bims-tricox 2023-04-02 papers

bioRxiv. 2023 Mar 14. pii: 2023.03.14.532478. [Epub ahead of print]

Principles of human pre-60 S biogenesis.

During early stages of human large ribosomal subunit (60 S ) biogenesis, an ensemble of assembly factors establishes and fine-tunes the essential RNA functional centers of pre-60 S particles by an unknown mechanism. Here, we report a series of cryo-electron microscopy structures of human nucleolar and nuclear pre-60 S assembly intermediates at resolutions of 2.5-3.2 Ã…. These structures show how protein interaction hubs tether assembly factor complexes to nucleolar particles and how GTPases and ATPases couple irreversible nucleotide hydrolysis steps to the installation of functional centers. Nuclear stages highlight how a conserved RNA processing complex, the rixosome, couples large-scale RNA conformational changes to pre-rRNA processing by the RNA degradation machinery. Our ensemble of human pre-60 S particles provides a rich foundation to elucidate the molecular principles of ribosome formation.
One-Sentence Summary: High-resolution cryo-EM structures of human pre-60S particles reveal new principles of eukaryotic ribosome assembly.

DOI: https://doi.org/10.1101/2023.03.14.532478

Biomolecules. 2023 03 20. pii: 566. [Epub ahead of print]13(3):

Structural Insights into the Distortion of the Ribosomal Small Subunit at Different Magnesium Concentrations.

Ting Yu, Junyi Jiang, Qianxi Yu, Xin Li, Fuxing Zeng.

Magnesium ions are abundant and play indispensable functions in the ribosome. A decrease in Mg2+ concentration causes 70S ribosome dissociation and subsequent unfolding. Structural distortion at low Mg2+ concentrations has been observed in an immature pre50S, while the structural changes in mature subunits have not yet been studied. Here, we purified the 30S subunits of E. coli cells under various Mg2+ concentrations and analyzed their structural distortion by cryo-electron microscopy. Upon systematically interrogating the structural heterogeneity within the 1 mM Mg2+ dataset, we observed 30S particles with different levels of structural distortion in the decoding center, h17, and the 30S head. Our model showed that, when the Mg2+ concentration decreases, the decoding center distorts, starting from h44 and followed by the shifting of h18 and h27, as well as the dissociation of ribosomal protein S12. Mg2+ deficiency also eliminates the interactions between h17, h10, h15, and S16, resulting in the movement of h17 towards the tip of h6. More flexible structures were observed in the 30S head and platform, showing high variability in these regions. In summary, the structures resolved here showed several prominent distortion events in the decoding center and h17. The requirement for Mg2+ in ribosomes suggests that the conformational changes reported here are likely shared due to a lack of cellular Mg2+ in all domains of life.

Keywords: CryoEM; magnesium concentration; ribosome; structural distortion

DOI: https://doi.org/10.3390/biom13030566

Curr Biol. 2023 Mar 27. pii: S0960-9822(23)00177-X. [Epub ahead of print]33(6): R219-R221

Evolution: 'Millefoglie' origin of mitochondrial cristae.

Paul A M Michels, Michael L Ginger.

Striated intracytoplasmic membranes in alphaproteobacteria are often reminiscent of millefoglie pastries. A new study reveals a protein complex homologous to that responsible for mitochondrial cristae formation drives intracytoplasmic membrane formation, thereby establishing bacterial ancestry for the biogenesis of mitochondrial cristae.

DOI: https://doi.org/10.1016/j.cub.2023.02.037