Structure-activity analysis of aging and reactivation of human butyrylcholinesterase inhibited by analogues of tabun

Eugénie Carletti , Nadine Aurbek , Emilie Gillon , Mélanie Loiodice , Yvain Nicolet , Juan-Carlos Fontecilla-Camps , Patrick Masson , Horst Thiermann , Florian Nachon (1) , Franz Worek

1 Toxicology

Human butyrylcholinesterase (hBChE) naturally scavenges organophosphorus nerve agents (OPs). This bioscavenger is currently in Clinical Phase I for pretreatment of OP intoxication. Phosphylated cholinesterases (ChEs) can undergo a spontaneous time-dependent process called « aging » during which the conjugate is dealkylated, leading to non-reactivable enzyme. hBChEs inhibited by phosphoramidates like tabun display a peculiar resistance to oximes mediated reactivation. We investigated the basis of oxime resistance of phosphoramidyl-BChE conjugates, by determining the kinetics of inhibition, reactivation (obidoxime, TMB-4, HLö 7, HI-6), aging, and the crystal structures of hBChE inhibited by different N-monoalkyl and N,N-dialkyl tabun analogues. The refined structures of aged hBChE conjugates show that aging proceeds through O-dealkylation of the P(R) enantiomer of N,N-diethyl and N-propyl analogues, with subsequent formation of a salt bridge preventing reactivation, similarly to previous observation made on tabun-ChEs conjugates. Interestingly, the N-methyl analogue projects its amino group towards the choline-binding pocket, so that aging proceeds through deamination. This orientation results from a preference of hBChE's acyl-binding pocket for larger than 2-atoms linear substituents. The correlation between the inhibitory potency and the N-monoalkyl chain length is related to increasingly optimized interactions with the acyl-binding pocket as shown by the X-ray structures. These kinetics and X-ray data lead to a structure-activity relationship that hightlights steric and electronic effects of the amino substituent of phosphoramidate. This study provides structural basis to design new oximes capable of reactivating phosphoramidyl-hBChE conjugates after intoxication, notably when hBChE is used as pretreatment or to design BChE-based catalytic bioscavengers.

Mots clés: Life Sciences

Eugénie Carletti, Nadine Aurbek, Emilie Gillon, Mélanie Loiodice, Yvain Nicolet, et al.. Structure-activity analysis of aging and reactivation of human butyrylcholinesterase inhibited by analogues of tabun. Biochemical Journal, 2009, 421 (1), pp.97-106. ⟨10.1042/BJ20090091⟩. ⟨hal-00479152⟩