Structural characterization of chemically and enzymatically derived standard oligosaccharides isolated from partially purified tamarind xyloglucan

High level expression of a xyloglucanase from Rhizomucor miehei in Pichia pastoris for production of xyloglucan oligosaccharides and its application in yoghurt

The xyloglucanase gene (RmXEG12A) from Rhizomucor miehei CAU432 was successfully expressed in Pichia pastoris. The highest xyloglucanase activity of 25,700 U mL^-1 was secreted using high cell density fermentation. RmXEG12A was optimally active at pH 7.0 and 65 °C, respectively. The xyloglucanase exhibited the highest specific activity towards xyloglucan (7915.5 U mg^-1). RmXEG12A was subjected to hydrolyze tamarind powder to produce xyloglucan oligosaccharides with the degree of polymerization (DP) 7-9. The hydrolysis ratio of xyloglucan in tamarind powder was 89.8%. Moreover, xyloglucan oligosaccharides (2.0%, w/w) improved the water holding capacity (WHC) of yoghurt by 1.1-fold and promoted the growth of Lactobacillus bulgaricus and Streptococcus thermophiles by 2.3 and 1.6-fold, respectively. Therefore, a suitable xyloglucanase for tamarind powder hydrolysis was expressed in P. pastoris at high level and xyloglucan oligosaccharides improved the quality of yoghurt.

Negative electrospray ionization mass spectrometry: a method for sequencing and determining linkage position in oligosaccharides from branched hemicelluloses

Xyloglucans of apple, tomato, bilberry and tamarind were hydrolyzed by commercial endo β-1-4-D-endoglucanase. The xylo-gluco-oligosaccharides (XylGos) released were separated on CarboPac PA 200 column in less than 15 min, and, after purification, they were structurally characterized by negative electrospray ionization mass spectrometry using a quadrupole time-of-flight (ESI-Q-TOF), a hybrid linear ion trap (LTQ)/Orbitrap and a hybrid quadrupole Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometers. In order to corroborate the fragmentation routes observed on XylGos, some commercial galacto-manno-oligosaccharides (GalMOs) and glucurono-xylo-oligosaccharides were also studied. The fragmentation pathways of the ionized GalMos were similar to those of XylGos ones. The product ion spectra were mainly characterized by prominent double cleavage (D) ions corresponding to the entire inner side chains. The directed fragmentation from the reducing end to the other end was observed for the main glycosylated backbone but also for the side-chains, allowing their complete sequencing. Relevant cross-ring cleavage ions from (0,2)X(j)-type revealed to be diagnostic of the 1-2-linked- glycosyl units from XylGos together with the 1-2-linked glucuronic acid unit from glucuronoxylans. Resonant activation in the LTQ Orbitrap allowed not only determining the type of all linkages but also the O-acetyl group location on fucosylated side-chains. Moreover, the fragmentation of the different side chains using the MS(n) capabilities of the LTQ/Orbitrap analyzer also allowed differentiating terminal arabinosyl and xylosyl substituents inside S and U side-chains of XylGos, respectively. The CID spectra obtained were very informative for distinction of isomeric structures differing only in their substitution pattern. These features together makes the fragmentation in negative ionization mode a relevant and powerful technique useful to highlight the subtle structural changes generally observed during the development of plant organs such as during fruit ripening and for the screening of cell wall mutants with altered hemicellulose structure.

Generation and structural validation of a library of diverse xyloglucan-derived oligosaccharides, including an update on xyloglucan nomenclature

Xyloglucans are structurally complex plant cell wall polysaccharides that are involved in cell growth and expansion, energy metabolism, and signaling. Determining the structure-function relationships of xyloglucans would benefit from the availability of a comprehensive and structurally diverse collection of rigorously characterized xyloglucan oligosaccharides. Here, we present a workflow for the semi-preparative scale generation and purification of neutral and acidic xyloglucan oligosaccharides using a combination of enzymatic and chemical treatments and size-exclusion chromatography. Twenty-six of these oligosaccharides were purified to near homogeneity and their structures validated using a combination of matrix-assisted laser desorption/ionization mass spectrometry, high-performance anion exchange chromatography, and 1H nuclear magnetic resonance spectroscopy. Mass spectrometry and analytical chromatography were compared as methods for xyloglucan oligosaccharide quantification. 1H chemical shifts were assigned using two-dimensional correlation spectroscopy. A comprehensive update of the nomenclature describing xyloglucan side-chain structures is provided for reference.

Distinguishing xyloglucanase activity in endo-β(1→4)glucanases

The ability of β-glucanases to cleave xyloglucans, a family of highly decorated β-glucans ubiquitous in plant biomass, has traditionally been overlooked in functional biochemical studies. An emerging body of data indicates, however, that a spectrum of xyloglucan specificity resides in diverse glycoside hydrolases from a range of carbohydrate-active enzyme families-including classic "cellulase" families. This chapter outlines a series of enzyme kinetic and product analysis methods to establish degrees of xyloglucan specificity and modes of action of glycosidases emerging from enzyme discovery projects.

Building custom polysaccharides in vitro with an efficient, broad-specificity xyloglucan glycosynthase and a fucosyltransferase

The current drive for applications of biomass-derived compounds, for energy and advanced materials, has led to a resurgence of interest in the manipulation of plant polymers. The xyloglucans, a family of structurally complex plant polysaccharides, have attracted significant interest due to their intrinsic high affinity for cellulose, both in muro and in technical applications. Moreover, current cell wall models are limited by the lack of detailed structure-property relationships of xyloglucans, due to a lack of molecules with well-defined branching patterns. Here, we have developed a new, broad-specificity "xyloglucan glycosynthase", selected from active-site mutants of a bacterial endoxyloglucanase, which catalyzed the synthesis of high molar mass polysaccharides, with complex side-chain structures, from suitable glycosyl fluoride donor substrates. The product range was further extended by combination with an Arabidopsis thaliana α(1→2)-fucosyltransferase to achieve the in vitro synthesis of fucosylated xyloglucans typical of dicot primary cell walls. These enzymes thus comprise a toolkit for the controlled enzymatic synthesis of xyloglucans that are otherwise impossible to obtain from native sources. Moreover, this study demonstrates the validity of a chemo-enzymatic approach to polysaccharide synthesis, in which the simplicity and economy of glycosynthase technology is harnessed together with the exquisite specificity of glycosyltransferases to control molecular complexity.

Polysaccharides purified from the submerged culture of Ganoderma formosanum stimulate macrophage activation and protect mice against Listeria monocytogenes infection

The bioactive components of Ganoderma formosanum have not yet been characterized. We investigated the immunomodulatory activities of the extracellular polysaccharides produced from a submerged mycelial culture of G. formosanum. The polysaccharides were mainly composed of D-mannose, D-galactose and D-glucose. After gel filtration chromatography, three polysaccharide fractions (PS-F1, PS-F2 and PS-F3) were purified. PS-F2 stimulated mouse RAW264.7 macrophages to produce TNF-α and nitric oxide, and enhanced the phagocytic activity of macrophages. PS-F2 challenge in mice triggered an acute inflammatory response characterized by the recruitment of neutrophils and monocytes, which protected mice from subsequent infection of Listeria monocytogenes. The results indicate that the heteropolysaccharides produced by G. formosanum can activate the innate immune response on macrophages.

Solid-state 13C NMR study of a composite of tobacco xyloglucan and Gluconacetobacter xylinus cellulose: molecular interactions between the component polysaccharides

To investigate possible molecular interactions between xyloglucans (XGs) and cellulose in plant cell walls, a model composite was produced using cellulose from the bacterium Gluconacetobacter xylinus and XG from the walls of a tobacco cell-suspension culture that had been incubated with (13)C-labeled glucose. Solid-state (13)C NMR with cross-polarization (CP) and magic-angle spinning (MAS) was used in combination with proton spin-relaxation editing to separate signals from crystalline (rigid) and less rigid domains of the composite. Signals from XG were confined to subspectra of less rigid domains, with no detectable signals from XG attached to surfaces of cellulose crystallites. Signal displacements indicated XGs were more rigid than the mobile coil (twisted backbone) conformation expected for unattached XGs. Similar (13)C chemical shifts were observed in a single-pulse excitation experiment. The results were not compatible with extensive hydrogen bonding between XG and cellulose, but were consistent with a composite structure in which cellulose crystallites were embedded in a matrix of XG with a semirigid (straightened backbone) conformation, that is, a matrix that is partly ordered rather than amorphous.

Xyloglucans of monocotyledons have diverse structures

Except in the Poaceae, little is known about the structures of the xyloglucans in the primary walls of monocotyledons. Xyloglucan structures in a range of monocotyledon species were examined. Wall preparations were isolated, extracted with 6 M sodium hydroxide, and the extracts treated with a xyloglucan-specific endo-(1-->4)-beta-glucanase preparation. The oligosaccharides released were analyzed by high-performance anion-exchange chromatography and by matrix-assisted laser-desorption ionization time-of-flight mass spectrometry. Oligosaccharide profiles of the non-commelinid monocotyledons were similar to those of most eudicotyledons, indicating the xyloglucans were fucogalactoxyloglucans, with a XXXG a core motif and the fucosylated units XXFG and XLFG. An exception was Lemna minor (Araceae), which yielded no fucosylated oligosaccharides and had both XXXG and XXGn core motifs. Except for the Arecales (palms) and the Dasypogonaceae, which had fucogalactoxyloglucans, the xyloglucans of the commelinid monocotyledons were structurally different. The Zingiberales and Commelinales had xyloglucans with both XXGn and XXXG core motifs; small proportions of XXFG units, but no XLFG units, were present. In the Poales, the Poaceae had xyloglucans with a XXGn core motif and no fucosylated units. In the other Poales families, some had both XXXG and XXGn core motifs, others had only XXXG; XXFG units were present, but XLFG units were not.

Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: An update for 2003-2004

This review is the third update of the original review, published in 1999, on the application of matrix-assisted laser desorption/ionization (MALDI) mass spectrometry to the analysis of carbohydrates and glycoconjugates and brings the topic to the end of 2004. Both fundamental studies and applications are covered. The main topics include methodological developments, matrices, fragmentation of carbohydrates and applications to large polymeric carbohydrates from plants, glycans from glycoproteins and those from various glycolipids. Other topics include the use of MALDI MS to study enzymes related to carbohydrate biosynthesis and degradation, its use in industrial processes, particularly biopharmaceuticals and its use to monitor products of chemical synthesis where glycodendrimers and carbohydrate-protein complexes are highlighted.

Recent developments in sample preparation for chromatographic analysis of carbohydrates

Carbohydrates are a very important group of compounds due to their roles as structural materials, sources of energy, biological functions and environmental analytes; they are characterized by their structural diversity and the high number of isomers they present. While many advances have been made in carbohydrate analysis, the sample preparation remains difficult. This review aims to summarize the most important treatments which have been recently developed to be applied prior to the analysis of carbohydrates by chromatographic techniques. Due to the multiplicity of structures and matrices, many different techniques are required for clean-up, fractionation and derivatization. A number of new techniques which could be potentially adequate for carbohydrate characterization have also been revised.

Characterization of oligosaccharides from industrial fermentation residues by matrix-assisted laser desorption/ionization, electro spray mass spectrometry, and gas chromatography mass spectrometry

We report here the preliminary characterization of oligosaccharides present in an enzyme-treated industrial fermentation residue using matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF-MS), electrospray ion trap mass spectrometry (ESI-ITMS), and gas chromatography mass spectrometry (GC-MS). After sample cleaning with carbon graphite columns, analysis of oligosaccharides present in the sample using MALDI-TOF-MS resulted in identification of molecular ions representing sodiated hexose and pentose oligo/polysaccharides. The GC-MS analyses revealed that the signals observed in the mass spectrum for hexose oligomers represent linear structures, whereas the pentose oligomers were identified as arabinoxylans with a (1-->4) linked Xylp backbone where the Xylp residues were either not substituted or singly substituted with Araf branching residues at positions C-2 or C-3 of the Xylp ring. Analyses by ESI-ITMS of the signals corresponding to arabinoxylan oligosaccharides with four and five monosaccharide residues showed the presence of isomeric structures differing in degree of branching and localization of the branched residue along the Xylp backbone.

Two xyloglucan xylosyltransferases catalyze the addition of multiple xylosyl residues to cellohexaose

Xyloglucan (XyG) is the principal hemicellulose found in the primary cell walls of most plants. XyG is composed of a beta-(1,4)-glucan backbone that is substituted in a regular pattern with xylosyl residues, which are added by at least one and likely two or three xylosyltransferase (XT) enzymes. Previous work identified seven Arabidopsis thaliana candidate genes, one of which (AtXT1) was shown to encode a protein with XT activity (Faik, A., Price, N. J., Raikhel, N. V., and Keegstra, K. (2002) Proc. Natl. Acad. Sci. U. S. A. 99, 7797-7802). We expressed both AtXT1 and a second closely related gene, now called AtXT2, in insect cells and demonstrated that both have XT activity for cellopentaose and cellohexaose acceptor substrates. Moreover, we showed that cellohexaose was a significantly better acceptor substrate than cellopentaose. Product structural characterization showed that AtXT1 and AtXT2 preferentially added the first xylosyl residue to the fourth glucosyl residue from the reducing end of both acceptors. Furthermore, when the ratio of UDP-xylose to cellohexaose and the reaction time were increased, both AtXT1 and AtXT2 added a second xylosyl residue adjacent to the first, which generated dixylosylated cellohexaose. On the basis of these results, we concluded that AtXT1 and AtXT2 have the same acceptor specificities and generate the same products in vitro. The implications of these results for understanding in vivo XyG biosynthesis are considered.

Differentiation of isomeric oligosaccharide structures by ESI tandem MS and GC–MS

A mixture of arabinoxylan oligosaccharides from wheat seedling was permethylated and analyzed by electrospray ion trap MS and GC-MS. The presence of isomeric structures differing in degree of branching and position of the branched residue along the xylose backbone was demonstrated for oligosaccharides with four and five monosaccharide residues. No isomeric structures were found for oligosaccharides with three monosaccharide residues. Linkage analysis by GC-MS reveals that xylose residues were substituted with single arabinoxyl residues at C-3.