C-terminal, alpha helical domain of Class Sigma-like Glutathione S-transferases
Glutathione S-transferase (GST) C-terminal domain family, Class Sigma_like; composed of GSTs belonging to class Sigma and similar proteins, including GSTs from class Mu, Pi, and Alpha. GSTs are cytosolic 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. Vertebrate class Sigma GSTs are characterized as GSH-dependent hematopoietic prostaglandin (PG) D synthases and are responsible for the production of PGD2 by catalyzing the isomerization of PGH2. The functions of PGD2 include the maintenance of body temperature, inhibition of platelet aggregation, bronchoconstriction, vasodilation, and mediation of allergy and inflammation. Other class Sigma-like members include the class II insect GSTs, S-crystallins from cephalopods, nematode-specific GSTs, and 28-kDa GSTs from parasitic flatworms. Drosophila GST2 is associated with indirect flight muscle and exhibits preference for catalyzing GSH conjugation to lipid peroxidation products, indicating an anti-oxidant role. S-crystallin constitutes the major lens protein in cephalopod eyes and is responsible for lens transparency and proper refractive index. The 28-kDa GST from Schistosoma is a multifunctional enzyme, exhibiting GSH transferase, GSH peroxidase, and PGD2 synthase activities, and may play an important role in host-parasite interactions. Members also include novel GSTs from the fungus Cunninghamella elegans, designated as class Gamma, and from the protozoan Blepharisma japonicum, described as a light-inducible GST.
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