Redox regulation and reversible methionine oxidation in the mitochondria

Geldon, Stefan (2022) Redox regulation and reversible methionine oxidation in the mitochondria. MSc(R) thesis, University of Glasgow.

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Mitochondria are double membrane bound organelles required for cellular respiration via the oxidative phosphorylation system (OXPHOS) that results in the generation of ATP. The OXPHOS system involves the use of an electron transport chain (ETC) comprised of several mitochondrial inner membrane embedded enzyme complexes (termed complexes I-V in mammals). The mitochondria contains its own genome, the mitochondrial DNA (mtDNA) that encodes the essential subunits of these complexes while the accompanying structural and assembly factors are cytosolically translated and imported into the mitochondria.
Reactive oxygen species (ROS) are generated inside the mitochondria at the ETC due to electron leakage at the complexes which results in the partial reduction of oxygen. An accumulation of ROS results in oxidative stress (OS) which can result in damage to nucleic acids, lipids, and proteins. Methionine residues in proteins are particularly susceptible to ROS modifications leading to the generation of methionine sulfoxidated groups which are harmful to proteins causing them to unfold and rendering them dysfunctional. Therefore, the reduction of these adducts by enzymes termed methionine sulfoxide reductases (Mxr) is essential to maintaining proteins in their native functional conformation.
In this thesis the mitochondrial targeted yeast methionine sulfoxide reductase enzyme (Mxr2) was studied. We discovered using radiolabelled protein import experiments that Mxr2 is targeted to the mitochondria and becomes dually localised to both the intermembrane space (IMS) and matrix compartments. In addition, we found that the presence of the Tom20 import receptor and the major IMS oxidative folding protein, Mia40, were required for efficient import. Studies involving knockout Mxr2 yeast cells revealed that the absence of Mxr2 resulted in a growth defect when cells were oxidatively stressed alongside alterations in respiratory capacity and metabolic substrate utilisation. Lastly the import and complex assembly of the small Tim chaperone Tim10 was demonstrated to be altered in the absence of Mxr2 using BN PAGE analysis as was the formation of respiratory supercomplexes. The second part of the thesis focused on the complex IV assembly factor 8 (COA8). Mutations in this protein have been implicated with complex IV deficiencies and mitochondrial encephalopathy phenotypes. Here we investigated how COA8 can be oxidatively regulated at several conserved cysteines residues to alter the import capacity of this matrix targeted protein.

Item Type: Thesis (MSc(R))
Qualification Level: Masters
Subjects: Q Science > QH Natural history > QH301 Biology
Colleges/Schools: College of Medical Veterinary and Life Sciences > School of Molecular Biosciences
Supervisor's Name: Tokatlidis, Professor Kostas
Date of Award: 2022
Depositing User: Theses Team
Unique ID: glathesis:2022-82894
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 20 May 2022 13:16
Last Modified: 20 May 2022 13:20
Thesis DOI: 10.5525/gla.thesis.82894

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