bims-tricox 2023-01-29 papers

EMBO J. 2023 Jan 27. e112309

MitoStores: chaperone-controlled protein granules store mitochondrial precursors in the cytosol.

Lena Krämer, Niko Dalheimer, Markus Räschle, Zuzana Storchová, Jan Pielage, Felix Boos, Johannes M Herrmann.

Hundreds of nucleus-encoded mitochondrial precursor proteins are synthesized in the cytosol and imported into mitochondria in a post-translational manner. However, the early processes associated with mitochondrial protein targeting remain poorly understood. Here, we show that in Saccharomyces cerevisiae, the cytosol has the capacity to transiently store mitochondrial matrix-destined precursors in dedicated deposits that we termed MitoStores. Competitive inhibition of mitochondrial protein import via clogging of import sites greatly enhances the formation of MitoStores, but they also form during physiological cell growth on nonfermentable carbon sources. MitoStores are enriched for a specific subset of nucleus-encoded mitochondrial proteins, in particular those containing N-terminal mitochondrial targeting sequences. Our results suggest that MitoStore formation suppresses the toxic potential of aberrantly accumulating mitochondrial precursor proteins and is controlled by the heat shock proteins Hsp42 and Hsp104. Thus, the cytosolic protein quality control system plays an active role during the early stages of mitochondrial protein targeting through the coordinated and localized sequestration of mitochondrial precursor proteins.

Keywords: chaperones; mitochondria; proteasome; protein aggregates; protein translocation

DOI: https://doi.org/10.15252/embj.2022112309

PLoS Comput Biol. 2023 Jan 23. 19(1): e1010870

Modelling ribosome kinetics and translational control on dynamic mRNA.

Eric C Dykeman.

The control of protein synthesis and the overall levels of various proteins in the cell is critical for achieving homoeostasis. Regulation of protein levels can occur at the transcriptional level, where the total number of messenger RNAs in the overall transcriptome are controlled, or at the translational level, where interactions of proteins and ribosomes with the messenger RNA determine protein translational efficiency. Although transcriptional control of mRNA levels is the most commonly used regulatory control mechanism in cells, positive-sense single-stranded RNA viruses often utilise translational control mechanisms to regulate their proteins in the host cell. Here I detail a computational method for stochastically simulating protein synthesis on a dynamic messenger RNA using the Gillespie algorithm, where the mRNA is allowed to co-translationally fold in response to ribosome movement. Applying the model to the test case of the bacteriophage MS2 virus, I show that the models ability to accurately reproduce experimental measurements of coat protein production and translational repression of the viral RNA dependant RNA polymerase at high coat protein concentrations. The computational techniques reported here open up the potential to examine the infection dynamics of a ssRNA virus in a host cell at the level of the genomic RNA, as well as examine general translation control mechanisms present in polycistronic mRNAs.

DOI: https://doi.org/10.1371/journal.pcbi.1010870

Methods Mol Biol. 2023 ;2586 1-14

Rtools: A Web Server for Various Secondary Structural Analyses on Single RNA Sequences.

Yukiteru Ono, Kiyoshi Asai.

Predicting the secondary structures of RNA molecules is an essential step to characterize their functions, but the thermodynamic probability of any prediction is generally small. On the other hand, there are a few tools for calculating and visualizing various secondary structural information from RNA sequences. We implemented a web server that calculates in parallel various features of secondary structures: different types of secondary structure predictions, the marginal probabilities for local structural contexts, accessibilities of the subsequences, the energy changes by arbitrary base mutations, and the measures for validations of the predicted secondary structures. The web server is available at http://rtools.cbrc.jp , which integrates software tools, CentroidFold, CentroidHomfold, IPknot, CapR, Raccess, Rchange, RintD, and RintW.

Keywords: Pseudoknot; RNA secondary structure analysis; Structure alignment; Web server

DOI: https://doi.org/10.1007/978-1-0716-2768-6_1

Nat Cell Biol. 2023 Jan 23.

Small heat shock proteins operate as molecular chaperones in the mitochondrial intermembrane space.

Elias Adriaenssens, Bob Asselbergh, Pablo Rivera-Mejías, Sven Bervoets, Leen Vendredy, Vicky De Winter, Katrien Spaas, Riet de Rycke, Gert van Isterdael, Francis Impens, Thomas Langer, Vincent Timmerman.

Mitochondria are complex organelles with different compartments, each harbouring their own protein quality control factors. While chaperones of the mitochondrial matrix are well characterized, it is poorly understood which chaperones protect the mitochondrial intermembrane space. Here we show that cytosolic small heat shock proteins are imported under basal conditions into the mitochondrial intermembrane space, where they operate as molecular chaperones. Protein misfolding in the mitochondrial intermembrane space leads to increased recruitment of small heat shock proteins. Depletion of small heat shock proteins leads to mitochondrial swelling and reduced respiration, while aggregation of aggregation-prone substrates is countered in their presence. Charcot-Marie-Tooth disease-causing mutations disturb the mitochondrial function of HSPB1, potentially linking previously observed mitochondrial dysfunction in Charcot-Marie-Tooth type 2F to its role in the mitochondrial intermembrane space. Our results reveal that small heat shock proteins form a chaperone system that operates in the mitochondrial intermembrane space.

DOI: https://doi.org/10.1038/s41556-022-01074-9