A novel endo-β-1,6-glucanase from the mushroom Coprinopsis cinerea and its application in studying of cross-linking of β-1,6-glucan and the wall extensibility in stipe cell walls

We previously reported that chitinases reconstituted heat-inactivated stipe cell wall extension in a steady and continuous extension profile by cleaving chitins cross-linked to various polysaccahrides, whereas, endo-β-1,3-glucanases reconstituted heat-inactivated stipe wall extension in a profile of an initially fast extension and subsequent termination of extension due to its degradation of β-1,3-glucan but not other polysaccharides such as β-1,6-glucans cross-linked to chitins. Thus, a novel endo-β-1,6-glucanase, GH30A, from Coprinopsis cinerea was cloned and characterized to study cross-linking of β-1,6-glucan and wall extensibility in stipe walls. GH30A had higher activity and better thermophilicity than reported β-1,6-glucanases. GH30A hydrolyzed pustulan having β-1,6-linkages but not other polysaccharides without β-1,6-linkages; GH30A did not cleave gentiobiose and single β-1,6-linkage branches in laminarin from Laminaria digitata but cut consecutive β-1,6-linkage branches in laminarin from Eisenia bicyclis. GH30A reconstituted heated-inactivated stipe cell wall extension with release of glucose and gentiobiose, indicating that β-1,6-glucans were present and cross-linked to chitins in stipe walls, and cleaving β-1,6-glucans cross-linked to chitins by GH30A led to wall loosening for extension. However, GH30A individually or in combination with endo-β-1,3-glucanase reconstituted-stipe wall extension profile was similar to individual endo-β-1,3-glucanase's, exploring that chitins were also cross-linked to other polysaccharides besides β-1,3-glucans and β-1,6-glucans.