1J79

Molecular Structure of Dihydroorotase: A Paradigm for Catalysis Through the Use of a Binuclear Metal Center


Experimental Data Snapshot

  • Method: X-RAY DIFFRACTION
  • Resolution: 1.70 Å
  • R-Value Free: 0.258 
  • R-Value Work: 0.191 
  • R-Value Observed: 0.193 

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Literature

Molecular structure of dihydroorotase: a paradigm for catalysis through the use of a binuclear metal center.

Thoden, J.B.Phillips Jr., G.N.Neal, T.M.Raushel, F.M.Holden, H.M.

(2001) Biochemistry 40: 6989-6997

  • DOI: 10.1021/bi010682i
  • Primary Citation of Related Structures:  
    1J79

  • PubMed Abstract: 
  • Dihydroorotase plays a key role in pyrimidine biosynthesis by catalyzing the reversible interconversion of carbamoyl aspartate to dihydroorotate. Here we describe the three-dimensional structure of dihydroorotase from Escherichia coli determined and refined to 1 ...

    Dihydroorotase plays a key role in pyrimidine biosynthesis by catalyzing the reversible interconversion of carbamoyl aspartate to dihydroorotate. Here we describe the three-dimensional structure of dihydroorotase from Escherichia coli determined and refined to 1.7 A resolution. Each subunit of the homodimeric enzyme folds into a "TIM" barrel motif with eight strands of parallel beta-sheet flanked on the outer surface by alpha-helices. Unexpectedly, each subunit contains a binuclear zinc center with the metal ions separated by approximately 3.6 A. Lys 102, which is carboxylated, serves as a bridging ligand between the two cations. The more buried or alpha-metal ion in subunit I is surrounded by His 16, His 18, Lys 102, Asp 250, and a solvent molecule (most likely a hydroxide ion) in a trigonal bipyramidal arrangement. The beta-metal ion, which is closer to the solvent, is tetrahedrally ligated by Lys 102, His 139, His 177, and the bridging hydroxide. L-Dihydroorotate is observed bound to subunit I, with its carbonyl oxygen, O4, lying 2.9 A from the beta-metal ion. Important interactions for positioning dihydroorotate into the active site include a salt bridge with the guanidinium group of Arg 20 and various additional electrostatic interactions with both protein backbone and side chain atoms. Strikingly, in subunit II, carbamoyl L-aspartate is observed binding near the binuclear metal center with its carboxylate side chain ligating the two metals and thus displacing the bridging hydroxide ion. From the three-dimensional structures of the enzyme-bound substrate and product, it has been possible to propose a unique catalytic mechanism for dihydroorotase. In the direction of dihydroorotate hydrolysis, the bridging hydroxide attacks the re-face of dihydroorotate with general base assistance by Asp 250. The carbonyl group is polarized for nucleophilic attack by the bridging hydroxide through a direct interaction with the beta-metal ion. During the cyclization of carbamoyl aspartate, Asp 250 initiates the reaction by abstracting a proton from N3 of the substrate. The side chain carboxylate of carbamoyl aspartate is polarized through a direct electrostatic interaction with the binuclear metal center. The ensuing tetrahedral intermediate collapses with C-O bond cleavage and expulsion of the hydroxide which then bridges the binuclear metal center.


    Organizational Affiliation

    Department of Biochemistry, University of Wisconsin, Madison, Wisconsin 53706, USA.



Macromolecules
Find similar proteins by:  (by identity cutoff)  |  3D Structure
Entity ID: 1
MoleculeChainsSequence LengthOrganismDetailsImage
dihydroorotaseA, B347Escherichia coliMutation(s): 1 
Gene Names: pyrC
EC: 3.5.2.3
UniProt
Find proteins for P05020 (Escherichia coli (strain K12))
Explore P05020 
Go to UniProtKB:  P05020
Protein Feature View
Expand
  • Reference Sequence
Small Molecules
Modified Residues  1 Unique
IDChainsTypeFormula2D DiagramParent
KCX
Query on KCX
A, BL-PEPTIDE LINKINGC7 H14 N2 O4LYS
Experimental Data & Validation

Experimental Data

  • Method: X-RAY DIFFRACTION
  • Resolution: 1.70 Å
  • R-Value Free: 0.258 
  • R-Value Work: 0.191 
  • R-Value Observed: 0.193 
  • Space Group: P 21 21 21
Unit Cell:
Length ( Å )Angle ( ˚ )
a = 51.6α = 90
b = 78.8β = 90
c = 180.3γ = 90
Software Package:
Software NamePurpose
SOLVEphasing
TNTrefinement
d*TREKdata reduction
HKL-2000data scaling

Structure Validation

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Entry History 

Deposition Data

Revision History  (Full details and data files)

  • Version 1.0: 2001-06-20
    Type: Initial release
  • Version 1.1: 2008-04-27
    Changes: Version format compliance
  • Version 1.2: 2011-07-13
    Changes: Version format compliance