Structural insights into the substrate recognition and catalytic mechanism of a fungal glycoside hydrolase family 81 β-1,3-glucanase

beta-1,3-Glucan constitutes a prominent cell wall component being responsible for rigidity and strength of the cell wall structure in filamentous fungi. Glycoside hydrolase (GH) family 81 endo-beta-1,3-glucanases which can cleave the long chain of beta-1,3-glucans play a major role in fungal cell wall remodeling. Here, we reported the complex structures of a fungal GH family 81 endo-beta-1,3-glucanase from Rhizomucor miehei (RmLam81A), revealing the triple-helical beta-glucan recognition and hydrolysis patterns. In the crystals, three structured oligosaccharide ligands simultaneously interact with one enzyme molecular via seven glucose residues, and the spatial arrangement of ligands to RmLam81A was almost identical to that of beta-1,3-glucan triple-helical structure. RmLam81A performed an inverting catalysis mechanism with Asp475 and Glu557 severing as the general acid and base catalyst, respectively. Furthermore, two hydrophobic patches involving Tyr93, Tyr106, Ile108, Phe619 and Tyr628 alongside the ligand-binding site possibly formed parts of the binding site. A ligand-binding motif, beta 31-beta 32, consisting of two key residues (Lys622 and Asp624), involved the recognition of a triple-helical beta-glucan. Our results provided a structural basis for the unique beta-1,3-glucan recognition pattern and catalytic mechanism of fungal GH family 81 endo-beta-1,3-glucanases, which may be helpful in further understanding the diverse physiological functions of beta-1,3-glucanases.

Automated summary

In this study, we reported the complex structures and recognition patterns of a fungal GH family 81 endo-beta-1,3-glucanase from Rhizomucor miehei (RmLam81A). Our results provide a structural basis for understanding the diverse physiological functions of beta-1,3-glucanases.