enzymology Enzymes () are proteins that act as biological catalysts 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 products. A ...

, a cyclomaltodextrin glucanotransferase (also cyclodextrin glycosyl transferase or CGTase for short) () is an

enzyme Enzymes () are proteins that act as biological catalysts 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 products. A ...

that catalyzes the

chemical reaction A chemical reaction is a process that leads to the IUPAC nomenclature for organic transformations, chemical transformation of one set of chemical substances to another. Classically, chemical reactions encompass changes that only involve the pos ...

of cyclizing part of a 1,4-alpha-D-

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 ...

molecule through the formation of a 1,4-alpha-D-glucosidic bond. They are

bacterial Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were among ...

s belonging to the same family of the

α-amylase α-Amylase is an enzyme (EC 3.2.1.1; systematic name 4-α-D-glucan glucanohydrolase) that hydrolyses α bonds of large, α-linked polysaccharides, such as starch and glycogen, yielding shorter chains thereof, dextrins, and maltose: :Endohyd ...

specifically known as glycosyl-hydrolase family 13. This peculiar enzyme is capable of catalyzing more than one reaction with the most important being the synthesis of non-reducing cyclic

dextrin Dextrins are a group of low-molecular-weight carbohydrates produced by the hydrolysis of starch and glycogen. Dextrins are mixtures of polymers of D-glucose units linked by α-(1→4) or α-(1→6) glycosidic bonds. Dextrins can be produced from ...

s known as

cyclodextrin Cyclodextrins are a family of cyclic oligosaccharides, consisting of a macrocyclic ring of glucose subunits joined by α-1,4 glycosidic bonds. Cyclodextrins are produced from starch by enzymatic conversion. They are used in food, pharmaceutical, ...

s starting from

starch Starch or amylum is a polymeric carbohydrate consisting of numerous glucose units joined by glycosidic bonds. This polysaccharide is produced by most green plants for energy storage. Worldwide, it is the most common carbohydrate in human diets ...

amylose Amylose is a polysaccharide made of α-D-glucose units, bonded to each other through α(1→4) glycosidic bonds. It is one of the two components of starch, making up approximately 20–30%. Because of its tightly packed helical structure, amylose ...

, and other

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 ...

s. CGTase is an enzyme common to many bacterial species, in particular of the ''Bacillus''

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...

(e.g. ''B. circulans'', ''B. macerans'' and ''B. stearothermophilus'') and ''Brevibacillus brevis.'' This enzyme belongs to the family of

glycosyltransferase Glycosyltransferases (GTFs, Gtfs) are enzymes ( EC 2.4) that establish natural glycosidic linkages. They catalyze the transfer of saccharide moieties from an activated nucleotide sugar (also known as the "glycosyl donor") to a nucleophilic glycos ...

s, specifically the hexosyltransferases. The

systematic name A systematic name is a name given in a systematic way to one unique group, organism, object or chemical substance, out of a specific population or collection. Systematic names are usually part of a nomenclature. A semisystematic name or semitrivial ...

of this enzyme class is 1,4-alpha-D-glucan 4-alpha-D-(1,4-alpha-D-glucano)-transferase (cyclizing). Other names in common use include Bacillus macerans amylase, cyclodextrin glucanotransferase, alpha-cyclodextrin glucanotransferase, alpha-cyclodextrin glycosyltransferase, beta-cyclodextrin glucanotransferase, beta-cyclodextrin glycosyltransferase, gamma-cyclodextrin glycosyltransferase, cyclodextrin glycosyltransferase, cyclomaltodextrin glucotransferase, cyclomaltodextrin glycosyltransferase, konchizaimu, alpha-1,4-glucan 4-glycosyltransferase, cyclizing, BMA, CGTase, and neutral-cyclodextrin glycosyltransferase.

Catalytic activities

All of the CGTases can catalyze up to four reactions: cyclization, coupling, disproportionation and hydrolysis. All these activities share the same catalytic mechanism which is common to all glycosyl-hydrolases. Cyclization is the process through which a linear polysaccharidic chain is cleaved and the two ends of the cleaved fragment are joined to produce a circular dextrin (cyclodextrin or CD): on the basis of the number of sugar residues this circular product is made of three main type of cyclodextrins can be distinguished, α-CD with six residues, β-CD with seven residues and γ-CD with eight residues. The coupling reaction can be easily described as the reverse process of cyclization: the enzyme cleaves a cyclodextrin to produce a linear dextrin which is subsequently joined to a linear oligosaccharide. Disproportionation is very similar to coupling, but the cleaved dextrin is not a cyclodextrin, but a linear oligosaccharide that is then joined to a second oligosaccharide. CGTase also has a weak hydrolyzing activity which consists in cleaving the longer polysaccharidic chains into shorter fragments.

Structural studies

As of late 2007, 47

structures A structure is an arrangement and organization of interrelated elements in a material object or system, or the object or system so organized. Material structures include man-made objects such as buildings and machines and natural objects such as ...

have been solved for this class of enzymes, with PDB accession codes , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , and .

References

* * * * * * {{Portal bar, Biology, border=no EC 2.4.1 Enzymes of known structure