Quantification of the amount of galacturonic acid residues in blocksequences in pectin homogalacturonan by enzymatic fingerprinting with exo- and endo-polygalacturonase II from Aspergillus niger

Viscoelastic Analysis of Pectin Hydrogels Regenerated from Citrus Pomelo Waste by Gelling Effects of Calcium Ion Crosslinking at Different pHs

Pectin was extracted from citrus pomelo waste, and the effects of calcium ions (Ca2+) on the gelation and hydrogels properties were investigated over a pH range of 3.2-8 by using viscoelastic analysis. The gelatinization of Ca2+-pectin was examined at concentrations of 0.9, 1.8, 2.4, and 3.6 M of Ca2+ in aqueous pectin solutions of 1%, 2%, 3%, and 4%. The gel transition of Ca2+-pectin solution to hydrogels was determined by measuring the storage modulus (G') and loss modulus (G") under mechanical strain from 0.01 to 100%. In a hydrogel of 3% pectin at Ca2+ = 2.4 M, as pH increased to 7, the G' at 0.01 strain % was 3 × 104 Pa, and 3 × 103 Pa at pH 5, indicating that the crosslinking weakened at acidic pH. Due to the crosslinking between the calcium ions and the ionized carboxylic acid groups of pectin, the resulting hydrogel became stiff. When the mechanical strain % was in the range of 0.01-1%, G' was unchanged and G" was an order of magnitude smaller than G', indicating that the mechanical stress was relieved by the gel. In the range of 1-100%, the gel deformation progressed and both the moduli values were dropped. Collapse from the gel state to the solution state occurred at 1-10 strain %, but the softer hydrogels with G' of 103 Pa had a larger strain % than the stiffer hydrogels with G' of 104 Pa.

Revealing methyl-esterification patterns of pectins by enzymatic fingerprinting: Beyond the degree of blockiness

Citrus pectins were studied by enzymatic fingerprinting using a simultaneous enzyme treatment with endo-polygalacturonase (endo-PG) from Kluyveromyces fragilis and pectin lyase (PL) from Aspergillus niger to reveal the methyl-ester distribution patterns over the pectin backbone. Using HILIC-MS combined with HPAEC enabled the separation and identification of the diagnostic oligomers released. Structural information on the pectins was provided by using novel descriptive parameters such as degree of blockiness of methyl-esterified oligomers by PG (DB_PGme) and degree of blockiness of methyl-esterified oligomers by PL (DB_PLme). This approach enabled us to clearly differentiate citrus pectins with various methyl-esterification patterns. The simultaneous use of PG and PL showed additional information, which is not revealed in digests using PG or PL alone. This approach can be valuable to differentiate pectins having the same DM and to get specific structural information on pectins and therefore to be able to better predict their physical and biochemical functionalities.

Immune Priming Triggers Cell Wall Remodeling and Increased Resistance to Halo Blight Disease in Common Bean

The cell wall (CW) is a dynamic structure extensively remodeled during plant growth and under stress conditions, however little is known about its roles during the immune system priming, especially in crops. In order to shed light on such a process, we used the Phaseolus vulgaris-Pseudomonas syringae (Pph) pathosystem and the immune priming capacity of 2,6-dichloroisonicotinic acid (INA). In the first instance we confirmed that INA-pretreated plants were more resistant to Pph, which was in line with the enhanced production of H₂O₂ of the primed plants after elicitation with the peptide flg22. Thereafter, CWs from plants subjected to the different treatments (non- or Pph-inoculated on non- or INA-pretreated plants) were isolated to study their composition and properties. As a result, the Pph inoculation modified the bean CW to some extent, mostly the pectic component, but the CW was as vulnerable to enzymatic hydrolysis as in the case of non-inoculated plants. By contrast, the INA priming triggered a pronounced CW remodeling, both on the cellulosic and non-cellulosic polysaccharides, and CW proteins, which resulted in a CW that was more resistant to enzymatic hydrolysis. In conclusion, the increased bean resistance against Pph produced by INA priming can be explained, at least partially, by a drastic CW remodeling.

Structural study of a pectic polysaccharide fraction isolated from "mountain tea" (Sideritis scardica Griseb.)

The present study was conducted to investigate the structural characteristics of an acid-extracted polysaccharide fraction from mountain tea. The monosaccharide composition revealed that uronic acids (72.4 mol%) considerably predominated in the fraction, followed by smaller amounts of galactose (14.5 mol%) and glucose (6.2 mol%). The fraction contained mostly a highly methyl-esterified homogalacturonan (HG) - 71 mol%. The pectin had a high molecular weight population (∼60-100 kDa). Enzymatic fingerprinting was employed with a combination of HG degrading enzymes and LC-HILIC-MS, HPAEC, HPSEC to examine the structure in greater detail. Unsaturated oligomers released indicated the presence of large blocks of highly methyl-esterified GalA residues. Furthermore, the presence of blocks of non-esterified GalA residues and partly methyl-esterified and acetylated GalA residues in HG domain was demonstrated. The research findings provide a basis for further investigations regarding biological activity and commercial exploitation of mountain tea.

Characterisation of pectin-xylan complexes in tomato primary plant cell walls

The primary plant cell wall is composed of a complex network of pectin, hemicellulose and cellulose. Potential interactions between these polysaccharides were studied for carrot, tomato and strawberry, with a focus on the role of pectin. The Chelating agent Unextractable Solids (ChUS), the residue after water- and EDTA extraction, was ball milled and subsequently water extracted. For tomato and strawberry, pectin and substantial amounts of hemicellulose were solubilised. Anion exchange chromatography (AEC) showed co-elution of pectin and acetylated glucuronoxylan in tomato, representing 18% of solubilised uronic acid and 48% of solubilised xylose by ball milling from ChUS. The existence of a covalently linked pectin-xylan complex was proposed since xylan co-precipitated with pectin under mild alkali conditions. It was proposed that pectin links with xylan through the RG-I region since degradation of HG did not alter AEC elution patterns for RG-I and xylan, suggesting RG-I - xylan interactions.

Interactions between pectin and cellulose in primary plant cell walls

To understand the architecture of the plant cell wall, it is of importance to understand both structural characteristics of cell wall polysaccharides and interactions between these polysaccharides. Interactions between polysaccharides were studied in the residue after water and chelating agent extraction by sequential extractions with H₂O and alkali. The 6 M alkali residue still represented 31%, 11% and 5% of all GalA present in carrot, tomato and strawberry, respectively, and these pectin populations were assumed to strongly interact with cellulose. Digestion of the carrot 6 M alkali residue by glucanases released ∼27% of the 6 M residue, mainly representing pectin. In tomato and strawberry alkali residues, glucanases were not able to release pectin populations. The ability of glucanases to release pectin populations suggests that the carrot cell wall contains unique, covalent interactions between pectin and cellulose.

Alteration of cell wall polysaccharides through transgenic expression of UDP-Glc 4-epimerase-encoding genes in potato tubers

Uridine diphosphate (UDP)-glucose 4-epimerase (UGE) catalyzes the conversion of UDP-glucose to UDP-galactose. Cell wall materials from the cv. Kardal (wild-type, background) and two UGE transgenic lines (UGE 45-1 and UGE 51-16) were isolated and fractionated. The galactose (Gal) content (mg/100g tuber) from UGE 45-1 transgenic line was 38% higher than that of wild-type, and resulted in longer pectin side chains. The Gal content present in UGE 51-16 was 17% lower than that of wild-type, although most pectin populations maintained the same level of Gal. Both UGE transgenic lines showed unexpectedly a decrease in acetylation and an increase in methyl-esterification of pectin. Both UGE transgenic lines showed similar proportions of homogalacturonan and rhamnogalacturonan I within pectin backbone as the wild-type, except for the calcium-bound pectin fraction exhibiting relatively less rhamnogalacturonan I. Next to pectin modification, xyloglucan populations from both transgenic lines were altered resulting in different XSGG and XXGG proportion in comparison to wild-type.

Modification of potato cell wall pectin by the introduction of rhamnogalacturonan lyase and β-galactosidase transgenes and their side effects

Genes encoding pectic enzymes were introduced to wild-type potato Karnico. Cell wall materials were extracted from Karnico and transgenic lines expressing β-galactosidase (β-Gal-14 mutant) or rhamnogalacturonan lyase (RGL-18 mutant). After sequential extraction, β-Gal-14 hot buffer-soluble solids (HBSS) of pectin contained 54% less galactose than Karnico HBSS, representing shorter galactan side chains. The individual pectin populations of β-Gal-14 HBSS showed different modifications extended to the two sub-populations as obtained by ion-exchange chromatography. Compared to wild-type, RGL-18 HBSS contained 27% more galacturonic acid and 55% less Gal on fresh potato weight basis, which was due to the removal of galactan-rich rhamnogalacturonan I (RG-I) segments. All pectin populations of RGL-18 showed consistently low levels of RG-I segments. Transgenic modification showed side effects on the methyl-esterification and acetyl substitution of RGL-18 HBSS (DM=53, DA=21), but not of the β-Gal-14 HBSS in comparison to wild-type (DM=29, DA=54).

Potential Application of Pectinase in Developing Functional Foods

The understanding that enzymatic degradation of fruit pectin can clarify juices and improve juice yields resulted in the search for microbial pectinases and application in vegetable- and fruit-processing industries. Identified enzymes were classified on the basis of their catalytic activity to pectin or its derivatives and in terms of industrial use. Discovery of gene sequences that coded the enzymes, protein engineering, and molecular biology tools resulted in defined microbial strains that over-produced the enzymes for cost-effective technologies. Recent perspectives on the use of pectin and its derivatives as dietary fibers suggest enzymatic synthesis of the right oligomers from pectin for use in human nutrition. While summarizing the activities of pectin-degrading enzymes, their industrial applications, and gene sources, this review projects another application for pectinases, which is the use of enzymatically derived pectin moieties in functional food preparation.

Mapping the polysaccharide degradation potential of Aspergillus niger

Background

The degradation of plant materials by enzymes is an industry of increasing importance. For sustainable production of second generation biofuels and other products of industrial biotechnology, efficient degradation of non-edible plant polysaccharides such as hemicellulose is required. For each type of hemicellulose, a complex mixture of enzymes is required for complete conversion to fermentable monosaccharides. In plant-biomass degrading fungi, these enzymes are regulated and released by complex regulatory structures. In this study, we present a methodology for evaluating the potential of a given fungus for polysaccharide degradation.

Results

Through the compilation of information from 203 articles, we have systematized knowledge on the structure and degradation of 16 major types of plant polysaccharides to form a graphical overview. As a case example, we have combined this with a list of 188 genes coding for carbohydrate-active enzymes from Aspergillus niger, thus forming an analysis framework, which can be queried. Combination of this information network with gene expression analysis on mono- and polysaccharide substrates has allowed elucidation of concerted gene expression from this organism. One such example is the identification of a full set of extracellular polysaccharide-acting genes for the degradation of oat spelt xylan.

Conclusions

The mapping of plant polysaccharide structures along with the corresponding enzymatic activities is a powerful framework for expression analysis of carbohydrate-active enzymes. Applying this network-based approach, we provide the first genome-scale characterization of all genes coding for carbohydrate-active enzymes identified in A. niger.

Enzymatic modification of a model homogalacturonan with the thermally tolerant pectin methylesterase from Citrus: 1. Nanostructural characterization, enzyme mode of action, and effect of pH

Methyl ester distribution in pectin homogalacturonan has a major influence on functionality. Enzymatic engineering of the pectin nanostructure for tailoring functionality can expand the role of pectin as a food-formulating agent and the use of in situ modification in prepared foods. We report on the mode of action of a unique citrus thermally tolerant pectin methylesterase (TT-PME) and the nanostructural modifications that it produces. The enzyme was used to produce a controlled demethylesterification series from a model homogalacturonan. Oligogalacturonides released from the resulting demethylesterified blocks introduced by TT-PME using a limited endopolygalacturonase digestion were separated and quantified by high-pressure anion-exchange chromatography (HPAEC) coupled to an evaporative light-scattering detector (ELSD). The results were consistent with the predictions of a numerical simulation, which assumed a multiple-attack mechanism and a degree of processivity ∼10, at both pH 4.5 and 7.5. The average demethylesterified block size (0.6-2.8 nm) and number of average-sized blocks per molecule (0.8-1.9) differed, depending upon pH of the enzyme treatment. The mode of action of this enzyme and consequent nanostructural modifications of pectin differ from a previously characterized citrus salt-independent pectin methylesterase (SI-PME).

Characterization of a pectic polysaccharide from the leaves of Diospyros kaki and its modulating activity on lymphocyte proliferation

Pectin is a group of carbohydrate polymers constructing the primary cell walls and the middle lamella of terrestrial plants. Herein, we demonstrated the structure and immunomodulatory activity of the major pectic polysaccharide DL-3B(2) isolated from the leaves of Diospyros kaki. Based on composition analysis, methylation analysis, two-step acid hydrolysis, lithium-mediated selective degradation, (13)C NMR spectroscopy, and electrospray ionization mass spectrometry, DL-3B(2) was found to contain an alpha-1, 4-linked galacturonic acid (GalA) backbone with some insertions of alpha-1, 2-linked rhamnose residues. The arabinan- and arabinogalactan-side chains were attached to O-4 of the rhamnose residues, whereas the linear arabinoxylan was probably linked to O-3 of the GalA residues. Immunological tests in vitro showed that DL-3B(2) could help stimulate lipopolysaccharide-induced B lymphocyte proliferation, but not ConA-induced T lymphocyte proliferation, and that the arabinose residues play a role in maintaining this immunological activity.

High-throughput screening of Erwinia chrysanthemi pectin methylesterase variants using carbohydrate microarrays

Pectin methylesterases (PMEs) catalyse the removal of methyl esters from the homogalacturonan (HG) backbone domain of pectin, a ubiquitous polysaccharide in plant cell walls. The degree of methyl esterification (DE) impacts upon the functional properties of HG within cell walls and plants produce numerous PMEs that act upon HG in muro. Many microbial plant pathogens also produce PMEs, the activity of which renders HG more susceptible to cleavage by pectin lyase and polygalacturonase enzymes and hence aids cell wall degradation. We have developed a novel microarray-based approach to investigate the activity of a series of variant enzymes based on the PME from the important pathogen Erwinia chrysanthemi. A library of 99 E. chrysanthemi PME mutants was created in which seven amino acids were altered by various different substitutions. Each mutant PME was incubated with a highly methyl esterified lime pectin substrate and, after digestion the enzyme/substrate mixtures were printed as microarrays. The loss of activity that resulted from certain mutations was detected by probing arrays with a mAb (JIM7) that preferentially binds to HG with a relatively high DE. Active PMEs therefore resulted in diminished JIM7 binding to the lime pectin substrate, whereas inactive PMEs did not. Our findings demonstrate the feasibility of our approach for rapidly testing the effects on PME activity of substituting a wide variety of amino acids at different positions.

Quantification of blockiness in pectins-A comparative study using vibrational spectroscopy and chemometrics

The gelling properties of pectins are related not only to the degree of esterification (DE), but also to the distribution of the ester groups. In this study, we have examined an experimentally designed series of 31 pectins originating from the same mother pectin and de-esterified using combinations of two different enzymatic mechanisms. The potential of using infrared (IR), Raman, and near infrared (NIR) spectroscopies combined with chemometrics for reliable and rapid determination of the DE and distribution patterns of methyl ester groups in a designed set of pectin powders was investigated. Quantitative calibration models using partial least squares (PLS) regression were developed and compared. The calibration models for prediction of DE obtained on extended inverse signal correction (EISC)-treated spectra of all three spectroscopic methods yielded models with cross-validated prediction errors (RMSECV) between 1.1%p and 1.6%p DE and correlation coefficients of 0.99. A calibration model predicting degree of random de-esterification (R) and block de-esterification (B) was developed for each spectroscopic method, yielding RMSECV values between 4.4 and 6.7 and correlation coefficients (r) between 0.79 and 0.92. Variable selection using interval PLS (iPLS) significantly improved the prediction of R for IR spectroscopy, yielding RMSECV of 3.5 and correlation coefficients of 0.95. All three spectroscopic methods were able to distinguish the spectral patterns of pectins with different enzyme treatments in simple classification models by principal component analysis (PCA). Extended canonical variate analysis revealed one specific signal in the Raman (1045cm(-1)) spectrum and one significant area (1250-1400cm(-1)) in the IR spectrum which are able to classify the pectin samples according to the four different enzyme treatments. In both Raman and IR spectra, the signal intensity decreased in the sequence R-B>B>B-R>R>re-methylated pectin.

Structural biology of pectin degradation by Enterobacteriaceae

SUMMARY

Pectin is a structural polysaccharide that is integral for the stability of plant cell walls. During soft rot infection, secreted virulence factors from pectinolytic bacteria such as Erwinia spp. degrade pectin, resulting in characteristic plant cell necrosis and tissue maceration. Catabolism of pectin and its breakdown products by pectinolytic bacteria occurs within distinct cellular environments. This process initiates outside the cell, continues within the periplasmic space, and culminates in the cytoplasm. Although pectin utilization is well understood at the genetic and biochemical levels, an inclusive structural description of pectinases and pectin binding proteins by both extracellular and periplasmic enzymes has been lacking, especially following the recent characterization of several periplasmic components and protein-oligogalacturonide complexes. Here we provide a comprehensive analysis of the protein folds and mechanisms of pectate lyases, polygalacturonases, and carbohydrate esterases and the binding specificities of two periplasmic pectic binding proteins from Enterobacteriaceae. This review provides a structural understanding of the molecular determinants of pectin utilization and the mechanisms driving catabolite selectivity and flow through the pathway.

Elaborate spatial patterning of cell-wall PME and PMEI at the pollen tube tip involves PMEI endocytosis, and reflects the distribution of esterified and de-esterified pectins

In dicots, pectins are the major structural determinant of the cell wall at the pollen tube tip. Recently, immunological studies revealed that esterified pectins are prevalent at the apex of growing pollen tubes, where the cell wall needs to be expandable. In contrast, lateral regions of the cell wall contain mostly de-esterified pectins, which can be cross-linked to rigid gels by Ca(2+) ions. In pollen tubes, several pectin methylesterases (PMEs), enzymes that de-esterify pectins, are co-expressed with different PME inhibitors (PMEIs). This raises the possibility that interactions between PMEs and PMEIs play a key role in the regulation of cell-wall stability at the pollen tube tip. Our data establish that the PME isoform AtPPME1 (At1g69940) and the PMEI isoform AtPMEI2 (At3g17220), which are both specifically expressed in Arabidopsis pollen, physically interact, and that AtPMEI2 inactivates AtPPME1 in vitro. Furthermore, transient expression in tobacco pollen tubes revealed a growth-promoting activity of AtPMEI2, and a growth-inhibiting effect of AtPPME1. Interestingly, AtPPME1:YFP accumulated to similar levels throughout the cell wall of tobacco pollen tubes, including the tip region, whereas AtPMEI2:YFP was exclusively detected at the apex. In contrast to AtPPME1, AtPMEI2 localized to Brefeldin A-induced compartments, and was found in FYVE-induced endosomal aggregates. Our data strongly suggest that the polarized accumulation of PMEI isoforms at the pollen tube apex, which depends at least in part on local PMEI endocytosis at the flanks of the tip, regulates cell-wall stability by locally inhibiting PME activity.

Restricted cell elongation in Arabidopsis hypocotyls is associated with a reduced average pectin esterification level

BACKGROUND

Cell elongation is mainly limited by the extensibility of the cell wall. Dicotyledonous primary (growing) cell walls contain cellulose, xyloglucan, pectin and proteins, but little is known about how each polymer class contributes to the cell wall mechanical properties that control extensibility.

RESULTS

We present evidence that the degree of pectin methyl-esterification (DE%) limits cell growth, and that a minimum level of about 60% DE is required for normal cell elongation in Arabidopsis hypocotyls. When the average DE% falls below this level, as in two gibberellic acid (GA) mutants ga1-3 and gai, and plants expressing pectin methyl-esterase (PME1) from Aspergillus aculeatus, then hypocotyl elongation is reduced.

CONCLUSION

Low average levels of pectin DE% are associated with reduced cell elongation, implicating PMEs, the enzymes that regulate DE%, in the cell elongation process and in responses to GA. At high average DE% other components of the cell wall limit GA-induced growth.

Homogalacturonan synthesis in Arabidopsis thaliana requires a Golgi-localized protein with a putative methyltransferase domain

Pectins are a family of complex cell-wall polysaccharides, the biosynthesis of which remains poorly understood. We identified dwarf mutants with reduced cell adhesion at a novel locus, QUASIMODO2 (QUA2). qua2-1 showed a 50% reduction in homogalacturonan (HG) content compared with the wild type, without affecting other cell-wall polysaccharides. The remaining HG in qua2-1 showed an unaltered degree of methylesterification. Positional cloning and GFP fusions showed that QUA2, consistent with a role in HG synthesis, encodes a Golgi-localized protein. In contrast to QUA1, another Golgi-localized protein required for HG-synthesis, QUA2 does not show sequence similarity to glycosyltransferases, but instead contains a putative methyltransferase (MT) domain. The Arabidopsis genome encodes 29 QUA2-related proteins. Interestingly, the transcript profiles of QUA1 and QUA2 are correlated and other pairs of QUA1 and QUA2 homologues with correlated transcript profiles can be identified. Together, the results lead to the hypothesis that QUA2 is a pectin MT, and that polymerization and methylation of homogalacturonan are interdependent reactions.

Differential fragmentation patterns of pectin oligogalacturonides observed by nanoelectrospray quadrupole ion-trap mass spectrometry using automated spectra interpretation

Oligogalacturonides of different degrees of polymerization (DP) and methyl esterification (DE) were structurally analyzed by nanoESI quadrupole ion-trap mass spectrometry. The fragmentation patterns of the oligogalacturonides were compared using the program 'Virtual Expert Mass Spectrometrist' (VEMS) for structural annotation. In the analyzed oligogalacturonides of lower DP, the generation of C/Y ions, i.e. ions retaining the glycosidic oxygen, was higher than that of B/Z ions. In general, with oligogalacturonides of higher DP, the B/Z ions were generated more abundantly. Oligogalacturonides with free carboxylic acid groups underwent higher water loss compared to fully methyl-esterified oligogalacturonides under the same fragmentation conditions. Cross-ring cleavage, in which fragmentation occurs across the ring system of the galacturonate residue and signified by unique mass losses, was observed to be higher in fully methyl-esterified oligogalacturonides than in non-methyl-esterified ones. This study demonstrates the different fragmentation patterns of oligogalacturonides as influenced by the presence or absence of methyl ester groups. For a detailed analysis of unknown oligogalacturonides, cross-ring fragmentation gives more structural information than glycosidic bond cleavage. One implication of this is that more structural information is obtained when analyzing methyl-esterified oligogalacturonides than non-methyl-esterified ones in an ion-trap instrument. This is of particular importance in pectin chemistry, where mass spectrometry has become the technique of choice for structural determination. Although this study was not designed to explain the mechanisms of oligogalacturonide fragmentation, possible explanations for why non-methyl-esterified oligogalacturonides undergo more water loss than methyl-esterified ones will be postulated. In addition, the VEMS program was extended to automatically interpret and assign the fragment ions peaks generated in this study.

Structural characterization of native high-methoxylated pectin using nuclear magnetic resonance spectroscopy and ultraviolet matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. Comparative use of 2,5-dihydroxybenzoic acid and nor-harmane as UV-MALDI matrices

The successful analysis by ultraviolet matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (UV-MALDI-TOF MS) of native and hydrolyzed high-methoxylated pectin samples is described. In order to find the optimal conditions for UV-MALDI-TOF MS analysis several experimental variables were studied such as: different UV-MALDI matrices (nor-harmane, 2,5-dihydroxybenzoic acid), sample preparation methods (mixture, sandwich), inorganic salt addition (doping salts, NaCl, KCl, NH(4)Cl), ion mode (positive, negative), linear and reflectron mode, etc. nor-Harmane has never been used as a UV-MALDI matrix for the analysis of pectins but its use avoids pre-treatment of the sample, such as an enzymatic digestion or an acid hydrolysis, and there is no need to add salts, making the analysis easier and faster. This study suggested an alternative way of analyzing native high-methoxylated pectins, with UV-MALDI-TOF MS, by using nor-harmane as the matrix in negative ion mode. The analysis by (1)H and (13)C nuclear magnetic resonance (NMR) spectroscopy of the native and hydrolyzed pectin is also briefly described.

On the simulation of enzymatic digest patterns: The fragmentation of oligomeric and polymeric galacturonides by endo-polygalacturonase II

A simulation methodology for predicting the time-course of enzymatic digestions is described. The model is based solely on the enzyme's subsite architecture and concomitant binding energies. This allows subsite binding energies to be used to predict the evolution of the relative amounts of different products during the digestion of arbitrary mixtures of oligomeric or polymeric substrates. The methodology has been specifically demonstrated by studying the fragmentation of a population of oligogalacturonides of varying degrees of polymerization, when digested by endo-polygalacturonase II (endo-PG II) from Aspergillus niger.

Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: An update covering the period 1999-2000

This review describes the use of matrix-assisted laser desorption/ionization (MALDI) mass spectrometry for the analysis of carbohydrates and glycoconjugates and continues coverage of the field from the previous review published in 1999 (D. J. Harvey, Matrix-assisted laser desorption/ionization mass spectrometry of carbohydrates, 1999, Mass Spectrom Rev, 18:349-451) for the period 1999-2000. As MALDI mass spectrometry is acquiring the status of a mature technique in this field, there has been a greater emphasis on applications rather than to method development as opposed to the previous review. The present review covers applications to plant-derived carbohydrates, N- and O-linked glycans from glycoproteins, glycated proteins, mucins, glycosaminoglycans, bacterial glycolipids, glycosphingolipids, glycoglycerolipids and related compounds, and glycosides. Applications of MALDI mass spectrometry to the study of enzymes acting on carbohydrates (glycosyltransferases and glycosidases) and to the synthesis of carbohydrates, are also covered.