1CFJ: Methylphosphonylated Acetylcholinesterase (Aged) Obtained By Reaction With O-Isopropylmethylphosphonofluoridate (Gb, Sarin)

Citation:
Abstract
Organophosphorus acid anhydride (OP) nerve agents are potent inhibitors which rapidly phosphonylate acetylcholinesterase (AChE) and then may undergo an internal dealkylation reaction (called "aging") to produce an OP-enzyme conjugate that cannot be reactivated. To understand the basis for irreversible inhibition, we solved the structures of aged conjugates obtained by reaction of Torpedo californica AChE (TcAChE) with diisopropylphosphorofluoridate (DFP), O-isopropylmethylphosponofluoridate (sarin), or O-pinacolylmethylphosphonofluoridate (soman) by X-ray crystallography to 2.3, 2.6, or 2.2 A resolution, respectively. The highest positive difference density peak corresponded to the OP phosphorus and was located within covalent bonding distance of the active-site serine (S200) in each structure. The OP-oxygen atoms were within hydrogen-bonding distance of four potential donors from catalytic subsites of the enzyme, suggesting that electrostatic forces significantly stabilize the aged enzyme. The active sites of aged sarin- and soman-TcAChE were essentially identical and provided structural models for the negatively charged, tetrahedral intermediate that occurs during deacylation with the natural substrate, acetylcholine. Phosphorylation with DFP caused an unexpected movement in the main chain of a loop that includes residues F288 and F290 of the TcAChE acyl pocket. This is the first major conformational change reported in the active site of any AChE-ligand complex, and it offers a structural explanation for the substrate selectivity of AChE.
PDB ID: 1CFJDownload
MMDB ID: 10683
PDB Deposition Date: 1999/3/19
Updated in MMDB: 2007/10
Experimental Method:
x-ray diffraction
Resolution: 2.6  Å
Source Organism:
Similar Structures:
Biological Unit for 1CFJ: monomeric; determined by author
Molecular Components in 1CFJ
Label Count Molecule
Protein (1 molecule)
1
Protein (Acetylcholinesterase)
Molecule annotation
Chemicals (3 molecules)
1
1
2
1
3
1
* Click molecule labels to explore molecular sequence information.

Citing MMDB
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