Mechanism of action of the endo ‐(1 → 3)‐α‐glucanase MutAp from the mycoparasitic fungus Trichoderma harzianum

(1 → 3)‐α‐Glucanases catalyze the hydrolysis of fungal cell wall (1 → 3)‐α‐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)‐α‐glucanase MutAp from the mycoparasitic fungus Trichoderma harzianum . We observed that MutAp releases predominantly β‐glucose upon hydrolysis of crystalline (1 → 3)‐α‐glucan, indicating inversion of the anomeric configuration. After having identified (1 → 3)‐α‐glucan tetrasaccharide as the minimal substrate for MutAp, we showed that reduced (1 → 3)‐α‐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)‐α‐glucan, and then continues its hydrolysis towards the non‐reducing end by releasing β‐glucose residues in a processive manner.