Auswahl der wissenschaftlichen Literatur zum Thema „Acid Oligogalacturonique“

Polygalacturonic acid (PGA) was hydrolyzed by polygalacturonases (PGs) purified from six fungi. The oligogalacturonide products were analyzed by HPAEC-PAD (high performance anion exchange chromatography-pulsed amperimetric detection) to assess their relative amounts and degrees of polymerization. The abilities of the fungal PGs to reduce the viscosity of a solution of PGA were also determined. The potential abilities of four polygalacturonase-inhibiting proteins (PGIPs) from three plant species to inhibit or to modify the hydrolytic activity of the fungal PGs were determined by colorimetric and HPAEC-PAD analyses, respectively. Normalized activities of the different PGs acting upon the same substrate resulted in one of two distinct oligogalacturonide profiles. Viscometric analysis of the effect of PGs on the same substrate also supports two distinct patterns of cleavage. A wide range of susceptibility of the various PGs to inhibition by PGIPs was observed. The four PGs that were inhibited by all PGIPs tested exhibited an endo/exo mode of substrate cleavage, while the three PGs that were resistant to inhibition by one or more of the PGIPs proceed by a classic endo pattern of cleavage.

Studies of the enzymic digestion of pectic substrates using different polygalacturonase (PG) preparations have revealed evidence for a previously unreported enzyme activity carried out by a contaminating enzyme in one of the preparations. This observed activity involves the demethylation of specific oligogalacturonides, namely 2-methyltrigalacturonic acid and 2,3-dimethyltetragalacturonic acid. However, no large-scale demethylation of highly methylated polymeric substrates is found, demonstrating that the enzyme responsible is not a conventional pectin methylesterase (PME). Furthermore, it has been shown that a commercial sample of fungal PME from Aspergillus niger demethylates all of the oligogalacturonides present as primary products of endo-PG digestion, in contrast with the activity observed here. On the basis of the known methyl ester distribution of the endo-PG-generated fragments and knowledge of which of these oligogalacturonides are demethylated, it is concluded that the observed activity can be explained by the existence of an exo-acting methylesterase that attacks the non-reducing end of the oligogalacturonide molecules.

Phytoalexin accumulation is one of a myriad of plant defense responses; these responses can be elicited by pathogens or molecules such as oligogalacturonides (OGAs). Phytoalexin production has been considered a vital component of the resistance mechanisms that determine the outcome of many plant-microbe interactions. Besides inducing defense responses, OGAs have been shown to affect plant development, which normally is controlled by plant hormones, particularly auxin. In this work we measured phytoalexin accumulation in roots of bean (Phaseolus vulgaris L.) seedlings grown in the presence or absence of the auxin 3-naphtalenacetic acid (NAA) and treated with a decagalacturonide (OGA10). We found that OGA10 (0.01 mM) caused phytoalexin production and also inhibited main root elongation and the formation of secondary roots by ca. 33%. Expression of Cycb 2-2 was also inhibited, while pal and chs were highly expressed. The root growth inhibition was not overcome by the addition of a stimulatory concentration of auxin (NAA 0.1 µM). The data suggests that elicitation of defense responses in the root alters metabolism in such a way that results in the modification of the architecture of bean roots.

Identification of Arabidopsis thaliana genes responsive to plant cell-wall-degrading enzymes of Erwinia carotovora subsp. carotovora led to the isolation of a cDNA clone with high sequence homology to the gene for allene oxide synthase, an enzyme involved in the biosynthesis of jasmonates. Expression of the corresponding gene was induced by the extracellular enzymes from this pathogen as well as by treatment with methyl jasmonate and short oligogalacturonides (OGAs). This suggests that OGAs are involved in the induction of the jasmonate pathway during plant defense response to E. carotovora subsp. carotovora attack.

ABSTRACT Paenibacillus amylolyticus 27C64, a Gram-positive bacterium with diverse plant cell wall polysaccharide deconstruction capabilities, was isolated previously from an insect hindgut. Previous work suggested that this organism’s pectin deconstruction system differs from known systems in that its sole pectin methylesterase is cytoplasmic, not extracellular. In this work, we have characterized the specific roles of key extracellular pectinases involved in homogalacturonan deconstruction, including four pectate lyases and one pectin lyase. We show that one newly characterized pectate lyase, PelC, has a novel substrate specificity, with a lower Km for highly methylated pectins than for polygalacturonic acid. PelC works synergistically with PelB, a high-turnover exo-pectate lyase that releases Δ4,5-unsaturated trigalacturonate as its major product. It is likely that PelC frees internal stretches of demethylated homogalacturonan which PelB can degrade. We also show that the sole pectin lyase has a high kcat value and rapidly depolymerizes methylated substrates. Three cytoplasmic GH105 hydrolases were screened for the ability to remove terminal unsaturated galacturonic acid residues from oligogalacturonide products produced by the action of extracellular lyases, and we found that two are active on demethylated oligogalacturonides. This work confirms that efficient homogalacturonan deconstruction in P. amylolyticus 27C65 does not require extracellular pectin methylesterase activity. Three of the extracellular lyases studied in this work are also thermostable, function well over a broad pH range, and have significant industrial potential. IMPORTANCE Pectin is an important structural polysaccharide found in most plant cell walls. In the environment, pectin degradation is part of the decomposition process that turns over dead plant material and is important to organisms that feed on plants. Industrially, pectinases are used to improve the quality of fruit juices and can also be used to process coffee cherries or tea leaves. These enzymes may also prove useful in reducing the environmental impact of paper and cotton manufacturing. This work is significant because it focuses on a Gram-positive bacterium that is evolutionarily distinct from other well-studied pectin-degrading organisms and differs from known systems in key ways. Most importantly, a simplified extracellular deconstruction process in this organism is able to break down pectins without first removing the methyl groups that inhibit other systems. Moreover, some of the enzymes described here have the potential to improve industrial processes that rely on pectin deconstruction.

Les maladies cardiovasculaires (MCV) sont classées en tête de liste parmi les principales causes de décès dans le monde. La calcification de la paroi vasculaire entraîne diverses conséquences cardiovasculaires critiques et explique les taux de mortalité élevés chez les patients atteints de nombreuses maladies comme le diabète, l'athérosclérose et la maladie rénale chronique (IRC). VC est un processus actif avec des caractéristiques de la physiologie osseuse et il est régulé par des processus inductifs et inhibiteurs multifactoriels. Au cours du processus de calcification, les cellules musculaires lisses vasculaires (VSMC) subissent un processus ostéogénique actif pour devenir des cellules de type ostéoblaste et libérer des populations hétérogènes de Vésicules Extracellulaires (EV). Les VE agissent comme des foyers de nucléation pour la cristallisation grâce à leur interaction avec le collagène de type 1 (Col1) via les intégrines et leur teneur en protéines procalcifiantes soutient fortement la progression de la calcification. Parce que ces deux mécanismes sont cruciaux pour le développement de la VC, ils représentent finalement deux cibles thérapeutiques pour la régression de la VC. Notre objectif principal était d'identifier de nouvelles molécules naturelles ou synthétisées chimiquement pouvant inhiber la VC. Nous avons démontré la capacité d'un acide oligogalacturonique spécifique (DP8), extrait de graines de lin, à inhiber la calcification induite par Pi in vitro et ex vivo en diminuant l'expression des marqueurs ostéogéniques, masquant une répétition consensus des acides aminés trouvée dans Col1 (séquence: GFOGER) , et empêchant ainsi les VE de se lier. Nous avons également synthétisé chimiquement un peptide GFOGER et vérifié sa capacité à inhiber la calcification. Semblable à DP8, le peptide GFOGER a été capable d'inhiber la calcification induite par Pi in vitro et ex vivo en régulant à la baisse l'expression des marqueurs ostéogéniques et en modifiant la teneur en protéines des EV dérivés des VSMC. Par conséquent, nos travaux suggèrent deux nouvelles approches thérapeutiques pour la prévention de la CV
Cardiovascular diseases (CVDs) are classified on top of the list among different death leading causes in the world. Calcification of the vessel wall leads to various critical cardiovascular consequences and accounts for high mortality rates in patients with many diseases like diabetes, atherosclerosis and chronic kidney disease (CKD). VC is an active process with features of bone physiology and it is regulated by multifactorial inductive and inhibitory processes. During the calcification process, Vascular Smooth Muscle Cells (VSMCs) undergo active osteogenic process to become osteoblast-like cells and release heterogeneous populations of Extracellular Vesicles (EVs). EVs act as nucleating foci for crystallization through their interaction with type 1 collagen (Col1) via integrins and their procalcifying protein content strongly supports calcification progression. Because these two mechanisms are crucial for the development of VC, they eventually represent two therapeutic targets for VC regression. Our primary objective was to identify new natural or chemically synthesized molecules that can inhibit VC. We demonstrated the ability of a specific oligogalacturonic acid (DP8), extracted from flax seeds, to inhibit in vitro and ex-vivo Pi-induced calcification by diminishing osteogenic markers expression, masking a consensus amino acid repeat found in Col1 (sequence: GFOGER), and thus preventing EVs from binding. Also we chemically synthesized a GFOGER peptide and checked its ability to inhibit calcification. Similar to DP8, GFOGER peptide was able to inhibit in vitro and ex-vivo Pi-induced calcification by downregulating osteogenic markers expression and through modifying the protein content of VSMCs derived EVs. Therefore, our work suggests two novel therapeutic approaches for the prevention of VC