3DRC

INVESTIGATION OF THE FUNCTIONAL ROLE OF TRYPTOPHAN-22 IN ESCHERICHIA COLI DIHYDROFOLATE REDUCTASE BY SITE-DIRECTED MUTAGENESIS


Experimental Data Snapshot

  • Method: X-RAY DIFFRACTION
  • Resolution: 1.90 Å
  • R-Value Observed: 0.156 

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This is version 1.4 of the entry. See complete history


Literature

Investigation of the functional role of tryptophan-22 in Escherichia coli dihydrofolate reductase by site-directed mutagenesis.

Warren, M.S.Brown, K.A.Farnum, M.F.Howell, E.E.Kraut, J.

(1991) Biochemistry 30: 11092-11103

  • DOI: https://doi.org/10.1021/bi00110a011
  • Primary Citation of Related Structures:  
    2DRC, 3DRC

  • PubMed Abstract: 

    We have applied site-directed mutagenesis methods to change the conserved tryptophan-22 in the substrate binding site of Escherichia coli dihydrofolate reductase to phenylalanine (W22F) and histidine (W22H). The crystal structure of the W22F mutant in a binary complex with the inhibitor methotrexate has been refined at 1.9-A resolution. The W22F difference Fourier map and least-squares refinement show that structural effects of the mutation are confined to the immediate vicinity of position 22 and include an unanticipated 0.4-A movement of the methionine-20 side chain. A conserved bound water-403, suspected to play a role in the protonation of substrate DHF, has not been displaced by the mutation despite the loss of a hydrogen bond with tryptophan-22. Steady-state kinetics, stopped-flow kinetics, and primary isotope effects indicate that both mutations increase the rate of product tetrahydrofolate release, the rate-limiting step in the case of the wild-type enzyme, while slowing the rate of hydride transfer to the point where it now becomes at least partially rate determining. Steady-state kinetics show that below pH 6.8, kcat is elevated by up to 5-fold in the W22F mutant as compared with the wild-type enzyme, although kcat/Km(dihydrofolate) is lower throughout the observed pH range. For the W22H mutant, both kcat and kcat/Km(dihydrofolate) are substantially lower than the corresponding wild-type values. While both mutations weaken dihydrofolate binding, cofactor NADPH binding is not significantly altered. Fitting of the kinetic pH profiles to a general protonation scheme suggests that the proton affinity of dihydrofolate may be enhanced upon binding to the enzyme. We suggest that the function of tryptophan-22 may be to properly position the side chain of methionine-20 with respect to N5 of the substrate dihydrofolate.


  • Organizational Affiliation

    Department of Chemistry, University of California, San Diego, La Jolla 92093.


Macromolecules
Find similar proteins by:  (by identity cutoff)  |  3D Structure
Entity ID: 1
MoleculeChains Sequence LengthOrganismDetailsImage
DIHYDROFOLATE REDUCTASE
A, B
159Escherichia coliMutation(s): 0 
EC: 1.5.1.3
UniProt
Find proteins for P0ABQ4 (Escherichia coli (strain K12))
Explore P0ABQ4 
Go to UniProtKB:  P0ABQ4
Entity Groups  
Sequence Clusters30% Identity50% Identity70% Identity90% Identity95% Identity100% Identity
UniProt GroupP0ABQ4
Sequence Annotations
Expand
  • Reference Sequence
Small Molecules
Binding Affinity Annotations 
IDSourceBinding Affinity
MTX Binding MOAD:  3DRC Kd: 0.7 (nM) from 1 assay(s)
BindingDB:  3DRC IC50: min: 3, max: 8.8 (nM) from 3 assay(s)
EC50: 1 (nM) from 1 assay(s)
Experimental Data & Validation

Experimental Data

  • Method: X-RAY DIFFRACTION
  • Resolution: 1.90 Å
  • R-Value Observed: 0.156 
  • Space Group: P 61
Unit Cell:
Length ( Å )Angle ( ˚ )
a = 93.12α = 90
b = 93.12β = 90
c = 73.87γ = 120
Software Package:
Software NamePurpose
TNTrefinement

Structure Validation

View Full Validation Report



Entry History 

Deposition Data

Revision History  (Full details and data files)

  • Version 1.0: 1994-01-31
    Type: Initial release
  • Version 1.1: 2008-03-03
    Changes: Version format compliance
  • Version 1.2: 2011-07-13
    Changes: Version format compliance
  • Version 1.3: 2017-11-29
    Changes: Derived calculations, Other
  • Version 1.4: 2024-02-21
    Changes: Data collection, Database references, Derived calculations