Crystal structure of the starch-binding domain of glucoamylase from Aspergillus niger

Glucoamylases are widely used commercially to produce glucose syrup from starch. The starch-binding domain (SBD) of glucoamylase from Aspergillus niger is a small globular protein containing a disulfide bond. The structure of A. niger SBD has been determined by NMR, but the conformation surrounding the disulfide bond was unclear. Therefore, X-ray crystal structural analysis was used to attempt to clarify the conformation of this region. The SBD was purified from an Escherichia coli-based expression system and crystallized at 293   K. The initial phase was determined by the molecular-replacement method, and the asymmetric unit of the crystal contained four protomers, two of which were related by a noncrystallographic twofold axis. Finally, the structure was solved at 2.0   Å resolution. The SBD consisted of seven β -strands and eight loops, and the conformation surrounding the disulfide bond was determined from a clear electron-density map. Comparison of X-ray- and NMR-determined structures of the free SBD showed no significant difference in the conformation of each β -strand, but the conformations of the loops containing the disulfide bond and the L5 loop were different. In particular, the difference in the position of the C α atom of Cys509 between the X-ray- and NMR-determined structures was 13.3   Å . In addition, the B factors of the amino-acid residues surrounding the disulfide bond are higher than those of other residues. Therefore, the conformation surroundi...
Source: Acta Crystallographica Section F - Category: Biochemistry Authors: Tags: starch-binding domain glucoamylase β -sheet structure disulfide bond Aspergillus niger research communications Source Type: research