Sandbox Reserved 771: Difference between revisions
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'''Glutathione synthetase''' (GSS) is an homo-dimeric, ATP-depending <scene name='56/564047/Biological_assembly/2'>ligase</scene> responsible for the condensation of γ-Glutamylcysteine and glycine to form Glutathione (GSH) during the second step of the glutathione biosynthesis pathway. Glutathione considered to be one of the most abundant and important antioxidants present in a wide range of cells - including bacterial, plant, and mammalian cells. In addition to protecting cells from the oxidative damage caused by free radicals, it is believed to be involved in the detoxification of xenobiotics, as well as membrane transport. | '''Glutathione synthetase''' (GSS) is an homo-dimeric, ATP-depending <scene name='56/564047/Biological_assembly/2'>ligase</scene> responsible for the condensation of γ-Glutamylcysteine and glycine to form Glutathione (GSH) during the second step of the glutathione biosynthesis pathway. Glutathione considered to be one of the most abundant and important antioxidants present in a wide range of cells - including bacterial, plant, and mammalian cells. In addition to protecting cells from the oxidative damage caused by free radicals, it is believed to be involved in the detoxification of xenobiotics, as well as membrane transport. | ||
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As stated previously, the catalytic active site of GSS is composed of the G-loop, S-loop, and A-loop. The G-loop has been termed the “Glycine Triad” due to the contribution of three glycine residues in this loop to the enzymatic activity of GSS – Gly369, Gly370, and Gly371. While all three residues are essential to the activity of the enzyme, kinetic experiments have shown Gly369 and Gly370 to have much more critical roles than Gly371. G369V and G370V variants were found to contain a mere 0.7% and 0.3% of the activity of the wild type GSS enzyme, respectively. G371V mutants still contained approximately 13% of the wild type activity, indicating a level of importance similar to the Asp458 residue of the A-loop. These experimental results suggest that the mechanism of activity interference lies in a decreased ligand binding and failure to close the active site once the ligand has bound. | As stated previously, the catalytic active site of GSS is composed of the G-loop, S-loop, and A-loop. The G-loop has been termed the “Glycine Triad” due to the contribution of three glycine residues in this loop to the enzymatic activity of GSS – Gly369, Gly370, and Gly371. While all three residues are essential to the activity of the enzyme, kinetic experiments have shown Gly369 and Gly370 to have much more critical roles than Gly371. G369V and G370V variants were found to contain a mere 0.7% and 0.3% of the activity of the wild type GSS enzyme, respectively. G371V mutants still contained approximately 13% of the wild type activity, indicating a level of importance similar to the Asp458 residue of the A-loop. These experimental results suggest that the mechanism of activity interference lies in a decreased ligand binding and failure to close the active site once the ligand has bound. | ||
==Alternative Splicing Variants== | ==Alternative Splicing Variants== | ||
While the expression of glutathione synthetase (GSS) has been studied and fairly well characterized, the sequence and alternative splicing of the gss gene has been studied very little. Using real-time polymerase chain reaction (qPCR) to quantify mRNA levels of the gss transcript within human cells has revealed one common alternative splicing variant present within colon, kidney, lung, liver, placenta, blood, and uterus cells. It has not, however, been detected within heart, skeletal muscle, and spleen tissue cells. This ASV is produced from a 333 bp in-frame deletion, including the complete removal of exons 4 and 5. | While the expression of glutathione synthetase (GSS) has been studied and fairly well characterized, the sequence and alternative splicing of the gss gene has been studied very little. Using real-time polymerase chain reaction (qPCR) to quantify mRNA levels of the gss transcript within human cells has revealed one common alternative splicing variant present within colon, kidney, lung, liver, placenta, blood, and uterus cells. It has not, however, been detected within heart, skeletal muscle, and spleen tissue cells. This ASV is produced from a 333 bp in-frame deletion, including the complete removal of exons 4 and 5. | ||
==Chronic Lung Infections Caused by Alterations to Glutathione Synthesis== | ==Chronic Lung Infections Caused by Alterations to Glutathione Synthesis== | ||
Though reduced levels of GSH have been observed in patients with Alzheimers and Parkinsons, inborn errors in the endogenous GSS enzyme resulting in significantly low levels of GSH is believed to be the cause of a metabolic deficiency termed 5-oxoprolinuria. | |||