Identification of a sigma‐class glutathione‐<i>S</i>‐transferase from the silkworm,<i>Bombyx mori</i>

Abstract

Abstract: A cDNA that encodes a glutathione‐ S ‐transferase belonging to sigma class (GSTS1) from the silkworm, Bombyx mori was cloned by reverse transcriptase‐polymerase chain reaction and sequenced. The deduced amino acid sequence revealed 66%, 48% and 41% identity to sigma‐class GSTs from Manduca sexta , Blattella germanica and Anopheles gambiae , respectively. The GSTS1 was also estimated to be close to those GSTs in a phylogenetic tree. GSTS1 mRNA was widely distributed in various tissues. The recombinant GST (rGSTS1) was functionally overexpressed in Escherichia coli in a soluble form, purified to homogeneity and characterized. The pH‐optimum of rGSTS1 was around pH 8. The rGSTS1 retained more than 75% of its original activity after incubation at pH 4–9. Incubation for 30 min at temperatures below 40°C did not affect its activity. rGSTS1 was able to catalyse the reaction of glutathione with 1‐chloro‐2,4‐dinitrobenzene, the universal substrate for GST, as well as with 4‐hydroxynonenal, the product of lipid peroxidation.