Xylan

Xylans are polysaccharides made up of β-1,4-linked xylose (a pentose sugar) residues with side branches of α-arabinofuranose and/or α-glucuronic acids. On the basis of substituted groups xylan can be categorized into three classes i) glucuronoxylan (GX) ii) neutral arabinoxylan (AX) and iii) glucuronoarabinoxylan (GAX).{{Cite journal|last=Faik|first=Ahmed|date=2010-06-01|title=Xylan Biosynthesis: News from the Grass|journal=Plant Physiology|language=en|volume=153|issue=2|pages=396–402|doi=10.1104/pp.110.154237|issn=0032-0889|pmid=20375115|pmc=2879768}} In some cases contribute to cross-linking of cellulose microfibrils and lignin through ferulic acid residues.{{Cite journal |last1=Balakshin |first1=Mikhail |last2=Capanema |first2=Ewellyn |last3=Gracz |first3=Hanna |last4=Chang |first4=Hou-min |last5=Jameel |first5=Hasan |date=2011-02-05 |title=Quantification of lignin–carbohydrate linkages with high-resolution NMR spectroscopy |journal=Planta |language=en |volume=233 |issue=6 |pages=1097–1110 |doi=10.1007/s00425-011-1359-2 |issn=0032-0935 |pmid=21298285 |bibcode=2011Plant.233.1097B |s2cid=13080720}}

Xylans play an important role in the integrity of the plant cell wall and increase cell wall recalcitrance to enzymatic digestion;{{cite journal |doi=10.1111/pbi.12292|title=Ferulic acid: A Key Component in Grass Lignocellulose Recalcitrance to Hydrolysis|year=2015|last1=De Oliveira|first1=Dyoni Matias|last2=Finger-Teixeira|first2=Aline|last3=Rodrigues Mota|first3=Thatiane|last4=Salvador|first4=Victor Hugo|last5=Moreira-Vilar|first5=Flávia Carolina|last6=Correa Molinari|first6=Hugo Bruno|last7=Craig Mitchell|first7=Rowan Andrew|last8=Marchiosi|first8=Rogério|last9=Ferrarese-Filho|first9=Osvaldo|last10=Dantas Dos Santos|first10=Wanderley|journal=Plant Biotechnology Journal|volume=13|issue=9|pages=1224–1232|pmid=25417596|s2cid=6171914 |url=https://repository.rothamsted.ac.uk/download/638b8a580f272980a73b13db257e1eafc75b53ca0d47a0acf2f294fd2af8f39f/492160/pbi.12292.pdf }}{{Citation|last=Faik|first=Ahmed|title="Plant Cell Wall Structure-Pretreatment" the Critical Relationship in Biomass Conversion to Fermentable Sugars|date=2013|pages=1–30|publisher=Springer Netherlands|language=en|doi=10.1007/978-94-007-6052-3_1|isbn=9789400760516|series=SpringerBriefs in Molecular Science}} thus, they help plants to defend against herbivores and pathogens (biotic stress). Xylan also plays a significant role in plant growth and development. Typically, xylans content in hardwoods is 10-35%, whereas they are 10-15% in softwoods. The main xylan component in hardwoods is O-acetyl-4-O-methylglucuronoxylan, whereas arabino-4-O-methylglucuronoxylans are a major component in softwoods. In general, softwood xylans differ from hardwood xylans by the lack of acetyl groups and the presence of arabinose units linked by α-(1,3)-glycosidic bonds to the xylan backbone.{{cite book |editor-last=Sixta |editor-first=Herbert |date=2006 |title=Handbook of pulp|volume=1 |pages= 28–30 |location=Weinheim, Germany |publisher= Wiley-VCH Verlag GmbH & Co. KGaA |isbn=978-3-527-30999-3 }}

Some macrophytic green algae contain xylan (specifically homoxylan{{Cite book|title=Hemicellulose|last1=Ebringerová|first1=Anna|last2=Hromádková|first2=Zdenka|last3=Heinze|first3=Thomas|date=2005-01-01|publisher=Springer Berlin Heidelberg|isbn=9783540261124|editor-last=Heinze|editor-first=Thomas|series=Advances in Polymer Science|pages=1–67|language=en|doi=10.1007/b136816}}) especially those within the Codium and Bryopsis genera{{Cite web|url=http://www.elicityl-oligotech.com/?fond=rubrique&id_rubrique=23|title=Xylan Glycoproducts for life sciences - Engineering and production|website=www.elicityl-oligotech.com|access-date=2016-04-20}} where it replaces cellulose in the cell wall matrix. Similarly, it replaces the inner fibrillar cell-wall layer of cellulose in some red algae.

The quality of cereal flours and the hardness of dough are affected by their xylan content, thus, playing a significant role in bread industry. The main constituent of xylan can be converted into xylitol (a xylose derivative), which is used as a natural food sweetener, which helps to reduce dental cavities and acts as a sugar substitute for diabetic patients. Poultry feed has a high percentage of xylan.

Xylan is one of the foremost anti-nutritional factors in common use feedstuff raw materials. Xylooligosaccharides produced from xylan are considered as "functional food" or dietary fibers{{cite journal|last1=Alonso |first1=JL |last2=Dominguez |first2=H |last3=Garrote |first3=G |last4=Parajo|first4=JC |last5=Vazques|first5=MJ |date=2003 |title=Xylooligosaccharides: properties and production technologies |journal= Electron. J. Environ. Agric. Food Chem |volume=2 |issue=1 |pages=230–232 |name-list-style=vanc}} due their potential prebiotic properties.{{Cite journal|title= Prebiotic and Other Health-Related Effects of Cereal-Derived Arabinoxylans, Arabinoxylan-Oligosaccharides, and Xylooligosaccharides|journal=Critical Reviews in Food Science and Nutrition|date= 2011|volume=51|issue=2|pages=178–194|first1 = W.F.|last1 = Broekaert|first2 = C.M.|last2 = Courtin|first3 = C.|last3 = Verbeke |first4 = T.|last4 = Van de Wiele |first5 = W.|last5 = Verstraete |first6 = J.A|last6 = Delcour |doi=10.1080/10408390903044768|pmid=21328111|s2cid=205689400}}

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The regular branching patterns of xylans may facilitate their co-crystallization with cellulose in the plant cell wall.{{Cite journal |last1=Simmons |first1=Thomas J. |last2=Mortimer |first2=Jenny C. |last3=Bernardinelli |first3=Oigres D. |last4=Pöppler |first4=Ann-Christin |last5=Brown |first5=Steven P. |last6=deAzevedo |first6=Eduardo R. |last7=Dupree |first7=Ray |last8=Dupree |first8=Paul |date=December 2016 |title=Folding of xylan onto cellulose fibrils in plant cell walls revealed by solid-state NMR |journal=Nature Communications |language=en |volume=7 |issue=1 |pages=13902 |doi=10.1038/ncomms13902 |issn=2041-1723 |pmc=5187587 |pmid=28000667|bibcode=2016NatCo...713902S }} Xylan also tends to crystallize from aqueous solution.{{Cite journal |last1=Smith |first1=Peter J. |last2=Curry |first2=Thomas M. |last3=Yang |first3=Jeong-Yeh |last4=Barnes |first4=William J. |last5=Ziegler |first5=Samantha J. |last6=Mittal |first6=Ashutosh |last7=Moremen |first7=Kelley W. |last8=York |first8=William S. |last9=Bomble |first9=Yannick J. |last10=Peña |first10=Maria J. |last11=Urbanowicz |first11=Breeanna R. |date=2022-07-13 |title=Enzymatic Synthesis of Xylan Microparticles with Tunable Morphologies |journal=ACS Materials Au |language=en |volume=2 |issue=4 |pages=440–452 |doi=10.1021/acsmaterialsau.2c00006 |issn=2694-2461 |pmc=9284610 |pmid=35856073}} Additional polymorphs of (1→4)-β-D-xylan have been obtained by crystallization from non-aqueous environments.{{Cite journal |last1=Meng |first1=Zhuojun |last2=Sawada |first2=Daisuke |last3=Laine |first3=Christiane |last4=Ogawa |first4=Yu |last5=Virtanen |first5=Tommi |last6=Nishiyama |first6=Yoshiharu |last7=Tammelin |first7=Tekla |last8=Kontturi |first8=Eero |date=2021-02-08 |title=Bottom-up Construction of Xylan Nanocrystals in Dimethyl Sulfoxide |url=https://pubs.acs.org/doi/10.1021/acs.biomac.0c01600 |journal=Biomacromolecules |language=en |volume=22 |issue=2 |pages=898–906 |doi=10.1021/acs.biomac.0c01600 |pmid=33410657 |s2cid=230818554 |issn=1525-7797}}

Several glycosyltransferases are involved in the biosynthesis of xylans.{{cite journal|doi=10.1007/s00425-013-1921-1|title=Hemicellulose biosynthesis |year=2013 |last1=Pauly |first1=Markus |last2=Gille |first2=Sascha |last3=Liu |first3=Lifeng |last4=Mansoori |first4=Nasim |last5=De Souza |first5=Amancio |last6=Schultink |first6=Alex |last7=Xiong |first7=Guangyan |journal=Planta |volume=238 |issue=4 |pages=627–642 |pmid=23801299 |bibcode=2013Plant.238..627P |s2cid=17501948 }}{{cite journal|doi=10.1093/pcp/pcu140|title=Secondary Cell Walls: Biosynthesis, Patterned Deposition and Transcriptional Regulation |year=2015 |last1=Zhong |first1=Ruiqin |last2=Ye |first2=Zheng-Hua |journal=Plant and Cell Physiology |volume=56 |issue=2 |pages=195–214 |pmid=25294860 |doi-access=free }}

In eukaryotes, GTs represent about 1% to 2% of gene products.{{Cite journal|last1=Lairson|first1=L.L.|last2=Henrissat|first2=B.|last3=Davies|first3=G.J.|last4=Withers|first4=S.G.|date=2008-06-02|title=Glycosyltransferases: Structures, Functions, and Mechanisms|journal=Annual Review of Biochemistry|language=en|volume=77|issue=1|pages=521–555|doi=10.1146/annurev.biochem.76.061005.092322|pmid=18518825|issn=0066-4154}} GTs are assembled into complexes existing in the Golgi apparatus. However, no xylan synthase complexes have been isolated from Arabidopsis tissues (dicot). The first gene involved in the biosynthesis of xylan was revealed on xylem mutants (irx) in Arabidopsis thaliana because of some mutation affecting xylan biosynthesis genes. As a result, abnormal plant growth due to thinning and weakening of secondary xylem cell walls was seen.{{Cite journal|last1=Wu|first1=Ai-Min|last2=Hörnblad|first2=Emma|last3=Voxeur|first3=Aline|last4=Gerber|first4=Lorenz|last5=Rihouey|first5=Christophe|last6=Lerouge|first6=Patrice|last7=Marchant|first7=Alan|date=2010-06-01|title=Analysis of the Arabidopsis IRX9/IRX9-L and IRX14/IRX14-L Pairs of Glycosyltransferase Genes Reveals Critical Contributions to Biosynthesis of the Hemicellulose Glucuronoxylan|journal=Plant Physiology|language=en|volume=153|issue=2|pages=542–554|doi=10.1104/pp.110.154971|issn=0032-0889|pmid=20424005|pmc=2879767}} Arabidopsis mutant irx9 (At2g37090), irx14 (At4g36890), irx10/gut2 (At1g27440), irx10-L/gut1 (At5g61840) showed defect in xylan backbone biosynthesis. Arabidopsis mutants irx7, irx8, and parvus are thought to be related to the reducing end oligosaccharide biosynthesis.{{Cite journal|last1=Peña|first1=Maria J.|last2=Zhong|first2=Ruiqin|last3=Zhou|first3=Gong-Ke|last4=Richardson|first4=Elizabeth A.|last5=O'Neill|first5=Malcolm A.|last6=Darvill|first6=Alan G.|last7=York|first7=William S.|last8=Ye|first8=Zheng-Hua|date=2007-02-01|title=Arabidopsis irregular xylem8 and irregular xylem9: Implications for the Complexity of Glucuronoxylan Biosynthesis|journal=The Plant Cell|language=en|volume=19|issue=2|pages=549–563|doi=10.1105/tpc.106.049320|issn=1040-4651|pmid=17322407|pmc=1867335|bibcode=2007PlanC..19..549P }} Thus, many genes have been associated with xylan biosynthesis but their biochemical mechanism is still unknown. Zeng et al. (2010) immuno-purified xylan synthase activity from etiolated wheat (Triticum aestivum) microsomes.{{Cite journal|last1=Zeng|first1=Wei|last2=Chatterjee|first2=Mohor|last3=Faik|first3=Ahmed|date=2008-05-01|title=UDP-Xylose-Stimulated Glucuronyltransferase Activity in Wheat Microsomal Membranes: Characterization and Role in Glucurono(arabino)xylan Biosynthesis|journal=Plant Physiology|language=en|volume=147|issue=1|pages=78–91|doi=10.1104/pp.107.115576|issn=0032-0889|pmid=18359844|pmc=2330321}} Jiang et al. (2016) reported a xylan synthase complex (XSC) from wheat that has a central core formed of two members of the GT43 and GT47 families (CAZy database). They purified xylan synthase activity from wheat seedlings through proteomics analysis and showed that two members of TaGT43 and TaGT47 are sufficient for the synthesis of a xylan-like polymer in vitro.{{Cite journal|last1=Jiang|first1=Nan|last2=Wiemels|first2=Richard E.|last3=Soya|first3=Aaron|last4=Whitley|first4=Rebekah|last5=Held|first5=Michael|last6=Faik|first6=Ahmed|date=2016-04-01|title=Composition, Assembly, and Trafficking of a Wheat Xylan Synthase Complex|journal=Plant Physiology|language=en|volume=170|issue=4|pages=1999–2023|doi=10.1104/pp.15.01777|issn=0032-0889|pmid=26917684|pmc=4825154}}

Xylanase converts xylan into xylose. Given that plants contain up to 30% xylan, xylanase is important to the nutrient cycle.{{cite journal|doi=10.1016/j.biotechadv.2011.11.006|title=Microbial xylanases: Engineering, production and industrial applications |year=2012 |last1=Juturu |first1=Veeresh |last2=Wu |first2=Jin Chuan |journal=Biotechnology Advances |volume=30 |issue=6 |pages=1219–1227 |pmid=22138412 }} The degradation of xylan and other hemicelluloses is relevant to the production of biofuels. Being less crystalline and more highly branched, these hemicelluloses are particularly susceptible to hydrolysis.{{cite journal|doi=10.1016/j.biombioe.2012.04.020|title=Review of pretreatment processes for lignocellulosic ethanol production, and development of an innovative method |year=2012 |last1=Chiaramonti |first1=David |last2=Prussi |first2=Matteo |last3=Ferrero |first3=Simone |last4=Oriani |first4=Luis |last5=Ottonello |first5=Piero |last6=Torre |first6=Paolo |last7=Cherchi |first7=Francesco |journal=Biomass and Bioenergy |volume=46 |pages=25–35 |bibcode=2012BmBe...46...25C }}{{cite journal|doi=10.1016/j.foodres.2012.11.021|title=Xylo-oligosaccharides from lignocellulosic materials: Chemical structure, health benefits and production by chemical and enzymatic hydrolysis |year=2013 |last1=Carvalho |first1=Ana Flávia Azevedo |last2=Neto |first2=Pedro de Oliva |last3=Da Silva |first3=Douglas Fernandes |last4=Pastore |first4=Gláucia Maria |journal=Food Research International |volume=51 |pages=75–85 }}

As a major component of plants, xylan is potentially a significant source of renewable energy especially for second generation biofuels.{{Cite journal|year=2018|title=Cell wall biomechanics: a tractable challenge in manipulating plant cell walls 'fit for purpose'!|journal=Current Opinion in Biotechnology|language=en|volume=49|pages=163–171|doi=10.1016/j.copbio.2017.08.013|pmid=28915438|issn=0958-1669|last1=Johnson|first1=Kim L.|last2=Gidley|first2=Michael J.|last3=Bacic|first3=Antony|last4=Doblin|first4=Monika S.}} However, xylose (backbone of xylan) is a pentose sugar that is hard to ferment during biofuel conversion because microorganisms like yeast cannot ferment pentose naturally.{{Cite journal|date=2014-04-01|title=Xylan biosynthesis|journal=Current Opinion in Biotechnology|language=en|volume=26|pages=100–107|doi=10.1016/j.copbio.2013.11.013|pmid=24679265|issn=0958-1669|last1=Rennie|first1=Emilie A.|last2=Scheller|first2=Henrik Vibe}}

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Category:Polysaccharides

Category:Cell biology