Structural characteristics of two pectic polysaccharides from Avicennia marina fruit.

Each year more than 100 billion tons of carbon dioxide are fixed via photosynthesis into plant biomass, the base of our food chain and a renewable resource for production of chemicals, fuels, materials and bio‐based products. The bulk of plant biomass is plant cell walls, which have evolved during hundreds of millions of years of biotic and abiotic challenge into very complex polymers that support plant longevity up to thousands of years and provide mechanical strength needed for trees to reach heights of 90 meters. Such striking mechanical and physical properties arise from the fine structure of individual wall polymers, the covalent and non‐covalent interactions between them, and the architectural arrangement between the polymers. Among the three major types of cell wall polysaccharides, cellulose, hemicellulose and pectin, pectin is the most complex. Pectin is comprised of the three pectic polysaccharides, homogalacturonan (HG), rhamnogalacturonan I (RG‐I) and rhamnogalacturonan II (RG‐II). Our research focuses on the synthesis of the most abundant pectic polysaccharide, HG, which is a partially methyl‐esterified and acetylated homoglycan of α‐1,4‐linked D‐galacturonic acid. HG is synthesized by the GAUT gene family of 15 proven and putative HG:α‐1,4‐galacturonosyltransferases (HG:GalATs) in Arabidopsis. This family has expanded in grasses and in trees. Our long term goal is to understand which HG glycans are synthesized by the diverse GAUTs, and how the polymers containing these HG glycans contribute to cell wall structure, integrity, plant growth, cell adhesion and plant development. The current biochemical, transgenic and mutant studies showing that at least 6 of the 15 Arabidopsis GAUTs encode HG:GalATs will be summarized and data in support of the hypothesis that different GAUTs synthesize HG glycan regions in unique polymers with different functions in the wall will be presented. Enzymatic properties of a heterologously expressed GAUT1:GAUT7 HG:GalAT complex will be described and a two‐phase model for the non‐processive biosynthesis of homogalacturonan polysaccharides by the GAUT1:GAUT7 complex will be presented. We show that the GAUT1:GAUT7 complex is a distributive glycosyltransferase that catalyzes polymerization of high‐molecular‐weight polysaccharides and has full activity only with acceptors longer than a critical chain length.Support or Funding InformationResearch was supported by USDA AFRI 2010‐65115‐20396 and the BioEnergy Science Center and the Center for Bioenergy Innovation which are US Department of Energy Bioenergy Research Centers supported by the Office of Biological and Environmental Research in the Department of Energy's Office of Science. Also partially funded by Department of Energy Center Grant DESC0015662.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Two pectic polysaccharide fractions were isolated form lucerne (Medicago sativa L) leaves and used in fermentation experiments with mixed ruminal microbes. Both fractions were similar in chemical composition, containing galacturonic acid (52‐58 mol%) and the neutral sugars arabinose (14‐18 mol%), galactose (6‐8 mol%) and rhamnose (8‐12 mol%). Fermentation of both fractions was rapid and complete with a half‐life of approximately 4 h. Production of total volatile fatty acids matched the degradation profile reaching a maximum level shortly after the rate of degradation began to decrease. The fermentation characteristics of citrus pectin and polygalacturonic acid were similar to those of the lucerne pectic fractions but galacturonic acid was much slower in its rate of degradation while soluble arabinogalactan from larchwood was virtually undegraded. Leaves of early bud stage lucerne and lower nodes and internodes of stems from full bloom lucerne were also fermented by mixed ruminal microbes. Pectic polysaccharides were rapidly and extensively degraded from both tissues. Initial rates were faster for leaves than for stems and the extent of pectic degradation was greater in leaves (8% residual) than in stems (17% residual). Selection of forage lines with increased pectic polysaccharides would provide greater amounts of rapidly available energy that could result in more efficient utilisation of the rapidly degraded protein in lucerne.

Pectic polysaccharides in cherry tomato fruits (Pepe) have been studied at three stages of ripening (immature-green, mature-green, and mature-red). The alcohol-insoluble solids obtained from the fruits were fractionated into four groups of pectic polysaccharides: water-soluble pectin (WP), hexametaphosphate-soluble pectin (PP), HCl-soluble pectin (HP), and KOH-soluble pectin (KP). The content of total pectic polysaccharides decreased with ripening of the fruits; especially, the main fraction HP at immature-green stage hardly existed at the mature-red stage. Instead, the content of WP increased with maturation. The pectic polysaccharide fractions were analyzed by gel-filtration, and the molecular weight of each fraction decreased with ripening. This phenomenon was accompanied by an increase in the activities of the pectin-hydrolyzing enzymes, polygalacturonase and pectinesterase. These results indicate that the softening of cherry tomato fruits during the ripening may depend on degradation and depolymerization of pectic polysaccharides by the pectin-hydrolyzing enzymes.

Cell wall material (CWM) prepared from apple cultivars, cv. Fuji with excellent storability and cv. Kinsei with poor storability, before and after storage were fractionated into four pectic polysaccharide fractions (CDTA-1, CDTA-2, Na2CO3-1 and Na2CO3-2), three hemicellulose fractions (KOH-1, KOH-2 and KOH-3) and CWM residue (cellulose rich fraction). Quantitative changes of their fractions from apple cultivars with different storability before and after storage were also compared. In cv. Fuji, the weight of each fraction changed only slighting after storage for 42 day at 20°C, but in cv. Kinsei, the weight of Na2CO3-1 fraction containing pectic polysaccharides decreased most markedly among 8 fractions after storage for 42 days at 20°C. The analysis of monosaccharide composition of Na2CO3-1 fraction showed that the release of arabinose and galactose from the pectic polysaccharide was markedly higher in cv. Kinsei than in cv. Fuji after storage for 42 days at 20°C, suggesting that the reduction of Na2CO3-1 fraction is closely correlated with the release of arabinose and galactose moieties from the pectic polysaccharide of Na2CO3-1 fraction accompanied by softening. This suggests that degradation of bulky arabinogalactan side chain in major pectic substances, rhamnogalcturonan I in Na2CO3-1, may have an important role in the softening process of apples.

In the present study, the water-soluble polysaccharides of Radix Aconiti, Radix Aconiti Lateralis and Radix Aconiti Kusnezoffii, were extracted and fractionated into four fractions of each material. The FT-IR and chemical analyses indicated the water-soluble polysaccharides of the three materials were all mainly composed of starch, non-starch type alpha-D-glucans and pectic polysaccharides with different molecular weight distributions and monosaccharide composition ratios. The antitumor assay showed that all the non-starch type polysaccharide fractions had good antitumor activities, and the tumor growth inhibition ratios were 37.24-70.42%. Specifically the inhibition ratios of pectic polysaccharides were over 60%. Moreover, the immunological tests using the Cyclophosphamide (Cy) induced immunosuppressive mice, including phagocytosis of macrophage, NK cell activity, concanavalin A (ConA)-induced T-cell proliferation, lipopolysaccharide (LPS)-induced B-cell proliferation, quantitative haemolysis of sheep red blood cells (SRBC) and dinitro-fluorobenzene (DNFB)-induced delayed-type hypersensitivity (DTH) response assays, exhibited that all the non-starch type polysaccharides, especially the pectic polysaccharide fractions, not only had remarkable immunostimulating activities including nonspecific immunity, cellular immunity and humoral immunity, but also could restore the antitumor drug-suppressed immune function. Therefore, the polysaccharides from Aconitum species might be conveniently exploited to be good immune stimulating modifiers and had the potential to apply in the tumor therapy.

Pectic polysaccharide fraction (BR-2) containing pharmacologically active pectic polysaccharide, bupleuran 2IIc, which was prepared from a medicinal herb, the roots of Bupleurum falcatum L., was administered orally to C3H/HeJ mice for 7 consecutive days. Proliferative responses of spleen cells were enhanced in the presence of the purified pectic polysaccharide, bupleuran 2IIc, but another B-cell mitogen, lipopolysaccharide (LPS) did not give a similar effect. In vitro studies using spleen cells showed that bupleuran 2IIc also stimulated lymphocytes, depleted of adherent cells or T cells. Bupleuran 2IIc treatment increased subpopulation of CD25+ and surface immunoglobulin M-positive (sIgM+) lymphocytes. Non-specific immunoglobulin secretion of spleen cells treated with bupleuran 2IIc was increased according to the culture time, and coexistence of interleukin-6 (IL-6) enhanced the secretion more than that of bupleuran 2IIc alone. These results suggest that bupleuran 2IIc proliferates B cells in the absence of macrophages, and the resulting activated B cells are then induced into antibody-forming cells in the presence of IL-6. Among the structural region of bupleuran 2IIc, ramified region (PG-1), which consists of rhamnogalacturonan core rich in neutral sugar chain, showed the potent mitogenic activity suggesting it to be an active site. Mitogenic activity of bupleuran 2IIc was reduced in the presence of antipolysaccharide antibody (antibupleuran 2IIc/PG-1-IgG), which recognizes the ramified region of bupleuran 2IIc as the antigenic epitope. Mitogenic activity of bupleuran 2IIc was also reduced by the addition of beta-d-GlcpA-(1-->6)-beta-d-Galp-(1-->6)-d-Galp or beta-d-GlcpA-(1-->6)-d-Galp, which are a part of the epitopes of antibupleuran 2IIc/PG-1-IgG. These results suggest that the epitopes in bupleuran 2IIc act as active sites of the polysaccharide during mitogenic activity.

Effect of Cations on the Elution of Pectic Polysaccharides from Anion-Exchange Resins

The aim of this work was to study the influence of the hydrolysis-extraction process parameters on the structural characteristics of pectic polysaccharides (PP) from pumpkin. After hydrolysis by rapid steam assisted flash extraction (SAFE) the solubilized PP was separated from the cell wall residue (CWR) and the supernatant was further separated into three fractions. On standing, pectin gel (PG) precipitated and was separated. On addition of alcohol to the supernatant, a second pectin substance (PS) precipitated. Alcohol soluble oligosaccharides (OS) remained in the supernatant. The structure of pumpkin PP (PS, PG and MG fractions) was investigated using 1H,13C and gHSQC NMR; ATR FT-IR spectra; and HPSEC. From 1H, 13C and 2D gHSQC data we observed the major components present were homogalacturonans (HG) and the minority were rhamnogalacturonans (RG). Analysing NMR data from the literature one might expect the presence of α-D-Galp-(1→3)-β-L-Arap-(1→4)-β-D-Galp attached to the HG or RG chain (minor resonance of terminal →4)-α-L-Rha). Further work is required to determine the primary and secondary structure of pumpkin fruit pectin. The molecular structure of pectin components from this source appear to be affected not only by the extraction mode, but also depend on the degree of esterification (DE) and the ability of the components to undergo intermolecular aggregation. The molar mass distribution (MMD) of PS fractions indicate the presence of two species. One has a high and the other a low molar mass. Furthermore, these species have narrow distribution profiles. Conformation plot analyses of sub-fractions showed that PS is a mixture of extended and spherical shaped molecules. Our results suggest that pumpkin pectin is comprised of three macromolecular patterns differing by DE. Changes in DE and the presence of divalent cations appear to lead to various kinds of aggregation. The yield of PP is about 15-16 %, which includes soluble PS, an alcohol insoluble fraction a part of which is pectin gel and OS. The soluble pectin has use as a food thickener and emulsifier. Pectin gel as a composite with OS fractions could be a functional food additive.

Rhizome of Ligusticum chuanxiong is an effective medical plant, which has been extensively applied for centuries in migraine and cardiovascular diseases treatment in China. Polysaccharides from this plant have been shown to have interesting bioactivities, but previous studies have only been performed on the neutral polysaccharides. In this study, LCP-I-I, a pectic polysaccharide fraction, was obtained from the 100 °C water extracts of L. chuangxiong rhizomes and purified by diethylaminethyl (DEAE) sepharose anion exchange chromatography and gel filtration. Monosaccharide analysis and linkage determination in addition to Fourier transform infrared (FT-IR) spectrometer and Nuclear magnetic resonance (NMR) spectrum, indicated that LCP-I-I is a typical pectic polysaccharide, with homo-galacturonan and rhamnogalacturonan type I regions and arabinogalactan type I and type II (AG-I/AG-II) side chains. LCP-I-I exhibited potent complement fixation activity, ICH50 of 26.3 ± 2.2 µg/mL, and thus has potential as a natural immunomodulator.

Pectic polysaccharides are a complex set of macromolecules of the primary cell wall matrix with distinct structural domains. The biosynthesis, organisation and function of these domains within cell wall matrices are poorly understood. An immersion immunofluorescence labelling technique was developed for the in-situ analysis of pectic polysaccharides at the surface of seeds and seedlings of Arabidopsis thaliana (L.) Heynh., and used to investigate the occurrence of pectic homogalacturonan (HG) and rhamnogalacturonan-I (RG-I) epitopes. Seed mucilage appeared to consist of two regions: a highly methyl-esterified HG was a major component throughout the mucilage, while an inner region with relatively low porosity was stabilized by calcium-based HG cross-linking. The small size and transparency of Arabidopsis roots allowed the occurrence of pectic HG and RG-I epitopes at root surfaces to be directly determined on whole-mount preparations. Pectic epitopes were not distributed evenly over root surfaces and were notably absent from lateral root apices and from the surface of root hairs. The use of defined antibody probes in the immersion immunolabelling protocol will be useful for the analysis of the influence of growth conditions and genetic factors on pectic polysaccharides in Arabidopsis.

Structural characteristics of three pectins isolated from white kidney bean

Pectins are viewed as multiblock cobiopolymers of different pectic polysaccharides, notably, homogalacturonan (HG) and rhamnogalacturonan I (RG I). Furthermore, on the basis of HGs isolated from different (pectins from) dicot cell walls, HG is supposed to have an average degree of polymerization (DP) of approximately 100 irrespective of the plant source. To validate or invalidate these suppositions, pectins from both monocot (pineapple and banana) and dicot (yellow passion fruit and lemon) cell walls were examined. The results show that all the extracted pectins comprise HGs as well as type I and II arabinogalactan side chain-containing RGs I, but of significantly (p < 0.05) different relative proportions; lemon pectin being the richest in HGs, followed by yellow passion fruit pectin. The HG building blocks of each pectin are homogeneous with respect to the molecular size but have a significantly (p < 0.05) reduced length in monocot pectins (59-67) compared to dicot ones (93-102). Lemon pectin displayed the highest degree of esterification (DE), viscosity-average molecular weight (M(v)), and gelling ability, whereas with similar DEs and a higher M(v), banana pectin exhibited a lower gelling ability than yellow passion fruit pectin. It is concluded that both the HG amount and DP strongly influence the gelling properties of pectin.

Differences in structure, antioxidant capacity and gut microbiota modulation of red raspberry pectic polysaccharides extracted by different methods.

Pectic polysaccharides from mature orange (Citrus sinensis) fruit albedo cell walls: Sequential extraction and chemical characterization

Purification and fine structural analysis of pectic polysacchrides from Osmunda japonica Thunb