50S ribosomal subunit, 23S rRNA nascent peptide exit tunnel (NPET) (NPET)

The 50S ribosomal subunit's 23S rRNA nascent peptide exit tunnel (NPET) is a critical structural conduit within the bacterial ribosome that allows newly synthesized polypeptides to exit the peptidyl transferase center and reach the cellular environment (Wilson & Beckmann, 2011). Spanning approximately 80-100 Å in length, the tunnel is primarily composed of 23S ribosomal RNA and is shaped by ribosomal proteins such as uL4 and uL22 (Nissen et al., 2000). This site is the primary pharmacological target for several classes of clinically important antibiotics, most notably the macrolides, ketolides, and streptogramins (Patsnap Synapse, 2024). These drugs bind to specific nucleotides within the 23S rRNA, such as A2058 and A2059, to physically obstruct the passage of the growing peptide chain. This blockage results in the premature release of peptidyl-tRNA and the cessation of bacterial protein synthesis, making it a vital target for treating various bacterial infections. Beyond its role as a passive channel, the NPET also participates in translational regulation by interacting with specific nascent peptide sequences to induce ribosome stalling (Vazquez-Laslop & Mankin, 2018). Resistance to drugs targeting this site often arises through ribosomal mutations or enzymatic modifications, such as methylation by Erm-family methyltransferases (PubMed, 2017).

Other names

Ribosomal exit tunnelPolypeptide exit tunnel23S rRNA exit tunnel50S exit tunnelNascent peptide exit tunnel

Antibiotics bind to the 23S rRNA within the 50S ribosomal subunit to sterically block the nascent peptide exit tunnel, which prevents the elongation of the polypeptide chain and leads to the premature dissociation of peptidyl-tRNA from the ribosome.