Cloning of the cyclodextrin glucanotransferase gene from alkalophilic Bacillus sp. A2-5a and analysis of the raw starch-binding domain.

The cyclodextrin glucanotransferase (CGTase) gene of alkalophilic Bacillus sp. A2-5a was cloned and expressed in Bacillus subtilis ANA-1 as a host. The DNA region included an open reading frame encoding a 704-amino-acid polypeptide with a typical raw starch-binding motif in its C-terminal region. The CGTase purified from Bacillus sp. A2-5a bound to raw starch as strongly as porcine pancreas alpha-amylase, as expected from the sequence motif. A chromosomal region (a DNA fragment of about 14.1 kbp) including the CGTase gene was also cloned and the nucleotide sequence was determined. Possible cyclodextrinase and putative cyclodextrin-binding protein genes were found in the flanking region of the CGTase gene, which implied that the novel starch-degradation pathway postulated for a gram-negative bacterium [Klebsiella oxytoca; Fiedler et al. (1996) J Mol Biol 256: 279-291] also exists in a gram-positive bacterium i.e. Bacillus.