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

The Bacterial 50S ribosomal subunit – 23S rRNA nascent peptide exit tunnel (NPET) is a critical structural channel within the large ribosomal subunit through which newly synthesized polypeptide chains pass to reach the exterior of the ribosome (Kannan & Mankin, 2011). Spanning approximately 100 Å in length and 10–20 Å in width, the tunnel is primarily composed of 23S ribosomal RNA (rRNA) and is constricted by the loops of ribosomal proteins uL4 and uL22 (Vázquez-Laslop & Mankin, 2018). Beyond its role as a passive conduit, the NPET actively participates in translation regulation and co-translational protein folding by sensing specific nascent peptide sequences (Kannan & Mankin, 2012). It serves as the primary therapeutic target for several major classes of antibiotics, including macrolides, lincosamides, and streptogramins, which bind within the tunnel to physically obstruct the passage of the growing peptide (Arenz & Wilson, 2016). This obstruction leads to the cessation of protein synthesis and subsequent inhibition of bacterial growth, making it a cornerstone of antimicrobial therapy for various infections (Patsnap, 2024). Resistance to these drugs often arises through modifications of the tunnel's components, such as the methylation of the A2058 residue in the 23S rRNA or mutations in the uL4 and uL22 proteins (Vázquez-Laslop & Mankin, 2018). Furthermore, the structural similarity between bacterial and human mitochondrial ribosomes can lead to off-target effects, presenting a significant challenge in drug design (Biomolecules, 2024). Understanding the complex interactions within the NPET is essential for developing next-generation antibiotics that can bypass existing resistance mechanisms (Kannan & Mankin, 2011).

Other names

Nascent peptide exit tunnelRibosomal exit tunnelPolypeptide exit tunnel50S exit tunnelRibosomal tunnel

Inhibition of protein synthesis by binding to the 23S rRNA within the upper chamber of the exit tunnel, physically obstructing the passage of the nascent peptide chain and inducing premature dissociation of peptidyl-tRNA from the ribosome.