MPV17L2 is required for ribosome assembly in mitochondria.

Ilaria Dalla Rosa,Romina Durigon,Elizabeth M.A Hirst,Joanna Rorbach,Michal Minczuk,Michael W Woellhaf,Ian J Holt,Martijn A Huynen,Sara Vidoni,Sarah F Pearce,Gloria Brea-Calvo,Antonella Spinazzola,Aurelio Reyes,Johannes M Herrmann

doi:10.1093/nar/gku513

Abstract

MPV17 is a mitochondrial protein of unknown function, and mutations in MPV17 are associated with mitochondrial deoxyribonucleic acid (DNA) maintenance disorders. Here we investigated its most similar relative, MPV17L2, which is also annotated as a mitochondrial protein. Mitochondrial fractionation analyses demonstrate MPV17L2 is an integral inner membrane protein, like MPV17. However, unlike MPV17, MPV17L2 is dependent on mitochondrial DNA, as it is absent from ρ0 cells, and co-sediments on sucrose gradients with the large subunit of the mitochondrial ribosome and the monosome. Gene silencing of MPV17L2 results in marked decreases in the monosome and both subunits of the mitochondrial ribosome, leading to impaired protein synthesis in the mitochondria. Depletion of MPV17L2 also induces mitochondrial DNA aggregation. The DNA and ribosome phenotypes are linked, as in the absence of MPV17L2 proteins of the small subunit of the mitochondrial ribosome are trapped in the enlarged nucleoids, in contrast to a component of the large subunit. These findings suggest MPV17L2 contributes to the biogenesis of the mitochondrial ribosome, uniting the two subunits to create the translationally competent monosome, and provide evidence that assembly of the small subunit of the mitochondrial ribosome occurs at the nucleoid.

Highlights

The mammalian mitochondrial proteome comprises 1500 or more gene products
The current study identifies MPV17L2 as an inner mitochondrial membrane protein with a key role in mitochondrial protein synthesis, as it is required for the assembly and stability of the mitochondrial ribosome
The dependence of MPV17L2 on mitochondria DNA (mtDNA) (Figure 4) and its association with the mitoribosome distinguish it from MPV17, and suggest it has evolved a new function after a gene duplication event

Summary

Introduction

The mammalian mitochondrial proteome comprises 1500 or more gene products. The deoxyribonucleic acid (DNA) inside mitochondria DNA (mtDNA) contributes only 13 of these proteins, and they make up ∼20% of the subunits of the oxidative phosphorylation (OXPHOS) system, which produces much of the cells energy. All the other proteins of the organelle are nuclear encoded, synthesized in the cytosol and imported into the mitochondria. A substantial number of these proteins have roles associated with the structure, production and maintenance of the respiratory chain and adenosine triphosphate synthase, being structural components or assembly factors thereof, or contributors to mtDNA maintenance and expression. The precise role of many mitochondrial proteins remains unknown, limiting our understanding of the organelle’s role in physiological and disease processes. The construction of a mitochondrial proteome database comprising over 1000 proteins has facilitated the discovery of mitochondrial disease-genes, such as MPV17 [1]. Neither the function of the MPV17 protein, nor the mechanism leading to mtDNA perturbation is currently known

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