Most mitochondrial proteins are encoded by nuclear DNA, and synthesised in the cytosol, then imported into the different mitochondrial subcompartments. To reach their destination, mitochondrial inner membrane proteins require import across the outer mitochondrial membrane, and through the intermembrane space. This passage through the IMS is assisted by the small Tim proteins. This family is characterised by conserved cysteine residues arranged in a twin CX3C motif. They can form Tim9-Tim10 and Tim8-Tim13 complexes, while Tim12 appears to form part of a Tim9-Tim10-Tim12 complex that is associated with the inner membrane translocase TIM22 complex. Current models suggest that the biogenesis of small Tim proteins and their assembly into complexes is dependent on the redox states of the proteins. However, the role of the conserved cysteine residues, and the disulphide bonds formed by them, in small Tim biogenesis and complex formation is not clear. As there is no research about the structural characterisation of Tim12 and double cysteine mutants of Tim9, purification of these proteins was attempted using different methods. To investigate how cysteine mutants affect complex formation, the purified double cysteine mutants of Tim9 were studied using in vitro methods. It showed that the double cysteine mutants were partially folded, and they can form complexes with Tim10 with low affinities, suggesting disulphide bonds are important for the structures and complex formation of small Tim proteins. The effect of cysteine mutants on mitochondrial function was addressed using in vivo methods. It showed that cysteines of small Tim proteins were not equally essential for cell viability, and growth defect of the lethal cysteine mutant was caused by low level of protein. Thus, the conclusion of this study is that disulphide bond formation is highly important for correct Tim9- Tim10 complex formation, and yeast can survive with low levels of complex, but it results in instability of the individual proteins.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:647366 |
| Date | January 2013 |
| Creators | Guo, Liang |
| Contributors | Xiao, Ping; Lu, Hui |
| Publisher | University of Manchester |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | https://www.research.manchester.ac.uk/portal/en/theses/structural-and-functional-studies-of-mitochondrial-small-tim-proteins(03dde6fd-6692-4af5-9023-b85a33803fcd).html |
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