Biology subjects

Waltz, F.

Publications and source records attributed to Waltz, F..

2 recordsLinked to original sources

bioRxiv2020

Specific features and assembly of the plant mitochondrial complex I revealed by cryo-EM

Mitochondria are the powerhouses of eukaryotic cells and the site of essential metabolic reactions. Their main purpose is to maintain the high ATP/ADP ratio that is required to fuel the countless biochemical reactions taking place in eukaryotic cells1. This high ATP/ADP ratio is maintained through oxidative phosphorylation (OXPHOS). Complex I or NADH:ubiquinone oxidoreductase is the main entry site for electrons into the mitochondrial respiratory chain and constitutes the largest of the respiratory complexes2. Its structure and composition varies across eukaryotes species. However, high resolution structures are available only for one group of eukaryotes, opisthokonts3-6. In plants, only biochemical studies were carried out, already hinting the peculiar composition of complex I in the green lineage. Here, we report several cryo-electron microscopy structures of the plant mitochondrial complex I at near-atomic resolution. We describe the structure and composition of the plant complex I including the plant-specific additional domain composed by carbonic anhydrase proteins. We show that the carbonic anhydrase is an heterotrimeric complex with only one conserved active site. This domain is crucial for the overall stability of complex I as well as a peculiar lipid complex composed cardiolipin and phosphatidylinositols. Moreover we also describe the structure of one of the plant-specific complex I assembly intermediate, lacking the whole PD module, in presence of the maturation factor GLDH. GLDH prevents the binding of the plant specific P1 protein, responsible for the linkage of the PP to the PD module. Finally, as the carbonic anhydrase domain is likely to be associated with complex I from numerous other known eukaryotes, we propose that our structure unveils an ancestral-like organization of mitochondrial complex I.

molecular biology↗

bioRxiv2019

Cryo-EM structure of the RNA-rich plant mitochondrial ribosome

The vast majority of eukaryotic cells contain mitochondria, essential powerhouses and metabolic hubs1. These organelles have a bacterial origin and were acquired during an early endosymbiosis event2. Mitochondria possess specialized gene expression systems composed of various molecular machines including the mitochondrial ribosomes (mitoribosomes). Mitoribosomes are in charge of translating the few essential mRNAs still encoded by mitochondrial genomes3. While chloroplast ribosomes strongly resemble those of bacteria4,5, mitoribosomes have diverged significantly during evolution and present strikingly different structures across eukaryotic species6-10. In contrast to animals and trypanosomatides, plants mitoribosomes have unusually expanded ribosomal RNAs and conserved the short 5S rRNA, which is usually missing in mitoribosomes11. We have previously characterized the composition of the plant mitoribosome6 revealing a dozen plant-specific proteins, in addition to the common conserved mitoribosomal proteins. In spite of the tremendous recent advances in the field, plant mitoribosomes remained elusive to high-resolution structural investigations, and the plant-specific ribosomal features of unknown structures. Here, we present a cryo-electron microscopy study of the plant 78S mitoribosome from cauliflower at near-atomic resolution. We show that most of the plant-specific ribosomal proteins are pentatricopeptide repeat proteins (PPR) that deeply interact with the plant-specific rRNA expansion segments. These additional rRNA segments and proteins reshape the overall structure of the plant mitochondrial ribosome, and we discuss their involvement in the membrane association and mRNA recruitment prior to translation initiation. Finally, our structure unveils an rRNA-constructive phase of mitoribosome evolution across eukaryotes.

molecular biology↗