Structural investigation of human mitochondrial translation and off-target antibiotic binding

Sammanfattning: Human mitochondrial translation machinery has evolved to translate 13 mitochondrial mRNAs encoding components of the oxidative phosphorylation pathway responsible for ATP production. The structural basis of human mitochondrial translation is distinct from the canonical bacterial and cytosolic translation systems. Further, mutations affecting mitochondrial protein synthesis disrupt ATP production resulting in myopathies and neurodegenerative diseases. Structural studies have identified the core components of the human mitoribosome and some of its associated translation factors but several important aspects such as the role of mito-specific proteins in translation, rRNA modifications, composition of its ultrastructure including ions, small molecule co-factors, and solvent content, remain poorly understood. Importantly, several important antibiotics that target bacterial translation also affect mitochondrial translation, thereby causing adverse effects in patients. Understanding the mechanism of off-target antibiotic binding to the mitoribosome could help in designing better antibiotics. In this work, we use electron cryo-microscopy to determine the structures of the human mitoribosome in complex with ligands: mRNA/tRNA and translation activators such as LRPPRC-SLIRP. This allows us to explore the structural basis of mitochondrial translation, identifying the roles of mito-specific protein elements in tRNA and mRNA binding and recruitment (Papers 1 and 2). We determine a 2.2 Å resolution structure of the human mitoribosome and a 2.4 Å resolution structure of the mitoribosomal small subunit in complex with the tuberculosis drug, streptomycin. Together, the structures represent the most detailed and complete models for the human mitoribosome, revealing rRNA and protein modifications; several novel small molecule cofactors: 2Fe-2S clusters, polyamines and nucleotides and mechanisms of antibiotic binding (Papers 3 and 4).