Molecular characterization and functional analysis of glutathione S-transferase kappa 1 (GSTκ1) from the big belly seahorse (Hippocampus abdominalis): Elucidation of its involvement in innate immune responses

Glutathione S-transferases (GSTs) are essential enzymes for the bioactivation of xenobiotics through the conjugation of the thiol group of glutathione (GSH). In this study, a kappa class of GST was identified from the big belly seahorse (Hippoccunpus abdominalis) (HaGST kappa 1) and its biochemical and functional properties were analyzed. HaGST kappa 1 has 231 amino acids encoded by a 696 by open reading frame (ORF). The protein has a predicted molecular mass of 26.04 kDa and theoretical isoelectric point (pI) of 8.28. It comprised a thioredoxin domain, disulfide bond formation protein A (DsbA) general fold, and Ser15 catalytic site as well as GSH-binding and polypeptide-binding sites. Phylogenetic analysis revealed that HaGST kappa 1 is closely clustered with the kappa class of GSTs from teleost fishes. The recombinant (rHaGST kappa 1) protein exhibited activity toward 1-chloro-2,4-dinitrobenzene (CDNB), 4-nitrobenzyl (4-NBC), and 4-nitrophenethyl bromide (4-NPB) but not 1,2-dichloro-4-nitrobenzene (DCNB). The optimum pH and temperature were 8 and 30 degrees C, respectively, for the catalysis of CDNB and the universal substrate of GSTs. The rHaGST kappa 1 activity was efficiently inhibited in the presence of Cibacron blue (CB) as compared with hematin. Most prominent expression of HaGST kappa 1 was observed in the liver and kidney among the fourteen different tissues of normal seahorse. After challenge with lipopolysaccharide (LPS), polyinosinic-polycytidylic (poly I:C), gram-negative Edwardsiella tarda, and gram-positive Streptococcus iniae, HaGST kappa 1 expression was significantly modulated in the liver and blood tissues. Altogether, our study proposes the plausible important role of HaGST kappa 1 in innate immunity and detoxification of harmful xenobiotics.