1QK5

TOXOPLASMA GONDII HYPOXANTHINE-GUANINE PHOSPHORIBOSYLTRANSFERASE WITH XMP, PYROPHOSPHATE AND TWO MG2+ IONS


Experimental Data Snapshot

  • Method: X-RAY DIFFRACTION
  • Resolution: 1.60 Å
  • R-Value Free: 0.261 
  • R-Value Work: 0.234 

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This is version 1.3 of the entry. See complete history


Literature

Crystal Structure of Toxoplasma Gondii Hypoxanthine-Guanine Phosphoribosyltransferase with Xmp, Pyrophosphate and Two Mg2+ Ions Bound: Insights Into the Catalytic Mechanism

Heroux, A.White, E.L.Ross, L.J.Davis, R.L.Borhani, D.W.

(1999) Biochemistry 38: 14495

  • DOI: 10.1021/bi990508i
  • Primary Citation of Related Structures:  
    1QK5

  • PubMed Abstract: 
  • The crystal structure of the Toxoplasma gondii hypoxanthine-guanine phosphoribosyltransferase (HGPRT)-xanthosine 5'-monophosphate (XMP)-pyrophosphate-Mg(2+) ternary complex has been determined at 1. 60 A resolution. This biproduct, post-transition st ...

    The crystal structure of the Toxoplasma gondii hypoxanthine-guanine phosphoribosyltransferase (HGPRT)-xanthosine 5'-monophosphate (XMP)-pyrophosphate-Mg(2+) ternary complex has been determined at 1. 60 A resolution. This biproduct, post-transition state structure is of a T. gondii HGPRT mutant (Asp150Ala or D150A). The D150A mutant has reduced activity (k(cat) lower by 11-, 296-, and 8.6-fold for hypoxanthine, guanine, and xanthine, respectively) compared to wild-type T. gondii HGPRT. The Michaelis constants for purine bases are altered only slightly, whereas those for alpha-D-5-phosphoribosyl 1-pyrophosphate (PRPP) are lower by approximately 6.5-fold. The ternary complex crystallizes in space group C222(1) (a = 55.21 A, b = 112.25 A, and c = 144.28 A) with two subunits in the asymmetric unit; the HGPRT tetramer is completed by the application of 2-fold crystallographic symmetry. All active sites contain XMP ¿bound in a fashion similar to that of the guanosine 5'-monophosphate (GMP) and inosine 5'-monophosphate (IMP) complexes reported in the preceding article [Héroux, A., et al. (1999) Biochemistry 38, 14485-14494]¿, pyrophosphate, and two Mg(2+) ions. Each Mg(2+) ion is octahedrally coordinated by two terminal pyrophosphate oxygen atoms and several ordered water molecules. This structure shows how HGPRT uses two Mg(2+) ions to orient and activate the pyrophosphate moiety of PRPP for attack by a purine base, and why mutation in humans of the residue corresponding to Asp206, the only HGPRT amino acid that directly contacts the Mg(2+) ions, causes Lesch-Nyhan syndrome (HGPRT(Kinston), D193N). The Leu78-Lys79 peptide bond in the active site adopts the cis configuration, which it must to bind PRPP or pyrophosphate. The contribution of cis-trans isomerization of this peptide bond to the energetics of substrate binding and product release is discussed. A comprehensive description of the HGPRT reaction mechanism is also proposed.


    Related Citations: 
    • Crystal Structures of the Toxoplasma Gondii Hypoxanthine-Guanine Phosphoribosyltransferase Gmp and Imp Complexes: Comparison of Purine Binding Interactions with the Xmp Complex
      Heroux, A., White, E.L., Ross, L.J., Borhani, D.W.
      (1999) Biochemistry 38: 14485
    • Isolation and Sequencing of a Cdna Encoding the Hypoxanthine-Guanine Phosphoribosyltransferase from Toxoplasma Gondii
      Vasanthakumar, G., Van Ginkel, S., Parish, G.
      (1994) Gene 147: 153

    Organizational Affiliation

    Drug Discovery Division, Southern Research Institute, Birmingham, Alabama 35205, USA.



Macromolecules
Find similar proteins by:  (by identity cutoff)  |  Structure
Entity ID: 1
MoleculeChainsSequence LengthOrganismDetailsImage
HYPOXANTHINE-GUANINE PHOSPHORIBOSYLTRANSFERASEAB233Toxoplasma gondii RHMutation(s): 1 
EC: 2.4.2.8 (PDB Primary Data), 2.4.2.22 (UniProt)
Find proteins for Q26997 (Toxoplasma gondii)
Explore Q26997 
Go to UniProtKB:  Q26997
Protein Feature View
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  • Reference Sequence
Experimental Data & Validation

Experimental Data

  • Method: X-RAY DIFFRACTION
  • Resolution: 1.60 Å
  • R-Value Free: 0.261 
  • R-Value Work: 0.234 
  • Space Group: C 2 2 21
Unit Cell:
Length ( Å )Angle ( ˚ )
a = 55.208α = 90
b = 112.255β = 90
c = 144.28γ = 90
Software Package:
Software NamePurpose
REFMACrefinement
MOSFLMdata reduction
SCALAdata scaling
AMoREphasing

Structure Validation

View Full Validation Report



Entry History 

Deposition Data

Revision History 

  • Version 1.0: 1999-10-17
    Type: Initial release
  • Version 1.1: 2011-05-08
    Changes: Version format compliance
  • Version 1.2: 2011-07-13
    Changes: Version format compliance
  • Version 1.3: 2019-03-06
    Changes: Data collection, Experimental preparation, Other