The evolution of cyclodextrin glucanotransferases, model enzymes of glycoside hydrolase family 13

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The evolution of cyclodextrin glucanotransferases, model enzymes of glycoside
hydrolase family 13 / Ronan Kelly. - [S.l. : s.n.], 2009. - 167 p. : ill. ; 24
cm
Proefschrift Groningen. - Met lit.opg. - Met samenvatting in het Nederlands en
Engels.

The complexity of starch is mirrored by the requirement of organisms to produce an array of enzymes for its breakdown, uptake and utilization. The glycoside hydrolase family 13 (GH13) (found in all kingdoms of life) represents the largest family of glycoside hydrolases acting on starch, with members attracting considerable commercial interest due to their applicability in the industrial modification and conversion of starch. All GH13 family members either hydrolyze or transglycosylate α-glucosidic linkages to produce α-anomeric mono- and oligosaccharides with catalysis proceeding via a double displacement mechanism with initial formation of a covalent glycosyl-enzyme intermediate. It is therefor the type of acceptor substrate utilized in the second half of the reaction which determines enzyme reaction specificity, a water molecule in the case of α-amylases and hydroxyl group of a sugar substrate for the glucanotransferases. Cyclodextrin glucanotransferases are unique members of the GH13 family in that they use the non-reducing end of a bound oligosaccharide as acceptor, for cicular α-(1,4)-linked oligosaccharide formation (cyclodextrin) in the cyclization reaction. These enzymes primarily produce three types of cyclodextrin, differing in hteir degree of polymerization α (6), ß (7) and Γ (8). Some bacteria and archaea excrete CGTases to convert starch into cyclodextrins which cannot be taken up by competing organisms thus monolpolizing on the starch substrate.

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