Improving organophosphate-hydrolyzing activity of human paraoxonase 1 by mutagenesis approach

O OPs) are extremely toxic compounds that are commonly used as pesticides and also as chemical warfare nerve agents. OP compounds irreversibly inhibit neurotransmitter metabolizing enzyme, acetylcholinesterase (AChE). Inhibition of AChE results in severe cholinergic crisis caused by increased concentration of acetylcholine at the cholinergic nerve–nerve and nerve–muscle synapses. Some of the examples of toxic OPs are pesticides and chemical warfare nerve agents like malathion, chlorpyrifos-oxon, parathion, soman, sarin, etc. The current treatment of OP-poisoning includes combination of anti-cholinergic drugs together with quaternary oxime reactivators which is not much effective. Human paraoxonase 1 (hPON1), a 40 kDa enzyme predominantly found associated with HDL in the blood circulation, can potentially hydrolyze numerous OPs and is thus considered as a promising catalytic scavenger candidate for the therapy of OP-poisoning. However, the OP-hydrolyzing capacity of native hPON1 is low. In an attempt to increase the OP-hydrolyzing capacity, random mutagenesis of recombinant human PON1 (rh-PON1) was carried out by both XL-1 Red mutator stain and error-prone PCR methods for two rounds of molecular evolution. The protein was expressed, purified and characterized. Some of the mutant in the second round of evolution showed 20-30 folds increase in OP-hydrolyzing activity. These novel mutants can be of therapeutic use against OP-poisoning.