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

• Author / Creator

  Wideman, Jeremy G

• 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.

• Subjects / Keywords

  • Mitochondrial protein import
  • Beta barrels
  • Neurospora

• Graduation date

  Fall 2012

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R3HK6N

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.