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J. Microbiol. Biotechnol. 1999; 9(5): 619-623

Published online October 28, 1999

Copyright © The Korean Society for Microbiology and Biotechnology.

Structure of the Starch-Binding Domain of Bacillus cereus β-Amylase

Hye-Jin Yoon , Akira Hirata , Motoyasu Adachi , Atsushi Sekine , Shigeru Utsumi and Bunzo Mikami

Research Institute for Food Science Kyoto University Uji Kyoto 611-0011 Japan

Abstract

The C-terminal starch-binding domain of Bacillus cereus $\beta$-amylase expressed in Escherichia coli was purified and crystallized using the vapor diffusion method. The crystals obtained belong to a space group of $P3_2$ 21 with cell dimensions, a=b=60.20${\AA},\; c=64.92{\AA},\; and \; \gamma = 120^{\circ}$ The structure was determined by the molecular replacement method and refined at 1.95 ${\AA}$, with R-factors of 0.181. The final model of the starch-binding domain comprised 99 amino acid residues and 108 water molecules. The starch-binding domain had a secondary structure of two 4-stranded antiparallel p-sheets similar to domain E of cyclodextrin glucanotransferase and the C-terminal starch-binding domain of glucoamylase. A comparison of the structures of these starch-binding domains revealed that the separated starch-binding domain of Bacillus cereus $\beta-Amylase$had only one starch-binding site (site 1) in contrast to two sites (site 1 and site 2) reported in the domains of cyclodextrin glucanotransferase and glucoamylase.

Keywords: Starch-bindingdomain, b-amylase, X-raycrystallography, 3Dstructure