Unusual triflic acid-promoted oligomerization of arabinofuranosides during glycosylation.

We discovered an unusual triflic acid-promoted oligomerization of arabinofuranosides during glycosylation of the primary hydroxy group of α-(1 â†’ 5)-linked tetraarabinofuranoside bearing 4-(2-chloroethoxy)phenyl aglycone with α-(1 â†’ 5), ß-(1 â†’ 2)-linked tetraarabinofuranoside containing N-phenyltrifluoroacetimidoyl leaving group, which led to octa-, dodeca- and hexadecaarabinofuranosides. The possible mechanism of triflic acid-promoted oligomerization was proposed. The choice of promoter was found to be a critical factor for the discovered oligomerization of arabinofuranosides. The obtained octa-, dodeca- and hexadecaarabinofuranosides may serve as useful blocks in the synthesis of oligosaccharide fragments of polysaccharides of Mycobacterium tuberculosis.

Enhancement mechanism of glycation with l-arabinose and xylose on texture properties of silver carp mince gel.

BACKGROUND: Glycation is a green processing technology. Based on our previous studies, glycation with l-arabinose and xylose was beneficial to enhance the texture properties of silver carp mince (SCM) gels. However, the possible enhancement mechanism remained unclear. Therefore, in this study, SCM gels with different types of reducing sugar (glucose, l-arabinose, and xylose) were prepared based on our previous study. The possible mechanism of texture enhancement of SCM gels was analyzed by investigating the changes in water distribution, protein structures, and microstructure in the gel system. RESULTS: The glycation of l-arabinose and xylose enhanced the hardness, cohesiveness, chewiness, and resilience of SCM gels. Hardness increased from 1883.04 (control group) to 3624.54 (l-arabinose group) and 4348.18 (xylose group). Low-field nuclear magnetic resonance (LF-NMR) showed that glycation promoted the tight binding of immobilized water to proteins. Raman spectroscopic analysis showed that glycation increased the surface hydrophobicity and promoted the formation of disulfide bonds. Scanning electron microscopy (SEM) showed that glycation promoted the formation of uniform and dense three-dimensional network structure in SCM gels. CONCLUSION: In summary, glycation enhanced the binding ability of immobilized water to proteins, improved the surface hydrophobicity, promoted the formation of disulfide bonds, and led to a more uniform and dense gel network structure of proteins, thus enhancing the texture properties of SCM gels. This research provided a theoretical basis for a better understanding of the mechanism of the effect of glycation on the quality of gel products and also provided technical support for the application of l-arabinose and xylose in new functional gel foods. © 2024 Society of Chemical Industry.

Atomic force microscopy measurements and model of DNA bending caused by binding of AraC protein.

Atomic force microscopy (AFM) was used to conduct single-molecule imaging of protein/DNA complexes involved in the regulation of the arabinose operon of Escherichia coli. In the presence of arabinose, the transcription regulatory protein AraC binds to a 38 bp region consisting of the araI1 and araI2 half-sites. The domain positioning of full-length AraC, when bound to DNA, was not previously known. In this study, AraC was combined with 302 and 560 bp DNA and arabinose, deposited on a mica substrate, and imaged with AFM in air. High resolution images of 560 bp DNA, where bound protein was visible, showed that AraC induces a bend in the DNA with an angle 60° ± 12° with a median of 55°. These results are consistent with earlier gel electrophoresis measurements that measured the DNA bend angle based on migration rates. By using known domain structures of AraC, geometric constraints, and contacts determined from biochemical experiments, we developed a model of the tertiary and quaternary structure of DNA-bound AraC in the presence of arabinose. The DNA bend angle predicted by the model is in agreement with the measurement values. We discuss the results in view of other regulatory proteins that cause DNA bending and formation of the open complex to initiate transcription.

A Novel Pectin-Like Glycopeptide Isolated from the Fruit of Fructus Mori Impedes Aggregation and Production of Aß42.

The fruit of Fructus Mori is food and medicine, which has been demonstrated to have a significant neuroprotective effect. However, the effective constituent remains unknown. We speculate that the glycopeptide in the extract of the fruit has similar activity. To address this hypothesis, we isolated a novel pectin-like glycopeptide (FMP-6-S4) with a molecular weight of 11.23 kDa from the fruit. It contains about 20% of peptide comprising 17 amino acids and 80% glycan consisting of L-rhamnose (L-Rha), D-galactose (D-Gal), D-galacturonic acid (D-GalA), L-arabinose (L-Ara) and d-glucose (D-Glc) in molar ratios of 7.25:4.62:77.66:5.62:4.85. The backbone of the glycan part consisted of 1,4-linked α-D-GalpA and 1, 2-linked α-L-Rhap, while the branches were composed of hexenuronic acid (HexA) substituted at the C-3 position of partial galacturonic acid, and traces of galactose, glucose, and arabinose were substituted at the C-4 position of rhamnose. The in vitro experiments revealed that FMP-6-S4 might inhibit Aß42 (ß-amyloid peptides 42) aggregation and decrease Aß42 production by modulating APP (amyloid precursor protein) processing.

Preparation, structural characteristics, and application of taro polysaccharides in food.

Taro, a staple food for residents in Africa and parts of Asia, is an important source of carbohydrate. China has abundant taro resources. Taro contains polysaccharide, vitamins, minerals and other substances. Taro polysaccharides, as a significant active ingredient in taro, are mainly composed of monosaccharide units such as glucose, galactose, arabinose, mannose, and so on. Taro polysaccharides have antioxidant, lipid-lowering, and immunomodulatory effects. In today's world, people are interested in food containing natural ingredients, which stimulates the potential of taro polysaccharides in the food, pharmaceutical, medical, and other fields. Herein, the extraction and purification, structural characterization, functional activity, and application of taro polysaccharides are reviewed to strengthen the cognition of taro polysaccharides. It provides references for further research and development of taro polysaccharides. © 2022 Society of Chemical Industry.

Crystal structure of L-arabinose 1-dehydrogenase as a short-chain reductase/dehydrogenase protein.

l-Arabinose 1-dehydrogenase (AraDH) catalyzes the NAD(P)+-dependent oxidation of l-arabinose to L-arabinono-1,4-lactone in the non-phosphorylative l-arabinose pathway, and is classified into glucose-fructose oxidoreductase and short-chain dehydrogenase/reductase (SDR). We herein report the crystal structure of a SDR-type AraDH (from Herbaspirillum huttiense) for the first time. The interactions between Asp49 and the 2'- and 3'-hydroxyl groups of NAD+ were consistent with strict specificity for NAD+. In a binding model for the substrate, Ser155 and Tyr168, highly conserved in the SDR superfamily, interacted with the C1 and/or C2 hydroxyl(s) of l-arabinose, whereas interactions between Asp107, Arg109, and Gln206 and the C2 and/or C3 hydroxyl(s) were unique to AraDH. Trp200 significantly contributed to the selectivities of the C4 hydroxyl and C6 methyl of substrates.

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 â†’ 3)]-ß-D-Galp-(1 â†’ 4)-ß-D-Galp-(1 â†’ 6)-[α-L-Araf-(1 â†’ 5)-{α-L-Araf-(1 â†’ 3)}-α-L-Araf-(1 â†’ 3)]-ß-D-Galp-(1 â†’ 4)-ß-D-Galp-(1 â†’ 6)-[ß-D-Galp-(1 â†’ 5)-α-L-Araf-(1 â†’ 5)-α-L-Araf-(1 â†’ 3)]-ß-D-Galp-(1 â†’ 6)-[ß-D-Galp-(1 â†’ 5)-α-L-Araf-(1 â†’ 5)-{α-L-Araf-(1 â†’ 3)}-α-L-Araf-(1 â†’ 3)]-ß-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.

Non-Specific GH30_7 Endo-ß-1,4-xylanase from Talaromyces leycettanus.

This study describes the catalytic properties of a GH30_7 xylanase produced by the fungus Talaromyces leycettanus. The enzyme is an ando-ß-1,4-xylanase, showing similar specific activity towards glucuronoxylan, arabinoxylan, and rhodymenan (linear ß-1,3-ß-1,4-xylan). The heteroxylans are hydrolyzed to a mixture of linear as well as branched ß-1,4-xylooligosaccharides that are shorter than the products generated by GH10 and GH11 xylanases. In the rhodymenan hydrolyzate, the linear ß-1,4-xylooligosaccharides are accompanied with a series of mixed linkage homologues. Initial hydrolysis of glucuronoxylan resembles the action of other GH30_7 and GH30_8 glucuronoxylanases, resulting in a series of aldouronic acids of a general formula MeGlcA2Xyln. Due to the significant non-specific endoxylanase activity of the enzyme, these acidic products are further attacked in the unbranched regions, finally yielding MeGlcA2Xyl2-3. The accommodation of a substituted xylosyl residue in the -2 subsite also applies in arabinoxylan depolymerization. Moreover, the xylose residue may be arabinosylated at both positions 2 and 3, without negatively affecting the main chain cleavage. The catalytic properties of the enzyme, particularly the great tolerance of the side-chain substituents, make the enzyme attractive for biotechnological applications. The enzyme is also another example of extraordinarily great catalytic diversity among eukaryotic GH30_7 xylanases.

Structure-Activity Relationships in Nonenzymatic Template-Directed RNA Synthesis.

The template-directed synthesis of RNA played an important role in the transition from prebiotic chemistry to the beginnings of RNA based life, but the mechanism of RNA copying chemistry is incompletely understood. We measured the kinetics of template copying with a set of primers with modified 3'-nucleotides and determined the crystal structures of these modified nucleotides in the context of a primer/template/substrate-analog complex. pH-rate profiles and solvent isotope effects show that deprotonation of the primer 3'-hydroxyl occurs prior to the rate limiting step, the attack of the alkoxide on the activated phosphate of the incoming nucleotide. The analogs with a 3 E ribose conformation show the fastest formation of 3'-5' phosphodiester bonds. Among those derivatives, the reaction rate is strongly correlated with the electronegativity of the 2'-substituent. We interpret our results in terms of differences in steric bulk and charge distribution in the ground vs. transition states.

A homogeneous polysaccharide from Lycium barbarum: Structural characterizations, anti-obesity effects and impacts on gut microbiota.

Lycium barbarum polysaccharides (LBPs) are known for their beneficial effects on diabetes, NAFLD and related chronic metabolic diseases induced by high-fat diet (HFD). However, the relevant researches are mainly about the whole crude polysaccharides, the specific active ingredient of LBPs and its bioactivity have been rarely explored. Herein, a homogeneous polysaccharide (LBP-W) was isolated and purified from crude LBPs. Structure characterizations indicated that LBP-W contained a main chain consisting of a repeated unit of →6)-ß-Galp(1 â†’ residues with branches composed of α-Araf, ß-Galp and α-Rhap residues at position C-3. The objective of this study was to evaluate the anti-obesogenic effect of LBP-W and figure out the underlying mechanisms. In vivo efficacy trial illustrated that LBP-W supplements can alleviate HFD-induced mice obesity significantly. Gut microbiota analysis showed that LBP-W not only improved community diversity of intestinal flora, but also regulated their specific genera. Moreover, LBP-W can increase the content of short-chain fatty acids (SCFAs), a metabolite of the intestinal flora. In summary, all these results demonstrated that the homogeneous polysaccharide purified from L. barbarum could be used as a prebiotic agent to improve obesity by modulating the composition of intestinal flora and the metabolism of SCFAs.

Structural characterization and anti-inflammatory activity of a polysaccharide from the lignified okra.

The polysaccharide (AP1-b) of molecular weight 6.59 × 105 Da was isolated from lignified okra (Abelmoschus esculentus (L.) Moench) by hot-water extraction, 40 % ethanol precipitation and purified by DEAE Cellulose chromatography, respectively. The structure and anti-inflammatory activity of AP1-b were investigated. AP1-b was composed of galactose, rhamnose, gluctose, arabinose and galacturonic acid in a molar ratio of 1.98:1.00:0.15:0.32:0.29. The structural features showed that the AP1-b consisted of →2)-α-d-Rhap-(1→, →4)-ß-d-Galp-(1→, →4)-α-d-GalpA-(1→, →6)-ß-d-Galp-(1→, ß-d-Glcp-(1→ and α-l-Araf-(1→. AP1-b could observably improve the inflammatory injury of LPS-induced RAW 264.7 cells by inhibiting the secretion of NO and decreasing the levels of pro-inflammatory factors (IL-1ß, iNOS and TNF-α). AP1-b also inhibited the phosphorylation levels of IκB and p65 proteins, manifesting the anti-inflammatory activity of AP1-b may associated with inhibition of NF-κB signaling pathway. Therefore, AP1-b had potential value in treating inflammatory injury.

The potential of extracellular biopolymer production by Mesorhizobium sp. from monosaccharide constituents of lignocellulosic biomass.

OBJECTIVE: The effects of monosaccharide constituents of lignocellulosic materials on exopolysaccharide (EPS) production by Mesorhizobium sp. Semia 816 were studied. RESULTS: According to the results, by using sugars commonly found in lignocellulosic biomass as carbon sources (glucose, arabinose and xylose), no significant differences were observed in the production of EPS, reaching 3.39 g/L, 3.33 g/L and 3.27 g/L, respectively. Differences were observed in monosaccharide composition, mainly in relation to rhamnose and glucuronic acid contents (1.8 times higher when arabinose was compared with xylose). However, the biopolymers showed no differences in relation to rheological properties, with EPS aqueous-based suspensions (1.0% w/v) presenting pseudoplastic behavior, and a slight difference in degradation temperatures. Using soybean hulls hydrolysate as carbon source, slightly higher values were obtained (3.93 g/L). CONCLUSION: The results indicate the potential of the use of lignocellulosic hydrolysates containing these sugars as a source of carbon in the cultivation of Mesorhizobium sp. Semia 816 for the production of EPS with potential industrial applications.

Synthesis and antitumor activity evaluation of oleanolic acid saponins bearing an acetylated l-arabinose moiety.

A series of oleanolic acid derivatives bearing acetyl-substituted l-arabinose moiety has been synthesized and screened in vitro for cytotoxicity against ten cancer cell lines and four normal cell lines. The antiproliferative evaluation indicated that synthetic derivatives showed excellent selectivity, as they were toxic against only A431 cell line. Among them, the compound 6 possesses the best inhibitory activity. A series of pharmacology experiments showed that compound 6 significantly induced A431 cells apoptosis and cell cycle arrest, which could serve as a promising lead candidate for further study.

Characterization of hemicellulose in Cassava (Manihot esculenta Crantz) stem during xylogenesis.

Cassava is one of the three major potato crops due to the high starch content in its tubers. Unlike most current studies on the utilization of cassava tubers, our research is mainly focused on the stem of cassava plant. Through nuclear magnetic resonance (NMR), fourier transform infrared spectrometer (FTIR) and other methods, we found that cassava stalk hemicellulose consists of ß-1,4 glycosidic bond-linked xylan backbone with a tetrasaccharide reducing end and decorated with methylated glucuronic acid, acetyl groups and a high degree of arabinose substitutions. Hemicellulose content gradually increased from the upper to the lower parts of the stem. The apical part of cassava stalk contained more branched and heterogeneous glycans than the middle and basal parts, and the molecular weight of hemicellulose increased from top to bottom. Our findings will be helpful in understanding of structural variations of cassava hemicellulose during xylogenesis, as well as in better utilization of cassava plant waste in industry.

High arabinoxylan fine structure specificity to gut bacteria driven by corn genotypes but not environment.

While gut bacteria have different abilities to utilize dietary fibers, the degree of fiber structural alignment to bacteria species is not well understood. Corn bran arabinoxylan (CAX) was used to investigate how minor polymer fine structural differences at the genotype × environment level influences the human gut microbiota. CAXs were extracted from 4 corn genotypes × 3 growing years and used in in vitro fecal fermentations. CAXs from different genotypes had varied contents of arabinose/xylose ratio (0.46-0.54), galactose (58-101 mg/g), glucuronic acid (18-32 mg/g). There was genotype- but not environment-specific differences in fine structures. After 24 h fermentation, CAX showed different acetate (71-86 mM), propionate (35-44 mM), butyrate (7-10 mM), and total short chain fatty acid (SCFA) (117-137 mM) production. SCFA profiles and gut microbiota both shifted in a genotype-specific way. In conclusion, the study reveals a very high specificity of fiber structure to gut bacteria use and SCFA production.

Structural elucidation and immuno-stimulatory activity of a novel polysaccharide containing glucuronic acid from the fungus Echinodontium tinctorium.

An immuno-stimulatory polysaccharide (EtISPFa) was purified from water extract of the fungus Echinodontium tinctorium. EtISPFa has an estimated weight average molecular weight (Mw) of 1354 kDa and is composed of glucose (66.2 %), glucuronic acid (10.1 %), mannose (6.7 %), galactose (6.4 %), xylose (5.6 %), rhamnose (3.1 %), fucose (1.8 %), and arabinose (0.2 %). It has multiple glycosidic linkages, with 3-Glcp (19.8 %), 4-GlcpA (10.8 %), 6-Glcp (10.7 %), and 3,6-Glcp (8.7 %) being the most prominent. NMR analysis showed that EtISPFa has a backbone containing mostly of 3-substituted ß-glucopyranose with 4-substituted glucopyranosyluronic acid. Short side chains consisting of an average of two ß-glycopyranose residues, connected through 1→6 linkages, are attached to the 6-position of about every 4th or 5th backbone glucose residue. EtISPFa is a novel glucuronic acid-containing ß-glucan capable of significantly inducing the production of cytokines IL-17, IL-16, MIP-2, G-CSF,GM-CSF, LIF, MIP-1α, MIP-1ß, and RANTES in vitro. EtISPFa should be further explored for its immuno-stimulatory activity in vivo.

Microwave-assisted extraction of arabinan-rich pectic polysaccharides from melon peels: Optimization, purification, bioactivity, and techno-functionality.

The effects of water to solids ratio (WSR, 10-30 mL/g), power (180-540 W), and irradiation time (IT, 5-15 min) in microwave-assisted extraction (MAE) were optimized to extract polysaccharides from melon peels (PMP). The maximum extraction yield (32.81 %) was obtained under 20.94 mL/g WSR, 414.4 W power, and 12.75 min IT. The main monosaccharide composition of purified PMP with an average molecular weight of 5.71 × 104 kDa were d-galacturonic acid, arabinose, glucose, and galactose. An ascending dose-dependent antiradical and antioxidant behavior for PMP (0-5.0 mg/mL) was found. The initial foaming capacity (38.6-110.3 %) and foaming stability (5.2-65.2 %) were significantly increased as a function of PMP concentration (1.0-5.0 %), while they reduced by increasing the mixing time (p < 0.05). The highest emulsifying activity index (44.1 m2/g) and emulsifying stability (69.3 %) at 5.0 % PMPs were determined. PMP gels with FTIR-identified functional groups can be formulated in new gluten-free functional products.

Ultrafiltration isolation, structures and anti-tumor potentials of two arabinose- and galactose-rich pectins from leaves of Aralia elata.

Two novel arabinose- and galactose-rich pectic polysaccharides, AELP-B5 (Mw, 4.25 × 104 g/mol) and B6 (Mw, 1.56 × 104 g/mol), were rapidly obtained from the leaves of Aralia elata (Miq.) Seem. with anion resin and sequenced ultrafiltration membrane columns. The structural backbone and branched chains of AELP-B5 and B6 were preliminarily elucidated by mild acid hydrolysis with HILIC-ESI--MS/MS. The planar structures and spatial configurations were further identified using UPLC-QDa and GC-MS for compositions, Smith degradation and methylation analysis, FT-IR, NMR (1H/13C, DEPT, HSQC, HMBC, COSY, NOESY and TOCSY) and SEC-MALLS-RID. (1) AELP-B5 possessed →4GalA1→ as smooth regions (HG) and a repeating disaccharide moiety of →4GalA1→2Rha1→ as hairy regions (RG-I) with a 1:5 molar ratio, whereas AELP-B6 had a distinguishing 1:1 molar ratio between the HG and RG-I; (2) complex side chains were constituted of T-α-Araf, 1,3-α-Araf, 1,5-α-Araf, T-ß-Galp, 1,3-ß-Galp, 1,4-ß-Galp, 1,6-ß-Galp, 1,3,4-ß-Galp and 1,3,4,6-ß-Galp connected at C-4 of the rhamnosyl units in RG-I of AELP-B5 and B6; and (3) both possessed highly branched and compact coil conformations. The CCK-8 assay illustrated that AELP-B6 possessed higher cytotoxicity against HepG2 and HT-29 than that of AELP-B5. Surface plasmon resonance showed the binding affinity of AELP-B6 to galectin-3 (6.488 × 10-5 M) was about 10 times stronger than that of AELP-B5 (4.588 × 10-4 M). The above findings provide a molecular structure and bioactivity basis for future potential applications of AELP in the food and medical industries.

Structural and immunological studies on the polysaccharide from spores of a medicinal entomogenous fungus Paecilomyces cicadae.

A neutral branched heteropolysaccharide (Pc0-1) was purified from the spores of Paecilomyces cicadae, which parasitized in the bamboo cicada (Platylomia pieli Kato). The structure of Pc0-1 was analyzed by HPLC, IR, methylation and NMR spectroscopy. The results reveal that Pc0-1, with an average molecular weight of 18 × 103 kDa, consists of glucose, galactose, mannose and arabinose in the molar ratio of 8:5:4:1. Some of the glucose residues have methyl modification at O-6 position. The Pc0-1 polysaccharide has a core structure containing 1,2-linked α-d-Manp residues as the backbone and branches at the O-3 and O-6 of the α-d-Manp residues. The inner part of the side-chains is comprised of 1,4-linked α-d-Glcp and 1,4-linked 6-O-Me-α-d-Glcp residues. 1,2-linked ß-Galf and minor 1,4-linked Arap and 1,3 or 4-linked Arap residues were occasionally linked at the outside of the side-chains. The side-chains have a single terminal residue of α-d-Glcp, α-Manp, ß-Galf or minor Arap (minor). Studies on the bioactivity of Pc0-1 on the macrophages show it exhibit moderate immunostimulating activity through increasing the production of nitric oxide (NO) and enhancing the secretion of major inflammatory cytokines by macrophages, such as TNF-α, IL-1ß, IL-6, in RAW 264.7 cells. We examined the effect of Pc0-1 on induced NO and cytokine production in macrophages using anti-PRR antibodies to investigate the membrane receptor for the polysaccharide. The results show that Pc0-1 mainly activates macrophages through their mannose receptor (MR). TLR4 and TLR2 also participated in the recognition of Pc0-1.

Deconstruction of banana peel for carbohydrate fractionation.

The deconstruction of banana peel for carbohydrate recovery was performed by sequential treatment (acid, alkaline, and enzymatic). The pretreatment with citric acid promoted the extraction of pectin, resulting in a yield of 8%. In addition, xylose and XOS, 348.5 and 17.3 mg/g xylan, respectively, were also quantified in acidic liquor as a result of partial depolymerization of hemicellulose. The spent solid was pretreated with alkaline solution (NaOH or KOH) for delignification and release of residual carbohydrates from the hemicellulose. The yields of xylose and arabinose (225.2 and 174.0 mg/g hemicellulose) were approximately 40% higher in the pretreatment with KOH, while pretreatment with NaOH promoted higher delignification (67%), XOS yield (32.6 mg/g xylan), and preservation of cellulosic fraction. Finally, the spent alkaline solid, rich in cellulose (76%), was treated enzymatically to release glucose, reaching the final concentration of 28.2 g/L. The mass balance showed that through sequential treatment, 9.9 g of xylose, 0.5 g of XOS, and 8.2 g of glucose were obtained from 100 g of raw banana peels, representing 65.8% and 46.5% conversion of hemicellulose and cellulose, respectively. The study of the fractionation of carbohydrates in banana peel proved to be a useful tool for valorization, mainly of the hemicellulose fraction for the production of XOS and xylose with high value applications in the food industry.