Bacterial 50S ribosomal subunit peptide exit tunnel (50S exit tunnel)

The bacterial 50S ribosomal subunit peptide exit tunnel is a critical structural component of the large ribosomal subunit, serving as the pathway for nascent polypeptide chains to exit the ribosome during translation. This tunnel, primarily composed of 23S ribosomal RNA (rRNA) and ribosomal proteins like L4 and L22, is the primary binding site for several major classes of antibiotics, including macrolides, lincosamides, and streptogramins (MLS antibiotics) [PMID: 25108494]. These drugs bind near the peptidyl transferase center at the tunnel's entrance, physically obstructing the passage of the growing peptide and causing premature peptidyl-tRNA dissociation [PMID: 16271889]. In addition to the mature tunnel, 50S assembly precursors—intermediate stages in the complex process of ribosome biogenesis—are increasingly recognized as viable targets for novel antimicrobial agents that disrupt the formation of functional ribosomes [PMID: 30305561]. Targeting this site is essential for treating a wide range of bacterial infections, although its clinical utility is threatened by resistance mechanisms such as rRNA methylation by Erm methyltransferases or mutations in ribosomal proteins [PMID: 24513071].

Other names

Large ribosomal subunit peptide exit tunnelRibosomal exit tunnelPolypeptide exit tunnel50S assembly precursors23S rRNA exit tunnel

Antibiotics targeting this site bind to the 23S rRNA at the entrance of the peptide exit tunnel, sterically hindering the elongation of the nascent polypeptide chain and triggering the release of incomplete proteins, thereby inhibiting bacterial protein synthesis [PMID: 25108494].