Crystal Structure of Ketosteroid Isomerase Y16S/D40N from Pseudomonas putida with Bound Equilenin

Experimental Data Snapshot

  • Resolution: 1.63 Å
  • R-Value Free: 0.245 
  • R-Value Work: 0.207 
  • R-Value Observed: 0.209 

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Dissecting the paradoxical effects of hydrogen bond mutations in the ketosteroid isomerase oxyanion hole.

Kraut, D.A.Sigala, P.A.Fenn, T.D.Herschlag, D.

(2010) Proc Natl Acad Sci U S A 107: 1960-1965

  • DOI: https://doi.org/10.1073/pnas.0911168107
  • Primary Citation of Related Structures:  

  • PubMed Abstract: 

    The catalytic importance of enzyme active-site interactions is frequently assessed by mutating specific residues and measuring the resulting rate reductions. This approach has been used in bacterial ketosteroid isomerase to probe the energetic importance of active-site hydrogen bonds donated to the dienolate reaction intermediate. The conservative Tyr16Phe mutation impairs catalysis by 10(5)-fold, far larger than the effects of hydrogen bond mutations in other enzymes. However, the less-conservative Tyr16Ser mutation, which also perturbs the Tyr16 hydrogen bond, results in a less-severe 10(2)-fold rate reduction. To understand the paradoxical effects of these mutations and clarify the energetic importance of the Tyr16 hydrogen bond, we have determined the 1.6-A resolution x-ray structure of the intermediate analogue, equilenin, bound to the Tyr16Ser mutant and measured the rate effects of mutating Tyr16 to Ser, Thr, Ala, and Gly. The nearly identical 200-fold rate reductions of these mutations, together with the 6.4-A distance observed between the Ser16 hydroxyl and equilenin oxygens in the x-ray structure, strongly suggest that the more moderate rate effect of this mutant is not due to maintenance of a hydrogen bond from Ser at position 16. These results, additional spectroscopic observations, and prior structural studies suggest that the Tyr16Phe mutation results in unfavorable interactions with the dienolate intermediate beyond loss of a hydrogen bond, thereby exaggerating the apparent energetic benefit of the Tyr16 hydrogen bond relative to the solution reaction. These results underscore the complex energetics of hydrogen bonding interactions and site-directed mutagenesis experiments.

  • Organizational Affiliation

    Department of Biochemistry, Stanford University, Stanford, CA 94305, USA.

Find similar proteins by:  (by identity cutoff)  |  3D Structure
Entity ID: 1
MoleculeChains Sequence LengthOrganismDetailsImage
Steroid Delta-isomerase
A, B, C, D
131Pseudomonas putidaMutation(s): 2 
Gene Names: ksi
Find proteins for P07445 (Pseudomonas putida)
Explore P07445 
Go to UniProtKB:  P07445
Entity Groups  
Sequence Clusters30% Identity50% Identity70% Identity90% Identity95% Identity100% Identity
UniProt GroupP07445
Sequence Annotations
  • Reference Sequence
Experimental Data & Validation

Experimental Data

  • Resolution: 1.63 Å
  • R-Value Free: 0.245 
  • R-Value Work: 0.207 
  • R-Value Observed: 0.209 
  • Space Group: P 1 21 1
Unit Cell:
Length ( Å )Angle ( ˚ )
a = 50.694α = 90
b = 72.401β = 91.16
c = 81.328γ = 90
Software Package:
Software NamePurpose
PDB_EXTRACTdata extraction
HKL-2000data collection
DENZOdata reduction
SCALEPACKdata scaling

Structure Validation

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Ligand Structure Quality Assessment 

Entry History 

Deposition Data

Revision History  (Full details and data files)

  • Version 1.0: 2010-01-12
    Type: Initial release
  • Version 1.1: 2011-07-13
    Changes: Version format compliance
  • Version 1.2: 2021-10-13
    Changes: Database references, Derived calculations
  • Version 1.3: 2023-09-06
    Changes: Data collection, Refinement description