Glutathione synthetase | |||||||
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Identifiers | |||||||
Symbol | GSS | ||||||
NCBI gene | 2937 | ||||||
HGNC | 4624 | ||||||
OMIM | 601002 | ||||||
RefSeq | NM_000178 | ||||||
UniProt | P48637 | ||||||
Other data | |||||||
EC number | 6.3.2.3 | ||||||
Locus | Chr. 20 q11.2 | ||||||
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Eukaryotic glutathione synthase | |||||||||
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Identifiers | |||||||||
Symbol | GSH_synthase | ||||||||
Pfam | PF03199 | ||||||||
Pfam clan | CL0483 | ||||||||
InterPro | IPR004887 | ||||||||
SCOP2 | 2hgs / SCOPe / SUPFAM | ||||||||
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glutathione synthase | |||||||||
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Identifiers | |||||||||
EC no. | 6.3.2.3 | ||||||||
CAS no. | 9023-62-5 | ||||||||
Databases | |||||||||
IntEnz | IntEnz view | ||||||||
BRENDA | BRENDA entry | ||||||||
ExPASy | NiceZyme view | ||||||||
KEGG | KEGG entry | ||||||||
MetaCyc | metabolic pathway | ||||||||
PRIAM | profile | ||||||||
PDB structures | RCSB PDB PDBe PDBsum | ||||||||
Gene Ontology | AmiGO / QuickGO | ||||||||
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Eukaryotic glutathione synthase, ATP binding domain | |||||||||
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Identifiers | |||||||||
Symbol | GSH_synth_ATP | ||||||||
Pfam | PF03917 | ||||||||
InterPro | IPR005615 | ||||||||
SCOP2 | 1m0t / SCOPe / SUPFAM | ||||||||
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Prokaryotic glutathione synthetase, N-terminal domain | |||||||||
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Identifiers | |||||||||
Symbol | GSH-S_N | ||||||||
Pfam | PF02951 | ||||||||
InterPro | IPR004215 | ||||||||
SCOP2 | 1glv / SCOPe / SUPFAM | ||||||||
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Prokaryotic glutathione synthetase, ATP-grasp domain | |||||||||
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Identifiers | |||||||||
Symbol | GSH-S_ATP | ||||||||
Pfam | PF02955 | ||||||||
Pfam clan | CL0179 | ||||||||
InterPro | IPR004218 | ||||||||
SCOP2 | 1glv / SCOPe / SUPFAM | ||||||||
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Glutathione synthetase (GSS) (EC 6.3.2.3) is the second enzyme in the glutathione (GSH) biosynthesis pathway. It catalyses the condensation of gamma-glutamylcysteine and glycine, to form glutathione. [2] Glutathione synthetase is also a potent antioxidant. It is found in many species including bacteria, yeast, mammals, and plants. [3]
In humans, defects in GSS are inherited in an autosomal recessive way and are the cause of severe metabolic acidosis, 5-oxoprolinuria, increased rate of haemolysis, and defective function of the central nervous system. [4] Deficiencies in GSS can cause a spectrum of deleterious symptoms in plants and human beings alike. [5]
In eukaryotes, this is a homodimeric enzyme. The substrate-binding domain has a three-layer alpha/beta/alpha structure. [6] This enzyme utilizes and stabilizes an acylphosphate intermediate to later perform a favorable nucleophilic attack of glycine.
Human and yeast glutathione synthetases are homodimers, meaning they are composed of two identical subunits of itself non-covalently bound to each other. On the other hand, E. coli glutathione synthetase is a homotetramer. [3] Nevertheless, they are part of the ATP-grasp superfamily, which consists of 21 enzymes that contain an ATP-grasp fold. [7] Each subunit interacts with each other through alpha helix and beta sheet hydrogen bonding interactions and contains two domains. One domain facilitates the ATP-grasp mechanism [8] and the other is the catalytic active site for γ-glutamylcysteine. The ATP-grasp fold is conserved within the ATP-grasp superfamily and is characterized by two alpha helices and beta sheets that hold onto the ATP molecule between them. [9] The domain containing the active site exhibits interesting properties of specificity. In contrast to γ-glutamylcysteine synthetase, glutathione synthetase accepts a large variety of glutamyl-modified analogs of γ-glutamylcysteine, but is much more specific for cysteine-modified analogs of γ-glutamylcysteine. [10] Crystalline structures have shown glutathione synthetase bound to GSH, ADP, two magnesium ions, and a sulfate ion. [11] Two magnesium ions function to stabilize the acylphosphate intermediate, facilitate binding of ATP, and activate removal of phosphate group from ATP. Sulfate ion serves as a replacement for inorganic phosphate once the acylphosphate intermediate is formed inside the active site. [6]
As of late 2007, 7 structures have been solved for this class of enzymes, with PDB accession codes 1GLV, 1GSA, 1GSH, 1M0T, 1M0W, 2GLT, and 2HGS.
Glutathione synthase catalyzes the chemical reaction
The 3 substrates of this enzyme are ATP, gamma-L-glutamyl-L-cysteine, and glycine, whereas its 3 products are ADP, phosphate, and glutathione.
This enzyme belongs to the family of ligases, specifically those forming carbon-nitrogen bonds as acid-D-amino-acid ligases (peptide synthases). The systematic name of this enzyme class is gamma-L-glutamyl-L-cysteine:glycine ligase (ADP-forming). Other names in common use include glutathione synthetase, and GSH synthetase. This enzyme participates in glutamate metabolism and glutathione metabolism. At least one compound, Phosphinate is known to inhibit this enzyme.
The biosynthetic mechanisms for synthetases use energy from nucleoside triphosphates, whereas synthases do not. [12] Glutathione synthetase stays true to this rule, in that it uses the energy generated by ATP. Initially, the carboxylate group on γ-glutamylcysteine is converted into an acyl phosphate by the transfer of an inorganic phosphate group of ATP to generate an acyl phosphate intermediate. Then the amino group of glycine participates in a nucleophilic attack, displacing the phosphate group and forming GSH. [13] After the final GSH product is made, it can be used by glutathione peroxidase to neutralize reactive oxygen species (ROS) such as H2O2 or Glutathione S-transferases in the detoxification of xenobiotics. [7]
Glutathione synthetase is important for a variety of biological functions in multiple organisms. In Arabidopsis thaliana , low levels of glutathione synthetase have resulted in increased vulnerability to stressors such as heavy metals, toxic organic chemicals, and oxidative stress. [15] The presence of a thiol functional group allows its product GSH to serve both as an effective oxidizing and reducing agent in numerous biological scenarios. Thiols can easily accept a pair of electrons and become oxidized to disulfides, and the disulfides can be readily reduced to regenerate thiols. Additionally, the thiol side chain of cysteines serve as potent nucleophiles and react with oxidants and electrophilic species that would otherwise cause damage to the cell. [16] Interactions with certain metals also stabilize thiolate intermediates. [17]
In humans, glutathione synthetase functions in a similar manner. Its product GSH participates in cellular pathways involved in homeostasis and cellular maintenance. For instance, glutathione peroxidases catalyze the oxidation of GSH to glutathione disulfide (GSSG) by reducing free radicals and reactive oxygen species such as hydrogen peroxide. [18] Glutathione S-transferase uses GSH to clean up various metabolites, xenobiotics, and electrophiles to mercapturates for excretion. [19] Because of its antioxidant role, GSS mostly produce GSH inside the cytoplasm of liver cells and imported to mitochondria where detoxification occurs. [20] GSH is also essential for the activation of the immune system to generate robust defense mechanisms against invading pathogens. [19] GSH is capable of preventing infection from the influenza virus. [21] [22]
Patients with mutations in the GSS gene develop glutathione synthetase (GSS) deficiency, an autosomal recessive disorder. [23] Patients develop a wide range of symptoms depending on the severity of the mutations. Mildly affected patients experience a compensated haemolytic anaemia because mutations affect stability of the enzyme. Moderately and severely affected individuals have enzymes with dysfunctional catalytic sites, rendering it unable to participate in detoxification reactions. Physiological symptoms include metabolic acidosis, neurological defects, and increased susceptibility to pathogenic infections. [4]
Treatment of individuals with glutathione synthetase deficiency generally involve therapeutic treatments to address mild to severe symptoms and conditions. In order to treat metabolic acidosis, severely affected patients are given large amounts of bicarbonate and antioxidants such as vitamin E and vitamin C. [24] In mild cases, ascorbate and N-acetylcysteine have been shown to increase glutathione levels and increase erythrocyte production. [25] It is important to note that because glutathione synthetase deficiency is so rare, it is poorly understood. The disease also appears on a spectrum, so it is even more difficult to generalize among the few cases that occur. [26]
Glutathione is an organic compound with the chemical formula HOCOCH(NH2)CH2CH2CONHCH(CH2SH)CONHCH2COOH. It is an antioxidant in plants, animals, fungi, and some bacteria and archaea. Glutathione is capable of preventing damage to important cellular components caused by sources such as reactive oxygen species, free radicals, peroxides, lipid peroxides, and heavy metals. It is a tripeptide with a gamma peptide linkage between the carboxyl group of the glutamate side chain and cysteine. The carboxyl group of the cysteine residue is attached by normal peptide linkage to glycine.
Sulfur assimilation is the process by which living organisms incorporate sulfur into their biological molecules. In plants, sulfate is absorbed by the roots and then transported to the chloroplasts by the transipration stream where the sulfur are reduced to sulfide with the help of a series of enzymatic reactions. Furthermore, the reduced sulfur is incorporated into cysteine, an amino acid that is a precursor to many other sulfur-containing compounds. In animals, sulfur assimilation occurs primarily through the diet, as animals cannot produce sulfur-containing compounds directly. Sulfur is incorporated into amino acids such as cysteine and methionine, which are used to build proteins and other important molecules.
Glutathione synthetase deficiency (GSD) is a rare autosomal recessive metabolic disorder that prevents the production of glutathione. Glutathione helps prevent damage to cells by neutralizing harmful molecules generated during energy production. Glutathione also plays a role in processing medications and cancer-causing compounds (carcinogens), and building DNA, proteins, and other important cellular components.
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