A novel β-glucanase gene fromBacillus haloduransC-125

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Abstract
A novel endo-β-1,3(4)-d-glucanase gene was found in the complete genome sequence of Bacillus halodurans C-125. The gene was previously annotated as an “unknown” protein and assigned an incorrect open reading frame (ORF). However, determining the biochemical characteristics has elucidated the function and correct ORF of the gene. The gene encodes 231 amino acids, and its calculated molecular mass was estimated to be 26743.16 Da. The amino acid sequence alignment showed that the highest sequence identity was only 28% with that of the β-1,3–1,4-glucanase from Bacillus subtilis. Moreover, the nucleotide sequence did not match any other known Bacillusβ-glucanase gene. The member of the gene cluster that includes this novel gene was apparently different from that of the gene cluster including the putative β-glucanase genes (bh3231 and bh3232) from B. halodurans C-125. Therefore, the novel gene is not a copy of either of these genes, and in B. halodurans cells, the putative role of the encoded protein may differ from that of bh3231 and bh3232. To examine the activity of the gene product, the gene was cloned as a His-tagged protein and expressed in Escherichia coli. The purified enzyme showed activity against lichenan, barley β-glucan, laminarin, and carboxymethyl curdlan. Thin-layer chromatography showed that the enzyme hydrolyzes substrates in an endo-type manner. When β-glucan was used as a substrate, the pH optimum was between 6 and 8, and the temperature optimum was 60°C. After 2 h incubation at 50 and 60°C, the residual activity remained 100% and 50%, respectively. The enzymatic activity was abolished after 30 min incubation at 70°C. Based on the results, the gene encodes an endo-type β-1,3(4)-d-glucanase (E.C. 3.2.1.6).

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