Molecular identification of a novel beta-1,3-glucanase from alkaliphilic Nocardiopsis sp. strain F96.

Alkaliphilic Nocardiopsis sp. strain F96 produced three beta-1,3-glucanase isozymes of different molecular masses (BglF1, BglF2 and BglF3). The N-terminal amino acid sequences of BglFs indicated that these isozymes were the products of a single gene. The beta-1,3-glucanase gene (bglF) was cloned from the chromosomal DNA of strain F96. The bglF gene encoded a polypeptide of 270 amino acids including a signal sequence. The deduced amino acid sequence of mature BglF exhibited the highest homology to those of glycoside hydrolase (GH) family 16 beta-1,3-glucanases, suggesting that the enzyme belonged to the GH family 16. The mature region of bglF gene was functionally expressed in Escherichia coli. The optimum pH and temperature of purified recombinant BglF were pH 9.0 and 70 degrees C, respectively. This enzyme efficiently hydrolyzed insoluble beta-1,3-glucans and showed the highest activity toward a beta-1,3-1,4-glucan rather than beta-1,3-glucans. These results suggested that BglF would be a novel beta-1,3-glucanse. Mutational analysis revealed that Glu123 and Glu128 should be the catalytic residues of BglF.