In eukaryotes, glutathione S-transferases (GSTs) participate in the detoxification of reactive electrophilic compounds by catalysing their conjugation to glutathione. GST is found as a domain in S-crystallins from squid, and proteins with no known GST activity, such as eukaryotic elongation factors 1-gamma and the HSP26 family of stress-related proteins, which include auxin-regulated proteins in plants and stringent starvation proteins in Escherichia coli. The major lens polypeptide of cephalopods is also a GST . Bacterial GSTs of known function often have a specific, growth-supporting role in biodegradative metabolism: epoxide ring opening and tetrachlorohydroquinone reductive dehalogenation are two examples of the reactions catalysed by these bacterial GSTs. Some regulatory proteins, like the stringent starvation proteins, also belong to the GST family . GST seems to be absent from Archaea in which gamma-glutamylcysteine substitute to glutathione as major thiol.
Glutathione S-transferases form homodimers, but in eukaryotes can also form heterodimers of the A1 and A2 or YC1 and YC2 subunits. The homodimeric enzymes display a conserved structural fold. Each monomer is composed of a distinct N-terminal sub-domain, which adopts the thioredoxin fold, and a C-terminal all-helical sub-domain, which adopts a 4-helical bundle fold. This entry is the C-terminal domain.
Glutaredoxin 2 (Grx2), glutathione-dependent disulphide oxidoreductases, is structurally similar to GSTs, even though they lack any sequence similarity. Grx2 is also composed of N and C terminal subdomains. It is thought that the primary function of Grx2 is to catalyse reversible glutathionylation of proteins with glutathione in cellular redox regulation including the response to oxidative stress. Grx2 is dissimilar to other glutaredoxins apart from containing the conserved active site residues .