Fungal cell walls contain β-glucan polysaccharides that stimulate immune responses when recognized by host immune cells. The fungal pathogen minimizes detection of β-glucan by host cells through at least two mechanisms: concealment of β-glucans beneath α-glucans and enzymatic removal of any exposed β-glucan polysaccharides by the secreted glucanase Eng1. yeasts also secrete the putative glucanase Exg8， which may serve a similar role as Eng1 in removing exposed β-glucans from the yeast cell surface. Here， we characterize the enzymatic specificity of the Eng1 and Exg8 proteins and show that Exg8 is an exo-β1，3-glucanase and Eng1 is an endo-β1，3-glucanase. Together， Eng1 and Exg8 account for ne... More
Fungal cell walls contain β-glucan polysaccharides that stimulate immune responses when recognized by host immune cells. The fungal pathogen minimizes detection of β-glucan by host cells through at least two mechanisms: concealment of β-glucans beneath α-glucans and enzymatic removal of any exposed β-glucan polysaccharides by the secreted glucanase Eng1. yeasts also secrete the putative glucanase Exg8， which may serve a similar role as Eng1 in removing exposed β-glucans from the yeast cell surface. Here， we characterize the enzymatic specificity of the Eng1 and Exg8 proteins and show that Exg8 is an exo-β1，3-glucanase and Eng1 is an endo-β1，3-glucanase. Together， Eng1 and Exg8 account for nearly all of the total secreted glucanase activity of yeasts. Both Eng1 and Exg8 proteins are secreted through a conventional secretion signal and are modified post-translationally by -linked glycosylation. Both glucanases have near maximal activity at temperature and pH conditions experienced during infection of host cells， supporting roles in pathogenesis. Exg8 has a higher specific activity than Eng1 for β1，3-glucans; yet despite this， Exg8 does not reduce detection of yeasts by the host β-glucan receptor Dectin-1. Exg8 is largely dispensable for virulence ， in contrast to Eng1. These results show that yeasts secrete two β1，3-glucanases and that Eng1 endoglucanase activity is the predominant factor responsible for removal of exposed cell wall β-glucans to minimize host detection of yeasts.
