MPV17L2 is required for ribosome assembly in mitochondria

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.

The Human Mitochondrial DEAD-Box Protein DDX28 Resides in RNA Granules and Functions in Mitoribosome Assembly

“…These studies suggest a close association among nucleoids, RNA granules and the mitochondrial protein synthesis machinery. Recent data has shown that mitoribosome assembly could be initiated within or near the nucleoids (Bogenhagen et al, 2014; Dalla Rosa et al, 2014; He et al, 2012a), possibly in a co-transcriptional manner as it occurs in bacteria (Shajani et al, 2011). Our data on the localization of DDX28 within RNA granules, its participation in mt-LSU assembly and the composition of its interactome, all point toward the conclusion that most steps of mitoribosome biogenesis, at least for the mt-LSU, could occur in the RNA granules.…”

The process of mammalian mitochondrial protein synthesis

“…C7orf30 (MALSU1) promotes the incorporation of uL14m into the mt-LSU, an event that is necessary for subunit stability (Rorbach et al 2012; Fung et al 2013). Depletion of the IMM protein MPV17L2, which is known to interact with the mt-LSU, leads to a reduction of both subunits, highlighting a possible role for this protein in their assembly (Dalla Rosa et al 2014). Finally, a small proportion of GRSF1 has been suggested to be involved in the assembly of the mt-SSU, as its depletion leads to the accumulation of incomplete mt-SSU; however, this has not been experimentally determined (Antonicka et al 2013; Jourdain et al 2013).…”

“…Its homologue in yeast has been suggested to interact with the mitoribosome (Jia et al 2003) and the C-terminus of the human protein has been cross-linked to components of the mt-LSU, namely uL13m, bL20m, bL28m, mL48, mL49 and mL51 (Haque et al 2010), although these are not located in close proximity to the PES. MPV17L2 is an integral membrane protein that has been co-localised with the mt-LSU on sucrose gradients, suggesting its involvement in anchoring the subunit to the IMM (Dalla Rosa et al 2014). LetM1, another IMM protein, contains a large matrix domain and its homologue in yeast (Mdm38) has been reported to interact with the mitoribosome (Lupo et al 2011).…”

Mitochondrial ribosomes in cancer

“…The precise role of mTERF3 (or mTERFD1) is not understood [64], but mTERF4 binds to the rRNA methyltransferase NSUN4 to promote its recruitment to the mt-LSU [65], possibly to facilitate monosome assembly [66]. A role in monosome formation has also been proposed for MPV17L2, a mtDNA maintenance factor [67], although its function remains intriguing. Two DEAD-box helicases, DDX28 and DHX30, participate in mt-LSU assembly [68, 69].…”