Bifunctional Carboxylesterase COE52 Mediates Xanthotoxin Detoxification through Hormonal Regulation and Structural Adaptation in <i>Spodoptera litura</i>

Polyphagous insects utilize carboxylesterases (COEs) to defense against plant allelochemicals, though the mechanisms underlying COE-mediated detoxification remain elusive. Using the xanthotoxin– Spodoptera litura model, we reveal a detoxification framework integrating hormonal regulation and catalytic plasticity. The 20-hydroxyecdysone receptor EcR/USP coordinates stage-specific COE induction during feeding phases, as evidenced by 30.87–43.21% COE052 suppression post-RNAi and increased larval xanthotoxin susceptibility. Promoter activation assays identified EcR/USP-responsive elements, with mutagenesis revealing the critical −495/–481 regulatory sequence in COE052 . Functionally, COE052 demonstrates dual functionality, achieving 31.41% xanthotoxin degradation concurrent with 44.34% ROS reduction. Structural analyses characterized three noncatalytic residues (Gly130/Thr463/His464) as an allosteric gatekeeper, whose mutations reduced metabolic efficiency (16.83–25.83%) via substrate-network destabilization. Furthermore, all mutants displayed impaired oxidative stress tolerance in prokaryotic systems, validating synergistic roles in redox maintenance. These discoveries culminate in a tripartite defense model integrating hormonal coordination, transcriptional adaptability, and structural evolution, wherein noncatalytic domains critically potentiate COE052’s functional spectrum.