Bacterial 50S ribosomal subunit (23S rRNA peptidyl transferase center and nascent peptide exit tunnel) (50S subunit)

The bacterial 50S ribosomal subunit is the larger component of the 70S prokaryotic ribosome and serves as the primary site for protein synthesis catalysis [1, 6]. It is composed of 23S ribosomal RNA (rRNA), 5S rRNA, and approximately 33 ribosomal proteins, with the 23S rRNA forming the core functional regions [9, 13]. Two critical sites within this subunit are the peptidyl transferase center (PTC), which facilitates the formation of peptide bonds between amino acids, and the nascent peptide exit tunnel (NPET), which provides a path for the growing polypeptide to leave the ribosome [2, 11, 13]. These regions are the targets of several major antibiotic classes, including macrolides, lincosamides, oxazolidinones, and pleuromutilins [1, 4, 6]. Macrolides typically bind within the NPET to block the progression of the nascent chain, while lincosamides and oxazolidinones interact with the PTC to inhibit the catalytic step of translation [1, 2, 8]. Because of the structural conservation between bacterial and human mitochondrial ribosomes, drugs targeting the 50S subunit can sometimes cause off-target mitochondrial toxicity, leading to adverse effects like myelosuppression [15, 18]. Resistance to these agents is a significant clinical challenge, often mediated by mutations in the 23S rRNA or enzymatic modification of the ribosomal RNA by methyltransferases [7, 16]. This target remains a cornerstone of antimicrobial therapy for a wide range of bacterial infections, from respiratory tract infections to skin and soft tissue infections [6, 17].

Other names

Large ribosomal subunit50S subunit23S rRNAPeptidyl transferase centerNascent peptide exit tunnelPTCNPET

Inhibition of bacterial protein synthesis by blocking peptide bond formation at the peptidyl transferase center or obstructing the nascent peptide exit tunnel.