an α-glucosidase inhibitor for reducing the postprandial blood glucose level and treating type II diabetes.

Analysis of the substrate specificity of α-L-arabinofuranosidases by DNA sequencer-aided fluorophore-assisted carbohydrate electrophoresis

Carbohydrate-active enzyme discovery is often not accompanied by experimental validation, demonstrating the need for techniques to analyze substrate specificities of carbohydrate-active enzymes in an efficient manner. DNA sequencer-aided fluorophore-assisted carbohydrate electrophoresis (DSA-FACE) is utmost appropriate for the analysis of glycoside hydrolases that have complex substrate specificities. DSA-FACE is demonstrated here to be a highly convenient method for the precise identification of the specificity of different α-L-arabinofuranosidases for (arabino)xylo-oligosaccharides ((A)XOS). The method was validated with two α-L-arabinofuranosidases (EC 3.2.1.55) with well-known specificity, specifically a GH62 α-L-arabinofuranosidase from Aspergillus nidulans (AnAbf62A-m2,3) and a GH43 α-L-arabinofuranosidase from Bifidobacterium adolescentis (BaAXH-d3). Subsequently, application of DSA-FACE revealed the AXOS specificity of two α-L-arabinofuranosidases with previously unknown AXOS specificities. PaAbf62A, a GH62 α-L-arabinofuranosidase from Podospora anserina strain S mat+, was shown to target the O-2 and the O-3 arabinofuranosyl monomers as side chain from mono-substituted β-D-xylosyl residues, whereas a GH43 α-L-arabinofuranosidase from a metagenomic sample (AGphAbf43) only removes an arabinofuranosyl monomer from the smallest AXOS tested. DSA-FACE excels ionic chromatography in terms of detection limit for (A)XOS (picomolar sensitivity), hands-on and analysis time, and the analysis of the degree of polymerization and binding site of the arabinofuranosyl substituent.

Structural and conformational characterization of arabinoxylans from flaxseed mucilage

The structure of neutral fraction gum from flaxseed mucilage (FM-NFG) was studied for better understanding of the relationship between primary structure and conformation. Based on methylation/GC-MS, nuclear magnetic resonance (NMR) spectroscopy, the structure of FM-NFG was proposed as arabinoxylans. Flaxseed mucilage arabinoxylans contained β-1,4-linked xylose backbones, which were mainly substituted at O-2 and/or O-3 positions by 1-3 sugar residues. The possible branches included → 5)-α-l-Araf-(1 → (17.3 mol%), → 3)-α-l-Araf-(1 → (4.9 mol%), and → 4)-α-d-Glcp-(1 → (3.5 mol%), which were ended with three terminal sugar units: T-β-d-Xylp-(1 → (15.5 mol%), T-α-d-Glap-(1 → (4.5 mol%), and T-α-l-Araf-(1 → (2.6 mol%). The weight average molecular weight (Mw) of flaxseed mucilage arabinoxylans was calculated to be 1747 kDa by static light scattering (SLS), and it exhibited random coil conformation. The proposed structure and conformational models confirmed that different backbone sugar units especially substitution positions directly contributed to the conformational diversity and rigidity of polysaccharide molecules.

NMR Spectroscopic Profiling of Arabinan and Galactan Structural Elements

Pectic arabinans and galactans presumably affect the physiological and technological properties of plant cell walls and dietary fiber. Their complex structures are usually analyzed by time-consuming methods, which are based on chemical cleavage to monomers. To gain more detailed insights into the arabinan and galactan structures, a time-efficient approach based on enzymatic cleavage and two-dimensional NMR spectroscopy was developed. Heteronuclear single quantum coherence spectroscopy (HSQC) marker signals were evaluated for various structural elements, and relative response factors were determined, allowing a semiquantitative estimation of the structural composition. The method was applied to analyze different insoluble plant materials and soluble polysaccharides. It was demonstrated that the developed approach yielded comparable information about various structural elements that can also be detected by using the conventional methylation analysis. However, by using the NMR method, additional structural information, such as the anomeric configuration of the monomers, is obtained, demonstrating the value of this novel approach.

Oligosaccharides: a boon from nature's desk

This article reviews the varied sources of oligosaccharides available in nature as silent health promoting, integral ingredients of plants as well as animal products like honey and milk. The article focuses on exotic and unfamiliar oligosaccharides like Galactooligosaccharides, Lactulose derived Galactooligosaccharides, Xylooligosaccharides, Arabinooligosaccharides and algae derived Marine oligosaccharides along with the most acknowledged prebiotic fructooligosaccharides. The oligosaccharides are named as on the grounds of the monomeric units forming oligomers with functional properties. The chemical structures, natural sources, microbial enzyme mediated synthesis and physiological effects are discussed. An elaborate account of the different types of oligosaccharides with special reference to fructooligosaccharides are presented. Finally, the profound health benefits of oligosaccharides are rigourously discussed limelighting its positive physiological sequel.

Efficient isomerization of methyl arabinofuranosides into corresponding arabinopyranosides in presence of pyridine

Fisher glycosylation, the oldest but efficient reaction towards alkyl glycosides, suffers nonetheless from lack of selectivity, especially when dealing with pentoses. In this case, a mixture of the four isomers, namely the furanosides and the pyranosides, is formed. According to previous studies, the rate and selectivity of the reaction depend greatly on the reaction time and the temperature. In this report, another factor was evaluated, the introduction of a weak nucleophilic base. Interestingly, addition of pyridine few hours after the reaction has started allowed rapid isomerization of the methyl pentofuranosides into its pyranoside counterparts. The reaction proceeds with great diastereoselectivity using arabinose, ribose, xylose and lyxose as starting pentoses. Corresponding methyl pyranosides were obtained as the sole isomers with yields ranging from 65% to 75%.

Metabolism of L-arabinose in plants

L-Arabinose (L-Ara) is a plant-specific sugar accounting for 5-10 % of cell wall saccharides in Arabidopsis (Arabidopsis thaliana) and rice (Oryza sativa). L-Ara occurs in pectic arabinan, rhamnogalacturonan II, arabinoxylan, arabinogalactan-protein (AGP), and extensin in the cell walls, as well as in glycosylated signaling peptides like CLAVATA3 and small glycoconjugates such as quercetin 3-O-arabinoside. This review focuses on recent advances towards understanding the generation of L-Ara and the metabolism of L-Ara-containing molecules in plants.

Arabinan and Galactan Oligosaccharide Profiling by High-Performance Anion-Exchange Chromatography with Pulsed Amperometric Detection (HPAEC-PAD)

Arabinans and galactans are complex pectic polysaccharides, which greatly influence the physicochemical and physiological properties of plants and plant-based foods. Conventional methods to characterize these challenging polymers are based on derivatization and/or unselective chemical cleavage of the glycosidic bonds of the polysaccharides, resulting in partial loss of essential information such as anomeric configuration. Here, endo-arabinanase and endo-galactanase were used to selectively cleave pectic arabinans and galactans. The liberated oligosaccharides were purified and characterized by LC-MS and one- and two-dimensional NMR spectroscopy resulting in known but also several previously unknown pectic structural elements. For the routine analysis of pectin hydrolysates by HPAEC-PAD, incubation conditions, chromatographic parameters, and relative response factors of the isolated pectic oligosaccharides against an internal standard were determined. The applicability of the method was demonstrated by analyzing different well-characterized plant cell wall materials. It was demonstrated that the developed method yields additional information about pectic arabinan and galactan structures that is not obtained from conventional methods such as methylation analysis.

Structural analysis and anti-obesity effect of a pectic polysaccharide isolated from Korean mulberry fruit Oddi (Morus alba L.)

A water-soluble polysaccharide JS-MP-1 was isolated from Korean mulberry fruits Oddi (Morus alba L.). Sugar linkage analysis and NMR data confirmed that it is a rhamnogalacturonan type I (RG I) polymer carrying arabinan and arabinogalactan (AG II) side chains. JS-MP-1 reduced dose-dependently the viability of 3T3-L1 pre-adipocyte cells, significantly stimulated the cleavage of caspases 9 and 3 and poly (ADP-ribose) polymerase (PARP) and decreased the ratio of Bcl-2 to Bax expression level that led to mitochondrial dysfunction and apoptosis in pre-adipocyte cells. The apoptotic death was mediated by stimulation of MAPKs (ERK and p38) signalling pathway. These results suggest that JS-MP-1 is able to reduce the number of fat cells and the mass of adipose tissue via inhibition of pre-adipocyte proliferation and thus JS-MP-1 itself or a crude aqueous Oddi extract containing this polysaccharide can be used as functional ingredient of health-beneficial food supplements for the treatment or prevention of obesity disorders.

Growth of Chitinophaga pinensis on Plant Cell Wall Glycans and Characterisation of a Glycoside Hydrolase Family 27 β-l-Arabinopyranosidase Implicated in Arabinogalactan Utilisation

The genome of the soil bacterium Chitinophaga pinensis encodes a diverse array of carbohydrate active enzymes, including nearly 200 representatives from over 50 glycoside hydrolase (GH) families, the enzymology of which is essentially unexplored. In light of this genetic potential, we reveal that C. pinensis has a broader saprophytic capacity to thrive on plant cell wall polysaccharides than previously reported, and specifically that secretion of β-l-arabinopyranosidase activity is induced during growth on arabinogalactan. We subsequently correlated this activity with the product of the Cpin_5740 gene, which encodes the sole member of glycoside hydrolase family 27 (GH27) in C. pinensis, CpArap27. Historically, GH27 is most commonly associated with α-d-galactopyranosidase and α-d-N-acetylgalactosaminidase activity. A new phylogenetic analysis of GH27 highlighted the likely importance of several conserved secondary structural features in determining substrate specificity and provides a predictive framework for identifying enzymes with the less common β-l-arabinopyranosidase activity.

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

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