1UJ6: Crystal Structure Of Thermus Thermophilus Ribose-5-Phosphate Isomerase Complexed With Arabinose-5-Phosphate

Ribose-5-phosphate isomerase (Rpi) acts as a key enzyme in the oxidative and reductive pentose-phosphate pathways for the conversion of ribose-5-phosphate (R5P) to ribulose-5-phosphate and vice versa. We have determined the crystal structures of Rpi from Thermus thermophilus HB8 in complex with the open chain form of the substrate R5P and the open chain form of the C2 epimeric inhibitor arabinose-5-phosphate as well as the apo form at high resolution. The crystal structures of both complexes revealed that these ring-opened epimers are bound in the active site in a mirror symmetry binding mode. The O1 atoms are stabilized by an oxyanion hole composed of the backbone amide nitrogens in the conserved motif. In the structure of the Rpi.R5P complex, the conversion moiety O1-C1-C2-O2 in cis-configuration interacts with the carboxyl oxygens of Glu-108 in a water-excluded environment. Furthermore, the C2 hydroxyl group is presumed to be highly polarized by short hydrogen bonding with the side chain of Lys-99. R5P bound as the ring-opened reaction intermediate clarified the high stereoselectivity of the catalysis and is consistent with an aldose-ketose conversion by Rpi that proceeds via a cis-enediolate intermediate.
PDB ID: 1UJ6Download
MMDB ID: 28768
PDB Deposition Date: 2003/7/26
Updated in MMDB: 2007/10
Experimental Method:
x-ray diffraction
Resolution: 1.74  Å
Source Organism:
Similar Structures:
Biological Unit for 1UJ6: monomeric; determined by author
Molecular Components in 1UJ6
Label Count Molecule
Protein (1 molecule)
Ribose 5-phosphate Isomerase
Molecule annotation
Chemicals (3 molecules)
* Click molecule labels to explore molecular sequence information.

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