4HHM: Crystal Structure Of A Mutant, G219a, Of Glucose Isomerase From Streptomyces Sp. Sk

Citation:
Abstract
The role of residue 219 in the physicochemical properties of D-glucose isomerase from Streptomyces sp. SK strain (SKGI) was investigated by site-directed mutagenesis and structural studies. Mutants G219A, G219N, and G219F were generated and characterized. Comparative studies of their physicochemical properties with those of the wild-type enzyme highlighted that mutant G219A displayed increased specific activity and thermal stability compared to that of the wild-type enzyme, while for G219N and G219F, these properties were considerably decreased. A double mutant, SKGI F53L/G219A, displayed a higher optimal temperature and a higher catalytic efficiency than both the G219A mutant and the wild-type enzyme and showed a half-life time of about 150 min at 85 degrees C as compared to 50 min for wild-type SKGI. Crystal structures of SKGI wild-type and G219A enzymes were solved to 1.73 and 2.15 A, respectively, and showed that the polypeptide chain folds into two structural domains. The larger domain consists of a (beta/alpha)8 unit, and the smaller domain forms a loop of alpha helices. Detailed analyses of the three-dimensional structures highlighted minor but important changes in the active site region as compared to that of the wild-type enzyme leading to a displacement of both metal ions, and in particular that in site M2. The structural analyses moreover revealed how the substitution of G219 by an alanine plays a crucial role in improving the thermostability of the mutant enzyme.
PDB ID: 4HHMDownload
MMDB ID: 108664
PDB Deposition Date: 2012/10/10
Updated in MMDB: 2013/11
Experimental Method:
x-ray diffraction
Resolution: 2.15  Å
Source Organism:
Similar Structures:
Biological Unit for 4HHM: tetrameric; determined by author and by software (PISA)
Molecular Components in 4HHM
Label Count Molecule
Proteins (4 molecules)
4
Xylose Isomerase
Molecule annotation
Chemicals (8 molecules)
1
4
2
4
* Click molecule labels to explore molecular sequence information.

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