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- Mannervik, Bengt, et al.
(författare)
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Glutathione Transferases as Efficient Ketosteroid Isomerases
- 2021
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Ingår i: Frontiers in Molecular Biosciences. - : Frontiers Media SA. - 2296-889X. ; 8
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Forskningsöversikt (refereegranskat)abstract
- In addition to their well-established role in detoxication, glutathione transferases (GSTs) have other biological functions. We are focusing on the ketosteroid isomerase activity, which appears to contribute to steroid hormone biosynthesis in mammalian tissues. A highly efficient GST A3-3 is present in some, but not all, mammals. The alpha class enzyme GST A3-3 in humans and the horse shows the highest catalytic efficiency with kcat/Km values of approximately 107 M−1s−1, ranking close to the most active enzymes known. The expression of GST A3-3 in steroidogenic tissues suggests that the enzyme has evolved to support the activity of 3β-hydroxysteroid dehydrogenase, which catalyzes the formation of 5-androsten-3,17-dione and 5-pregnen-3,20-dione that are substrates for the double-bond isomerization catalyzed by GST A3-3. The dehydrogenase also catalyzes the isomerization, but its kcat of approximately 1 s−1 is 200-fold lower than the kcat values of human and equine GST A3-3. Inhibition of GST A3-3 in progesterone-producing human cells suppress the formation of the hormone. Glutathione serves as a coenzyme contributing a thiolate as a base in the isomerase mechanism, which also involves the active-site Tyr9 and Arg15. These conserved residues are necessary but not sufficient for the ketosteroid isomerase activity. A proper assortment of H-site residues is crucial to efficient catalysis by forming the cavity binding the hydrophobic substrate. It remains to elucidate why some mammals, such as rats and mice, lack GSTs with the prominent ketosteroid isomerase activity found in certain other species. Remarkably, the fruit fly Drosophila melanogaster, expresses a GSTE14 with notable steroid isomerase activity, even though Ser14 has evolved as the active-site residue corresponding to Tyr9 in the mammalian alpha class.
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- Mannervik, Bengt, et al.
(författare)
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The quest for molecular quasi-species in ligand-activity space and its application to directed enzyme evolution
- 2010
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Ingår i: FEBS Letters. - : Wiley. - 0014-5793 .- 1873-3468. ; 584:12, s. 2565-2571
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Forskningsöversikt (refereegranskat)abstract
- We propose that the proper evolving unit in enzyme evolution is not a single "fittestmolecule", but a cluster of related variants denoted a "quasi-species". A distribution of variantsprovides genetic variability and thereby reduces the risk of inbreeding and evolutionary dead-ends.Different matrices of substrates or activity modulators will lead to different selection criteria anddivergent evolutionary trajectories. We provide examples from our directed evolution of glutathionetransferases illustrating the interplay between libraries of enzyme variants and ligand matrices in theidentification of quasi-species. The ligand matrix is shown to be crucial to the outcome of the search fornovel activities. In this sense the experimental system resembles the biological environment ingoverning the evolution of enzymes.
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- Segura-Aguilar, Juan, et al.
(författare)
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A Preclinical Model for Parkinson's Disease Based on Transcriptional Gene Activation via KEAP1/NRF2 to Develop New Antioxidant Therapies
- 2023
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Ingår i: Antioxidants. - : MDPI AG. - 2076-3921. ; 12:3
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Forskningsöversikt (refereegranskat)abstract
- Investigations of the effect of antioxidants on idiopathic Parkinson’s disease have been unsuccessful because the preclinical models used to propose these clinical studies do not accurately represent the neurodegenerative process of the disease. Treatment with certain exogenous neurotoxins induces massive and extremely rapid degeneration; for example, MPTP causes severe Parkinsonism in just three days, while the degenerative process of idiopathic Parkinson´s disease proceeds over many years. The endogenous neurotoxin aminochrome seems to be a good alternative target since it is formed in the nigrostriatal system neurons where the degenerative process occurs. Aminochrome induces all the mechanisms reported to be involved in the degenerative processes of idiopathic Parkinson’s disease. The presence of neuromelanin-containing dopaminergic neurons in the postmortem brain of healthy elderly people suggests that neuromelanin synthesis is a normal and harmless process despite the fact that it requires oxidation of dopamine to three ortho-quinones that are potentially toxic, especially aminochrome. The apparent contradiction that neuromelanin synthesis is harmless, despite its formation via neurotoxic ortho-quinones, can be explained by the protective roles of DT-diaphorase and glutathione transferase GSTM2-2 as well as the neuroprotective role of astrocytes secreting exosomes loaded with GSTM2-2. Increasing the expression of DT-diaphorase and GSTM2-2 may be a therapeutic goal to prevent the degeneration of new neuromelanin-containing dopaminergic neurons. Several phytochemicals that induce DT-diaphorase have been discovered and, therefore, an interesting question is whether these phytochemical KEAP1/NRF2 activators can inhibit or decrease aminochrome-induced neurotoxicity.
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- Segura-Aguilar, Juan, et al.
(författare)
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Astrocytes protect dopaminergic neurons against aminochrome neurotoxicity
- 2022
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Ingår i: Neural Regeneration Research. - : Medknow. - 1673-5374 .- 1876-7958. ; 17:9, s. 1861-1866
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Forskningsöversikt (refereegranskat)abstract
- Astrocytes protect neurons by modulating neuronal function and survival. Astrocytes support neurons in several ways. They provide energy through the astrocyte-neuron lactate shuttle, protect neurons from excitotoxicity, and internalize neuronal lipid droplets to degrade fatty acids for neuronal metabolic and synaptic support, as well as by their high capacity for glutamate uptake and the conversion of glutamate to glutamine. A recent reported astrocyte system for protection of dopamine neurons against the neurotoxic products of dopamine, such as aminochrome and other o-quinones, were generated under neuromelanin synthesis by oxidizing dopamine catechol structure. Astrocytes secrete glutathione transferase M2-2 through exosomes that transport this enzyme into dopaminergic neurons to protect these neurons against aminochrome neurotoxicity. The role of this new astrocyte protective mechanism in Parkinson´s disease is discussed.
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