The interactions between piperonyl butoxide and E4, a resistance‐associated esterase from the peach‐potato aphid, Myzus persicae Sulzer (Hemiptera: Aphididae)

Abstract

PBO binds with E4 to accelerate small substrates to the active-site triad, while acting as a blockade to larger, insecticidal molecules. Structure-activity studies with analogues of PBO also reveal the essential chemical moieties present in the molecule.

The interactions of piperonyl butoxide and analogues with the metabolic enzymes FE4 and CYP6CY3 of the green peach aphidMyzus persicae(Hemiptera: Aphididae)

“…The docking energy for FE4 with PBO was calculated to be −7.6 kcal mol −1 , with a hydrogen bond predicted between PBO and Arg‐412. This places PBO just within the gorge of FE4, as found previously for E4 . The docking energy for structure 37 , as a representative of the novel analogues, was calculated at −9.3 kcal mol −1 , with the hydrogen bond remaining to Arg‐412, and alignment of the aromatic moiety with that in Tyr 416, suggesting probable aromatic stacking.…”

“…Derivatives 2–5 , 7 , 8 , 10–22 , 25 , 28 and 29 were synthesised according to Philippou et al . Dihydrobenzofuran derivatives 23 and 24 were synthesised through a four‐step synthesis, namely acylation with the corresponding anhydride, reduction, chloromethylation and etherification starting from commercially available dihydrobenzofuran.…”

“…Esterase FE4 was purified from aphid samples using size exclusion and ion exchange chromatography, as described by Philippou et al . Aphids (1 g), stored at −20 °C, were homogenised on ice in 20 mL of 0.02 M phosphate buffer pH 7.0 and centrifuged at 10 000 × g for 5 min.…”

“…Fractions (5 mL) were collected and tested for total esterase activity using the colorimetric assay as described by Grant et al . and modified by Philippou et al . The assay was performed in a Tmax kinetic microplate reader (Molecular Devices, Corporation, Menlo Park, CA), taking readings every 20 s at 450 nm for 5 min.…”

Insect P450 inhibitors and insecticides: challenges and opportunities

“…The inhibition of some esterase activities by PBO has cast some doubts on the utility of PBO as a diagnostic tool for the role of P450 in resistance . This ought not be the case, because esterase inhibition is seen only at very high concentrations, and results from binding not to the active site but to the outside of the substrate access channel . This results in a physicochemical hindrance to the entry of some large (but not smaller) substrates in the active site and is not a classical inhibition based on a defined enzyme mechanism.…”