Butyrylcholinesterase with altered catalytic triad, acting as a promising bioscavenger against organophosphorus agents

Abstract

Cholinesterases (ChEs) are irreversibly inhibited by organophosphorus compounds (OP) through phosphylation of their active site serine. OPs can be regarded as pseudo-substrates of ChEs in which water-mediated dephosphylation is very slow or impossible. Then, it has been attempted by genetic engineering to convert ChEs into OP hydrolases by speeding up dephosphylation rates. The knowledge of ChEs crystal structure and implementation of potent in silico methods allow rational computer design of new mutants. Such ChE mutants could be used as catalytic bioscavengers in medical counter-measures of OP poisoning. In the present work, using QM/MM MD, we designed a new mutant of human butyrylcholinesterase (BChE). This double mutant, Glu325Gly/Asn322Glu, alters the functioning of the catalytic triad (Ser198.His438.Glu325 in wild-type enzyme), making a new one Ser198.His438.Glu322. Calculations with echothiophate as a model OP showed that the new catalytic triad is stable and capable of hydrolysing the phosphorylated serine. Thus, self-reactivation of the mutated enzyme is possible. Although the calculated dephosphylation rate constant is low, it is expected that the introduction of a third mutation will lead to a much faster turnover.