Bacterial 50S ribosomal subunit P-site (50S P-site)

The bacterial 50S ribosomal subunit P-site (peptidyl site) region near the 3' CCA end of tRNA is a critical functional domain within the peptidyl transferase center (PTC). This site is responsible for accommodating the acceptor stem of the peptidyl-tRNA, positioning the nascent peptide chain for the addition of the next amino acid during translation elongation (PNAS, 2013; NAR, 2021). Antibiotics targeting this region, such as pleuromutilins (e.g., lefamulin) and blasticidin S, exert their antimicrobial effects by physically obstructing the P-site or inducing conformational distortions in the tRNA's CCA terminus (NIH, 2016; PNAS, 2013). These interactions prevent the proper alignment of substrates required for peptide bond formation and can also interfere with translation termination by blocking release factor access (NAR, 2021; NIH, 2018). Because this site is highly conserved and essential for bacterial viability, it serves as a potent target for antimicrobial therapy, particularly against multidrug-resistant Gram-positive pathogens (NIH, 2019). However, therapeutic challenges include the potential for cross-reactivity with mitochondrial ribosomes and the emergence of resistance mechanisms such as Cfr-mediated rRNA methylation or specific mutations in ribosomal proteins (NIH, 2007; NIH, 2016).

Other names

P-site of the peptidyl transferase centerCCA-binding region of the P-site23S rRNA P-siteBacterial large ribosomal subunit P-sitePeptidyl-tRNA binding site

Antibiotics targeting this region bind to the peptidyl transferase center (PTC) of the 50S subunit, specifically interacting with the P-site. This binding either sterically blocks the accommodation of the 3' CCA end of the peptidyl-tRNA or induces a conformational distortion (e.g., bending the CCA end toward the A-site), which prevents peptide bond formation and inhibits translation termination by interfering with release factor binding (PNAS, 2013; NIH, 2016).