Mechanism of action of the endo-(1-->3)-alpha-glucanase MutAp from the mycoparasitic fungus Trichoderma harzianum.
(1-->3)-alpha-glucanases catalyze the hydrolysis of fungal cell wall (1-->3)-alpha-glucan, and function during cell division of yeasts containing this cell wall component or act in mycoparasitic processes. Here, we characterize the mechanism of action of the (1-->3)-alpha-glucanase MutAp from the mycoparasitic fungus Trichoderma harzianum. We observed that MutAp releases predominantly beta-glucose upon hydrolysis of crystalline (1-->3)-alpha-glucan, indicating inversion of the anomeric configuration. After having identified (1-->3)-alpha-glucan tetrasaccharide as the minimal substrate for MutAp, we showed that reduced (1-->3)-alpha-glucan pentasaccharide is cleaved into a trisaccharide and a reduced disaccharide, demonstrating that MutAp displays endo-hydrolytic activity. We propose a model for the catalytic mechanism of MutAp, whereby the enzyme breaks an intrachain glycosidic linkage of (1-->3)-alpha-glucan, and then continues its hydrolysis towards the non-reducing end by releasing beta-glucose residues in a processive manner.
Grün
Christian H
CH
Bijvoet Center, Department of Bio-Organic Chemistry, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands.
Dekker
Nick
N
Nieuwland
Alexander A
AA
Klis
Frans M
FM
Kamerling
Johannis P
JP
Vliegenthart
Johannes F G
JF
Hochstenbach
Frans
F
D002236:Carbohydrate Conformation; D002384:Catalysis; D005936:Glucans / Q000737:chemistry / Q000378:metabolism; D005947:Glucose / Q000378:metabolism; D006026:Glycoside Hydrolases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D006868:Hydrolysis; D008954:Models, Biological; D011134:Polysaccharides / Q000378:metabolism; D013379:Substrate Specificity; D014242:Trichoderma / Q000201:enzymology*
D005936:Glucans; D011134:Polysaccharides; C045788:alpha-1,3-glucan; D006026:Glycoside Hydrolases; C028760:endo-1,3-alpha-glucanase; D005947:Glucose