This view shows enzymes only for those organisms listed below, in the list of taxa known to possess the pathway. If an enzyme name is shown in bold, there is experimental evidence for this enzymatic activity.
|Superclasses:||Degradation/Utilization/Assimilation → Carbohydrates Degradation → Polysaccharides Degradation → Glycans Degradation|
|Degradation/Utilization/Assimilation → Carbohydrates Degradation → Polysaccharides Degradation → Xyloglucan Degradation|
|Degradation/Utilization/Assimilation → Polymeric Compounds Degradation → Polysaccharides Degradation → Glycans Degradation|
|Degradation/Utilization/Assimilation → Polymeric Compounds Degradation → Polysaccharides Degradation → Xyloglucan Degradation|
Some taxa known to possess this pathway include
Komagataella pastoris GS115
Xylan is found in the cell walls of plants and some green and red algae, and is the major constituent of hemicellulose. The most common type of xylan is by far a (1→4)-β-D-xylan, a linear polymer of β-D-xylopyranose residues linked by (1→4) glycosidic bonds. This polysaccharide backbone is often decorated by additional sugars, forming complex polymers such as arabinoxylan and glucuronoxylan.
Arabinoxylans have been identified in wheat, rye, barley, oat, rice, and sorghum, as well as in some less common plants, including pangola grass, bamboo shoots and rye grass. Glucuronoxylans and glucuronoarabinoxylans are located mainly in the secondary wall and function as an adhesive by forming covalent and non-covalent bonds with lignin, cellulose, and other polymers essential to the integrity of the cell wall.
Angiosperm (hardwood) glucuronoxylans also have a high rate of substitution (70-80%) by acetyl groups, at position 2 and/or 3 of the β-D-xylopyranosyl. The degradation of cell wall is immensely important in industrial production as a supplement in animal feed, food and beverages, textiles, bleaching and production of biofuels. The main enzymes involved in xylan degradation are the xylanases. These enzymes are produced mainly by microorganisms that break down plant cell walls, but are also present in marine algae, protozoans, crustaceans, insects, snails and seeds of land plants [Sunna97].
The principle source of xylanases for the industry are filamentous fungi, since they secrete these enzymes into the medium and their xylanase levels are very high [Polizeli05]. In recent years there has been a focus on xylanases from extremophiles that can withstand high temperatures and extreme pH found during industrial processes [Zhang10e]. Due to the complex structure of xylan polymers, degradation requires a number of different types of enzymes working in tandem. These include endoxylanases (EC 220.127.116.11, endo-1,4-β-xylanase; EC 18.104.22.168, glucuronoarabinoxylan endo-1,4-β-xylanase), β-xylosidases (EC 22.214.171.124, oligosaccharide reducing-end xylanase; EC 126.96.36.199, xylan 1,4-β-xylosidase), ferulate esterases (EC 188.8.131.52), acetylxylan esterases (EC 184.108.40.206), α-glucuronidases (EC 220.127.116.11), arabinases (EC 18.104.22.168 and arabinofuranosidases (EC 22.214.171.124).
Carpita93: Carpita NC, Gibeaut DM (1993). "Structural models of primary cell walls in flowering plants: consistency of molecular structure with the physical properties of the walls during growth." Plant J 3(1);1-30. PMID: 8401598
Gordillo06: Gordillo F, Caputo V, Peirano A, Chavez R, Van Beeumen J, Vandenberghe I, Claeyssens M, Bull P, Ravanal MC, Eyzaguirre J (2006). "Penicillium purpurogenum produces a family 1 acetyl xylan esterase containing a carbohydrate-binding module: characterization of the protein and its gene." Mycol Res 110(Pt 10);1129-39. PMID: 17008082
Polizeli05: Polizeli ML, Rizzatti AC, Monti R, Terenzi HF, Jorge JA, Amorim DS (2005). "Xylanases from fungi: properties and industrial applications." Appl Microbiol Biotechnol 67(5);577-91. PMID: 15944805
Schadel10: Schadel C, Richter A, Blochl A, Hoch G (2010). "Hemicellulose concentration and composition in plant cell walls under extreme carbon source-sink imbalances." Physiol Plant 139(3);241-55. PMID: 20113432
SchooneveldBerg99: Schooneveld-Bergmans, M.E. F., Dignum, M. J. W., Grabber, J. H.., Beldman, G., Voragen, A. G. J. (1999). "Studies on the oxidative cross-linking of feruloylated arabinoxylans from wheat flour and wheat bran." Carbohydrate Polymers 38:309-317.
Vignon98: Vignon, M. R., Gey, C. (1998). "Isolation, 1H and 13C NMR studies of (4-O-methyl-D-glucurono)-D-xylans from luffa fruit fibres, jute bast fibres and mucilage of quince tree seeds." Carbohydrate Research 307(1-2):107-111.
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