Glucanases are Enzyme that break down glucans Polysaccharide via hydrolysis. The product of the hydrolysis reaction are smaller , a linear or branched polysaccharide made of up to 1200 glucose monomers, linked by glycosidic bonds.
Structure
β-glucanases
The secondary and tertiary structures of β-glucanases involves the stacking of multiple β-sheets, each of which are made of several anti-parallel strands that bend and form a cleft crossing the active site of the enzyme.
This type of structure has been called the "jelly roll fold."
Some common β-glucanases
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1,3-β-glucanases (laminarinases, EC 3.2.1.39)
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Endo-1,3(4)-β-glucanase
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β-1,3-glucanase, an enzyme in plants that breaks down β-1,3-glucans such as callose or curdlan
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β-1,6 glucanase, an enzyme that breaks down β-1,6-glucans
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Cellulase, an enzyme that perform the hydrolysis of 1,4-beta-D-glycosidic linkages in cellulose, lichenin and cereal β-D-glucans.
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Xyloglucan-specific endo-β-1,4-glucanase
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Xyloglucan-specific exo-β-1,4-glucanase
α-glucanases
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α-1,4-glucanase, an enzyme that breaks down α-1,4-glucans
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α-1,6-glucanase, an enzyme that breaks down α-1,6-glucans
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Pullulanase, a specific kind of glucanase that degrade pullulan
The functional formation of the enzyme-substrate complex is dictated by the induced-fit mechanism.
Mechanism of Enzyme Action
The main function of glucanase is to catalyze the
hydrolysis of glycosidic bonds in glucan polysaccharides. This function is sometimes not highly specific, and the enzymes distinguish among substrates mostly by the types of bonds present and α- or β- configuration.
In 1953, Dr. D. E. Koshland proposed a double-displacement mechanism for this enzyme action.
Glucanases can also catalyze transglycosylation, resulting in new β-glycosidic bonds between donor and acceptor saccharides.
Microbial Occurrence and Agricultural Significance
Microbial Production
Bacteria such as
Escherichia coli, and
Bacillus spp. produce 1,3-1,4-β-glucanases in order to degrade and use glucans from their environment as an energy source.
These bacterial glucanases are an example of convergent evolution as they share similarity or relation with plant glucanases primary, secondary, or tertiary structure.
Glucanases have also been found to be secreted by fungi such as
Trichoderma harzianum,
Saccharomyces cerevisiae and the anaerobic fungi
Orpinomyces and Neocallimastigomycota, found in the digestive tracts of
Herbivore.
is also used as a
fungicide, which is linked to the ability of its β-gluanases to hydrolyze
phytopathogenic fungi via a
Mycoparasitism attack.
Beer and Wine
Barley 1,3-1,4-β-glucanases are heat inactivated during malting, which can cause the build-up of high molecular-weight glucans which in turn result in reduced extract yield, lower filtration rates, and even gelatinous precipitates in the finished product. As a remedy, heat-resistant bacterial 1,3-1,4-β-glucanases are added.
Used in enological practices during the aging process of wine, particularly when aged on lees with microxygenation. The enzyme aids in autolysis of yeast cells to release polysaccharides and mannoproteins, which is believed to aid in the color and texture of the wine.
Livestock Feed
In the production of feedstuff for broiler chickens and piglets, it has been found that β-glucanases improve digestibility of barley-based diets.
See also
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Glycoside hydrolases, a family of enzyme that cut a glycoside from a non-glycosidic molecule
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Glycoside hydrolase family 5
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Glycoside hydrolase family 16
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Glycoside hydrolase family 17
