Immune and xenobiotic responses of glutathione S-Transferase theta (GST-θ) from marine invertebrate disk abalone (Haliotis discus discus): With molecular characterization and functional analysis

Representing a multifunctional complex group of proteins, glutathione S-transferases (GSTs) play a major role in the phase II detoxification process in a wide range of organisms. This study focused on the potential detoxification ability of disk abalone (Haliotis discus discus) GST theta (AbGST-theta) under different stress conditions with special reference to post immune challenges. Characterization of AbGST-theta revealed with 226 amino acids, 26.6 kDa of predicted molecular mass and 8.9 of theoretical isoelectric point. As illustrated in the multiple sequence alignment, eight glutathione binding sites (G-sites) and ten substrate binding sites (H-sites) were identified in well-distinct N-terminal and C-terminal domains of AbGST-theta, respectively. AbGST-theta exhibited its highest sequence identity with Mizuhopecten yessoensis (59.1%) and the phylogenetic tree clearly positioned AbGST-theta with pre-defined GST-theta molluscan homologues. The AbGST-8 was highly expressed in the digestive tract of un-challenged abalones. Upon administering the challenge experiment, AbGST-theta showed significant modulations in their transcriptional levels depending on the time and the tissue type. The optimum temperature was 37 degrees C and optimum pH was 7.5 for AbGST-theta. The determined enzyme kinetic parameters of AbGST-theta showed low affinity towards 1-Chloro-2,4-dinitrobenzene (CDNB) and glutathione (GSH) as substrates. Nonetheless, with Cibacron blue IC50 (half maximal inhibitory concentration) was calculated to be 0.08 mu M while observing 100% inhibition with 100 mu M. Furthermore, AbGST-theta resulted in significant protection ability towards H2O2, CdCl2, and ZnCl2 in the disk diffusion assay. Collectively, this study provides evidences for the detoxification ability and the immunological host defensive capability of AbGST-theta in disk abalone.