Difference between revisions 1496899 and 1597559 on enwiki

Group of 7 languages in [[Tupi-Guarani]] sublanguage family. It includes the best-known language [[Tupi Antigo[[Image:CGTase_domains.jpg|thumb|200px|[[Cyclodextrin_glycosyltransferase|CGTase]] ribbon diagram]]
'''Cyclodextrin glycosyl transferase''' or '''CGTase''' for short ([[EC number|EC]] [http://www.expasy.org/cgi-bin/nicezyme.pl?2.4.1.19 2.4.1.19]) is a [[Bacterium|bacterial]] [[enzyme]] belonging to the same family of the [[Alpha-amilase]] 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]] known as cyclodextrins starting from [[starch]], [[amylose]], and other [[polysaccharide|polysaccharides]].
CGTase is an enzyme common to many bacterial species, in particular of the ''Bacillus'' [[genus]] (e.g. ''B. circulans'', ''B. macerans'' and ''B. stearothermophilus''), as well as to some [[archaea]], but it is not present in any other species.

==Catalytic activities==

All of the CGTases can catalyze up to four reactions: cyclization, coupling, disproportionation and hydrolisis. All these activities share the same catalytic mechanism which is common to all glycosyl-hydrolases. 

Cyclyzation 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, [[Alpha-cyclodextrin|Alpha-CD]] with six residues, [[Beta-cyclodextrin|Beta-CD]] with seven residues and [[Gamma-cyclodextrin|Gamma-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 polisaccharidic chains into shorter fragments.

==References==
* Biwer A., Antranikian G. and Heinzle E., "Enzymatic production of cyclodextrins" Appl. Microbiol. Biotechnol. (2002) 59, 609- 617
* Dijkhuizen L. et al., "Rational Design of Cyclodextrin Glycosyltransferase from Bacillus circulans Strain 251 to Increase alpha-Cyclodextrin Production", J. Mol. Biol. (2000) 296, 1027-1038

[[Category:EC 2.4.1]]