Glucanases are

enzymes An enzyme () is a protein that acts as a biological catalyst by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as pro ...

that break down lucans

polysaccharides 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 wat ...

via

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

. The product of the hydrolysis reaction are smaller

glucan A glucan is a polysaccharide derived from D-glucose, linked by glycosidic bonds. Glucans are noted in two forms: alpha glucans and beta glucans. Many beta-glucans are medically important. They represent a drug target for antifungal medications of ...

s, a linear or branched polysaccharide made of up to 1200

glucose Glucose is a sugar with the Chemical formula#Molecular formula, molecular formula , which is often abbreviated as Glc. It is overall the most abundant monosaccharide, a subcategory of carbohydrates. It is mainly made by plants and most algae d ...

monomers, linked by glycosidic bonds. Glucans are abundant in the

endosperm The endosperm is a tissue produced inside the seeds of most of the flowering plants following double fertilization. It is triploid (meaning three chromosome sets per nucleus) in most species, which may be auxin-driven. It surrounds the Embryo#Pla ...

cell walls of cereals such as

barley Barley (), a member of the grass family, is a major cereal grain grown in temperate climates globally. It was one of the first cultivated grains; it was domesticated in the Fertile Crescent around 9000 BC, giving it nonshattering spikele ...

rye Rye (''Secale cereale'') is a grass grown extensively as a grain, a cover crop and a forage crop. It is grown principally in an area from Eastern and Northern Europe into Russia. It is much more tolerant of cold weather and poor soil than o ...

sorghum ''Sorghum bicolor'', commonly called sorghum () and also known as great millet, broomcorn, guinea corn, durra, imphee, jowar, or milo, is a species in the Poaceae, grass genus ''Sorghum (genus), Sorghum'' cultivated for its grain. The grain i ...

rice Rice is a cereal grain and in its Domestication, domesticated form is the staple food of over half of the world's population, particularly in Asia and Africa. Rice is the seed of the grass species ''Oryza sativa'' (Asian rice)—or, much l ...

, and

wheat Wheat is a group of wild and crop domestication, domesticated Poaceae, grasses of the genus ''Triticum'' (). They are Agriculture, cultivated for their cereal grains, which are staple foods around the world. Well-known Taxonomy of wheat, whe ...

. Glucanases are also referred to as lichenases,

hydrolases In biochemistry, hydrolases constitute a class of enzymes that commonly function as biochemical catalysts that use water to break a chemical bond: :\ce \quad \xrightarrowtext\quad \ce This typically results in dividing a larger molecule into s ...

glycosidases In biochemistry, glycoside hydrolases (also called glycosidases or glycosyl hydrolases) are a class of enzymes which catalyze the hydrolysis of glycosidic bonds in complex sugars. They are extremely common enzymes, with roles in nature inclu ...

, glycosyl hydrolases, and/or laminarinases. Many types of glucanases share similar amino acid sequences but vastly different substrates. Of the known endo-glucanases, 1,3-1,4-β-glucanase is considered the most active.

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 The jelly roll or Swiss roll fold is a protein fold or supersecondary structure composed of eight beta strands arranged in two four-stranded sheets. The name of the structure was introduced by Jane S. Richardson in 1981, reflecting its resemblance ...

Some common β-glucanases

* 1,3-β-glucanases (laminarinases, EC 3.2.1.39) * Endo-1,3(4)-β-glucanase * β-1,3-glucanase, an enzyme in plants that breaks down β-1,3-glucans such as

callose Callose is a plant polysaccharide. Its production is due to the glucan synthase-like gene (GLS) in various places within a plant. It is produced to act as a temporary cell wall in response to stimuli such as stress or damage. Callose is composed ...

curdlan Curdlan is a water-insoluble linear beta-1,3-glucan, a high-molecular-weight polymer of glucose. Curdlan consists of β-(1,3)-linked glucose residues and forms elastic gels upon heating in aqueous suspension. It was reported to be produced by '' ...

* β-1,6 glucanase, an enzyme that breaks down β-1,6-glucans *

Cellulase Cellulase (; systematic name 4-β-D-glucan 4-glucanohydrolase) is any of several enzymes produced chiefly by fungi, bacteria, and protozoans that catalyze cellulolysis, the decomposition of cellulose and of some related polysaccharides: : Endo ...

, an enzyme that perform the hydrolysis of 1,4-beta-D-glycosidic linkages in

cellulose Cellulose is an organic compound with the chemical formula, formula , a polysaccharide consisting of a linear chain of several hundred to many thousands of glycosidic bond, β(1→4) linked glucose, D-glucose units. Cellulose is an important s ...

lichenin Lichenin, also known as lichenan or moss starch, is a complex glucan occurring in certain species of lichens. It can be extracted from ''Cetraria islandica'' ( Iceland moss). It has been studied since about 1957. Structure Chemically, lichenin ...

and cereal β-D-glucans. * Xyloglucan-specific endo-β-1,4-glucanase * Xyloglucan-specific exo-β-1,4-glucanase

α-glucanases

* α-1,4-glucanase, an enzyme that breaks down α-1,4-glucans * α-1,6-glucanase, an enzyme that breaks down α-1,6-glucans *

Pullulanase Pullulanase (, ''limit dextrinase'', ''amylopectin 6-glucanohydrolase'', ''bacterial debranching enzyme'', ''debranching enzyme'', ''α-dextrin endo-1,6-α-glucosidase'', ''R-enzyme'', ''pullulan α-1,6-glucanohydrolase'') is a specific kind of g ...

, 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

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. The first step of his proposed mechanism is rate-limiting step independent of the concentration of the substrate and involves an amino acid

nucleophile In chemistry, a nucleophile is a chemical species that forms bonds by donating an electron pair. All molecules and ions with a free pair of electrons or at least one pi bond can act as nucleophiles. Because nucleophiles donate electrons, they are ...

and an acid/base catalyst. In this step, the nucleophile, with help from the acid residue, displaces the

aglycone An aglycone (aglycon or genin) is the chemical compound remaining after the glycosyl group on a glycoside is replaced by a hydrogen atom. For example, the aglycone of a cardiac glycoside would be a steroid A steroid is an organic compoun ...

and forms a covalent glycosyl-enzyme intermediate. The second step involves a water molecule, assisted by the

conjugate base A conjugate acid, within the Brønsted–Lowry acid–base theory, is a chemical compound formed when an acid gives a proton () to a base—in other words, it is a base with a hydrogen ion added to it, as it loses a hydrogen ion in the reve ...

of the acid catalyst, rendering the free sugar while retaining an anomeric configuration of the molecule. Glucanases can also catalyze transglycosylation, resulting in new β-glycosidic bonds between donor and acceptor saccharides. This reaction, which has the same region- and stereo-specificity as the hydrolysis reaction, involves either the direct reversal of hydrolysis (known as

condensation Condensation is the change of the state of matter from the gas phase into the liquid phase, and is the reverse of vaporization. The word most often refers to the water cycle. It can also be defined as the change in the state of water vapor ...

) or kinetic control of a glycosyl donor substrate. Hydrolysis_Condensation_reaction

Microbial Occurrence and Agricultural Significance

Microbial Production

Bacteria such as ''

Escherichia coli ''Escherichia coli'' ( )Wells, J. C. (2000) Longman Pronunciation Dictionary. Harlow ngland Pearson Education Ltd. is a gram-negative, facultative anaerobic, rod-shaped, coliform bacterium of the genus '' Escherichia'' that is commonly fo ...

'', and ''

Bacillus ''Bacillus'', from Latin "bacillus", meaning "little staff, wand", is a genus of Gram-positive, rod-shaped bacteria, a member of the phylum ''Bacillota'', with 266 named species. The term is also used to describe the shape (rod) of other so-sh ...

'' 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 Primary or primaries may refer to: Arts, entertainment, and media Music Groups and labels * Primary (band), from Australia * Primary (musician), hip hop musician and record producer from South Korea * Primary Music, Israeli record label Work ...

, secondary, or

tertiary structure Protein tertiary structure is the three-dimensional shape of a protein. The tertiary structure will have a single polypeptide chain "backbone" with one or more protein secondary structures, the protein domains. Amino acid side chains and the ...

. Glucanases have also been found to be secreted by fungi such as ''

Trichoderma harzianum ''Trichoderma harzianum'' is a fungus that is also used as a fungicide. It is used for foliar application, seed treatment and soil treatment for suppression of fungal pathogens causing various fungal plant diseases. Commercial biotechnological ...

'', ''

Saccharomyces cerevisiae ''Saccharomyces cerevisiae'' () (brewer's yeast or baker's yeast) is a species of yeast (single-celled fungal microorganisms). The species has been instrumental in winemaking, baking, and brewing since ancient times. It is believed to have be ...

'' and the

anaerobic Anaerobic means "living, active, occurring, or existing in the absence of free oxygen", as opposed to aerobic which means "living, active, or occurring only in the presence of oxygen." Anaerobic may also refer to: *Adhesive#Anaerobic, Anaerobic ad ...

fungi '' Orpinomyces'' and

Neocallimastigomycota Neocallimastigomycota is a phylum containing anaerobic fungi, which are symbionts found in the digestive tracts of larger herbivores. Anaerobic fungi were originally placed within phylum Chytridiomycota, within Order Neocallimastigales but lat ...

, found in the digestive tracts of

herbivores A herbivore is an animal anatomically and physiologically evolved to feed on plants, especially upon vascular tissues such as foliage, fruits or seeds, as the main component of its diet. These more broadly also encompass animals that eat ...

. ''T. harzianum'' is also used as a

fungicide Fungicides are pesticides used to kill parasitic fungi or their spores. Fungi can cause serious damage in agriculture, resulting in losses of yield and quality. Fungicides are used both in agriculture and to fight fungal infections in animals, ...

, which is linked to the ability of its β-gluanases to hydrolyze phytopathogenic fungi via a mycoparasitic 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.