Mitochondrial protein synthesis: figuring the fundamentals, complexities and complications, of mammalian mitochondrial translation

Abstract

Mitochondrial protein synthesis is essential for all mammals, being responsible for providing key components of the oxidative phosphorylation complexes. Although only thirteen different polypeptides are made, the molecular details of this deceptively simple process remain incomplete. Central to this process is a non-canonical ribosome, the mitoribosome, which has evolved to address its unique mandate. In this review, we integrate the current understanding of the molecular aspects of mitochondrial translation with recent advances in structural biology. We identify numerous key questions that we will need to answer if we are to increase our knowledge of the molecular mechanisms underlying mitochondrial protein synthesis.

Keywords: Gene expression; Mitochondria; RNA; Ribosomes; Translation.

Fig. 1

Intact 5S rRNA does not co-localise with the large subunit of mitochondrial mitoribosomes. Cell lysates (850 μg), prepared from human HEK293 cells, were separated by isokinetic sucrose gradients . RNA was isolated from each fraction (1 – 10) and the subsequent northern blot was interrogated to determine the distribution of ribosomal RNA species . Positions of the cytosolic and mitochondrial small and large subunits are indicated underneath the panels. ‘Load’ represents RNA extracted from 85 μg cell lysate, equivalent to 10% of the lysate that was loaded onto the gradient. The position of the mt-LSU is boxed together with the corresponding fractions for the 5S rRNA panel.