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The role of the ERMES complex in the assembly of mitochondrial outer membrane proteins in the filamentous fungus Neurospora crassa Open Access


Other title
mitochondrial protein import
beta barrels
Type of item
Degree grantor
University of Alberta
Author or creator
Wideman, Jeremy G
Supervisor and department
Nargang, Frank (Biological Sciences)
Examining committee member and department
Gallin, Warren (Biological Sciences)
Srayko, Martin (Biological Sciences)
Locke, John (Biological Sciences)
Lapointe, Paul (Cell Biology)
Campbell, Shelagh (Biological Sciences)
Department of Biological Sciences
Molecular biology and genetics
Date accepted
Graduation date
Doctor of Philosophy
Degree level
The ERMES (endoplasmic reticulum-mitochondria encounter structure) is composed of the Mdm10, Mdm12, Mmm1 and Mmm2 proteins, and acts as a tether between mitochondria and the endoplasmic reticulum (ER). Mutations affecting any of the proteins in the structure are associated with a variety of phenotypes including altered mitochondrial morphology and defects in mitochondrial protein import. I have focused on ERMES components and their roles in the import and assembly of proteins into the mitochondrial outer membrane in the filamentous fungus Neurospora crassa. In one study I investigated the relationship between the TOM (translocase of the mitochondrial outer membrane) complex subunit Tom7 and Mdm10 with respect to their roles in the assembly of the β-barrel proteins, Tom40 and porin. Previous work showed that mitochondria lacking Tom7 assemble Tom40 more efficiently, and porin less efficiently, than wild-type mitochondria. Here I demonstrate that mutants lacking Mdm10 assemble both Tom40 and porin less efficiently than wild-type mitochondria. My analysis of mdm10 and tom7 single and double mutants, demonstrated that the effects of the two mutations are additive. Loss of Tom7 partially compensated for the decrease in Tom40 assembly resulting from loss of Mdm10 while porin assembly is more severely reduced in the double mutant than in either single mutant. The additive effects observed in the double mutant suggest that different steps in β-barrel assembly are affected in the individual mutants I further examined the role of Mmm1 in the assembly of β-barrel proteins by mutational analysis. I showed that the N. crassa Mmm1 protein is an ER protein containing a Cys residue near its N-terminus that is conserved in the class Sordariomycetes. The residue is within the predicted ER lumen domain of the protein and is involved in disulphide bond formation. Mutation of the residue resulted in a defect in Tom40 assembly, but did not affect porin assembly or mitochondrial morphology. This demonstrates a specificity of function and suggests a direct role for Mmm1 in Tom40 assembly. Taken together, my research has provided evidence suggesting that the ERMES complex plays a direct role in the assembly of specific mitochondrial outer membrane proteins.
Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of these terms. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.
Citation for previous publication
Wideman, J.G., Go, N.E., Klein, A., Redmond, E., Lackey, S.W., Tao, T., Kalbacher, H., Rapaport, D., Neupert, W., and Nargang, F.E. (2010). Roles of the Mdm10, Tom7, Mdm12, and Mmm1 proteins in the assembly of mitochondrial outer membrane proteins in Neurospora crassa. Mol Biol Cell 21, 1725-1736.Lackey, S.W., Wideman, J.G., Kennedy, E.K., Go, N.E., and Nargang, F.E. (2011). The Neurospora crassa TOB complex: analysis of the topology and function of Tob38 and Tob37. PLoS One 6, e25650.

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