The Roles of Assembly Factors in Mammalian Mitoribosome Biogenesis

AbstractAssembly of the mitoribosome is largely enigmatic and involves numerous assembly factors. Little is known about their function and the architectural transitions of the pre-ribosomal intermediates. Here, we solve cryo-EM structures of the human 39S large subunit pre-ribosomes, representing five distinct late states. Besides the MALSU1 complex used as bait for affinity purification, we identify several assembly factors, including the DDX28 helicase, MRM3, GTPBP10 and the NSUN4-mTERF4 complex, all of which keep the 16S rRNA in immature conformations. The late transitions mainly involve rRNA domains IV and V, which form the central protuberance, the intersubunit side and the peptidyltransferase center of the 39S subunit. Unexpectedly, we find deacylated tRNA in the ribosomal E-site, suggesting a role in 39S assembly. Taken together, our study provides an architectural inventory of the distinct late assembly phase of the human 39S mitoribosome.

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Ubiquitin and Ubiquitin-Like Proteins and Domains in Ribosome Production and Function: Chance or Necessity?

International Journal of Molecular Sciences ◽

10.3390/ijms22094359 ◽

2021 ◽

Vol 22 (9) ◽

pp. 4359

Author(s):

Sara Martín-Villanueva ◽

Gabriel Gutiérrez ◽

Dieter Kressler ◽

Jesús de la Cruz

Keyword(s):

Ribosomal Proteins ◽

Ribosome Biogenesis ◽

Ribosome Assembly ◽

Cellular Processes ◽

Substrate Protein ◽

Precursor Proteins ◽

Assembly Factors ◽

Ubiquitin Moiety ◽

And Function

Ubiquitin is a small protein that is highly conserved throughout eukaryotes. It operates as a reversible post-translational modifier through a process known as ubiquitination, which involves the addition of one or several ubiquitin moieties to a substrate protein. These modifications mark proteins for proteasome-dependent degradation or alter their localization or activity in a variety of cellular processes. In most eukaryotes, ubiquitin is generated by the proteolytic cleavage of precursor proteins in which it is fused either to itself, constituting a polyubiquitin precursor, or as a single N-terminal moiety to ribosomal proteins, which are practically invariably eL40 and eS31. Herein, we summarize the contribution of the ubiquitin moiety within precursors of ribosomal proteins to ribosome biogenesis and function and discuss the biological relevance of having maintained the explicit fusion to eL40 and eS31 during evolution. There are other ubiquitin-like proteins, which also work as post-translational modifiers, among them the small ubiquitin-like modifier (SUMO). Both ubiquitin and SUMO are able to modify ribosome assembly factors and ribosomal proteins to regulate ribosome biogenesis and function. Strikingly, ubiquitin-like domains are also found within two ribosome assembly factors; hence, the functional role of these proteins will also be highlighted.

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Prokaryotic assembly factors for the attachment of flavin to complex II

Biochimica et Biophysica Acta (BBA) - Bioenergetics ◽

10.1016/j.bbabio.2012.09.003 ◽

2013 ◽

Vol 1827 (5) ◽

pp. 637-647 ◽

Cited By ~ 17

Author(s):

Matthew B. McNeil ◽

Peter C. Fineran

Keyword(s):

Complex Ii ◽

Assembly Factors

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Assembly factors monitor sequential hemylation of cytochrome b to regulate mitochondrial translation

The Journal of Cell Biology ◽

10.1083/jcb.201401009 ◽

2014 ◽

Vol 205 (4) ◽

pp. 511-524 ◽

Cited By ~ 40

Author(s):

Markus Hildenbeutel ◽

Eric L. Hegg ◽

Katharina Stephan ◽

Steffi Gruschke ◽

Brigitte Meunier ◽

...

Keyword(s):

Electron Transport ◽

Cytochrome B ◽

Mitochondrial Respiratory Chain ◽

Complex Iii ◽

Mitochondrial Translation ◽

Respiratory Chain Complexes ◽

Mitochondrial Inner Membrane ◽

Sequence Of Events ◽

Chain Complexes ◽

Assembly Factors

Mitochondrial respiratory chain complexes convert chemical energy into a membrane potential by connecting electron transport with charge separation. Electron transport relies on redox cofactors that occupy strategic positions in the complexes. How these redox cofactors are assembled into the complexes is not known. Cytochrome b, a central catalytic subunit of complex III, contains two heme bs. Here, we unravel the sequence of events in the mitochondrial inner membrane by which cytochrome b is hemylated. Heme incorporation occurs in a strict sequential process that involves interactions of the newly synthesized cytochrome b with assembly factors and structural complex III subunits. These interactions are functionally connected to cofactor acquisition that triggers the progression of cytochrome b through successive assembly intermediates. Failure to hemylate cytochrome b sequesters the Cbp3–Cbp6 complex in early assembly intermediates, thereby causing a reduction in cytochrome b synthesis via a feedback loop that senses hemylation of cytochrome b.

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The Human Cytochrome c Oxidase Assembly Factors SCO1 and SCO2 Have Regulatory Roles in the Maintenance of Cellular Copper Homeostasis

Cell Metabolism ◽

10.1016/j.cmet.2006.12.001 ◽

2007 ◽

Vol 5 (1) ◽

pp. 9-20 ◽

Cited By ~ 149

Author(s):

Scot C. Leary ◽

Paul A. Cobine ◽

Brett A. Kaufman ◽

Guy-Hellen Guercin ◽

Andre Mattman ◽

...

Keyword(s):

Cytochrome C ◽

Cytochrome C Oxidase ◽

Copper Homeostasis ◽

Human Cytochrome ◽

Assembly Factors ◽

Cellular Copper ◽

Human Cytochrome C

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A conserved rRNA switch is central to decoding site maturation on the small ribosomal subunit

10.1101/2020.10.19.334821 ◽

2020 ◽

Author(s):

Andreas Schedlbauer ◽

Idoia Iturrioz ◽

Borja Ochoa-Lizarralde ◽

Tammo Diercks ◽

Jorge Pedro López-Alonso ◽

...

Keyword(s):

Molecular Mechanisms ◽

Structural Information ◽

Ribosomal Subunit ◽

Ribosome Assembly ◽

Structural Description ◽

Sequential Order ◽

Bacterial Ribosome ◽

Core Set ◽

Assembly Factors ◽

Conformational Landscape

While a structural description of the molecular mechanisms guiding ribosome assembly in eukaryotic systems is emerging, bacteria employ an unrelated core set of assembly factors for which high-resolution structural information is still missing. To address this, we used single-particle cryo-EM to visualize the effects of bacterial ribosome assembly factors RimP, RbfA, RsmA, and RsgA on the conformational landscape of the 30S ribosomal subunit and obtained eight snapshots representing late steps in the folding of the decoding center. Analysis of these structures identifies a conserved secondary structure switch in the 16S rRNA central to decoding site maturation, and suggests both a sequential order of action and molecular mechanisms for the assembly factors in coordinating and controlling this switch. Structural and mechanistic parallels between bacterial and eukaryotic systems indicate common folding features inherent to all ribosomes.

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