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An α-glucosidase gene (aglA) from thermophilic Bacillus sp. DG0303 was cloned, sequenced, and expressed in Escherichia coli. The aglA was localized to the 2.1-kb PvuI-XmnI region within the 5.9-kb DNA insert of the hybrid plasmid pAG1. The gene consisted of an open reading frame of 1,686bp with an unusual GTG initiation codon and TGA termination codon. The amino acid sequence deduced from the nucleotide sequence predicted a protein of 562 amino acid residues with a M_r of 66,551 dalton. A comparative amino acid sequence analysis revealed that DG0303 α-glucosidase is related to bacillary oligo-1,6-glucosidases. The Bacillus sp. DG0303 α-glucosidase showed a high sequence identity (36-59%) to the B. flavocaldarius, B. cereus, and B. thermoglucosidasius oligo-1,6-glucosidases. The number of prolines in these four α-glucosidases was observed to increase with increasing thermostability of these enzymes. The cloned α-glucosidase was purified from E. coli DH5α bearing pAG1 and characterized. The recombinant enzyme was identical with the native enzyme in its optimum pH and in its molecular mass, estimated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The temperature optimum of the cloned α-glucosidase was lower than that of the native enzyme.
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