Dittenhafer-Reed Research Group

Understanding mitochondrial function in human health and disease

Mitochondria, the cell’s powerhouse, exist at the center of cellular biosynthetic pathways and play a major role in energy production, controlling cell death and oxidative stress. Defects in mitochondrial function cause a multitude of inherited human diseases and contribute significantly to age-related pathologies, like neurodegenerative disorders and cancer. Work in Dr. Dittenhafer-Reed’s lab combines biochemistry, systems biology and chemistry approaches to study the basic biochemical mechanisms governing mitochondrial function and metabolism to allow for a deeper understanding of these diseases.

Mechanisms of control of mitochondrial DNA transcription

The nearly 10 million billion mitochondria found in the human body arose nearly two billion years ago when a eukaryotic cell precursor engulfed an energy producing proteobacterium. This proteobacterium evolved into the modern mitochondrion, known for producing the majority of cellular energy currency in the form of ATP. Over time, the mitochondrion has acquired a number of new functions central to cellular existence. Interestingly, mitochondria have retained their own small circular genome with single mammalian cells possessing hundreds of copies of mitochondrial DNA (mtDNA), a 16.6 kilobase circular double stranded molecule encoding 13 essential subunits of electron transport chain complexes. The rest of the approximately 1,500 member mitochondrial proteome, including an additional 70 oxidative phosphorylation components and the machinery required for mtDNA replication, transcription and translation, is encoded by the nuclear genome, which is inherited and treated independently of the mitochondrial genome. Therefore, coordination of nuclear and mitochondrial gene expression is essential for mitochondrial function. While core components of mitochondrial transcription initiation are known, a detailed understanding of transcriptional control is lacking. A goal of the research in the Dittenhafer-Reed lab is to uncover biochemical mechanisms that govern mitochondrial gene expression and mtDNA stability.

Characterization of mtDNA nucleoid proteins in genome maintenance and transcriptional regulation

Analogous to chromosomal DNA that wraps around histone proteins to fit in the nucleus, mtDNA molecules are compacted into mtDNA-protein complexes termed nucleoids. Mitochondrial nucleoid proteins compact and protect mtDNA and impact mtDNA transcription. Mass spectrometry studies identified nearly 60 proteins in nucleoid complexes. These proteins include the core transcriptional machinery, the factors required for mtDNA replication and translation and mitochondrial metabolic enzymes. A number of nucleoid proteins were identified by quantitative mass spectrometry approaches to be post-translationally modified. Reversible post-translational modification (PTM) of proteins involves the covalent addition of chemical moieties to specific amino acids, and includes phosphorylation of serine, threonine and tyrosine and acetylation/acylation of lysine. PTMs were first recognized as regulators of nuclear histone proteins; however it is now clear that PTMs regulate protein function in diverse biological processes. Mitochondrial proteins are subject to extensive acetylation and phosphorylation; however, much remains to be explored regarding their functional significance. To understand the maintenance and gene expression of human mtDNA, the Dittenhafer-Reed lab will use biochemical approaches to analyze nucleoid protein structure, post-translational modification and function.