Aged form of mouse acetylcholinesterase inhibited by tabun

Experimental Data Snapshot

  • Resolution: 2.50 Å
  • R-Value Free: 0.220 
  • R-Value Work: 0.182 
  • R-Value Observed: 0.183 

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Structural Changes of Phenylalanine 338 and Histidine 447 Revealed by the Crystal Structures of Tabun-Inhibited Murine Acetylcholinesterase.

Ekstrom, F.Akfur, C.Tunemalm, A.-K.Lundberg, S.

(2006) Biochemistry 45: 74

  • DOI: https://doi.org/10.1021/bi051286t
  • Primary Citation of Related Structures:  
    2C0P, 2C0Q

  • PubMed Abstract: 

    Organophosphorus compounds (OPs) interfere with the catalytic mechanism of acetylcholinesterase (AChE) by rapidly phosphorylating the catalytic serine residue. The inhibited enzyme can at least partly be reactivated with nucleophilic reactivators such as oximes. The covalently attached OP conjugate may undergo further intramolecular dealkylation or deamidation reactions, a process termed "aging" that results in an enzyme considered completely resistant to reactivation. Of particular interest is the inhibition and aging reaction of the OP compound tabun since tabun conjugates display an extraordinary resistance toward most reactivators of today. To investigate the structural basis for this resistance, we determined the crystal structures of Mus musculus AChE (mAChE) inhibited by tabun prior to and after the aging reaction. The nonaged tabun conjugate induces a structural change of the side chain of His447 that uncouples the catalytic triad and positions the imidazole ring of His447 in a conformation where it may form a hydrogen bond to a water molecule. Moreover, an unexpected displacement of the side chain of Phe338 narrows the active site gorge. In the crystal structure of the aged tabun conjugate, the side chains of His447 and Phe338 are reversed to the conformation found in the apo structure of mAChE. A hydrogen bond between the imidazole ring of His447 and the ethoxy oxygen of the aged tabun conjugate stabilizes the side chain of His447. The displacement of the side chain of Phe338 into the active site gorge of the nonaged tabun conjugate may interfere with the accessibility of reactivators and thereby contribute to the high resistance of tabun conjugates toward reactivation.

  • Organizational Affiliation

    Swedish Defense Research Agency, Division of NBC Defense, S-901 82 Umeå, Sweden. fredrik.ekstrom@foi.se

Find similar proteins by:  (by identity cutoff)  |  3D Structure
Entity ID: 1
MoleculeChains Sequence LengthOrganismDetailsImage
A, B
548Mus musculusMutation(s): 0 
UniProt & NIH Common Fund Data Resources
Find proteins for P21836 (Mus musculus)
Explore P21836 
Go to UniProtKB:  P21836
IMPC:  MGI:87876
Entity Groups  
Sequence Clusters30% Identity50% Identity70% Identity90% Identity95% Identity100% Identity
UniProt GroupP21836
Sequence Annotations
  • Reference Sequence
Small Molecules
Experimental Data & Validation

Experimental Data

  • Resolution: 2.50 Å
  • R-Value Free: 0.220 
  • R-Value Work: 0.182 
  • R-Value Observed: 0.183 
  • Space Group: P 21 21 21
Unit Cell:
Length ( Å )Angle ( ˚ )
a = 79.02α = 90
b = 110.88β = 90
c = 226.38γ = 90
Software Package:
Software NamePurpose
XDSdata reduction
SCALAdata scaling

Structure Validation

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Entry History 

Deposition Data

Revision History  (Full details and data files)

  • Version 1.0: 2006-01-09
    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: 2018-01-17
    Changes: Data collection
  • Version 1.4: 2021-05-12
    Changes: Derived calculations, Other
  • Version 1.5: 2023-12-13
    Changes: Data collection, Database references, Refinement description