engleski

Interactions of AChE site-directed mutants with nerve agent tabun

We studied the inhibition of mouse acetylcholinesterase site-directed mutants by nerve agent tabun to see whether the active site differences influence the rate of inhibition compared to the wild-type enzyme (w.t. AChE). Residues at the AChE choline binding site (Tyr337), the acyl pocket (Phe295, Phe297) and the peripheral binding site (Tyr72, 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. Our results are showing that mutation at the choline binding site Tyr337Ala or peripheral site Tyr72Asp/ Tyr124Gln/Trp286Arg and single Tyr124Gln decrease tabun inhibition rate by 20 %-40 % compared to the w.t. AChE (7.7x106 min-1M-1). For two mutations including the acyl pocket we have observed an inverse effect: Phe297Ile/Tyr337Ala mutations significantly decreased (80 %) tabun inhibition rate, the Phe295Leu/Tyr337Ala slightly increased the inhibition rate (5 %). Moreover, the spontaneous reactivation of tabun-inhibited AChE mutant was observed for Phe295Leu/Tyr337Ala (50 % in 14 h, ks= 0.002 min-1). Such results imply importance of Phe295Leu residues in interaction with tabun. Therefore, we also tested the reactivation of tabun-inhibited Phe295Leu/Tyr337Ala by several pyridinium oximes (K048, K033, K203, K127, K117, Obidoxime, 2-PAM, HI-6) to see if an enzyme-oxime pair could act as a pseudo catalytic scavenger of tabun and be applied in detoxification or decontamination. However, none of the selected oximes displayed a significant improvement in reactivation of this tabun-inhibited AChE mutant compared to the w.t. AChE.

cholinesterase; inhibition; reactivation; nerve agent; oxime

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