Glucanases are

enzymes Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrate (chemistry), substrates, and the enzyme converts the substrates into different molecule ...

that break down large

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 w ...

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 is called a

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 ...

, a linear polysaccharide made of up to 1200

glucose Glucose is a simple sugar with the molecular formula . Glucose is overall the most abundant monosaccharide, a subcategory of carbohydrates. Glucose is mainly made by plants and most algae during photosynthesis from water and carbon dioxide, using ...

monomers, held together with 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 and ...

cell walls of cereals such as

barley Barley (''Hordeum vulgare''), a member of the grass family, is a major cereal grain grown in temperate climates globally. It was one of the first cultivated grains, particularly in Eurasia as early as 10,000 years ago. Globally 70% of barley pr ...

, rye,

sorghum ''Sorghum'' () is a genus of about 25 species of flowering plants in the grass family (Poaceae). Some of these species are grown as cereals for human consumption and some in pastures for animals. One species is grown for grain, while many othe ...

rice Rice is the seed of the grass species ''Oryza sativa'' (Asian rice) or less commonly ''Oryza glaberrima ''Oryza glaberrima'', commonly known as African rice, is one of the two domesticated rice species. It was first domesticated and grown i ...

, and

wheat Wheat is a grass widely cultivated for its seed, a cereal grain that is a worldwide staple food. The many species of wheat together make up the genus ''Triticum'' ; the most widely grown is common wheat (''T. aestivum''). The archaeologi ...

. Glucanases are also referred to as lichenases,

hydrolases Hydrolase is a class of enzyme that commonly perform as biochemical catalysts that use water to break a chemical bond, which typically results in dividing a larger molecule into smaller molecules. Some common examples of hydrolase enzymes are este ...

glycosidases Glycoside hydrolases (also called glycosidases or glycosyl hydrolases) catalyze Catalysis () is the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the rea ...

, 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 Glucanases are enzymes that break down large polysaccharides via hydrolysis. The product of the hydrolysis reaction is called a glucan, a linear polysaccharide made of up to 1200 glucose monomers, held together with glycosidic bonds. Glucans are ab ...

, 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 (EC 3.2.1.4; 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 polysaccharide ...

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

cellulose Cellulose is an organic compound with the formula , a polysaccharide consisting of a linear chain of several hundred to many thousands of β(1→4) linked D-glucose units. Cellulose is an important structural component of the primary cell wall ...

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 i ...

and cereal β-D-glucans. *

Xyloglucan-specific endo-beta-1,4-glucanase In enzymology, a xyloglucan-specific endo-beta-1,4-glucanase () is an enzyme that catalyzes the chemical reaction :xyloglucan + H2O \rightleftharpoons xyloglucan oligosaccharides Thus, the two substrates of this enzyme are xyloglucan and H2O ...

Xyloglucan-specific exo-beta-1,4-glucanase In enzymology, a xyloglucan-specific exo-beta-1,4-glucanase () is an enzyme that catalyzes the chemical reaction :xyloglucan + H2O \rightleftharpoons xyloglucan oligosaccharides (exohydrolysis of 1,4-beta-D-glucosidic linkages in xyloglucan) T ...

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'', ''alpha-dextrin endo-1,6-alpha-glucosidase'', ''R-enzyme'', ''pullulan alpha-1,6-glucanohydrolase'') is a specific ki ...

, 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 polysaccharides. This function is 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 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 molecule. Detection A way to identify aglycone ...

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 donates a proton () to a base—in other words, it is a base with a hydrogen ion added to it, as in the reverse reaction it loses a ...

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 to ...

) 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. also known as ''E. coli'' (), is a Gram-negative, facultative anaerobic, rod-shaped, coliform bacterium of the genus ''Escher ...

'', and ''

Bacillus ''Bacillus'' (Latin "stick") 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-shaped bacteria; and the plural ''Bacilli ...

'' spp. produce 1,3-1,4-β-glucanases in order to degrade and use polysaccharides from their environment as an energy source. These bacterial glucanases are an example of convergent evolution as they share similarity or relation with plant glucanase

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 Works * ...

secondary Secondary may refer to: Science and nature * Secondary emission, of particles ** Secondary electrons, electrons generated as ionization products * The secondary winding, or the electrical or electronic circuit connected to the secondary winding i ...

, 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 may int ...

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

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

'' 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: * Anaerobic adhesive, a bonding a ...

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 late ...

, found in the digestive tracts of

herbivores A herbivore is an animal anatomically and physiologically adapted to eating plant material, for example foliage or marine algae, for the main component of its diet. As a result of their plant diet, herbivorous animals typically have mouthpart ...

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

fungicide Fungicides are biocidal chemical compounds or biological organisms used to kill parasitic fungi or their spores. A fungistatic inhibits their growth. Fungi can cause serious damage in agriculture, resulting in critical losses of yield, quality, ...

, which is linked to the ability of its β-gluanases to hydrolyze

phytopathogenic Plant pathology (also phytopathology) is the scientific study of diseases in plants caused by pathogens (infectious organisms) and environmental conditions (physiological factors). Organisms that cause infectious disease include fungi, oomyc ...

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.