engleski

Oxime-assisted reactivation of tabun-phosphorylated acetylcholinesterase mutants

In the cholinergic system, acetylcholinesterase (AChE) is the primary target of nerve agent tabun. We investigated the reactivation of tabun-inhibited AChE and its site-directed mutants assisted by two bispyridinium oximes, K048 [1-(4-hydroxyiminomethylpyridinium)-4-(4-carbamoylpyridinium) butane dibromide] and K033 [1, 4-bis(2-hydroxyiminomethylpyridinium) butane dibromide]. AChE was modified within the acyl (Phe295Leu) and choline (Tyr337Ala) binding site of the active site gorge by replacing the aromatic amino acid residues with the aliphatic ones. K048, having para-positioned oxime group on the pyridinium ring, showed a high potency for the reactivation of tabun-inhibited w.t. AChE, because relatively low concentrations of oxime were able to completely reactivate AChE within 30– 60 min. On the other hand, reactivation of tabun-inhibited w.t. AChE by K033, having ortho-positioned oxime group on the pyridinium ring, was slow reaching only 50% after 24 h. Introduced mutations, Phe295Leu and Tyr337Ala, significantly lowered the reactivation efficacy of K048 but slightly enhanced the potency of K033 to reactivate tabun-inhibited AChE. The reason may be that the replacement of aromatic residues at the acyl and choline binding site interfered with the stabilization of the oxime’ s pyridinium ring(s) within the active site gorge in order to obtain the proper orientation of the oxime group forward to the phosphorylated active site serine. Although site-directed mutants of AChE are a powerful tool for investigating the role of some residues in reactivation, mutant that displays significant improvement in reactivation compared to the w.t. enzyme could be used as a pseudo catalytic scavenger of tabun in detoxification or decontamination.

acetylcholinesterase; mutants; reactivation; oximes; tabun; K048; K033

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