Steve Ealick's Research Group

Klebsiella pneumoniae HpxQ

PDB files:

3O7H (P1 – unliganded)

3O7I (P41 – unliganded)

3O7J (C2 – allantoin complex)

3O7K (C2 – allopurinol soak).


The stereospecific oxidative degradation of uric acid to (S)-allantoin was recently shown to proceed via three enzymatic steps. Klebsiella pneumoniae 2-oxo-4-hydroxy-4-carboxy-5-ureidoimidazoline decarboxylase catalyzes the final conversion, which is the decarboxylation of the unstable intermediate 2-oxo-4-hydroxy-4-carboxy-5-ureidoimidazoline (OHCU). KpOHCU decarboxylase is an all α-helical protein that belongs to the newly discovered 2-oxo-4-hydroxy-4-carboxy-5-ureidoimidazoline (OHCU) decarboxylase fold (as classified by the protein family database PFAM). 

KpOHCU decarboxylase consists of nine helices in two domains, with the N-terminal domain containing the first four helices and the C-terminus of helix nine.

Click the image to enlarge.

KpOHCU decarboxylase contains one active site per monomer and all of the contacts with the ligand are made by a single monomer.  The active site is formed primarily by the loops connecting helices 5 and 6 and helices 7 and 8.  Upon binding, KpOHCU decarboxylase forms a significant number of hydrogen bonds to the ligand.
Click the image to enlarge.


French JB and Ealick SE. Structural and Mechanistic Studies on Klebsiella pneumoniae 2-Oxo-4-hydroxy-4-carboxy-5-ureidoimidazoline Decarboxylase. J. Biol. Chem. 285:35446-35454 (2010).

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