Cryo-EM structure of ribosome from pathogenic protozoa Entamoeba histolytica reveals unique features of its architecture.

Entamoeba histolytica, an anaerobic protozoan parasite, is the causative agent of amoebiasis, bloody diarrhea, and liver abscesses in humans. Amoebiasis is more predominant in tropical areas with poor sanitation conditions, and it remains the fourth leading cause of death due to a protozoan infection. E. histolytica life cycle spans between an infective 'cyst stage' and an active disease-causing 'trophozoite stage'. We have isolated ribosomes from the trophozoite stage of E. histolytica. Here, we report single particle cryo-EM structures of the 53S ribosome large subunit (LSU), and 75S associated ribosomes, with P-tRNA, A/P and P/E tRNAs, and with paromomycin antibiotic, at 2.8 Å to 3.4 Å resolution. The E. histolytica possesses a reduced ribosome with a conserved core, and the periphery evolved with species-specific unique features. The most notable features are the presence of the rRNA triple helix near the peptide exit tunnel, the expansion segment H88ES102 near the exit site on LSU, and unique insertions in r-proteins. Furthermore, the 75S ribosome paromomycin complex structure provides the atomic details of its interactions. These structures provide insights into the evolutionary adaptation of the E. histolytica translational machinery and may be explored further for amoebicidal therapeutic intervention.