Evgeny G. Shakhmatov

Structural studies of the pectic polysaccharide from Siberian fir (Abies sibirica Ledeb.).

The pectic polysaccharide named abienan AS-A was isolated from the wood greenery of Abies sibirica using dilute hydrochloric acid (pH 4.0) at 70°C. The structure of abienan AS-A was elucidated using sugar composition analysis, ion-exchange chromatography and partial acid hydrolysis followed by NMR spectroscopy. The linear region of abienan AS-A was shown to contain linear 1,4-α-D-galactopyranosyluronan partially substituted with methyl esters or 3-O-acetyl groups and rhamnogalacturonan blocks consisting of 1,4-α-D-galacturonan partially substituted with methyl ester groups and connected by 2-O-substituted α-rhamnopyranose residues. The branched region of abienan AS-A was found to be made of RG-I. The side chains of RG-I were shown to contain 1,4-β-galactan and branched arabinan. Some 4-O-substituted β-galactopyranose residues were shown to be attached to the 4-position of the 2-O-substituted α-rhamnopyranose residues of the RG-I backbone. The arabinan groups were made up of a 1,5-linked α-L-arabinofuranan backbone that was 3-O-, 2-O-, and 2,3-di-O-substituted with the terminal and 1,3-linked α-L-arabinofuranose residues.

Structural studies of arabinan-rich pectic polysaccharides from Abies sibirica L. Biological activity of pectins of A. sibirica

Highly branched arabinan-rich pectic polysaccharides, containing 84% of arabinose, was extracted from wood greenery of Abies sibirica L. The structure of arabinan was studied by the 1D and 2D NMR spectroscopy. The macromolecule backbone was represented mainly by RG-I (molar ratio GalA:Rha ∼ 1.3:1) patterns with high degree of rhamnose branching. Side chains were comprised of 1,5-linked α-L-Araf residues (the major part of polymer mass), 1,3,5-di-O- and 1,2,3,5-tri-O-linked α-L-Araf residues, confirming the presence of highly branched 1,5-α-L-arabinan. Although most L-Araf were in α-anomeric form, minor terminal β-L-Araf-(1 →... was detected. 1,4-β-D-linked Galp residues found in the side chains account for minor AG-I or 1,4-galactan, as compared to arabinan. A tentative structure was proposed. Polysaccharides obtained from Siberian fir greenery were screened for biological activity. Galacturonan had a strongest stimulating effect on germination and growth rate of seeds, germs and roots of Triticum aestivum, Avena sativa, and Secale cereale.

Structural characteristics of water-soluble polysaccharides from Heracleum sosnowskyi Manden

Fractions containing arabinogalactan proteins (AGPs) and pectic polysaccharides were isolated from above-ground parts of Heracleum sosnowskyi. Major units of their structure were elucidated using ion-exchange chromatography, gel chromatography, and NMR spectroscopy. The carbohydrate backbone of the polysaccharides consisted of 1,3-β-D-galactopyranosyl residues, whereas side chains of the branched region consisted of the residues of 1,6-β-galactopyranose, 1,5-α-L-arabinofuranose, 1,4-β-D-glucuronic acid, and 1,6-β-D-glucopyranose. The branching points were identified as 1,3,6-β-D-galactopyranose residues. Side chains were terminated with β-D-galactopyranose, α-L-arabinofuranose and α-L-rhamnopyranose. A significant part of the side-chain β-1,6-galactan was substituted at C6 by 4-OMe-β-D-glucuronic acid. A minor part of glucuronic acid was included in the α-Rhap-(1 → 4)-β-GlcA-(→ fragment. All the studied fractions contained 1,4-β-D-galacturonic acid as well.

Extraction and structural characteristics of pectic polysaccharides from Abies sibirica L

Structurally different pectins were isolated from the wood greenery of Abies sibirica L. by the sequential extraction with water (ASW), HCl solution (pH∼4) (ASA), and NH3 solution (pH∼8.5) (ASN). The GalA/Rha molar ratios for the ASW (15), ASA (8.9), and ASN (3.9) polysaccharides diminish in the order ASW>ASA>ASN, indicating a decrease in homogalacturonans and increase in rhamnogalacturonan I in this series. The ASWH, ASAH, and ASNH homogalacturonans derived by acid hydrolysis of ASW, ASA, and ASN have similar Mw 23.8, 21.1, and 18.9kDa, respectively, corresponding to a mean polymerization degree of 97-122 for the GalA residue. The macromolecule backbone of ASN was represented mainly by moieties of partially methylesterified homogalacturonan and partially 2-O- and/or 3-O-acetylated rhamnogalacturonan I. The carbohydrate side chains of the branched region are primarily made up of terminal, 1,5-O-, 1,3,5-di-O- and 1,2,3,5-tri-O-substituted α-L-Araf residues and terminal, 1,3-O- and 1,3,6-di-O-substituted β-D-Galp residues. The currently known pectin models were refined.

Structural characteristics of pectic polysaccharides and arabinogalactan proteins from Heracleum sosnowskyi Manden

Polymers with different structures were isolated from the aboveground part of Heracleum sosnowskyi Manden. The sequential treatment of Heracleum with water, HCl solution, and (NH4)2C2O4 solution was observed to decrease the arabinogalactan proteins (AGP) content and increase the pectins content in the extracted polysaccharides. The linear region of the HSO-I polysaccharide having the highest yield was found to be composed mainly of partially methylesterified homogalacturonan fragments, whereas the branched region was made up of fragments of rhamnogalacturonan I whose core represents 1,2-α-L-rhamno-1,4-α-D-galacturonan. The carbohydrate side chains of the branched region are linked to the α-L-Rhap core residues via the 1,4-glycosidic bond and consist chiefly of T-β-D-Galp, 1,4-β-D-Galp and 1,6-β-D-Galp residues indicating the presence of the 1,4-β-D-galactan. NMR spectroscopy revealed the carbohydrate moiety of the AGP molecule to consist mainly of 1,3- and 1,3,6-β-D-Galp residues. The side chains comprised 1,6-β-D-Galp, terminal 4-O-Me-β-D-GlcpA, and β-D-Galp.

Structural characteristics of oxalate-soluble polysaccharides of Sosnowsky's hogweed (Heracleum sosnowskyi Manden)

Arabinogalactan proteins (AGP) and pectic polysaccharides were isolated from above-ground parts of Heracleum sosnowskyi. The structural study has shown that a linear region of the pectic macromolecules consists of 1,4-α-d-galactopyranosyluronan blocks partially methyl esterified and acetylated. The branched region consists of 3-O- and partially 2-O-acetylated rhamnogalacturonan I. Side chains of the RG-I backbone include the regions of arabinogalactan I and branched 1,5-α-l-arabinan. The carbohydrate part of AGP consists of arabinogalactan II with a 1,3-β-d-Galp main chain. The side chains of the branched area of AG-II are composed of 1,6-β-d-Galp, 1,5-, 1,3,5-α-l-Araf, 4-O-Me-β-d-GlcA and 1,4-β-d-GlcpA, and non-reducing ends residues of β-d-Galp, α-l-Araf, α-l-Rhap and α-l-Fucp. The branch points of the main and side chains are formed by 3,6-di-O-substituted β-d-Galp. It was found that at least a portion of pectin is probably covalently linked to AGP, wherein AGP is linked to RG-I, but not with galacturonan.

Structural and chemical charactertistics of pectins, arabinogalactans, and arabinogalactan proteins from conifers

In this review, we summarized the research data on the contents and chemical structures of pectic polysaccharides, arabinogalactans, and arabinogalactan proteins from coniferous species. The presently known structures of these polymers are given. Special attention is given to the description of chemical structural features of pectic polysaccharides from the Abies sibirica and Picea abies tree verdures (branches and needles). Three models presently suggested for the description of pectin macromolecular structures are discussed.

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

Arabinogalactan proteins and pectic polysaccharides were isolated from greenery of Picea abies by water extraction. Main elements of their structure were determined by ion-exchange chromatography, partial acid and enzymatic hydrolysis, and NMR spectroscopy. It was established that the backbone of pectin macromolecules of greenery of P. abies is represented by segments of partially methyl-esterified and acetylated 1,4-α-d-galactopyranosyluronan, and partially 2-O- and/or 3-O-acetylated RG-I with side chains consisting of highly-branched 1,5-α-l-arabinan segments. The carbohydrate part of AGP of greenery of P. abies consists of AG-II, the main chain of which is represented by 1,3-β-d-Galp and 1,3,6-β-d-Galp residues. The side chains of AG-II are formed of 1,6- and 1,3,6-β-d-Galp, 1,3- and 1,5-α-l-Araf, β-d-GlcpA and 1,4-β-d-GlcpA, T-α-l-Araf, T-α-l-Rhap and T-α-l-Fucp residues. The AGPs of P. abies are also characterized by the presence of an unusual 4-O-Me-α-l-Fucp monosaccharide, which, as far as we know, was not found in pectins or AGP earlier.

Seasonal dynamics of polysaccharides in Norway spruce (Picea abies)

Annual dynamics of accumulation and changes in the monosaccharide composition of pectin-, arabinan- and galactan-containing polysaccharides and binding glycans isolated from greenery (thin branches with needles) of Norway spruce were investigated in this study. The polysaccharides were compared with polysaccharides of Siberian fir according to the yields, composition and content of typical components. It was shown that Norway spruce greenery contains lowly methyl-esterified pectin extracted with ammonium oxalate, which is a part of protopectic complex and is bound with components of cell walls via ionic bonds. In contrast, Siberian fir greenery contains mainly water-extracted highly methyl-esterified pectin, weakly bound to cell wall components. It was concluded that an autumn-winter period is the optimal time for harvesting Norway spruce and Siberian fir greenery for isolation of the pectic polysaccharides. The revealed regularities indicate that there is a certain biorhythm of accumulation of the compounds, probably determined by genetic factors.

Structural studies of water-extractable pectic polysaccharides and arabinogalactan proteins from Picea abies greenery

Water-extractable arabinogalactan proteins (AGP) (the main constituent) and pectic polysaccharides were isolated from tree greenery of Picea abies. The carbohydrate part of AGP macromolecules consisted of AG-II, the side chains of which were represented by 1,6- and 1,3,6-β-d-Galp, T-α-l-Araf, 1,3- and 1,5-α-l-Araf, T-β-D-GlcpA and 1,4-β-D-GlcpA, T-α-l-Rhap, T-α-l-Fucp and 4-O-Me-α-l-Fucp residues. It was established that the unusual 4-O-Me-α-l-Fucp monosaccharide are located on the non-reducing ends of the side chains of carbohydrate part of AGP macromolecules, and are bound to 1,4-β-d-GlcpA residues by 1,4-bonds. The backbone of pectin macromolecules consisted mostly of 1,4-α-d-galactopyranosyluronan and RG-I, which side chains were represented by highly branched 1,5-α-l-arabinan. It was shown that RG-I is characterized mainly by short segments, which are alternated with the regions of the non-acetylated and non-methyl-esterified galacturonan. The study revealed that at least a part of the pectin is strongly associated with AGP. It was indicated that the RG-I segments are separated from the AGP-bound pectin by regions of 1,4-α-d-galactopyranosyluronane.