Characterization of an antifungal β-1,3-glucanase from Ficus microcarpa latex and comparison of plant and bacterial β-1,3-glucanases for fungal cell wall β-glucan degradation.

Each β-1,3-glucanase with antifungal activity or yeast lytic activity hydrolyzes different structures of β-1,3-glucans in the fungal cell wall, respectively. Plants express several glycoside hydrolases that target chitin and β-glucan in fungal cell walls and inhibit pathogenic fungal infection. An antifungal β-1,3-glucanase was purified from gazyumaru (Ficus microcarpa) latex, designated as GlxGluA, and the corresponding gene was cloned and expressed in Escherichia coli. The sequence shows that GlxGluA belongs to glycoside hydrolase family 17 (GH17). To investigate how GlxGluA acts to degrade fungal cell wall β-glucan, it was compared with β-1,3-glucanase with different substrate specificities. We obtained recombinant β-1,3-glucanase (designated as CcGluA), which belongs to GH64, from the bacterium Cellulosimicrobium cellulans. GlxGluA inhibited the growth of the filamentous fungus Trichoderma viride but was unable to lyse the yeast Saccharomyces cerevisiae. In contrast, CcGluA lysed yeast cells but had a negligible inhibitory effect on the growth of filamentous fungi. GlxGluA degraded the cell wall of T. viride better than CcGluA, whereas CcGluA degraded the cell wall of S. cerevisiae more efficiently than GlxGluA. These results suggest that the target substrates in fungal cell walls differ between GlxGluA (GH17 class I β-1,3-glucanase) and CcGluA (GH64 β-1,3-glucanase).