1K9F image
Deposition Date 2001-10-29
Release Date 2002-10-29
Last Version Date 2023-08-16
Entry Detail
PDB ID:
1K9F
Keywords:
Title:
Crystal structure of a mutated family-67 alpha-D-glucuronidase (E285N) from Bacillus stearothermophilus T-6, complexed with aldotetraouronic acid
Biological Source:
Source Organism:
Host Organism:
Method Details:
Experimental Method:
Resolution:
1.75 Å
R-Value Free:
0.21
R-Value Work:
0.18
R-Value Observed:
0.18
Space Group:
P 41 21 2
Macromolecular Entities
Polymer Type:polypeptide(L)
Molecule:alpha-D-glucuronidase
Mutations:E285N
Chain IDs:A
Chain Length:679
Number of Molecules:1
Biological Source:Geobacillus stearothermophilus
Ligand Molecules
Primary Citation
Crystal Structures of Geobacillus stearothermophilus {alpha}-Glucuronidase Complexed with Its Substrate and Products: MECHANISTIC IMPLICATIONS.
J.Biol.Chem. 279 3014 3024 (2004)
PMID: 14573597 DOI: 10.1074/jbc.M310098200

Abstact

Alpha-glucuronidases cleave the alpha-1,2-glycosidic bond between 4-O-methyl-d-glucuronic acid and short xylooligomers as part of the hemicellulose degradation system. To date, all of the alpha-glucuronidases are classified as family 67 glycosidases, which catalyze the hydrolysis via the investing mechanism. Here we describe several high resolution crystal structures of the alpha-glucuronidase (AguA) from Geobacillus stearothermophilus, in complex with its substrate and products. In the complex of AguA with the intact substrate, the 4-O-methyl-d-glucuronic acid sugar ring is distorted into a half-chair conformation, which is closer to the planar conformation required for the oxocarbenium ion-like transition state structure. In the active site, a water molecule is coordinated between two carboxylic acids, in an appropriate position to act as a nucleophile. From the structural data it is likely that two carboxylic acids, Asp(364) and Glu(392), activate together the nucleophilic water molecule. The loop carrying the catalytic general acid Glu(285) cannot be resolved in some of the structures but could be visualized in its "open" and "closed" (catalytic) conformations in other structures. The protonated state of Glu(285) is presumably stabilized by its proximity to the negative charge of the substrate, representing a new variation of substrate-assisted catalysis mechanism.

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