engleski

Enhancement in oxime-assisted reactivation of tabun-inhibited AChE achieved by a mutation of the peripheral site

We studied the reactivation of nerve agent tabun-inhibited mouse acetylcholinesterase (AChE) site-directed mutants to see whether any of the active site differences will enhance oxime-assisted reactivation compared to the wild-type enzyme (w.t. AChE). Residues at the AChE choline binding site (Tyr337, Tyr338), the acyl pocket (Phe295) and the peripheral site (Tyr124, Trp286) were replaced with the ones found at the equivalent position in butyrylcholinesterase (BChE) active site gorge. The active site catalytic triad (Ser-His-Glu) was intact. The reactivation of tabun-inhibited AChE site-directed mutants was studied by two bispyridinium oximes K203 (N-[4-(4-hydroxyiminomethylpyridinio)-(E)-but-2-enyl]-4-carbamoylpyridinium dibromide) and K117 ((N, N´-3-oxapentano)bis(4-hydroxy iminomethylpyridinium bromide)). These oximes have been confirmed previously as efficient reactivators of tabun-inhibited AChE or BChE, respectively.1, 2 Among three single mutants (Tyr337Ala, TyrY124Gln, Trp286Ala) and two double mutants (Phe295Leu/Tyr337Ala, Tyr337Ala/PheF338Ala) tested for oxime-assisted reactivation, improvement in reactivation compared to the w.t. AChE was observed only for Trp286Ala. This effect was more pronounced for K203 than for K117. K203 maximum first order reactivation rate constant, kmax, was for Trp286Ala two times higher than kmax determined for the w.t. AChE (0.31 min-1 compared to the 0.14 min-1, respectively) even if the mutation lowered the affinity of the AChE for K203. As shown by the results obtained using the molecular docking technique, it seems that such reactivation improvement can be explained by disruption of the π-π sandwich formed between one of the oxime pyridinium rings and the amino acids of the peripheral site (Y124, W286). In this way, the oxime gets into the more favourable position for nucleophilic attack on the phosphylated catalytic serine. Further more, Trp286Ala has similar tabun inhibition rate as the w.t. AChE which means that this mutant will be able to bind tabun in in vivo condition as fast as synaptic AChE. Based on this results Trp286Ala may lead to development of catalytic scavenger for detoxification or decontamination of tabun. 1. Kovarik Z, Lucić Vrdoljak A, Berend S, Čalić M, Kuča K, Musilek K, Radić B (2009) Evaluation of oxime K203 as antidote in tabun poisoning. Arh. Hig. Rada Toksikol. 60, 19-26. 2. Kovarik Z, Katalinić M, Šinko G, Binder J, Holas O, Jung Y-S, Musilova L, Jun D, Kuča K (2010) Pseudo-catalytic scavenging: searching for a suitable reactivator of phosphorylated butyrylcholinesterase. Chem.-Biol. Interact. 187, 167-171.

AChE; tabun; reactivation; oximes; mutants

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