title: The cytochrome P450 CYP6P4 is responsible for the high pyrethroid resistance in knockdown resistance-free Anopheles arabiensis.
abstract: Pyrethroid insecticides are the front line vector control tools used in bed nets to reduce malaria transmission and its burden. However, resistance in major vectors such as Anopheles arabiensis is posing a serious challenge to the success of malaria control. Herein, we elucidated the molecular and biochemical basis of pyrethroid resistance in a knockdown resistance-free Anopheles arabiensis population from Chad, Central Africa. Using heterologous expression of P450s in Escherichia coli coupled with metabolism assays we established that the over-expressed P450 CYP6P4, located in the major pyrethroid resistance (rp1) quantitative trait locus (QTL), is responsible for resistance to Type I and Type II pyrethroid insecticides, with the exception of deltamethrin, in correlation with field resistance profile. However, CYP6P4 exhibited no metabolic activity towards non-pyrethroid insecticides, including DDT, bendiocarb, propoxur and malathion. Combining fluorescent probes inhibition assays with molecular docking simulation, we established that CYP6P4 can bind deltamethrin but cannot metabolise it. This is possibly due to steric hindrance because of the large vdW radius of bromine atoms of the dihalovinyl group of deltamethrin which docks into the heme catalytic centre. The establishment of CYP6P4 as a partial pyrethroid resistance gene explained the observed field resistance to permethrin, and its inability to metabolise deltamethrin probably explained the high mortality from deltamethrin exposure in the field populations of this Sudano-Sahelian An. arabiensis. These findings describe the heterogeneity in resistance towards insecticides, even from the same class, highlighting the need to thoroughly understand the molecular basis of resistance before implementing resistance management/control tools.
authors.affiliation: Vector Biology Department, Liverpool School of Tropical Medicine, Liverpool, L3 5QA, United Kingdom. Electronic address: SulaimanSadi.Ibrahim@lstmed.ac.uk.
authors.forename: Sulaiman S
authors.initials: SS
authors.lastname: Ibrahim
authors.affiliation: Vector Biology Department, Liverpool School of Tropical Medicine, Liverpool, L3 5QA, United Kingdom. Electronic address: jacob.riveron@lstmed.ac.uk.
authors.forename: Jacob M
authors.initials: JM
authors.lastname: Riveron
authors.affiliation: Vector Biology Department, Liverpool School of Tropical Medicine, Liverpool, L3 5QA, United Kingdom; Department of Health and Social Sciences, Leeds Beckett University, LS1 3HE, Leeds, United Kingdom. Electronic address: r.stott@leedsbeckett.ac.uk.
authors.forename: Robert
authors.initials: R
authors.lastname: Stott
authors.affiliation: Vector Biology Department, Liverpool School of Tropical Medicine, Liverpool, L3 5QA, United Kingdom. Electronic address: helen.irving@lstmed.ac.uk.
authors.forename: Helen
authors.initials: H
authors.lastname: Irving
authors.affiliation: Vector Biology Department, Liverpool School of Tropical Medicine, Liverpool, L3 5QA, United Kingdom. Electronic address: charles.wondji@lstmed.ac.uk.
authors.forename: Charles S
authors.initials: CS
authors.lastname: Wondji
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D000852:Anopheles / Q000187:drug effects* / Q000235:genetics; D003577:Cytochrome P-450 Enzyme System / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D005260:Female; D020869:Gene Expression Profiling; D055785:Gene Knockdown Techniques; D019476:Insect Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D007305:Insecticide Resistance / Q000235:genetics*; D007306:Insecticides / Q000378:metabolism; D008969:Molecular Sequence Data; D009570:Nitriles; D011487:Protein Conformation; D011722:Pyrethrins / Q000378:metabolism
chemical_list: D019476:Insect Proteins; D007306:Insecticides; D009570:Nitriles; D011722:Pyrethrins; C017180:decamethrin; D003577:Cytochrome P-450 Enzyme System
keywords: Anopheles arabiensis; CYP6P4; Metabolic; Pyrethroids resistance