Unravelling the functional interconnections among the mitochondrial uniporter complex components

Goh, Valerie (2021): Unravelling the functional interconnections among the mitochondrial uniporter complex components. Dissertation, LMU München: Faculty of Biology

Abstract

The mitochondrial calcium uniporter is a highly selective ion channel composed of species and tissue-specific subunits. However, the functional role of each component still remains unclear. Here, we establish a synthetic biology approach to dissect the interdependence between the pore-forming subunit MCU and the calcium-sensing regulator MICU1. Correlated evolutionary patterns across 247 eukaryotes indicate that their co-occurrence may have conferred a positive fitness advantage. We find that, while the heterologous reconstitution of MCU and EMRE in vivo in yeast enhances manganese stress, this is prevented by coexpression of MICU1. Accordingly, MICU1 deletion sensitizes human cells to manganese dependent cell death by disinhibiting MCU-mediated manganese uptake. As a result, manganese overload increases oxidative stress, which can be effectively prevented by NAC treatment. Our study identifies a critical contribution of MICU1 to the uniporter selectivity, with important implications for patients with MICU1 deficiency, as well as neurological disorders arising upon chronic manganese exposure. Calcium (Ca2+) influx into mitochondria occurs through a Ca2+-selective uniporter channel, which regulates essential cellular processes in eukaryotic organisms. Previous evolutionary analyses of its pore-forming subunits MCU and EMRE, and gatekeeper MICU1, pinpointed an evolutionary paradox: the presence of MCU homologs in fungal species devoid of any other uniporter components and of mt-Ca2+ uptake. Here, we trace the mt-Ca2+ uniporter evolution across 1,156 fully sequenced eukaryotes and show that animal and fungal MCUs represent two distinct paralogous subfamilies originating from an ancestral duplication. Accordingly, we find EMRE orthologs outside Holoza and uncover the existence of an animal-like uniporter within chytrid fungi, which enables mt-Ca2+ uptake when reconstituted in vivo in the yeast Saccharomyces cerevisiae. Our study represents the most comprehensive phylogenomic analysis of the mt-Ca2+ uptake system and demonstrates that MCU, EMRE, and MICU formed the core of the ancestral opisthokont uniporter, with major implications for comparative structural and functional studies.

• Item Type: Theses (Dissertation, LMU Munich)
• Keywords: Mitochondria, calcium, uniporter, manganese
• Subjects: 500 Natural sciences and mathematics; 500 Natural sciences and mathematics > 570 Life sciences
• Faculties: Faculty of Biology
• Language: English
• Date of oral examination: 3. February 2021
• 1. Referee: Conradt, Barbara
• Signature of the printed copy: 0001/UMC 27857