Molecular and functional characterization of an antenna-enriched glutathione S-transferase BminGSTd3 involved in undecanol degradation in the citrus fruit fly, Bactrocera minax (Enderlein) (Diptera Tephritidae)

Bactrocera minax is a disastrous pest of citrus crops in China. Numerous studies focused on the molecular mechanism of odorant perception of B. minax, but the molecular mechanism of odorant degradation remains unclear. Glutathione S-transferases (GSTs) are considered as a class of odorant-degrading enzymes involved in degrading odorant molecules in insects' olfactory system. Here, we identified a delta-class GST gene, BminGSTd3, from B. minax. It was predominantly expressed in adult's olfactory organ antennae. The bacterially expressed recombinant BminGSTd3 was able to catalyze the conjugation of glutathione (GSH) with 2, 4-dinitrochlorobenzene (CDNB). Spectrophotometric analysis showed that undecanol can inhibit catalytic activities of BminGSTd3. Metabolic assays exhibited that undecanol can be depleted by BminGSTd3. Undecanol is believed to be an important B. minax sex pheromone component. The other components of the pheromone remain unclear. To understand how BminGSTd3 specifically recognizes undecanol, a 3D model of BminGSTd3 was constructed by homology modeling. Molecular docking based on this model revealed that E64 and S65 are the key amino acids recognizing undecanol, and this was proven by site-directed mutagenesis and intrinsic fluorescence assays. We suggest that BminGSTd3 is an undecanol metabolizing GST in B.minax, and E64 and S65 may serve as the key binding sites.