抄録
The gene that coded for the subunit of an molecular weight (Mr) 540,000 homohexameric α-glucosidase II (α-D-glucoside glucohydrolase, EC 3.2.1.20) produced by Bacillus thermoamyloliquefaciens KP1071 (FERM-P8477) growing at 30 to 66°C was expressed in Escherichia coli HB101. The resulting homohexameric enzyme had a half-life of 10 min at 80°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 Mr of 91,070 deduced from the gene was 24-34% identical to the corresponding sequences of 15 α-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 Rost and Sander [Rost, B. and Sander, C., Proteins: Struct. Funct. Genet., 19, 55-72 (1994)], we inferred that α-glucosidase II might make each subunit of 3 secondary structural regions, i.e., one N-terminal β region, one central α/β region with two catalytic residues Asp407 and Asp484, and one C-terminal β region.
