C-terminal, alpha helical domain of Class Lambda Glutathione S-transferases
Glutathione S-transferase (GST) C-terminal domain family, Class Lambda subfamily; composed of plant-specific class Lambda GSTs. GSTs are cytosolic, usually dimeric, proteins involved in cellular detoxification by catalyzing the conjugation of glutathione (GSH) with a wide range of endogenous and xenobiotic alkylating agents, including carcinogens, therapeutic drugs, environmental toxins, and products of oxidative stress. The GST fold contains an N-terminal thioredoxin-fold domain and a C-terminal alpha helical domain, with an active site located in a cleft between the two domains. GSH binds to the N-terminal domain while the hydrophobic substrate occupies a pocket in the C-terminal domain. The class Lambda subfamily was recently discovered, together with dehydroascorbate reductases (DHARs), as two outlying groups of the GST superfamily in Arabidopsis thaliana, which contain conserved active site cysteines. Characterization of recombinant A. thaliana proteins show that Lambda class GSTs are monomeric, similar to DHARs. They do not exhibit GSH conjugating or DHAR activities, but are active as thiol transferases, similar to glutaredoxins. Members of this subfamily were originally identified as encoded proteins of the In2-1 gene, which can be induced by treatment with herbicide safeners.
Comment:The GST active site is composed of a specific GSH binding site (G-site), common to all GSTs, and a nonspecific substrate binding site (H-site), which varies between different classes and isotypes. Residues from the N-terminal TRX-fold domain form the G-site while the H-site is comprised mainly of residues from the C-terminal alpha helical domain.
Comment:The H-site is nonspecific and degenerate. Multiple overlapping hydrophobic subsites exist within a single GST isoform to comprise the larger substrate binding H-site. In addition, a single substrate may occupy multiple positions and orientations within a single H-site.
Comment:Based on the GST-substrate complex structures of other family members.
Jiyao W et al.(2023). "The conserved domain database in 2023.",