4QEH: Room Temperature X-ray Structure Of D-xylose Isomerase In Complex With Two Mg2+ Ions And L-ribose

D-xylose isomerase (XI) is capable of sugar isomerization and slow conversion of some monosaccharides into their C2-epimers. We present X-ray and neutron crystallographic studies to locate H and D atoms during the respective isomerization and epimerization of L-arabinose to L-ribulose and L-ribose, respectively. Neutron structures in complex with cyclic and linear L-arabinose have demonstrated that the mechanism of ring-opening is the same as for the reaction with D-xylose. Structural evidence and QM/MM calculations show that in the reactive Michaelis complex L-arabinose is distorted to the high-energy (5)S1 conformation; this may explain the apparent high KM for this sugar. MD-FEP simulations indicate that amino acid substitutions in a hydrophobic pocket near C5 of L-arabinose can enhance sugar binding. L-ribulose and L-ribose were found in furanose forms when bound to XI. We propose that these complexes containing Ni(2+) cofactors are Michaelis-like and the isomerization between these two sugars proceeds via a cis-ene-diol mechanism.
PDB ID: 4QEHDownload
MMDB ID: 122918
PDB Deposition Date: 2014/5/16
Updated in MMDB: 2014/09
Experimental Method:
x-ray diffraction
Resolution: 1.55  Å
Source Organism:
Similar Structures:
Biological Unit for 4QEH: tetrameric; determined by author and by software (PISA)
Molecular Components in 4QEH
Label Count Molecule
Proteins (4 molecules)
Xylose Isomerase
Molecule annotation
Chemicals (12 molecules)
* Click molecule labels to explore molecular sequence information.

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