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

Abstract Entamoeba histolytica, an anaerobic parasite protozoan, is the causative agent of amoebiasis, the 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 and determined its single particle cryo- EM structures. The 53S, ribosome large subunit (LSU), at 2.8 Å resolution, and the 75S, associated ribosome, at 3.3 Å resolution. The E. histolytica possesses a reduced ribosome with a conserved core, and the periphery evolved with Entamoeba specific unique features. The most notable features are the presence of the rRNA triple helix near the peptide exit tunnel on LSU and the co-evolution of rRNA expansion segments and extensions in r-proteins. These structures provide valuable insights into the evolutionary adaption of the Entamoeba translational machinery and could be explored further for amoebicidal therapeutic intervention.