Crystal structures of oxime-bound fenamiphos-acetylcholinesterases: reactivation involving flipping of the His447 ring to form a reactive Glu334-His447-oxime triad.
Organophosphorus insecticides and nerve agents inhibit the vital enzyme acetylcholinesterase by covalently bonding to the catalytic serine residue of the enzyme. Oxime-based reactivators, such as [(E)-[1-[(4-carbamoylpyridin-1-ium-1-yl)methoxymethyl]pyridin-2-ylidene]methyl]-oxoazanium dichloride (HI-6) and 1,7-heptylene-bis-N,N'-2-pyridiniumaldoxime dichloride (Ortho-7), restore the organophosphate-inhibited enzymatic activity by cleaving the phosphorous conjugate. In this article, we report the intermolecular interactions between Mus musculus acetylcholinesterase inhibited by the insecticide fenamiphos (fep-mAChE) and HI-6 or Ortho-7 revealed by a combination of crystallography and kinetics. The crystal structures of the two oxime-bound fep-mAChE complexes show that both oximes interact with the peripheral anionic site involving different conformations of Trp286 and different peripheral-site residues (Tyr124 for HI-6 and Tyr72 for Ortho-7). Moreover, residues at catalytic site of the HI-6-bound fep-mAChE complex adopt conformations that are similar to those in the apo mAChE, whereas significant conformational changes are observed for the corresponding residues in the Ortho-7-bound fep-mAChE complex. Interestingly, flipping of the His447 imidazole ring allows the formation of a hydrogen bonding network among the Glu334-His447-Ortho-7 triad, which presumably deprotonates the Ortho-7 oxime hydroxyl group, increases the nucleophilicity of the oxime group, and leads to cleavage of the phosphorous conjugate. These results offer insights into a detailed reactivation mechanism for the oximes and development of improved reactivators.
Hörnberg
Andreas
A
Swedish Defence Research Agency, Division of CBRN Defence and Security, S-901 82 Umeå, Sweden.
Artursson
Elisabet
E
Wärme
Rikard
R
Pang
Yuan-Ping
YP
Ekström
Fredrik
F
D000110:Acetylcholinesterase / Q000737:chemistry* / Q000378:metabolism; D000818:Animals; D020134:Catalytic Domain / Q000502:physiology; D003460:Crystallization; D018360:Crystallography, X-Ray; D018698:Glutamic Acid / Q000737:chemistry* / Q000378:metabolism; D006639:Histidine / Q000737:chemistry* / Q000378:metabolism; D006801:Humans; D051379:Mice; D008956:Models, Chemical; D008958:Models, Molecular; D009943:Organophosphorus Compounds / Q000737:chemistry* / Q000378:metabolism; D010091:Oximes / Q000737:chemistry* / Q000378:metabolism; D011485:Protein Binding / Q000502:physiology
D009943:Organophosphorus Compounds; D010091:Oximes; D018698:Glutamic Acid; D006639:Histidine; D000110:Acetylcholinesterase; C002698:fenamiphos