Cloning and sequencing of the gene encoding thermophilic beta-amylase of Clostridium thermosulfurogenes.

A gene coding for thermophilic beta-amylase of Clostridium thermosulfurogenes was cloned into Bacillus subtilis, and its nucleotide sequence was determined. The nucleotide sequence suggested that the thermophilic beta-amylase is translated from monocistronic mRNA as a secretory precursor with a signal peptide of 32 amino acid residues. The deduced amino acid sequence of the mature beta-amylase contained 519 residues with a molecular weight of 57,167. The amino acid sequence of the C. thermosulfurogenes beta-amylase showed 54, 32, and 32% homology with those of the Bacillus polymyxa, soybean, and barley beta-amylases, respectively. Twelve well-conserved regions were found among the amino acid sequences of the four beta-amylases. To elucidate the mechanism rendering the C. thermosulfurogenes beta-amylase thermophilic, its amino acid sequence was compared with that of the B. polymyxa beta-amylase. The C. thermosulfurogenes beta-amyulase contained more Cys residues and fewer hydrophilic amino acid residues than the B. polymyxa beta-amylase did. Several regions were found in the amino acid sequence of the C. thermosulfurogenes beta-amylase, where the hydrophobicity was remarkably high as compared with that of the corresponding regions of the B. polymyxa beta-amylase.