Mechanismus der Thioloxidase Mia40
Final Report Abstract
Mia40 catalyzes disulfide bond formation in proteins in the mitochondrial intermembrane space. By using Cox17 as a natural substrate, we discovered that in the presence of Mia40 the formation of native disulfides is strongly favored. The catalytic mechanism of Mia40 involves a functional interplay between the chaperone site and the catalytic disulfide. Mia40 forms a specific native disulfide in Cox17 much more rapidly than other disulfides, in particular non-native ones, which originates from the high affinity for hydrophobic regions near target cysteines and the long life time of the mixed disulfide. We show that the distinctive properties of Mia40 originate neither from particular properties of mitochondrial substrates nor from the CPC motif of Mia40. The catalytic cysteines of Mia40 display unusually low chemical reactivity, as expressed in conventional pK values and reduction potentials. The stability of the mixed disulfide intermediate is coupled energetically with hydrophobic interactions between Mia40 and the substrate. Mia40 is active also as a disulfide reductase and isomerase. Based on these properties, we proposed a molecular mechanism for Mia40, where the hydrophobic binding site is employed to select a substrate thiol for forming the initial mixed disulfide. Its long lifetime is used to retain partially folded proteins in the mitochondria and to direct folding towards forming the native disulfide bonds.
Publications
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Mia40 combines thiol oxidase and disulfide isomerase activity to efficiently catalyze oxidative folding in mitochondria J. Mol. Biol. 426 (2014) 4087-4098
J. R. Koch & F. X. Schmid
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Mia40 Is Optimized for Function in Mitochondrial Oxidative Protein Folding and Import. ACS Chem. Biol. 9 (2014) 2049-2057
J. R. Koch & F. X. Schmid
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Mia40 targets cysteines in a hydrophobic environment to direct oxidative protein folding in the mitochondria. Nature Commun. 5 (2014)
J. R. Koch & F. X. Schmid
