Identification and functional characterization of an antennal glutathione S-transferase in Protegira songi (Lepidoptera Noctuidae)

Glutathione S-transferases (GSTs) in insects are essential biotransformation enzymes that play an important role in the degradation of endogenous and exogenous compounds, including xenobiotics, odorant molecules and many other substrates. In this study, nineteen GSTs were identified in Protegira songi, which is a monophagous pest that specifically infests the valuable medicinal and rubber producing plant Eucommia ulmoides. These PsGSTs are members of the cytosolic GST family and contain the N-terminal glutathione (GSH) binding domain and the C-terminal substrate binding domain. Expression analysis revealed that eighteen PsGSTs are expressed in the antennae of both males and females. Among them, PsGSTd2 is a signal peptide containing GST and is primarily expressed in male and female antennae. Phylogenetic analysis showed that PsGSTd2 shares close relationship with olfactory GSTs in other insects. Protein structure analysis showed that the GSH and substrate binding sites in PsGSTd2 form a reaction center in the monomer. In the catalytic assays, recombinant PsGSTd2 exhibited high degradation activity towards 1-chloro-2, 4-dinitrobenzene (CDNB) and the host plant volatile trans-beta-damascenone, but no degradation activity towards cis-geraniol and 2-furanmethanol was observed. These results suggest that PsGSTd2 is an extracellular GST primarily expressed in the olfactory tissues and may function as an odorant degrading enzyme by specifically inactivating host plant volatiles.