bims-tricox 2024-07-28 papers

Issue of 2024–07–28
two papers selected by
Yash Verma, University of Zurich

Nucleic Acids Res. 2024 Jul 22. pii: gkae645. [Epub ahead of print]

The human mitochondrial translation factor TACO1 alleviates mitoribosome stalling at polyproline stretches.

Michele Brischigliaro, Annika Krüger, J Conor Moran, Hana Antonicka, Ahram Ahn, Eric A Shoubridge, Joanna Rorbach, Antoni Barrientos.

The prokaryotic translation elongation factor P (EF-P) and the eukaryotic/archaeal counterparts eIF5A/aIF5A are proteins that serve a crucial role in mitigating ribosomal stalling during the translation of specific sequences, notably those containing consecutive proline residues (1,2). Although mitochondrial DNA-encoded proteins synthesized by mitochondrial ribosomes also contain polyproline stretches, an EF-P/eIF5A mitochondrial counterpart remains unidentified. Here, we show that the missing factor is TACO1, a protein causative of a juvenile form of neurodegenerative Leigh's syndrome associated with cytochrome c oxidase deficiency, until now believed to be a translational activator of COX1 mRNA. By using a combination of metabolic labeling, puromycin release and mitoribosome profiling experiments, we show that TACO1 is required for the rapid synthesis of the polyproline-rich COX1 and COX3 cytochrome c oxidase subunits, while its requirement is negligible for other mitochondrial DNA-encoded proteins. In agreement with a role in translation efficiency regulation, we show that TACO1 cooperates with the N-terminal extension of the large ribosomal subunit bL27m to provide stability to the peptidyl-transferase center during elongation. This study illuminates the translation elongation dynamics within human mitochondria, a TACO1-mediated biological mechanism in place to mitigate mitoribosome stalling at polyproline stretches during protein synthesis, and the pathological implications of its malfunction.

DOI: https://doi.org/10.1093/nar/gkae645

Biomolecules. 2024 Jul 22. pii: 882. [Epub ahead of print]14(7):

The Beak of Eukaryotic Ribosomes: Life, Work and Miracles.

Sara Martín-Villanueva, Carla V Galmozzi, Carmen Ruger-Herreros, Dieter Kressler, Jesús de la Cruz.

Ribosomes are not totally globular machines. Instead, they comprise prominent structural protrusions and a myriad of tentacle-like projections, which are frequently made up of ribosomal RNA expansion segments and N- or C-terminal extensions of ribosomal proteins. This is more evident in higher eukaryotic ribosomes. One of the most characteristic protrusions, present in small ribosomal subunits in all three domains of life, is the so-called beak, which is relevant for the function and regulation of the ribosome's activities. During evolution, the beak has transitioned from an all ribosomal RNA structure (helix h33 in 16S rRNA) in bacteria, to an arrangement formed by three ribosomal proteins, eS10, eS12 and eS31, and a smaller h33 ribosomal RNA in eukaryotes. In this review, we describe the different structural and functional properties of the eukaryotic beak. We discuss the state-of-the-art concerning its composition and functional significance, including other processes apparently not related to translation, and the dynamics of its assembly in yeast and human cells. Moreover, we outline the current view about the relevance of the beak's components in human diseases, especially in ribosomopathies and cancer.

Keywords: Ubi3; eS10; eS12; eS31; ribosomal protuberances; ribosome biogenesis; translation accuracy

DOI: https://doi.org/10.3390/biom14070882