Molecular analysis of Mdm38 function in mitochondrial protein expression
Final Report Abstract
Mdm38 is a matrix exposed mitochondrial inner membrane protein. Its human homolog, LETM1, has been implicated in the pathophysiology of the Wolf-Hirschhorn Syndrome. Two functions have been attributed to the protein family: i) a role in mitochondrial ion homeostasis and ii) a function in respiratory chain biogenesis. Our analyses have shown that Mdm38 and LETM1 interact with mitochondrial ribosomes. This ribosome association is functionally integrated into a network of the ribosome-binding proteins Mba1 and the protein insertase Oxa1. While Mba1 is as a peripheral membrane protein, Oxa1 and Mdm38 are integral to the inner membrane. Oxa1 mediates the co- translational insertion of mitochondria-encode proteins into the inner membrane. We found that for this process Oxa1 forms an aquas pore that is activated by the exported precursor substrate to allow for membrane passage. While a genetic and physical interaction between Oxa1 and Mdm38 was not apparent, we were able to demonstrate that Mdm38 and the ribosome receptor Mba1 associate in a common protein complex and display functional overlaps in the translation of Cox1 and cytochrome b on mitochondrial ribosomes. In case of COX1 mRNA, the role of Mdm38 in mitochondrial translational appears to be independent of early assembly intermediates of the Cox1 protein, so called COA-complexes, which regulate the COX1 mRNA-specific translational activator Mss51. Instead, Mdm38 associates with Pet309, the second activator required for translation of the COX1 mRNA. These findings suggest an early role of Mdm38 in the synthesis of mitochondrial translation products. In agreement with this complex formation between Mdm38 and translation factors for cytochrome b have been found by us and others. Mdm38 exposes a conserved C-terminal domain into the matrix that consists of a ribosome-binding domain followed by two predicted coiled coils. While the coiled coil-containing region is dispensable for respiratory chain biogenesis, the ribosome- binding domain is required. The crystal structure of Mdm38’s ribosome-binding domain represents a 14-3-3-like fold with a conserved binding groove. While this groove interacts with phosphopeptides in case of 14-3-3 proteins, Mdm38’s binding groove is uncharged suggesting a non-ionic interaction with binding partners. Besides an association of Mdm38 with ribosomes, mass spectrometric analyses demonstrate that a fraction of Mdm38 is associated with respiratory chain supercomplexes. Along the same lines we observed copurification of respiratory chain complexes with Oxa1 and a role for Oxa1 in coordinate the assembly of cytochrome c oxidase. These findings suggest that translation of mitochondria-encoded proteins and assembly of respiratory chain complexes are spatially coordinated processes. These findings might add another piece to the puzzle on how feedback regulation between mitochondrial protein complex assembly and de novo synthesis on mitochondrial ribosomes can be coordinated.
Publications
- (2010) Ribosome binding proteins Mdm38 and Mba1 display overlapping functions for regulation of mitochondrial translation. Mol. Biol. Cell 15: 1937-1944
Bauerschmitt, H., Mick, D.U. Deckers, M., Vollmer, C., Funes, S., Kehrein, K., Ott, M., Rehling, P., and Herrmann, J.M.
(See online at https://doi.org/10.1091/mbc.e10-02-0101) - (2011) Inventory control: cytochrome c oxidase assembly regulates mitochondrial translation. Nature Rev. Mol. Cell Biol. 12: 14-20
Mick, D.U., Fox, T.D, and Rehling, P.
(See online at https://doi.org/10.1038/nrm3029) - (2011) Mdm38 is a 14-3-3-like receptor and associates with the protein synthesis machinery at the inner mitochondrial membrane. Traffic 12: 1457-1466
Lupo, D., Vollmer, C., Deckers, M., Mick, D.U., Tews, I., Sinning, I., and Rehling, P.
(See online at https://doi.org/10.1111/j.1600-0854.2011.01239.x) - (2011) Mimicking a SURF1 allele reveals uncoupling of cytochrome c oxidase assembly from translational regulation in yeast. Hum. Mol. Genet. 20: 2379-2393
Reinhold, R., Bareth, B., Balleininger, M., Wissel, M., Rehling, P., and Mick, D.U.
(See online at https://doi.org/10.1093/hmg/ddr145) - (2012) Oxa1-ribosome complexes coordinate the assembly of cytochrome c oxidase in mitochondria. J. Biol. Chem. 287: 34484-34493
Keil, M., Bareth, B., Woellhaf, M.M., Peleh, V., Prestele, M. Rehling, P., and Herrmann, J.M.
(See online at https://doi.org/10.1074/jbc.M112.382630) - (2012) The mitochondrial Oxidase Assembly Protein 1 (Oxa1) Insertase Forms a Membrane Pore in Lipid Bilayers J. Biol. Chem. 287: 33314-33326
Krüger, V., Deckers, M., Hildenbeutel, M., van der Laan, M., Hellmers, M., Dreker, C., Preuss, M. Herrmann, J.M., Rehling, P., Wagner, R., and Meinecke, M.
(See online at https://doi.org/10.1074/jbc.M112.387563) - (2012), Rcf1 Mediates Cytochrome Oxidase Assembly and Respirasome Formation, Revealing Heterogeneity of the Enzyme Complex. Cell Metabolism 15: 336-347
Vukotic, M., Oeljeklaus, S., Wiese, S., Vögtle, F.N., Meisinger, C., Meyer, H.E., Zieseniss, A., Katschinski, D.M., Jans, D.C., Jakobs, S., Warscheid, B., Rehling, P., Deckers, M.
(See online at https://doi.org/10.1016/j.cmet.2012.01.016) - (2013) Mitochondrial protein import: Common principles and physiological networks. Biochim. Biophys. Acta 1833: 274-285
Dudek, J., Rehling, P., van der Laan, M.
(See online at https://doi.org/10.1016/j.bbamcr.2012.05.028)
