The primary structure of the subunit in Bacillus thermoamyloliquefaciens KP1071 molecular weight 540,000 homohexameric α-glucosidase II belonging to the glycosyl hydrolase family 31

The gene that coded for the subunit of an molecular weight (M-r) 540,000 homohexameric alpha-glucosidase II (alpha-D-glucoside glucohydrolase, EC 3.2.1.20) produced by Bacillus thermoamyloliquefaciens KP1071 (FERM-P8477) growing at 30 to 66 degrees C was expressed in Escherichia coli HB101. The resulting homohexameric enzyme had a half-life of 10 min at 80 degrees C. Its purification and characterization showed that the enzyme was identical with the native one except for the latter deleting 7 N-terminal residues found in the former. The primary sequence of the subunit with 787 residues and an M-r of 91,070 deduced from the gene was 24-34% identical to the corresponding sequences of 15 alpha-glucosidases In the glycosyl hydrolase family 31 from 14 eukaryotic origins and the archaeon Sulfolobus solfataricus 98/2. From the sequence analysis by the neural network method of Rest and Sander [Rost, B. and Sander, C., Proteins: Struct. Funct. Genet., 19, 55-72 (1994)], we inferred that alpha-glucosidase II might make each subunit of 3 secondary structural regions, i.e., one N-terminal beta region, one central alpha/beta region with two catalytic residues Asp407 and Asp484, and one C-terminal beta region.