Rational design of Lepidoptera-specific insecticidal inhibitors targeting farnesyl diphosphate synthase, a key enzyme of the juvenile hormone biosynthetic pathway

Abstract

Reducing the use of broad-spectrum insecticides is one of the many challenges currently faced by insect pest management practitioners. For this reason, efforts are being made to develop environmentally benign pest-control products through bio-rational approaches that aim at disrupting physiological processes unique to specific groups of pests. Perturbation of hormonal regulation of insect development and reproduction is one such strategy. It has long been hypothesized that some enzymes in the juvenile hormone biosynthetic pathway of moths, butterflies and caterpillars (order Lepidoptera) display unique structural features that could be targeted for the development of Lepidoptera-specific insecticides, a promising avenue given the numerous agricultural and forest pests belonging to this order. Farnesyl diphosphate synthase, FPPS, is one such enzyme, with recent work suggesting that it has structural characteristics that may enable its selective inhibition. This review synthesizes current knowledge on FPPS and summarizes recent advances in its use as a target for insecticide development.

Keywords: Lepidoptera; bisphosphonate; enzyme inhibitors; farnesyl diphosphate synthase; juvenile hormone; short-chain isoprenyl diphosphate synthases.

Fig. 1. Overview of the Juvenile Hormone Biosynthetic Pathway (Adapted from Goodman and Cusson⁵⁾). This pathway is divided in two branches, the mevalonate pathway and the JH-specific steps. The order of the last two enzymatic steps may vary. Precursors are in bold and enzymes are in italics.

Fig. 2. Mechanism of “head-to-tail” condensation in eukaryotic FPPSs. For detail, see the main text.

Fig. 3. Structures of the known lepidopteran juvenile hormones, four of which feature ethyl branches (arrows).

Fig. 4. Maximum likelihood tree for a selection of insect FPPSs. The tree was constructed using the PhyML tool (http://www.phylogeny.fr), after alignment of the amino acid sequences using MUSCLE (https://www.ebi.ac.uk/Tools/msa/muscle/). Branch support was assessed using the approximate Likelihood-Ratio Test functionality of PhyML. The tree was drawn using TreeDyn (http://www.treedyn.org/). Species, FPPS labels and accession numbers (except for Papilio glaucus): Aedes aegypti, AeFPPS: XP_001663796.1. Anopheles gambiae, AgFPPS: XP_308653.4. Apis mellifera, AmFPPS1: XP_001122575.3; AmFPPS2: XP_026300402.1; AmFPPS3: XP_006572097.2; AmFPPS4: XP_026300405.1; AmFPPS5: XP_624298.3; AmFPPS6: XP_016772838.2. Bombyx mori, BmFPPS1: BAB69490.1; BmFPPS2: NP_001093301.1; BmFPPS3: NP_001093302.1. Choristoneura fumiferana, CfFPPS1: AAY26575.1; CfFPPS2: AAY33485.1. Danaus plexipus, DpFPPS1: OWR45492.1; DpFPPS2: OWR45491.1. Drosophila melanogaster, DmFPPS: NP_477380.1. Helicoverpa armigera, HaFPPS1: XP_021182121.1; HaFPPS2: XP_021182149.1; HaFPPS3: XP_021182134.1; HaFPPS4: XP_021182148.1. Leptinotarsa decemlineata, LdFPPS: XP_023019940.1. Myzus persicae, MpFPPS1: AAY33491.1. Papilio glaucus (IDs from official gene set; see Table S4F in⁴⁷⁾), PgFPPS1: pgl854.12; PgFPPS2: pgl854.13; PgFPPS3: pgl854.9; PgFPPS4: pgl854.11; PgFPPS5: pgl10805.1; PgFPPS6: pgl854.10; PgFPPS7: pgl123.5; PgFPPS8: pgl123.3; PgFPPS9: pgl3843.1; PgFPPS10: pgl3843.2; PgFPPS11: pgl1544.3; PgFPPS12: pgl10805.9; PgFPPS13: pgl2397.1; PgFPPS14: pgl2898.1; PgFPPS15: pgl2898.3; PgFPPS17: pgl2898.5; PgFPPS18: pgl10805.8; PgFPPS19: pgl2898.4. Papilio xuthus: PxFPPS1: KPJ05697.1; PxFPPS2: KPJ05696.1. Pieris rapae: PrFPPS1: XP_022112553.1; PrFPPS2: XP_022112560.1. Pseudaletia (Mythimna) unipuncta: PuFPPS1: AAY33487.1; PuFPPS2: unpublished. Tetropium fuscum: TfFPPS: AFR31785.1.

Fig. 5. General chemical structure of the bisphosphonate group compared with pyrophosphate. The general chemical structure of N-alkylated ortho-substituted pyridinium BPs is also shown on the right.

Fig. 6. Crystal structure of CfFPPS2. Top panel: homodimeric representation of CfFPPS2 with N-methyl pyridinium BP inhibitor (1b, purple sticks) and co-substrate IPP (magenta sticks) (PDB Code: 6B06). One subunit is shown in grey and the second subunit is shown in a rainbow color scheme indicating the N-terminal (blue) and C-terminal (red) regions. Bottom panel: closeup of 1b and IPP interactions with the receptor allylic and homoallylic binding sites. The aspartates from the FARM are shown in turquoise sticks while those from the SARM are shown in yellow sticks.