Structural insights into mammalian mitochondrial translation elongation catalyzed by mt EFG 1

Abstract

Mitochondria are eukaryotic organelles of bacterial origin where respiration takes place to produce cellular chemical energy. These reactions are catalyzed by the respiratory chain complexes located in the inner mitochondrial membrane. Notably, key components of the respiratory chain complexes are encoded on the mitochondrial chromosome and their expression relies on a dedicated mitochondrial translation machinery. Defects in the mitochondrial gene expression machinery lead to a variety of diseases in humans mostly affecting tissues with high energy demand such as the nervous system, the heart, or the muscles. The mitochondrial translation system has substantially diverged from its bacterial ancestor, including alterations in the mitoribosomal architecture, multiple changes to the set of translation factors and striking reductions in otherwise conserved tRNA elements. Although a number of structures of mitochondrial ribosomes from different species have been determined, our mechanistic understanding of the mitochondrial translation cycle remains largely unexplored. Here, we present two cryo‐EM reconstructions of human mitochondrial elongation factor G1 bound to the mammalian mitochondrial ribosome at two different steps of the tRNA translocation reaction during translation elongation. Our structures explain the mechanism of tRNA and mRNA translocation on the mitoribosome, the regulation of mtEFG1 activity by the ribosomal GTPase‐associated center, and the basis of decreased susceptibility of mtEFG1 to the commonly used antibiotic fusidic acid.

Structures of the human mitochondrial ribosome recycling complexes reveal distinct mechanisms of recycling and antibiotic resistance

“…Superimposition of our Class I complex with the RRFmt-unbound human (Amunts et al, 2015), bovine (Sharma et al, 2003) and porcine (Greber et al, 2015) 55S mitoribosomes showed that the small 28S subunit was rotated counter-clockwise by about 8.5° with respect to the large 39S subunit (Fig. S3B), similar to the "ratchet-like inter-subunit rotation" observed in the bacterial 70S ribosome Agrawal, 2000, 2001) and the 55S mitoribosomes complexed with translational factors (Koripella et al, 2020;Koripella et al, 2019b;Kummer and Ban, 2020;Kummer et al, 2018). In addition to the inter-subunit rotation, the head domain of the 28S subunit is rotated by about 4° towards the tRNA exit (E) site in a direction roughly orthogonal to the inter-subunit motion (Fig.…”

“…EF-G2mt has about 36 % aa sequence identity to EF-G1mt and about 30 % aa identity to both its bacterial homologues. Some mammalian mitochondrial translation steps are now better understood through determination of the cryo-EM structures of the initiation (Koripella et al, 2019a;Kummer et al, 2018;Yassin et al, 2011) and the elongation (Koripella et al, 2020;Kummer and Ban, 2020) complexes at highresolution. Our previous study of the human mitoribosome recycling complex of the RRFmtbound 55S (Koripella et al, 2019b) provided useful insights into the mito-specific aspects of the recycling process, but a complete 55S mitoribosomal recycling complex comprising both RRFmt and EF-Gmt remained elusive.…”

Analysis of translating mitoribosome reveals functional characteristics of translation in mitochondria of fungi

“…This structural rearrangement during mtSSU rotation suggests a coordinated movement of the mtSSU rotation and mL108 to the L1 stalk. The involvement of mitochondria-specific elements in coordination of tRNA movement has been recently reported also in other systems 20–22 .…”

Analysis of translating mitoribosome reveals functional characteristics of translation in mitochondria of fungi

“…coordinated movement of the mtSSU rotation and mL108 to the L1 stalk. The involvement of mitochondria-specific elements in coordination of tRNA movement has been recently reported also in other systems [21][22][23] .…”