Human Mitochondrial Cytochrome b Variants Studied in Yeast: Not All Are Silent Polymorphisms

Abstract

Variations in mitochondrial DNA (mtDNA) cytochrome b (mt‐cyb) are frequently found within the healthy population, but also occur within a spectrum of mitochondrial and common diseases. mt‐cyb encodes the core subunit (MT‐CYB) of complex III, a central component of the oxidative phosphorylation system that drives cellular energy production and homeostasis. Despite significant efforts, most mt‐cyb variations identified are not matched with corresponding biochemical data, so their functional and pathogenic consequences in humans remain elusive. While human mtDNA is recalcitrant to genetic manipulation, it is possible to introduce human‐associated point mutations into yeast mtDNA. Using this system, we reveal direct links between human mt‐cyb variations in key catalytic domains of MT‐CYB and significant changes to complex III activity or drug sensitivity. Strikingly, m.15257G>A (p.Asp171Asn) increased the sensitivity of yeast to the antimalarial drug atovaquone, and m.14798T>C (p.Phe18Leu) enhanced the sensitivity of yeast to the antidepressant drug clomipramine. We demonstrate that while a small number of mt‐cyb variations had no functional effect, others have the capacity to alter complex III properties, suggesting they could play a wider role in human health and disease than previously thought. This compendium of new mt‐cyb‐biochemical relationships in yeast provides a resource for future investigations in humans.

Integrated Approach Reveals Role of Mitochondrial Germ-Line Mutation F18L in Respiratory Chain, Oxidative Alterations, Drug Sensitivity, and Patient Prognosis in Glioblastoma

“…Clomipramine is a tricyclic antidepressant drug that is effective at killing glioblastoma cells via mitochondrially-mediated apoptosis [15,16,17,18]. It has also been shown that clomipramine inhibits MRC complex III activity in isolated rat, bovine and yeast mitochondria (reviewed in [31]). These studies raised the possibility that clomipramine sensitivity may be affected by the presence of mtDNA mutations that influence complex III properties.…”

Discordant evolution of mitochondrial and nuclear yeast genomes at population level

“…Given the difficulty to engineer mtDNA in human cell lines, model genetic systems have paved the way for functional characterization. In particular, the budding yeast Saccharomyces cerevisiae has been widely used to study the phenotypic effect of mtDNA mutations [25][26][27]. S. cerevisiae mtDNA is unusually large, 85 kb; made of mostly non-coding A+T-rich sequence; and organized as either circular monomer or head-to-tail tandemrepeated linear structures [23].…”

Leber's Hereditary Optic Neuropathy–Specific Heteroplasmic Mutation m.14495A>G Found in a Chinese Family

“…The frequency data derived from MITOMAP database, show a frequency of more than 1% (1.08%) in M7b haplogroup, suggesting that it plays a role of polymorphism. m.15257G>A was reported to be associated with 9% of LHON cases,24 but some controversies exist with respect to its pathogenic power. It either appears alone or in combination with a primary mutation like m.11778G>A and m.14484T>C, respectively, suggesting it more likely to act as an intermediate mutation 25.…”