1QHO: Five-Domain Alpha-Amylase From Bacillus Stearothermophilus, MaltoseACARBOSE COMPLEX

The three-dimensional structure of the Bacillus stearothermophilus "maltogenic" alpha-amylase, Novamyl, has been determined by X-ray crystallography at a resolution of 1.7 A. Unlike conventional alpha-amylases from glycoside hydrolase family 13, Novamyl exhibits the five-domain structure more usually associated with cyclodextrin glycosyltransferase. Complexes of the enzyme with both maltose and the inhibitor acarbose have been characterized. In the maltose complex, two molecules of maltose are found in the -1 to -2 and +2 to +3 subsites of the active site, with two more on the C and E domains. The C-domain maltose occupies a position identical to one previously observed in the Bacillus circulans CGTase structure [Lawson, C. L., et al. (1994) J. Mol. Biol. 236, 590-600], suggesting that the C-domain plays a genuine biological role in saccharide binding. In the acarbose-maltose complex, the tetrasaccharide inhibitor acarbose is found as an extended hexasaccharide species, bound in the -3 to +3 subsites. The transition state mimicking pseudosaccharide is bound in the -1 subsite of the enzyme in a 2H3 half-chair conformation, as expected. The active site of Novamyl lies in an open gully, fully consistent with its ability to perform internal cleavage via an endo as opposed to an exo activity.
PDB ID: 1QHODownload
MMDB ID: 13374
PDB Deposition Date: 1999/5/25
Updated in MMDB: 2012/10
Experimental Method:
x-ray diffraction
Resolution: 1.7  Å
Source Organism:
Similar Structures:
Biological Unit for 1QHO: monomeric; determined by author
Molecular Components in 1QHO
Label Count Molecule
Protein (1 molecule)
Molecule annotation
Chemicals (7 molecules)
* Click molecule labels to explore molecular sequence information.

Citing MMDB