Comparative study of β-glucan-degrading enzymes from Coprinopsis cinerea for their capacities to induce stipe cell wall extension.

We previously reported endo-β-1,3-glucanase ENG in combination with β-glucosidase BGL2 at low concentration induced stipe cell wall extension. This study further explored ENG could be replaced by endo-β-1,3(4)-glucanase ENG16A in combination with BGL2 to induce stipe cell wall extension; similarly, BGL2 could be replaced by β-glucosidase BGL1 to cooperate with ENG to induce stipe cell wall extension. However, ENG could not be replaced by exo-β-1,3-glucanase EXG in combination with BGL2 to induce stipe cell wall extension, although EXG alone released higher level of soluble sugars from the stipe cell walls during the reconstituted wall extension than that released from the stipe cell walls by a combination of ENG16A or ENG and BGL2 or BGL1, which was different from chitinase-mediated stipe cell wall extension. These results indicate endo-β-1,3-glucanases loosen the stipe cell wall, whereas exo-β-1,3-glucanases and β-glucosidases play a synergistic role to maintain a low and efficient concentration of endo-β-1,3-glucanases for stipe cell wall extension. Furthermore, ENG was expressed at a very high level in the matured pilei, in contrast, ENG16A was expressed at a very high level in the elongating apical stipe. Therefore, ENG16A might be involved in stipe elongation growth, while ENG might participate in autolysis of pilei.