Purification, characterization and synergism in autolysis of a group of 1,3-β-glucan hydrolases from the pilei of Coprinopsis cinerea fruiting bodies

Using a combined chromatography method, we simultaneously purified three protein fractions (II-2, II-3 and II-4) with 1,3-β-glucanase activity from extraction of pilei of Coprinopsis cinerea fruiting bodies. MALDI-TOF/TOF amino acid sequencing showed that these three fractions matched a putative exo-1,3-β-glucanase, a putative glucan 1,3-β-glucosidase and a putative glycosyl hydrolase family 16 protein annotated in the C. cinerea genome, respectively; however, they were characterized as a 1,3-β-glucosidase, an exo-1,3-β-glucanase and an endo-1,3-β-glucanase, respectively, by analysis of their substrate specificities and modes of action. This study explored how these three 1,3-β-glucoside hydrolases synergistically acted on laminarin: the endo-1,3-β-glucanase hydrolysed internal glycosidic bonds of laminarin to generate 1,3-β-oligosaccharides of various lengths, the exo-1,3-β-glucanase cleaved the longer-chain laminarioligosaccharides into short-chain disaccharides, laminaribiose and gentiobiose, and the 1,3-β-glucosidase further hydrolysed laminaribiose to glucose. The remaining gentiobiose must be hydrolysed by other 1,6-β-glucosidases. Therefore, the endo-1,3-β-glucanase, exo-1,3-β-glucanase and 1,3-β-glucosidase may act synergistically to completely degrade the 1,3-β-glucan backbone of the C. cinerea cell wall during fruiting body autolysis. These three 1,3-β-glucoside hydrolases share a similar optimum pH and optimum temperature, supporting the speculation that these enzymes work together under the same conditions to degrade 1,3-β-glucan in the C. cinerea cell wall during fruiting body autolysis.