bims-tricox 2023-03-19 papers

bioRxiv. 2023 Feb 28. pii: 2023.02.28.530191. [Epub ahead of print]

The chemical landscape of the human ribosome at 1.67 Å resolution.

Alexandre Faille, Kyle C Dent, Simone Pellegrino, Pekka Jaako, Alan J Warren.

The ability of ribosomes to translate the genetic code into protein requires a finely tuned ion and solvent ecosystem. However, the lack of high-resolution structures has precluded accurate positioning of all the functional elements of the ribosome and limited our understanding of the specific role of ribosomal RNA chemical modifications in modulating ribosome function in health and disease. Here, using a new sample preparation methodology based on functionalised pristine graphene-coated grids, we solve the cryo-EM structure of the human large ribosomal subunit to a resolution of 1.67 Å. The accurate assignment of water molecules, magnesium and potassium ions in our model highlights the fundamental biological role of ribosomal RNA methylation in harnessing unconventional carbon-oxygen hydrogen bonds to establish chemical interactions with the environment and fine-tune the functional interplay with tRNA. In addition, the structures of three translational inhibitors bound to the human large ribosomal subunit at better than 2 Å resolution provide mechanistic insights into how three key druggable pockets of the ribosome are targeted and illustrate the potential of this methodology to accelerate high-throughput structure-based design of anti-cancer therapeutics.

DOI: https://doi.org/10.1101/2023.02.28.530191

Elife. 2023 Mar 17. pii: e84877. [Epub ahead of print]12

Concurrent remodeling of nucleolar 60S subunit precursors by the Rea1 ATPase and Spb4 RNA helicase.

Valentin Mitterer, Matthias Thoms, Robert Buschauer, Otto Berninghausen, Ed Hurt, Roland Beckmann.

Biogenesis intermediates of nucleolar ribosomal 60S precursor particles undergo a number of structural maturation steps before they transit to the nucleoplasm and are finally exported into the cytoplasm. The AAA+-ATPase Rea1 participates in the nucleolar exit by releasing the Ytm1-Erb1 heterodimer from the evolving pre-60S particle. Here, we show that the DEAD-box RNA helicase Spb4 with its interacting partner Rrp17 is further integrated into this maturation event. Spb4 binds to a specific class of late nucleolar pre-60S intermediates, whose cryo-EM structure revealed how its helicase activity facilitates melting and restructuring of 25S rRNA helices H62 and H63/H63a prior to Ytm1-Erb1 release. In vitro maturation of such Spb4-enriched pre-60S particles, incubated with purified Rea1 and its associated pentameric Rix1-complex in the presence of ATP, combined with cryo-EM analysis depicted the details of the Rea1-dependent large-scale pre-ribosomal remodelling. Our structural insights unveil how the Rea1 ATPase and Spb4 helicase remodel late nucleolar pre-60S particles by rRNA restructuring and dismantling of a network of several ribosomal assembly factors.

Keywords: S. cerevisiae; biochemistry; chemical biology; molecular biophysics; structural biology

DOI: https://doi.org/10.7554/eLife.84877

Mol Cell. 2023 Mar 16. pii: S1097-2765(23)00123-5. [Epub ahead of print]83(6): 890-910

Mitochondrial protein transport: Versatility of translocases and mechanisms.

Jakob D Busch, Laura F Fielden, Nikolaus Pfanner, Nils Wiedemann.

Biogenesis of mitochondria requires the import of approximately 1,000 different precursor proteins into and across the mitochondrial membranes. Mitochondria exhibit a wide variety of mechanisms and machineries for the translocation and sorting of precursor proteins. Five major import pathways that transport proteins to their functional intramitochondrial destination have been elucidated; these pathways range from the classical amino-terminal presequence-directed pathway to pathways using internal or even carboxy-terminal targeting signals in the precursors. Recent studies have provided important insights into the structural organization of membrane-embedded preprotein translocases of mitochondria. A comparison of the different translocases reveals the existence of at least three fundamentally different mechanisms: two-pore-translocase, β-barrel switching, and transport cavities open to the lipid bilayer. In addition, translocases are physically engaged in dynamic interactions with respiratory chain complexes, metabolite transporters, quality control factors, and machineries controlling membrane morphology. Thus, mitochondrial preprotein translocases are integrated into multi-functional networks of mitochondrial and cellular machineries.

DOI: https://doi.org/10.1016/j.molcel.2023.02.020

Front Young Minds. 2022 May;pii: 686804. [Epub ahead of print]10

How Do Bacteria "See" Molecules Inside Themselves?

Andrew Knappenberger, David Hiller.

RNA, like its close cousin DNA, is used to store information in the cell. Unlike DNA, it is really good at folding up into interesting shapes, which makes it good at lots of other important jobs. Some kinds of RNA, called riboswitches, can sense what is going on inside a cell. Each riboswitch fits a specific small molecule. When the riboswitch and small molecule interact it changes what the cell does. For example, if the small molecule is harmful the cell might start making a protein that will get rid of it. Recently, scientists discovered some riboswitches that look very similar to each other but recognize very different small molecules. We used X-ray crystallography to get pictures of these riboswitches. We saw how changing just one piece of the riboswitch changed which small molecule it recognized. This shows us how RNA can gain new functions as an organism evolves.

Keywords: RNA; Riboswitch; crystallography; evolution

DOI: https://doi.org/10.3389/frym.2022.686804