The μ-class glutathione S-transferase (SbGSTμ) involved in immune defense and detoxification in the ark shell...

Glutathione S-transferases (GSTs) constitute a superfamily of multifunctional detoxification isoenzymes that play essential roles in innate immunity. In this study, a μ-class GST gene was identified from Scapharca broughtonii (designated SbGSTμ) using the RACE approach. The full-length cDNA of SbGSTμ is 1040 bp and encodes a cytosolic protein of 215 amino acids. Sequence analysis revealed that SbGSTμ contains conserved structural features characteristic of the μ-class GST family, including an N-terminal thioredoxin-like domain with glutathione (GSH)-binding sites and a C-terminal domain harboring substrate-binding sites. Tissue distribution analysis showed that SbGSTμ is ubiquitously expressed across all examined tissues, with the highest expression level detected in the foot. Upon challenge with Staphylococcus aureus or Vibrio anguillarum, or exposure to Cu²⁺, SbGSTμ mRNA expression was significantly upregulated compared to controls. Recombinant SbGSTμ protein was successfully expressed in Escherichia coli, purified, and functionally characterized. The enzyme exhibited optimal activity at temperatures between 30 °C and 40 °C and at pH 7.4. Furthermore, benzo [a]pyrene exposure assays demonstrated the detoxification capacity of SbGSTμ through a significant reduction in 8-hydroxy-2'-deoxyguanosine (8-OHdG) levels. Collectively, these findings support the classical role of GSTs in xenobiotic detoxification while providing evidence for their involvement in immunological host defense mechanisms in the ark shell S. broughtonii.