Bacterial 50S ribosomal subunit peptidyl transferase center A-site (PTC A-site)

The Bacterial 50S ribosomal subunit peptidyl transferase center (PTC) A-site is a vital catalytic region within the large ribosomal subunit, primarily composed of 23S ribosomal RNA [6, 8]. It serves as the binding site for the incoming aminoacyl-tRNA, positioning it for the nucleophilic attack on the peptidyl-tRNA located in the adjacent P-site [7, 8]. This process is essential for peptide bond formation and the elongation of the nascent polypeptide chain during bacterial translation [6, 7]. As a ribozyme, the PTC's activity is mediated by RNA rather than protein, making it a unique and highly conserved target for antimicrobial therapy [3, 6]. Various antibiotic classes, such as oxazolidinones (e.g., linezolid), phenicols (e.g., chloramphenicol), and lincosamides (e.g., clindamycin), target this site to inhibit protein synthesis and arrest bacterial proliferation [1, 2, 3]. These drugs typically function by sterically blocking the A-site or interfering with the catalytic mechanism of the peptidyl transferase reaction [1, 2]. Resistance often emerges through rRNA mutations or enzymatic modifications, such as methylation by the Cfr enzyme, which can lead to broad-spectrum resistance across multiple drug classes [1, 3]. Due to the evolutionary conservation between bacterial and human mitochondrial ribosomes, therapeutic agents targeting the PTC A-site must be carefully designed to minimize off-target toxicity, such as myelosuppression [1, 2].

Other names

Ribosomal A-siteAminoacyl-tRNA binding site50S A-sitePeptidyl transferase center A-sitePTC A-site

Inhibition of protein synthesis by sterically blocking aminoacyl-tRNA binding at the A-site or inhibiting the peptidyl transferase reaction [1, 2, 8].