High-resolution structures of mitochondrial ribosomes and their functional implications.

Mitochondrial ribosomes (mitoribosomes) almost exclusively synthesize essential components of the oxidative phosphorylation machinery. Dysfunction of mitochondrial protein biosynthesis leads to human diseases and plays an important role in the altered metabolism of cancer cells. Recent developments in cryo-electron microscopy enabled the structural characterization of complete yeast and mammalian mitoribosomes at near-atomic resolution. Despite originating from ancestral bacterial ribosomes, mitoribosomes have diverged in their composition and architecture. Mitoribosomal proteins are larger and more numerous, forming an extended network around the ribosomal RNA, which is expanded in yeast and highly reduced in mammals. Novel protein elements at the entrance or exit of the mRNA channel imply a different mechanism of mRNA recruitment. The polypeptide tunnel is optimized for the synthesis of hydrophobic proteins and their co-translational membrane insertion.