A Dedicated Chaperone Mediates the Safe Transfer of Mitoribosomal Proteins to Their Site of Assembly

Author(s)

Gabrielle Ashley Hillman, Rowan University

Date Approved

5-2019

Document Type

Dissertation

Degree Name

PhD in Cell & Molecular Biology

Department

Molecular Biology

College

Graduate School of Biomedical Sciences

Sponsor

This work was supported, in part, by a grant from the New Jersey Health Foundation (PC130-13; to MH), a grant from the NIH (GM117483; to MH), Rowan University Graduate School of Biomedical Sciences, Dept. of Molecular Biology, and Rowan University Society of Research Scholars (to GH).

First Advisor

Michael Henry, PhD

Committee Member 1

Mikhail Anikin, PhD

Committee Member 2

Dimitri Pestov, PhD

Committee Member 3

Salvatore Caradonna, PhD

Committee Member 4

Randy Strich, PhD

Subject(s)

Mitochondrial Ribosomes, Molecular Chaperones, Mitochondria, Mutation, Respiration, Transcription, Genetic

Disciplines

Cancer Biology | Cell Biology | Cellular and Molecular Physiology | Genetics and Genomics | Laboratory and Basic Science Research | Medicine and Health Sciences | Molecular Biology | Molecular Genetics

Abstract

Mitochondrial ribosomes are functionally specialized for the synthesis of several essential inner membrane proteins of the respiratory chain. While remarkable progress has recently been made towards understanding the structure of mitoribosomes, the unique pathways and factors that facilitate their biogenesis remain largely unknown. This dissertation defines the physiological role of an evolutionarily conserved yeast protein called Mam33 in mitochondrial ribosome assembly. The biomedical relevance of this finding stems from the fact that mutations or changes in its expression of the human ortholog p32 result in mitochondrial dysfunction. In human patients, bi-allelic mutations cause severe multisystemic defects in mitochondrial energy metabolism, which directly result from OXPHOS deficiencies and mitochondrial genome instability. Furthermore, p32 overexpression has been detected in nearly all the tissue-specific forms of cancer. For these reasons, understanding the physiological role of this protein in the mitochondrion is timely.

Mam33 is not required for exponential-phase respiratory growth in budding yeast, but rather to efficiently adapt from fermentation to respiration. During fermentation, the absence of Mam33 disrupts the translation of cytochrome c oxidase subunit I. Thus, cells poorly adapt to respiratory conditions because they lack basal fermentative levels of this essential respiratory chain component. A genetic screen was employed to reveal proteins that functionally compensate for Mam33 during respiration, and those identified suggested a role for Mam33 in mitoribosome biogenesis. The absence of Mam33 results in misassembled, aggregated ribosomes and a respiratory lethal phenotype in combination with other ribosome assembly mutants. While Mam33 does not associate with the mature mitoribosome, it directly binds a subset of unassembled large subunit proteins. Together, the genetic relationships, physical interactions, and mutant phenotypes described in this dissertation indicate that Mam33 chaperones a subset of newly-imported mitoribosomal proteins and facilitates incorporation into the assembling large subunit. The acidic face of the Mam33 trimer likely protects the unstructured, positively charged regions of ribosomal proteins, which are unusually prone to misfolding and aggregation. Furthermore, the specific phenotypes of mtRNA polymerase mutants identified in this dissertation suggest a new mechanism for the coordination of mitochondrial transcription with translation.

Recommended Citation

Hillman, Gabrielle Ashley, "A Dedicated Chaperone Mediates the Safe Transfer of Mitoribosomal Proteins to Their Site of Assembly" (2019). Graduate School of Biomedical Sciences Theses and Dissertations. 19.
https://rdw.rowan.edu/gsbs_etd/19