Polypeptide Folding of Bacillus cereus ATCC7064 Oligo-1,6-Glucosidase Revealed by 3.0 A Resolution X-Ray Analysis

The crystal structure of an oligo-l,6-glucosida8e from Bacillus cereus ATCC7064 was determined by the X-ray diffraction method at 3.0 Å resolution. The structure was solved by the multiple isomorphous replacement method and refined to a crystallographic R-factor of 0.208, using the molecular dynamics refinement program, X-PLOR. The electron density map revealed the folding of a polypeptide chain consisting of 658 amino acid residues. The molecule can be subdivided into three domains (N-terminal domain, subdomain, and C-terminal domain). The N-terminal domain has an (α/β)B-barrel structure called the TTM-barrel structure. The C-terminal domain is characterized by a β-barrel structure composed of eight antiparallel β-strands, while the subdomain has a loop-rich structure with a small α-helix and a β-sheet. The enzyme has a large cleft between the N-terminal domain and the subdomain. The cleft leads from the molecular surface to the molecular center. The bottom of the cleft is at the C-terminal end of the parallel β- strands of the (α/β)B-barrel. These structural features closely resemble those of a-amylases from Aspergillus oryzae and pig pancreas.