Molecular and biochemical characterization of a plant-like iota-class glutathione S-transferase from the halotolerant cyanobacterium Halothece sp. PCC7418.

This article focuses on the identification and characterization of a unique iota-class glutathione S-transferase (GST) encoded by the gene H0729 in the halotolerant cyanobacterium Halothece sp. PCC7418. Using phylogenetic, bioinformatics, structural, and enzymatic analyses, H0729 was shown to possess a distinctive glutaredoxin Cys-Pro-Tyr-Cys (C-P-Y-C) motif and a thioredoxin-like fold, features typical of iota-class GSTs previously known mainly from plants. Recombinant H0729 exhibited significantly higher catalytic efficiency toward glutathione and the xenobiotic substrate 1-chloro-2,4-dinitrobenzene compared to other Halothece GSTs, and its gene expression was notably upregulated under salt stress, highlighting its role in abiotic stress response. These findings expand understanding of GST diversity and evolution in cyanobacteria and underscore the functional importance of GSTs in cellular detoxification and oxidative stress adaptation in extremophilic microorganisms.