Gene cloning, heterologous expression and characterization of a Coprinopsis cinerea endo-β-1,3(4)-glucanase.

A gene coding endo-β-1,3(4)-glucanase (ENG16A) was cloned from Coprinopsis cinerea and heterologously expressed in Pichia pastoris. ENG16A only acts on substrates containing β-1,3 glycosidic bonds but not on substrates containing only β-1,4- or β-1,6-glycosidic bonds. Interestingly, compared to the activity of this enzyme towards carboxymethyl (CM)-pachyman containing only β-1,3-glycosidic bonds, its activity towards barley β-glucan containing both β-1,3-glycosidic and β-1,4-glycosidic bonds was increased by 64.72 %,, its activity towards laminarin containing both β-1,3-glycosidic and β-1,6-glycosidic bonds was decreased by 50.83 %. In addition, ENG16A has a higher Km value and Vmax for barley β-glucan than laminarin, which may be related to the fact that barley β-glucan contains mainly β-1,4-glycosidic bonds mixed with a few β-1,3-glycosidic bonds, whereas laminarin mainly contains β-1,3-glycosidic bonds with a few β-1,6-branched glucose residues. The adjacent β-1,4-glycosidic bond promotes ENG16A to hydrolyse β-1,3-glycosidic bonds, leading to an increased Vmax; the nearby β-1,6-glycosidic bonds inhibited its hydrolysis of β-1,3-glycosidic bonds, resulting in a decreased Vmax. This property is suggested to be related to the mechanism that C. cinerea uses to degrade and utilize hemicellulose in straw medium and to protect its cell wall during the mycelium growth stage.