50S ribosomal subunit (50S subunit)

The 50S ribosomal subunit is the larger component of the 70S ribosome found in bacteria and the apicoplast organelle of apicomplexan parasites such as Plasmodium falciparum (Dahl & Rosenthal, 2007, Antimicrobial Agents and Chemotherapy). It is a complex ribonucleoprotein assembly responsible for the peptidyl transferase activity that catalyzes peptide bond formation and contains the exit tunnel through which the nascent polypeptide chain emerges (NCBI Bookshelf, 'The Ribosome'). Because the apicoplast is an essential organelle of endosymbiotic bacterial origin, its translation machinery is highly conserved with bacterial systems and distinct from the human 80S cytosolic ribosome. This structural divergence allows for the selective targeting of pathogens by several classes of antimicrobial agents, including macrolides, lincosamides, and oxazolidinones (StatPearls, 'Macrolides'). In malaria treatment, drugs targeting the apicoplast 50S subunit often exhibit a 'delayed death' effect, where the parasite's progeny are unable to survive due to the loss of apicoplast function in the second generation (Botté et al., 2012, Genes & Development). However, the structural similarity between the 50S subunit and human mitochondrial ribosomes can lead to off-target effects and clinical toxicity, such as myelosuppression or lactic acidosis, during prolonged treatment (Wilson, 2014).

Other names

Large ribosomal subunitBacterial 50S ribosomeApicoplast 50S ribosomeProkaryotic 50S subunit70S ribosome large subunit

Inhibition of protein synthesis by binding to the 50S ribosomal subunit, which blocks the peptidyl transferase center (PTC) or the ribosomal exit tunnel, thereby preventing peptide bond formation or the translocation of the nascent peptide chain (Wilson, 2014, Nature Reviews Microbiology).