Glycogen phosphorylase (GP) catalyzes the rate-limiting step of glycogenolysis and occupies a central position in insect carbohydrate metabolism, supplying precursors for chitin biosynthesis. Acyl urea compounds structurally related to benzoylphenylurea (BPU) insecticides are potent inhibitors of mammalian GP, raising the question of whether insect GP could serve as an independent insecticidal target. Here, we systematically evaluate this possibility in the diamondback moth Plutella xylostella. We show that a mammalian GP inhibitor (GPI) potently inhibits recombinant PxGP (IC50 = 2.96 nM), while the BPU insecticide diflubenzuron (DFB) does not. Molecular docking and MM/GBSA analysis reveal that this selectivity reflects differential side-chain engagement: GPI binds the allosteric site at the dimer interface via seven cross-subunit contacts ({Delta}G = -34.63 kcal/mol), whereas DFBs difluorobenzoyl moiety fails to establish productive protein contacts ({Delta}G = -29.29 kcal/mol). Despite potent in vitro inhibition, GPI exhibits no insecticidal activity, and RNAi-mediated knockdown of PxGP (confirmed by enzyme activity measurements showing [~]27-30% reduction in per-larva GP-a activity) does not impair development or survival. We demonstrate that insects compensate through a multi-layered metabolic response: upregulation of gluconeogenic enzymes (PEPCK, G-6-Pase), selective activation of glycogen branching enzyme (GBE) but not -amylase, and protein catabolism providing gluconeogenic substrates. Fitness assessment reveals transient larval weight loss (24-48 h) with complete recovery of pupal weight, adult wing morphology, and female fecundity, confirming that metabolic compensation is ultimately effective. These findings establish GP as functionally non-essential due to gluconeogenic rescue and highlight the importance of considering metabolic network redundancy in target-based insecticide design.
Zhou, Y. et al. · CC-BY 4.0