Discovery of EMRE in fungi resolves the true evolutionary history of the mitochondrial calcium uniporter

Alexandros A. Pittis, Valerie Goh, Alberto Cebrian-Serrano, Jennifer Wettmarshausen, Fabiana Perocchi, Toni Gabaldón

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Received Date: 12th March 20

Mitochondrial calcium (mt-Ca2+) uptake is central for the regulation of numerous cellular processes in eukaryotes (1). This occurs through a highly selective Ca2+ uniporter located at the inner mitochondrial membrane and driven by the membrane potential (2–4). While the physiological role of the uniporter was extensively studied for decades, its genetic identity was only recently determined, with MCU (5,6), MICU1 (7) and EMRE (8) constituting pore-forming and regulatory subunits. Preliminary evolutionary analyses suggested an ancient eukaryotic origin of mt-Ca2+ uptake, but also pinpointed inconsistent phylogenetic distributions of MCU, MICU1, and EMRE within fungi, where homologs of MCU were present in the absence of the supposedly essential regulators, MICU1 and EMRE (9,10). Here, we perform the most comprehensive phylogenomic analysis of the mt-Ca2+ uptake system and trace its evolution across 1,156 fully-sequenced eukaryotes. In contrast to earlier assumptions (9–11) we find compelling evidence that previously identified animal and fungal MCUs, the targets of several structural and functional efforts11–16, represent two distinct paralogous subfamilies originating from an ancestral duplication. We further uncover a complete “animal-like” uniporter complex within chytrid fungi, including bona-fide orthologs of MCU, MICU1, and EMRE. This first identification of EMRE outside Holozoa (animals and their unicellular relatives) and its strong coevolution with “animal-like” MICU1 and MCU indicates that these three components formed the core of the ancestral opisthokont uniporter. We confirm this finding experimentally, by showing that chytrid EMRE orthologs in combination with either human or “animal-like” MCUs, but not with “fungal-specific” MCUs, can reconstitute mt-Ca2+ uptake in vivo in the yeast Saccharomyces cerevisiae. Hence, we here solve a purported evolutionary paradox: the presence of MCU homologs in fungal species devoid of other uniporter components and with no detectable mt-Ca2+ uptake. Altogether, our study clarifies the evolution of the mt-Ca2+ uniporter and identifies new important targets for comparative structural and functional studies.

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This is an abstract of a preprint hosted on an independent third party site. It has not been peer reviewed but is currently under consideration at Nature Communications.

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