Grün Christian H, Dekker Nick, Nieuwland Alexander A, Klis Frans M, Kamerling Johannis P, Vliegenthart Johannes F G, Hochstenbach Frans
Bijvoet Center, Department of Bio-Organic Chemistry, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands.
FEBS Lett. 2006 Jul 10;580(16):3780-6. doi: 10.1016/j.febslet.2006.05.062. Epub 2006 Jun 9.
(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.
（1→3）-α-葡聚糖酶催化真菌细胞壁（1→3）-α-葡聚糖的水解，并在含有这种细胞壁成分的酵母细胞分裂过程中发挥作用，或在真菌寄生过程中起作用。在此，我们阐述了来自真菌寄生菌哈茨木霉的（1→3）-α-葡聚糖酶MutAp的作用机制。我们观察到，MutAp在水解结晶（1→3）-α-葡聚糖时主要释放β-葡萄糖，这表明异头构型发生了翻转。在确定（1→3）-α-葡聚糖四糖是MutAp的最小底物后，我们表明还原型（1→3）-α-葡聚糖五糖被裂解为一个三糖和一个还原型二糖，这表明MutAp具有内切水解活性。我们提出了一个MutAp催化机制的模型，即该酶断裂（1→3）-α-葡聚糖的链内糖苷键，然后通过以连续方式释放β-葡萄糖残基继续向非还原端进行水解。
