Abstract
Glutathione S-Transferases (GSTs) comprise a diverse group of protein superfamily involved in cellular detoxification of various harmful xenobiotics and endobiotics. Cyanobacteria, being the primordial photosynthetic prokaryotes, served as an origin for the evolution of GSTs with diversity in their structures, substrate recognition, and catalytic functions. This study analysed the diversity of GSTs in cyanobacteria for the first time. Based on the sequence alignment and phylogenetic tree analysis, 12 GST classes were identified, which are distributed variedly within cyanobacterial orders such as four in Pleurocapsales, eight in Chroococcales, seven in Oscillatoriales, five in Stigonematales, and nine in Nostocales. Detailed evolutionary analysis of cyanobacterial GSTs suggested that the order Pleurocapsales served as the ancestry for GST evolution. The analysis also identified a conserved motif S[GLNTARS][ADE]I[LAI] with signature residues, cysteine, serine, and tyrosine at the N-terminal end that serves as the initiating residue for detoxification. Alternatively, the grouping of cyanobacterial GSTs and their unique signature residues were located, which serve as a possible discriminating factor. The study also described the mode of glutathione binding between the identified cyanobacterial GST groups highlighting the differences among the GST classes. New GST sequence data may improve further our understanding on GST evolution and other possible divergences in cyanobacteria.
Highlights
Glutathione (GSH, reduced form) metabolism is considered as ancient as the history of life, dating back to the evolution of the oxygen-containing atmosphere [1]
Many prokaryotic and eukaryotic Glutathione S-Transferases (GSTs) proteins are classified into a collection of family-like classes mainly based on the sequence, structural similarities, and differences in the organization and composition of their active sites [28]
It was observed that cyanobacterial GST, an important class of detoxification enzyme, has evolved in hierarchy and might possess a divergent functional role
Summary
Glutathione (GSH, reduced form) metabolism is considered as ancient as the history of life, dating back to the evolution of the oxygen-containing atmosphere [1]. The detoxification process is performed in three phases, phase I enzyme oxidation, reduction or hydrolysis of the substrate, introducing a reactive group that can be attacked by phase II enzymes, which conjugate the active substrate with small molecules making the conjugate more water-soluble for excretion from cells by phase III enzymes [4] Among these key enzymes, GSTs represent an integral part of the phase II step and detoxify xenobiotics through catalysing the nucleophilic attack by GSH on electrophilic carbon, sulphur, or nitrogen atoms of nonpolar xenobiotic substrates, thereby preventing their interaction with crucial cellular proteins and nucleic acids. This generates water-soluble glutathione conjugates linked by a thioether bond (GS-R) that can be degraded, or excreted out of the cell [5,6]
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