1R38

Crystal structure of H114A mutant of Candida tenuis xylose reductase


Experimental Data Snapshot

  • Method: X-RAY DIFFRACTION
  • Resolution: 2.2 Å
  • R-Value Free: 0.226 
  • R-Value Work: 0.185 

wwPDB Validation 3D Report Full Report


This is version 1.2 of the entry. See complete history

Literature

Studies of the enzymic mechanism of Candida tenuis xylose reductase (AKR 2B5): X-ray structure and catalytic reaction profile for the H113A mutant

Kratzer, R.Kavanagh, K.L.Wilson, D.K.Nidetzky, B.

(2004) Biochemistry 43: 4944-4954

  • DOI: 10.1021/bi035833r

  • PubMed Abstract: 
  • Xylose reductase from the yeast Candida tenuis (CtXR) is a family 2 member of the aldo-keto reductase (AKR) superfamily of proteins and enzymes. Active site His-113 is conserved among AKRs, but a unified mechanism of how it affects catalytic activity ...

    Xylose reductase from the yeast Candida tenuis (CtXR) is a family 2 member of the aldo-keto reductase (AKR) superfamily of proteins and enzymes. Active site His-113 is conserved among AKRs, but a unified mechanism of how it affects catalytic activity is outstanding. We have replaced His-113 by alanine using site-directed mutagenesis, determined a 2.2 A structure of H113A mutant bound to NADP(+), and compared catalytic reaction profiles of NADH-dependent reduction of different aldehydes catalyzed by the wild type and the mutant. Deuterium kinetic isotope effects (KIEs) on k(cat) and k(cat)/K(m xylose) show that, relative to the wild type, the hydride transfer rate constant (k(7) approximately 0.16 s(-1)) has decreased about 1000-fold in H113A whereas xylose binding was not strongly affected. No solvent isotope effect was seen on k(cat) and k(cat)/K(m xylose) for H113A, suggesting that proton transfer has not become rate-limiting as a result of the mutation. The pH profiles of log(k(cat)/K(m xylose)) for the wild type and H113A decreased above apparent pK(a) values of 8.85 and 7.63, respectively. The DeltapK(a) of -1.2 pH units likely reflects a proximally disruptive character of the mutation, affecting the position of Asp-50. A steady-state kinetic analysis for H113A-catalyzed reduction of a homologous series of meta-substituted benzaldehyde derivatives was carried out, and quantitative structure-reactivity correlations were used to factor the observed kinetic substituent effect on k(cat) and k(cat)/K(m aldehyde) into an electronic effect and bonding effects (which are lacking in the wild type). Using the Hammett sigma scale, electronic parameter coefficients (rho) of +0.64 (k(cat)) and +0.78 (k(cat)/K(m aldehyde)) were calculated and clearly differ from rho(k(cat)/K(aldehyde)) and rho(k(cat)) values of +1.67 and approximately 0.0, respectively, for the wild-type enzyme. Hydride transfer rate constants of H113A, calculated from kinetic parameters and KIE data, display a substituent dependence not seen in the corresponding wild-type enzyme rate constants. An enzymic mechanism is proposed in which His-113, through a hydrogen bond from Nepsilon2 to aldehyde O1, assists in catalysis by optimizing the C=O bond charge separation and orbital alignment in the ternary complex.


    Organizational Affiliation

    Institute of Biotechnology, Graz University of Technology, Petersgasse 12/I, A-8010 Graz, Austria.




Macromolecules

Find similar proteins by: Sequence  |  Structure

Entity ID: 1
MoleculeChainsSequence LengthOrganismDetails
xylose reductase
A, B, C, D
322Candida tenuisMutation(s): 1 
Gene Names: XYL1 (XYLR)
EC: 1.1.1.307
Find proteins for O74237 (Candida tenuis)
Go to UniProtKB:  O74237
Small Molecules
Ligands 1 Unique
IDChainsName / Formula / InChI Key2D Diagram3D Interactions
NAP
Query on NAP

Download SDF File 
Download CCD File 
A, B, C, D
NADP NICOTINAMIDE-ADENINE-DINUCLEOTIDE PHOSPHATE
2'-MONOPHOSPHOADENOSINE 5'-DIPHOSPHORIBOSE
C21 H28 N7 O17 P3
XJLXINKUBYWONI-NNYOXOHSSA-N
 Ligand Interaction
Experimental Data & Validation

Experimental Data

  • Method: X-RAY DIFFRACTION
  • Resolution: 2.2 Å
  • R-Value Free: 0.226 
  • R-Value Work: 0.185 
  • Space Group: C 1 2 1
Unit Cell:
Length (Å)Angle (°)
a = 179.980α = 90.00
b = 129.089β = 90.82
c = 79.872γ = 90.00
Software Package:
Software NamePurpose
CNSrefinement
DENZOdata reduction
SCALEPACKdata scaling
EPMRphasing

Structure Validation

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Entry History 

Deposition Data

Revision History 

  • Version 1.0: 2004-10-12
    Type: Initial release
  • Version 1.1: 2008-04-29
    Type: Version format compliance
  • Version 1.2: 2011-07-13
    Type: Version format compliance