Endo-β-1,3-Glucanase GLU1, from the Fruiting Body of Lentinula edodes, Belongs to a New Glycoside Hydrolase Family

The cell wall of the fruiting body of the mushroom Lentinula edodes is degraded after harvesting by enzymes such as beta-1,3-glucanase. In this study, a novel endo-type beta-1,3-glucanase, GLU1, was purified from L. edodes fruiting bodies after harvesting. The gene encoding it, glu1, was isolated by rapid amplification of cDNA ends (RACE)-PCR using primers designed from the N-terminal amino acid sequence of GLU1. The putative amino acid sequence of the mature protein contained 247 amino acid residues with a molecular mass of 26 kDa and a pI of 3.87, and recombinant GLU1 expressed in Pichia pastoris exhibited beta-1,3-glucanase activity. GLU1 catalyzed depolymerization of glucans composed of beta-1,3-linked main chains, and reaction product analysis by thin-layer chromatography (TLC) clearly indicated that the enzyme had an endolytic mode. However, the amino acid sequence of GLU1 showed no significant similarity to known glycoside hydrolases. GLU1 has similarity to several hypothetical proteins in fungi, and GLU1 and highly similar proteins should be classified as a novel glycoside hydrolase family (GH128).