Reactivation of tabun-hAChE investigated by structurally analogous oximes and mutagenesis.
The nerve agent tabun inhibits the essential enzyme acetylcholinesterase (AChE) by a rapid phosphoramidation of the catalytic serine residue. Oximes, such as K027 and HLö-7, can reactivate tabun-inhibited human AChE (tabun-hAChE) whereas the activity of their close structural analogue HI-6 is notably low. To investigate HI-6, K027 and HLö-7, residues lining the active-site gorge of hAChE were substituted and the effects on kinetic parameters for reactivation were determined. None of the mutants (Asp74Asn, Asp74Glu, Tyr124Phe, Tyr337Ala, Tyr337Phe, Phe338Val and Tyr341Ala) were able to facilitate HI-6-mediated reactivation of tabun-hAChE. In contrast, Tyr124Phe and Tyr337Phe induce a 2-2.5-fold enhancement of the bimolecular rate constant for K027 and HLö-7. The largest effects on the dissociation constant (3.5-fold increase) and rate constant (20-fold decrease) were observed for Tyr341Ala and Asp74Asn, respectively. These findings demonstrate the importance of residues located distant from the conjugate during the reactivation of tabun-hAChE.
Artursson
Elisabet
E
Swedish Defence Research Agency, CBRN Defence and Security, SE-90182 Umeå, Sweden.
Akfur
Christine
C
Hörnberg
Andreas
A
Worek
Franz
F
Ekström
Fredrik
F
D000110:Acetylcholinesterase / Q000032:analysis / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D002800:Cholinesterase Inhibitors / Q000494:pharmacology*; D002801:Cholinesterase Reactivators / Q000494:pharmacology*; D003001:Cloning, Molecular; D006801:Humans; D015394:Molecular Structure; D016297:Mutagenesis, Site-Directed; D010755:Organophosphates / Q000737:chemistry / Q000494:pharmacology; D010091:Oximes / Q000737:chemistry*; D011726:Pyridinium Compounds / Q000737:chemistry; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D017422:Sequence Analysis, DNA; D013698:Templates, Genetic
C481758:1-(4-hydroxyiminomethylpyridinium)-3-(carbamoylpyridinium) propane dibromide; D002800:Cholinesterase Inhibitors; D002801:Cholinesterase Reactivators; D010755:Organophosphates; D010091:Oximes; D011726:Pyridinium Compounds; D011994:Recombinant Proteins; C058577:HLo 7; D000110:Acetylcholinesterase; C022870:asoxime chloride; C009374:tabun