View source for Mannans

{{Short description|Polysaccharides formed from mannose}}
{{otheruses|Mannan (disambiguation){{!}}Mannan}}
[[File:Mannan with galactose side chain.svg|thumb|500px|Subunit of a typical mannan showing four 1,4-linked beta-D-mannose units, one with a galactose side chain.]]
'''Mannans''' are [[polymer]]s containing the sugar [[mannose]] as a principal component.<ref name=overview>{{cite journal |doi=10.1007/s00253-008-1423-4|title=An overview of mannan structure and mannan-degrading enzyme systems |year=2008 |last1=Moreira |first1=L. R. S. |last2=Filho |first2=E. X. F. |journal=Applied Microbiology and Biotechnology |volume=79 |issue=2 |pages=165–178 |pmid=18385995 |s2cid=9746196 }}</ref><ref>{{MeshName|Mannan}}</ref>
They are a type of [[polysaccharide]] found in [[hemicellulose]], a major source of biomass found in higher plants such as softwoods.  These polymers also typically contain two other sugars, [[galactose]] and [[glucose]].  They are often branched (unlike cellulose).

== Structural diversity ==
[[Plant]] mannans have β(1-4) linkages, occasionally with α(1-6) [[galactose]] branches, forming [[galactomannan]]s. They are insoluble and a form of storage polysaccharide. [[Ivory nut]] is a source of mannans. An additional type is [[galactoglucomannan]] found in soft wood with a mixed mannose/glucose β(1-4) backbone.{{citation needed|date=September 2025}}  [[Conjac]] and [[salep]] have [[glucomannan]]s with β(1-4) linkages.<ref>{{cite journal|vauthors=Ye S, Zongo AW, Shah BR, Li J, Li B|title=Konjac Glucomannan (KGM), Deacetylated KGM (Da-KGM), and Degraded KGM Derivatives: A Special Focus on Colloidal Nutrition|journal=Journal of Agricultural and Food Chemistry|volume=69|issue=44|year=2021|doi=10.1021/acs.jafc.1c03647|pages=12921-12932}}</ref><ref>{{cite journal|vauthors=Kurt A, Kahyaoglu T|title=Purification of glucomannan from salep: Part 1. Detailed rheological characteristics|volume=168|year=2017|pages=138-146|journal=Carbohydrate Polymers|doi=10.1016/j.carbpol.2017.03.060}}</ref>  Many mannans are [[acetylated]] and some from marine sources, have [[sulfate ester]]s side chains.

[[Yeast]] have a different type of glucomannan in their cell wall, with a α(1-6) linked backbone and α(1-2) and α(1-3) linked [[glucose]] branches, which may also contain [[phosphodiester bond]]s.<ref>{{cite journal|vauthors=Baek KR, Ramakrishnan SR, Kim SJ, Seo SO|title=Yeast cell wall mannan structural features, biological activities, and production strategies|journal=Heliyon|volume=10|issue=6|year=2024|id=Art. No. e27896|doi=10.1016/j.heliyon.2024.e27896|doi-access=free|pmc=10958358|pmid=38524613}}</ref>  Enzymatic digestion or acid catalysis can help solubilize the glucomannan.<ref>{{cite journal|vauthors=de Souza Theodoro S, Putarov TC, Tiemi C, Volpe LM, de Oliveira CA, de Abreu Glória MB, Carciofi AC|journal=PLoS One|volume=14|issue=11|id=Art. No. e0225659|doi=10.1371/journal.pone.0225659|doi-access=free|pmid=31765439|pmc=6878821|title=Effects of the solubility of yeast cell wall preparations on their potential prebiotic properties in dogs}}</ref>  It is serologically similar to structures found on mammalian glycoproteins. Detection of mannan leads to lysis in the [[mannan-binding lectin pathway]].{{cn|date=December 2020}}

==Synthesis and degradation==

[[File:GDP-mannose.svg|thumb|right|Guanosine diphosphate mannose is the precursor to mannans.<ref name="Reeves">{{cite journal |vauthors=Samuel G, Reeves P |title=Biosynthesis of O-antigens: genes and pathways involved in nucleotide sugar precursor synthesis and O-antigen assembly |journal=Carbohydrate Research |volume=338 |issue=23 |pages=2503–19 |year=2003 |pmid=14670712 |doi=10.1016/j.carres.2003.07.009}}</ref>  As a simplification, the diphosphate group is shown in its protonated form.]]

[[GDP-mannose]] is a substrate for [[glycosyltransferase]] for enzymes called [[mannosyltransferase]]s.<ref>{{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 }}</ref>

==Biosynthesis==
GDP-mannose is produced from [[Guanosine triphosphate|GTP]] and [[mannose-6-phosphate]] by the enzyme [[mannose-1-phosphate guanylyltransferase]].

The degradation of mannans (and many related forms of hemicellulose) has been well studied.  The hydrolysis of the main mannan backbone is catalyzed by various enzymes including β-[[mannosidase]], β-[[glucosidase]], and β-[[mannase]]. The side chains are degraded by [[esterase]]s and α-galactosidase.<ref name=overview/>

When a long chain of mannan is [[hydrolyzed]] into shorter chains, these smaller molecules are known as '''mannan [[oligosaccharide]]''' (MOS). MOS by definition can be produced from either insoluble galactomannan or soluble glucomannan, although the latter type is more widely marketed.<ref name=review>{{cite journal |last1=Nopvichai |first1=C |last2=Charoenwongpaiboon |first2=T |last3=Luengluepunya |first3=N |last4=Ito |first4=K |last5=Muanprasat |first5=C |last6=Pichyangkura |first6=R |title=Production and purification of mannan oligosaccharide with epithelial tight junction enhancing activity. |journal=PeerJ |date=2019 |volume=7 |article-number=e7206 |doi=10.7717/peerj.7206 |pmid=31304065 |pmc=6611449 |quote=MOS is often prepared by hydrolysis reaction of a mannose-contained glucan polymer, mainly glucomannan and galactomannan. |doi-access=free }}</ref>

[[Glucomannan]] MOS is used as prebiotics in animal husbandry and nutritional supplements due to its bioactivity.{{cn|date=December 2020}}

==Etymology==
From 'manna', produced by several species of tree and shrub e.g. ''[[Fraxinus ornus]]'' from whose secretions [[mannitol]] was originally isolated.

==See also==
* [[Alfa mannan degradation]]
* [[Mannan oligosaccharide-based nutritional supplements|Mannan oligosaccharides]] (MOS)

==References==
{{reflist}}

==Further reading==
*{{Cite journal|last1=Stewart|first1=James|last2=Curtis|first2=Joan|last3=Spurck|first3=Timothy P.|last4=Ilg|first4=Thomas|last5=Garami|first5=Attila|last6=Baldwin|first6=Tracey|last7=Courret|first7=Nathalie|last8=McFadden|first8=Geoffrey I.|last9=Davis|first9=Antony|last10=Handman|first10=Emanuela|date=July 2005 |title=Characterisation of a Leishmania mexicana knockout lacking guanosine diphosphate-mannose pyrophosphorylase|journal=International Journal for Parasitology|language=en|volume=35|issue=8|pages=861–873|doi=10.1016/j.ijpara.2005.03.008|pmid=15936761}}

{{Carbohydrates}}

[[Category:Carbohydrates]]
[[Category:Polysaccharides]]