“Structures of mitochondrial ribosomes determined entirely by cryo-EM.”
During 2 billion years of separate evolution, mitochondrial ribosomes (mitoribosomes) have evolved unique features by acquisition of ~50% more proteins and alteration of their RNA composition.
We resolved structures of large ribosomal subunit from yeast and human mitochondria by cryo-EM to the nominal resolution of 3.2 Å and 3.4 Å respectively. The quality of the density maps enabled de novo model building by following amino acid side chains and nucleic acid bases. Thus methodologically, this work shows that recent advances in cryo-EM can be used to determine structures of a comparable quality to X-ray crystallography, without a priory biochemical knowledge and from much smaller amount of more heterogeneous material.
Structure of large ribosomal subunit from human mitochondria reveals highly divergent architecture from all other known ribosomes. This includes unique design of the central protuberance, rearrangement of tRNA binding sites, new elements of the L7/L12 stalk and adaptation of the polypeptide exit tunnel to the synthesis of highly hydrophobic polypeptides.
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