| 1. |
- Kock Flygaard, Rasmus, et al.
(författare)
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Type III ATP synthase is a symmetry-deviated dimer that induces membrane curvature through tetramerization
- 2020
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 11:1
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Tidskriftsartikel (refereegranskat)abstract
- Mitochondrial ATP synthases form functional homodimers to induce cristae curvature that is a universal property of mitochondria. To expand on the understanding of this fundamental phenomenon, we characterized the unique type III mitochondrial ATP synthase in its dimeric and tetrameric form. The cryo-EM structure of a ciliate ATP synthase dimer reveals an unusual U-shaped assembly of 81 proteins, including a substoichiometrically bound ATPTT2, 40 lipids, and co-factors NAD and CoQ. A single copy of subunit ATPTT2 functions as a membrane anchor for the dimeric inhibitor IF1. Type III specific linker proteins stably tie the ATP synthase monomers in parallel to each other. The intricate dimer architecture is scaffolded by an extended subunit-a that provides a template for both intra- and inter-dimer interactions. The latter results in the formation of tetramer assemblies, the membrane part of which we determined to 3.1 angstrom resolution. The structure of the type III ATP synthase tetramer and its associated lipids suggests that it is the intact unit propagating the membrane curvature.
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| 2. |
- Mühleip, Alexander, et al.
(författare)
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Structural basis of mitochondrial membrane bending by the I–II–III2–IV2 supercomplex
- 2023
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 615:7954, s. 934-938
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Tidskriftsartikel (refereegranskat)abstract
- Mitochondrial energy conversion requires an intricate architecture of the inner mitochondrial membrane. Here we show that a supercomplex containing all four respiratory chain components contributes to membrane curvature induction in ciliates. We report cryo-electron microscopy and cryo-tomography structures of the supercomplex that comprises 150 different proteins and 311 bound lipids, forming a stable 5.8-MDa assembly. Owing to subunit acquisition and extension, complex I associates with a complex IV dimer, generating a wedge-shaped gap that serves as a binding site for complex II. Together with a tilted complex III dimer association, it results in a curved membrane region. Using molecular dynamics simulations, we demonstrate that the divergent supercomplex actively contributes to the membrane curvature induction and tubulation of cristae. Our findings highlight how the evolution of protein subunits of respiratory complexes has led to the I–II–III2–IV2 supercomplex that contributes to the shaping of the bioenergetic membrane, thereby enabling its functional specialization
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| 3. |
- Naschberger, Andreas, et al.
(författare)
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Algal photosystem I dimer and high-resolution model of PSI-plastocyanin complex
- 2022
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Ingår i: Nature Plants. - : Springer Science and Business Media LLC. - 2055-0278. ; 8:10, s. 1191-1201
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Tidskriftsartikel (refereegranskat)abstract
- Photosystem I (PSI) enables photo-electron transfer and regulates photosynthesis in the bioenergetic membranes of cyanobacteria and chloroplasts. Being a multi-subunit complex, its macromolecular organization affects the dynamics of photosynthetic membranes. Here we reveal a chloroplast PSI from the green alga Chlamydomonas reinhardtii that is organized as a homodimer, comprising 40 protein subunits with 118 transmembrane helices that provide scaffold for 568 pigments. Cryogenic electron microscopy identified that the absence of PsaH and Lhca2 gives rise to a head-to-head relative orientation of the PSI–light-harvesting complex I monomers in a way that is essentially different from the oligomer formation in cyanobacteria. The light-harvesting protein Lhca9 is the key element for mediating this dimerization. The interface between the monomers is lacking PsaH and thus partially overlaps with the surface area that would bind one of the light-harvesting complex II complexes in state transitions. We also define the most accurate available PSI–light-harvesting complex I model at 2.3 Å resolution, including a flexibly bound electron donor plastocyanin, and assign correct identities and orientations to all the pigments, as well as 621 water molecules that affect energy transfer pathways.
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| 4. |
- Perez Boerema, Annemarie, et al.
(författare)
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Structure of the chloroplast ribosome with chl-RRF and hibernation-promoting factor
- 2018
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Ingår i: Nature Plants. - : Springer Science and Business Media LLC. - 2055-026X .- 2055-0278. ; 4, s. 212-217
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Tidskriftsartikel (refereegranskat)abstract
- Oxygenic photosynthesis produces oxygen and builds a variety of organic compounds, changing the chemistry of the air, the sea and fuelling the food chain on our planet. The photochemical reactions underpinning this process in plants take place in the chloroplast. Chloroplasts evolved ~1.2 billion years ago from an engulfed primordial diazotrophic cyanobacterium, and chlororibosomes are responsible for synthesis of the core proteins driving photochemical reactions. Chlororibosomal activity is spatiotemporally coupled to the synthesis and incorporation of functionally essential co-factors, implying the presence of chloroplast-specific regulatory mechanisms and structural adaptation of the chlororibosome1,2. Despite recent structural information3,4,5,6, some of these aspects remained elusive. To provide new insights into the structural specialities and evolution, we report a comprehensive analysis of the 2.9–3.1 Å resolution electron cryo-microscopy structure of the spinach chlororibosome in complex with its recycling factor and hibernation-promoting factor. The model reveals a prominent channel extending from the exit tunnel to the chlororibosome exterior, structural re-arrangements that lead to increased surface area for translocon binding, and experimental evidence for parallel and convergent evolution of chloro- and mitoribosomes.
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| 5. |
- Tobiasson, Victor, et al.
(författare)
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Ciliate mitoribosome illuminates evolutionary steps of mitochondrial translation
- 2020
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Ingår i: eLIFE. - 2050-084X. ; 9
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Tidskriftsartikel (refereegranskat)abstract
- To understand the steps involved in the evolution of translation, we used Tetrahymena thermophila, a ciliate with high coding capacity of the mitochondrial genome, as the model organism and characterized its mitochondrial ribosome (mitoribosome) using cryo-EM. The structure of the mitoribosome reveals an assembly of 94-ribosomal proteins and four-rRNAs with an additional protein mass of ~700 kDa on the small subunit, while the large subunit lacks 5S rRNA. The structure also shows that the small subunit head is constrained, tRNA binding sites are formed by mitochondria-specific protein elements, conserved protein bS1 is excluded, and bacterial RNA polymerase binding site is blocked. We provide evidence for anintrinsic protein targeting system through visualization of mitochondria-specific mL105 by the exit tunnel that would facilitate the recruitment of a nascent polypeptide. Functional protein uS3m is encoded by three complementary genes from the nucleus and mitochondrion, establishing a link between genetic drift and mitochondrial translation. Finally, we reannotated nine open reading frames in the mitochondrial genome that code for mitoribosomal proteins.
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| 6. |
- Tobiasson, Victor, et al.
(författare)
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Interconnected assembly factors regulate the biogenesis of mitoribosomal large subunit
- 2021
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Ingår i: EMBO Journal. - : EMBO. - 0261-4189 .- 1460-2075. ; 40:6
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Tidskriftsartikel (refereegranskat)abstract
- Mitoribosomes consist of ribosomal RNA and protein components, coordinated assembly of which is critical for function. We used mitoribosomes from Trypanosoma brucei with reduced RNA and increased protein mass to provide insights into the biogenesis of the mitoribosomal large subunit. Structural characterization of a stable assembly intermediate revealed 22 assembly factors, some of which have orthologues/counterparts/homologues in mammalian genomes. These assembly factors form a protein network that spans a distance of 180 angstrom, shielding the ribosomal RNA surface. The central protuberance and L7/L12 stalk are not assembled entirely and require removal of assembly factors and remodeling of the mitoribosomal proteins to become functional. The conserved proteins GTPBP7 and mt-EngA are bound together at the subunit interface in proximity to the peptidyl transferase center. A mitochondrial acyl-carrier protein plays a role in docking the L1 stalk, which needs to be repositioned during maturation. Additional enzymatically deactivated factors scaffold the assembly while the exit tunnel is blocked. Together, this extensive network of accessory factors stabilizes the immature sites and connects the functionally important regions of the mitoribosomal large subunit.
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| 7. |
- Tobiasson, Victor, 1994-
(författare)
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On the Origin and Evolution of the Mitochondrial Ribosome
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The ribosome is among the most ancient, intricate and well studied macromolecular complexes in biology. Predating the earliest divergence of life, its core molecular structure has remained mostly unchanged for more than three billion years. In stark contrast to its monolithic ancestor, the mitochondrial ribosome represents one of the most architecturally diverse protein complexes investigated. This work is an attempt at reconciling these two paradigms. In this thesis I first briefly cover the evolutionary history of the mitochondrial ribosome: from its ancient origins, through the process of Eukaryogenesis and the development of mitochondria, to its current state. Following this I present a comprehensive and integrated comparative analysis of the current mitoribosomal structures. Using these structural observations as a starting point I then summarise the current knowledge regarding the evolutionary trends of mitochondrial ribosomes. Finally I review and discuss potential genetic mechanisms and evolutionary pressures which could have produced such a vibrant diversity of structures. Together with this analysis I present monosome structures from the ciliate Tetrahymena thermophila and chlorophycean Polytomella magna together with an assembly intermediate of the large subunit from Trypanosoma brucei. Together, I hope to demonstrate the impact of the unique mitochondrial environment on the evolution of the mitochondrial ribosome.
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| 8. |
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| 9. |
- Tobiasson, Victor, et al.
(författare)
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Structure of a mitochondrial ribosome with fragmented rRNA in complex with membrane-targeting elements
- 2022
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 13:1
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Tidskriftsartikel (refereegranskat)abstract
- Mitoribosomes of green algae display a great structural divergence from their tracheophyte relatives, with fragmentation of both rRNA and proteins as a defining feature. Here, we report a 2.9 angstrom resolution structure of the mitoribosome from the alga Polytomella magna harbouring a reduced rRNA split into 13 fragments. We found that the rRNA contains a non-canonical reduced form of the 5S, as well as a permutation of the LSU domain I. The mt-5S rRNA is stabilised by mL40 that is also found in mitoribosomes lacking the 5S, which suggests an evolutionary pathway. Through comparison to other ribosomes with fragmented rRNAs, we observe that the pattern is shared across large evolutionary distances, and between cellular compartments, indicating an evolutionary convergence and supporting the concept of a primordial fragmented ribosome. On the protein level, eleven peripherally associated HEAT-repeat proteins are involved in the binding of 3' rRNA termini, and the structure features a prominent pseudo-trimer of one of them (mL116). Finally, in the exit tunnel, mL128 constricts the tunnel width of the vestibular area, and mL105, a homolog of a membrane targeting component mediates contacts with an inner membrane bound insertase. Together, the structural analysis provides insight into the evolution of the ribosomal machinery in mitochondria.
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| 10. |
- Tobiasson, Victor, et al.
(författare)
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Structure of a mitochondrial ribosome with fragmented rRNA in complexwith membrane-targeting elements
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Mitoibosomes of green alga belong to a diverged type with extreme fragmentation in rRNA andprotein material. We present a 2.9-Å resolution structure of an algal mitoribosome with reducedrRNA that is split in to 13 fragments. The architecture features a fragmentation pattern that hassimilarities with apicomplexan parasites. The unique phenomena of the rRNA include permutationand incorporation of a non-canonical and reduced mt-5S rRNA. On the protein level, elevenperipherally associated HEAT-repeat proteins involved in rRNA binding, and a specific trimer ofmL116 binds 3’ termini of three rRNA fragments. In the exit tunnel, mL128 constricts the path,and mL105 a homolog of a membrane targeting component mediates contacts with an innermembrane-bound insertase. Although overall protein content at the tunnel exit site of themitoribosome varies among eukaryotes, we find that the mechanisms of the constriction andmembrane tethering are shared between the algal and mammalian lineages. Therefore, our datareveals characteristics of fragmented rRNA an unexpected convergent evolution in the regulationof protein synthesis in mitochondria.
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