Mitochondrial DNA mutations in disease and aging

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454

406

Mammalian mtDNA is packaged in DNA-protein complexes denoted mitochondrial nucleoids. The organization of the nucleoid is a very fundamental question in mitochondrial biology and will determine tissue segregation and transmission of mtDNA. We have used a combination of stimulated emission depletion microscopy, enabling a resolution well below the diffraction barrier, and molecular biology to study nucleoids in a panel of mammalian tissue culture cells. We report that the nucleoids labeled with antibodies against DNA, mitochondrial transcription factor A (TFAM), or incorporated BrdU, have a defined, uniform mean size of approximately 100 nm in mammals. Interestingly, the nucleoid frequently contains only a single copy of mtDNA (average approximately 1.4 mtDNA molecules per nucleoid). Furthermore, we show by molecular modeling and volume calculations that TFAM is a main constituent of the nucleoid, besides mtDNA. These fundamental insights into the organization of mtDNA have broad implications for understanding mitochondrial dysfunction in disease and aging

Section: Discussionmentioning

confidence: 99%

mentioning

confidence: 99%

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Super-resolution microscopy reveals that mammalian mitochondrial nucleoids have a uniform size and frequently contain a single copy of mtDNA

Kukat

Wurm

Spåhr

et al. 2011

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454

406

“…Having two separate genomes is a costly arrangement for the cell. Approximately 250 proteins encoded in the nuclear (nu) genome are needed just to maintain and express the few remaining mitochondrial genes (7). Mitochondrial sequences are frequently copied to the nuclear genomes (8)(9)(10), confirming that mechanisms for the transfer of mitochondrial genes to the nuclear genome are in place.…”

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confidence: 99%

Mitochondrial genomes are retained by selective constraints on protein targeting

Björkholm

Harish

Hagström

et al. 2015

Mitochondria are energy-producing organelles in eukaryotic cells considered to be of bacterial origin. The mitochondrial genome has evolved under selection for minimization of gene content, yet it is not known why not all mitochondrial genes have been transferred to the nuclear genome. Here, we predict that hydrophobic membrane proteins encoded by the mitochondrial genomes would be recognized by the signal recognition particle and targeted to the endoplasmic reticulum if they were nuclear-encoded and translated in the cytoplasm. Expression of the mitochondrially encoded proteins Cytochrome oxidase subunit 1, Apocytochrome b, and ATP synthase subunit 6 in the cytoplasm of HeLa cells confirms export to the endoplasmic reticulum. To examine the extent to which the mitochondrial proteome is driven by selective constraints within the eukaryotic cell, we investigated the occurrence of mitochondrial protein domains in bacteria and eukaryotes. The accessory protein domains of the oxidative phosphorylation system are unique to mitochondria, indicating the evolution of new protein folds. Most of the identified domains in the accessory proteins of the ribosome are also found in eukaryotic proteins of other functions and locations. Overall, one-third of the protein domains identified in mitochondrial proteins are only rarely found in bacteria. We conclude that the mitochondrial genome has been maintained to ensure the correct localization of highly hydrophobic membrane proteins. Taken together, the results suggest that selective constraints on the eukaryotic cell have played a major role in modulating the evolution of the mitochondrial genome and proteome. mitochondria | protein domain | evolution | endoplasmatic reticulum | signal recognition particle

“…This study provides a molecular explanation for MTERF4-dependent recruitment of NSUN4 to ribosomal RNA and suggests a unique mechanism by which other members of the large MTERF-family of proteins can regulate ribosomal biogenesis. mitochondria | translation | X-ray crystallography D eficient oxidative phosphorylation is heavily implicated in human disease and aging and this has led to a surge in the interest to understand underlying molecular mechanisms (1). Regulation of mitochondrial DNA (mtDNA) expression is of key importance for control of oxidative phosphorylation capacity because mtDNA encodes 13 essential subunits of the respiratory chain and the ATP synthase (2).…”

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confidence: 99%

Structure of the human MTERF4–NSUN4 protein complex that regulates mitochondrial ribosome biogenesis

Spåhr

Habermann

Gustafsson

et al. 2012

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105

Proteins crucial for the respiratory chain are translated by the mitochondrial ribosome. Mitochondrial ribosome biogenesis is therefore critical for oxidative phosphorylation capacity and disturbances are known to cause human disease. This complex process is evolutionary conserved and involves several RNA processing and modification steps required for correct ribosomal RNA maturation. We recently showed that a member of the mitochondrial transcription termination factor (MTERF) family of proteins, MTERF4, recruits NSUN4, a 5-methylcytosine RNA methyltransferase, to the large ribosomal subunit in a process crucial for mitochondrial ribosome biogenesis. Here, we describe the 3D crystal structure of the human MTERF4-NSUN4 complex determined to 2.9 Å resolution. MTERF4 is composed of structurally repeated MTERF-motifs that form a nucleic acid binding domain. NSUN4 lacks an N-or C-terminal extension that is commonly used for RNA recognition by related RNA methyltransferases. Instead, NSUN4 binds to the C-terminus of MTERF4. A positively charged surface forms an RNA binding path from the concave to the convex side of MTERF4 and further along NSUN4 all of the way into the active site. This finding suggests that both subunits of the protein complex likely contribute to RNA recognition. The interface between MTERF4 and NSUN4 contains evolutionarily conserved polar and hydrophobic amino acids, and mutations that change these residues completely disrupt complex formation. This study provides a molecular explanation for MTERF4-dependent recruitment of NSUN4 to ribosomal RNA and suggests a unique mechanism by which other members of the large MTERF-family of proteins can regulate ribosomal biogenesis. mitochondria | translation | X-ray crystallography