Mannans are polymers containing the sugar mannose as a principal component. They are a type of

polysaccharide Polysaccharides (), or polycarbohydrates, are the most abundant carbohydrates found in food. They are long chain polymeric carbohydrates composed of monosaccharide units bound together by glycosidic linkages. This carbohydrate can react with wa ...

comprise 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 galactomannans. They are insoluble and a form of storage polysaccharide.

Ivory nut ''Phytelephas'' is a genus containing six known species of dioecious palms (family Arecaceae), occurring from southern Panama along the Andes to Ecuador, Bolivia, Colombia, northwestern Brazil, and Peru. They are commonly known as ivory palms, ...

is a source of mannans. An additional type is galactoglucomannan found in soft wood with a mixed mannose/glucose β(1-4) backbone. Many mannans are acetylated and some from marine sources, have

sulfate ester Organosulfates are a class of organic compounds sharing a common functional group with the structure R-O-SO3−. The SO4 core is a sulfate group and the R group is any organic residue. All organosulfates are formally esters derived from alcohols ...

s side chains. Yeast and some plants such as

conjac Konjac (or konjak, ) is a common name of the East and Southeast Asian plant ''Amorphophallus konjac'' (syn. ''A. rivieri''), which has an edible corm (bulbo-tuber). It is also known as konjaku, konnyaku potato, devil's tongue, voodoo lily, ...

and salep have a different type of mannans in their cell wall, with a α(1-6) linked backbone and α(1-2) and α(1-3) linked glucose branches, hence " glucomannan". It is water soluble. It is serologically similar to structures found on mammalian glycoproteins. Detection of mannan leads to lysis in the mannan-binding lectin pathway.

Synthesis and degradation

GDP-mannose is a substrate for glycosyltransferase for enzymes called mannosyltransferases.

Biosynthesis

GDP-mannose is produced from GTP and

mannose-6-phosphate Mannose-6-phosphate (M6P) is a molecule bound by lectin in the immune system. M6P is converted to fructose 6-phosphate by mannose phosphate isomerase. M6P is a key targeting signal for acid hydrolase precursor proteins that are destined for transp ...

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 esterases and α-galactosidase. When a long chain of mannan is

hydrolyzed Hydrolysis (; ) is any chemical reaction in which a molecule of water breaks one or more chemical bonds. The term is used broadly for substitution, elimination, and solvation reactions in which water is the nucleophile. Biological hydrolysis ...

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. Glucomannan MOS is used as prebiotics in animal husbandry and nutritional supplements due to its bioactivity.

Etymology

From ' manna', produced by several species of tree and shrub e.g. ''

Fraxinus ornus ''Fraxinus'' (), commonly called ash, is a genus of flowering plants in the olive and lilac family, Oleaceae. It contains 45–65 species of usually medium to large trees, mostly deciduous, though a number of subtropical species are evergr ...

'' from whose secretions mannitol was originally isolated.

References

Carbohydrates Polysaccharides {{chemistry-stub

Structural diversity

Synthesis and degradation

Biosynthesis

Etymology

Further reading

See also

References