Cloning and sequencing of an exoglucanase gene from Streptomyces sp. M23, and its expression in Streptomyces lividans TK-24

A gene encoding exoglucanase (CBHII) of Streptomyces sp. M23 was cloned and sequenced. The cbhII gene consisted of 1359 bp capable of encoding a polypeptide of 453 amino acids with a calculated molecular mass of 45,175 Da. The deduced amino acid sequence showed homology with those of cellulases belonging to family 6 of the glycosyl hydrolases. The cbhII gene was subcloned into the plasmid pSEV1 and expressed in Streptomyces lividans TK-24. The transformed cells were able to secrete the enzyme efficiently in an active form. The CBHII expressed by S. lividans TK-24 was purified to homogeneity by SDS–polyacrylamide gel and characterized. The recombinant CBHII was stable up to 50°C and more than 30% of the original activity remained after heating at 100°C for 10 min. The amino-terminal amino acid sequence of the recombinant CBHII was identified as GPAAPTARVD. These results agreed well with the properties of the authentic CBHII.