engleski

Oxime assisted reactivation of tabun-inhibited mouse AChE and its mutants

We investigated the reactivation of tabun-inhibited mouse acetylcholinesterase (w.t. AChE) and its mutants assisted by bispyridinium monooxime, K048 [1-(4-hydroxyiminomethylpyridinium)-4-(4-carbamoylpyridinium) butane dibromide]. Residues at the choline binding site (Tyr337) and the acyl pocket (Phe295, Phe297) of the active site gorge 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. K048 is the oxime whose high reactivation potency was recently determined for the tabun-inhibited human erythrocyte AChE [1]. The reactivation of w.t. AChE was as fast as that of human AChE, with the overall reactivation rate constant of 632 M-1min-1, reaching 100% with 1 mM of the oxime within 30 min. Tyr337Ala, as a single-mutant, had 10 times slower reactivation rate constant than the w.t. AChE, and the maximum of 80% of reactivation was observed. The reactivation of double mutants, Phe295Leu/Tyr337Ala and Phe297Ile/Tyr337Ala, was even slower and reached only 40% with the overall rate constants of 27 M-1min-1 and 2.3 M-1min-1, respectively. As our results show, the replacement of the choline binding site residue Tyr337 with the Ala could be responsible for the loss of the stabilization of one of the K048 pyridinium rings during reactivation. In addition, the replacement of the acyl pocket aromatic residues Phe295 or Phe297 made the AChE active site gorge even wider, which completely disturbed stabilization of the K048 within the active site gorge as well as the appropriate orientation of the oxime group forward to a phosphorylated moiety bound to the active site serin. Since AChE mutants mimicked BChE, it is to be expected that K048 assisted reactivation of w.t. BChE would follow the same slow-rate pattern. [1] Čalić, M. et al (2006) Toxicology 219, 85-96.

oxime; acetylcholinesterase; AChE; AChE mutants; tabun; reactivation

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