Some fungi express β-1,3-glucanases similar to thaumatin-like proteins

Abstract

Mycelial clarified homogenates from Lentinus edodes, Agaricus bisporus, Rhizoctonia solani and extracts from commercial sources of lysing enzymes from Rhizoctonia solani or Irpex lacteus contained enzymes of ca 25 kDa hydrolyzing polymeric carboxy-methylated (CM)-pachyman with an in-gel β-1,3-glucanase assay. Proteins were purified from Rhizoctonia solani, Lentinus edodes and Irpex lacteus and their Nterminal amino acid sequences showed homology to thaumatin-like (TL) proteins. As with plant TL proteins with β-1,3-glucanase activity, little or no activity was observed on oligomeric laminarin by the in-gel hydrolase assay. The fungal TL proteins varied in specific activity from 60 to 760 nkat mg-1 with CM-pachyman as substrate and were thus more active than most plant TL proteins. Thin-layer chromatography indicated that the fungal TL proteins generated various oligoglucosides from an endo β-1,3-glucanase activity. The TL proteins were detected in several, but not all, anastomosis groups of Rhizoctonia solani. The purified Rhizoctonia solani TL protein was the most potent enzyme, inhibiting the growth of Saccharomyces cerevisiae when compared to two fungal or three plant TL proteins. Moreover, the Rhizoctonia TL protein was able to hydrolyze live Saccharomyces yeast cells. This is the first report of fungal TL proteins with endo-β-1,3-glucanase activity and strong binding to polymeric β-1,3-glucans.