As an indispensable molecular machine universal in all living organisms,the ribosome has been selected by evolution to be the natural target of many antibiotics and small-molecule inhibitors.High-resolution structures of pathogen ribosomes are crucial for understanding the general and unique aspects of translation control in disease-causing microbes.With cryo-electron microscopy technique,we have determined structures of the cytosolic ribosomes from two human parasites,Trichomonas vaginalis and Toxoplasma gondii,at resolution of 3.2-3.4,(A).Although the ribosomal proteins from both pathogens are typical members of eukaryotic families,with a co-evolution pattern between certain species-specific insertions/extensions and neighboring ribosomal RNA (rRNA) expansion segments,the sizes of their rRNAs are sharply different.Very interestingly,rRNAs of T.vaginalis are in size comparable to prokaryotic counterparts,with nearly all the eukaryote-specific rRNA expansion segments missing.These structures facilitate the dissection of evolution path for ribosomal proteins and RNAs,and may aid in design of novel translation inhibitors.
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