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The Effect of Organophosphate (OP)‐Induced Structural Changes in Acetylcholinesterase on Kinetics of OP Inhibition and Oxime Reactivation
Author(s) -
Yu Wanlu,
Kovalevsky Andrey,
Blumenthal Donald K.,
Cheng Xiaolin,
Gerlits Oksana,
Fajer Mikolai,
Ho KwokYiu,
Taylor Palmer,
Radic Zoran
Publication year - 2018
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.2018.32.1_supplement.526.40
Subject(s) - acetylcholinesterase , oxime , chemistry , paraoxon , organophosphate , nerve agent , nucleophile , stereochemistry , sarin , kinetics , enzyme , pharmacology , biochemistry , pesticide , biology , physics , quantum mechanics , agronomy , catalysis
Organophosphate (OP) pesticides and nerve warfare agents covalently inhibit human acetylcholinesterase (hAChE) compromising cholinergic neurotransmission that can lead to fatal outcome. Effective therapy of OP intoxication requires that both, excess OP is removed from circulation and that activity of OP inhibited tissue hAChE is recovered. For both reactions nucleophilic oxime reactivation can play an essential role. For oxime assisted OP bioscavenging it is also important that the rate of inhibition of bioscavenger AChE is not compromised. Recently determined structures of diethylphosphorylated hAChE (POX‐hAChE) formed by paraoxon (POX) inhibition, both our unpublished and PDB released (5HF5 and 5HF8) show significant structural changes of the acyl pocket, immediately close to the active Ser203 when compared to the non‐inhibited enzyme. Those are likely to compromise nucleophilic oxime attack and rate of reactivation, but could also influence rate of hAChE inhibition by POX. Inhibition of AChE by dimethylphosphate analogue of POX (dmPOX) does not lead to conformational changes in the conjugated AChE (dmPOX‐AChE). In order to investigate effect of conformational changes in POX‐hAChE on rates of POX inhibition and oxime reactivation we studied dependence of rates of those reactions on reaction temperatures compared to dmPOX reactions. No difference was observed in temperature dependences of inhibition by diethyl‐ and dimethylphosphates. However, we observed strong temperature dependence of the oxime 2PAM reactivation, where reactivation of POX‐hAChE at 37 °C appeared an order of magnitude faster than the reaction at 22 °C. Reactivation of dimethylphosphorylated hAChE (dmPOX‐hAChE), as well as both dimetyhyl‐ and diethyl‐ phosphorylated Y337A/F338A hAChE mutant by 2PAM was significantly less temperature dependent, consistent with the absence of compromising conformational changes in dmPOX‐hAChE and in the mutant. This result indicates that formation of distorted acyl pocket loop in POX‐hAChE is not limiting for inhibition reaction but affects rates of oxime reactivation. Ability of POX‐hAChE to change acyl pocket loop conformation at the higher temperature allows for faster oxime reactivation and emphasizes the importance of conformational flexibility of hAChE for the efficient oxime reactivation. Support or Funding Information This work was supported by the CounterACT Program, National Institutes of Health Office of the Director, Grant 1U01NS083451 from NINDS. This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .