Molecular cloning and transcriptional expression analysis of an intracellular beta-glucosidase, a family 3 glycosyl hydrolase, from the edible straw mushroom, Volvariella volvacea.
A beta-glucosidase, with a molecular mass of 95 kDa, was isolated from extracts of Volvariella volvacea mycelium grown on crystalline cellulose. Degenerate primers based on the N-terminal sequences of purified beta-glucosidase and two protease-generated peptides were used to generate cDNA fragments encoding a portion of the beta-glucosidase gene (bgl), and rapid amplification of cDNA ends was used to obtain full-length cDNA clones. The cDNA of bgl contained an ORF of 2586 bp coding for 862 amino acids. Alignment of the deduced amino-acid sequence of beta-glucosidase with deduced amino acid sequences of other microbial beta-glucosidases showed the highest overall homology with glycoside hydrolase family 3 beta-glucosidases from fungi. Transcripts of bgl were detected in total RNA extracted from mycelium grown on cellulose and cellobiose, and from mycelium pre-grown for 72 h in basal medium containing 1% (w/v) sorbitol following addition of alpha-lactose, beta-lactose, cellobiose, d- xylose, l-sorbose, beta-gentiobiose, sophorose or d-galactose. Addition of l-sorbose and d-glucosamine to mycelium grown on 1% (w/v) crystalline cellulose greatly increased the level of bgl expression. bgl Was expressed at various stages of the mushroom developmental cycle (substrate colonization to mature fruit body), although the number of bgl transcripts in pinhead and button stages was slightly smaller.