Structure of raw starch-digesting Bacillus cereus beta-amylase complexed with maltose.
The crystals of beta-amylase from Bacillus cereus belong to space group P21 with the following cell dimensions: a = 57.70 A, b = 92.87 A, c = 65.93 A, and beta =101.95 degrees. The structures of free and maltose-bound beta-amylases were determined by X-ray crystallography at 2.1 and 2.5 A with R-factors of 0.170 and 0.164, respectively. The final model of the maltose-bound form comprises 516 amino acid residues, four maltose molecules, 275 water molecules, one Ca2+, one acetate, and one sulfate ion. The enzyme consists of a core (beta/alpha)8-barrel domain (residues 5-434) and a C-terminal starch-binding domain (residues 435-613). Besides the active site in the core where two maltose molecules are bound in tandem, two novel maltose-binding sites were found in the core L4 region and in the C-terminal domain. The structure of the core domain is similar to that of soybean beta-amylase except for the L4 maltose-binding site, whereas the C-terminal domain has the same secondary structure as domain E of cyclodextrin glucosyltransferase. These two maltose-binding sites are 32-36 A apart from the active site. These results indicate that the ability of B. cereus beta-amylase to digest raw starch can be attributed to the additional two maltose-binding sites.
Mikami
B
B
Research Institute for Food Science, Kyoto University, Japan. mikami@soya.food.kyoto-u.ac.jp
Adachi
M
M
Kage
T
T
Sarikaya
E
E
Nanmori
T
T
Shinke
R
R
Utsumi
S
S
D000085:Acetates / Q000737:chemistry / Q000378:metabolism; D000595:Amino Acid Sequence; D001409:Bacillus cereus / Q000201:enzymology*; D001665:Binding Sites; D002118:Calcium / Q000737:chemistry / Q000378:metabolism; D002236:Carbohydrate Conformation; D018360:Crystallography, X-Ray; D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D046911:Macromolecular Substances; D008320:Maltose / Q000737:chemistry* / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000737:chemistry / Q000378:metabolism; D017434:Protein Structure, Tertiary; D017386:Sequence Homology, Amino Acid; D013025:Glycine max / Q000201:enzymology; D013213:Starch / Q000737:chemistry* / Q000378:metabolism; D013431:Sulfates / Q000737:chemistry / Q000378:metabolism; D001614:beta-Amylase / Q000737:chemistry* / Q000378:metabolism
D000085:Acetates; D046911:Macromolecular Substances; D010446:Peptide Fragments; D013431:Sulfates; D008320:Maltose; D013213:Starch; D001614:beta-Amylase; D002118:Calcium