Glucanases areenzymes that break down [glucans]polysaccharides viahydrolysis. The product of the hydrolysis reaction are smallerglucans, a linear or branched polysaccharide made of up to 1200glucose monomers, linked by glycosidic bonds.^[1] Glucans are abundant in theendosperm cell walls of cereals such asbarley,rye,sorghum,rice, andwheat.^[1] Glucanases are also referred to aslichenases,hydrolases,glycosidases, glycosyl hydrolases, and/orlaminarinases.^[1] Many types of glucanases share similar amino acid sequences but vastly different substrates.^[1] Of the known endo-glucanases, 1,3-1,4-β-glucanase is considered the most active.^[1]

Glucanase
3D crystalline structure of the endoglucanase Cel10 from Klebsiella pneumoniae.
Identifiers
EC no.	3.2.1.
CAS no.	9015-78-5
Databases
IntEnz	IntEnz view
BRENDA	BRENDA entry
ExPASy	NiceZyme view
KEGG	KEGG entry
MetaCyc	metabolic pathway
PRIAM	profile
PDB structures	RCSB PDBPDBePDBsum
Search PMC articles PubMed articles NCBI proteins

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.^[1] This type of structure has been called the "jelly roll fold."

• 1,3-β-glucanases (laminarinases, EC 3.2.1.39)^[1]
• Endo-1,3(4)-β-glucanase
• β-1,3-glucanase, an enzyme in plants that breaks downβ-1,3-glucans such ascallose orcurdlan
• β-1,6 glucanase, an enzyme that breaks downβ-1,6-glucans
• Cellulase, an enzyme that perform the hydrolysis of 1,4-beta-D-glycosidic linkages incellulose,lichenin and cerealβ-D-glucans.^[2]
• Xyloglucan-specific endo-β-1,4-glucanase
• Xyloglucan-specific exo-β-1,4-glucanase

• α-1,4-glucanase, an enzyme that breaks downα-1,4-glucans
• α-1,6-glucanase, an enzyme that breaks downα-1,6-glucans
• Pullulanase, a specific kind of glucanase that degrade pullulan

The functional formation of the enzyme-substrate complex is dictated by the induced-fit mechanism.^[1]

The main function of glucanase is to catalyze thehydrolysis 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.^[3]

In 1953, Dr. D. E. Koshland proposed a double-displacement mechanism for this enzyme action.^[4] The first step of his proposed mechanism is rate-limiting step independent of the concentration of the substrate and involves an amino acidnucleophile and an acid/base catalyst.^[4] In this step, the nucleophile, with help from the acid residue, displaces theaglycone and forms a covalent glycosyl-enzyme intermediate.^[4][1] The second step involves a water molecule, assisted by theconjugate base of the acid catalyst, rendering the free sugar while retaining an anomeric configuration of the molecule.^[1]

Glucanases can also catalyzetransglycosylation, resulting in new β-glycosidic bonds between donor and acceptor saccharides.^[1] This reaction, which has the same region- and stereo-specificity as the hydrolysis reaction, involves either the direct reversal of hydrolysis (known ascondensation) or kinetic control of a glycosyl donor substrate.^[1]

Bacteria such asEscherichia coli, andBacillus spp. produce 1,3-1,4-β-glucanases in order to degrade and use glucans from their environment as an energy source.^[1] These bacterial glucanases are an example of convergent evolution as they share similarity or relation with plant glucanasesprimary,secondary, ortertiary structure.^[1] Glucanases have also been found to be secreted by fungi such asTrichoderma harzianum,Saccharomyces cerevisiae and theanaerobic fungiOrpinomyces andNeocallimastigomycota, found in the digestive tracts ofherbivores.^[1][5][6]T. harzianum is also used as afungicide, which is linked to the ability of its β-gluanases to hydrolyzephytopathogenic fungi via amycoparasitic attack.^[6]

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.^[1]

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.

In the production of feedstuff for broiler chickens and piglets, it has been found that β-glucanases improve digestibility of barley-based diets.^[1]

• Glycoside hydrolases, a family of enzyme that cut a glycoside from a non-glycosidic molecule
• Glycoside hydrolase family 5
• Glycoside hydrolase family 16
• Glycoside hydrolase family 17