60S ribosomal subunit peptidyl-transferase center A-site (60S PTC A-site)

The 60S ribosomal subunit peptidyl-transferase center (PTC) A-site is a critical functional domain within the eukaryotic ribosome responsible for the catalysis of peptide bond formation during translation. Located primarily within the 28S ribosomal RNA, the A-site (aminoacyl site) serves as the docking point for incoming aminoacyl-tRNA molecules that carry the next amino acid for the growing polypeptide chain (Ben-Shem et al., 2011; Science). The PTC acts as a ribozyme, where the ribosomal RNA itself catalyzes the nucleophilic attack required for protein synthesis. This site is a significant therapeutic target; for instance, the FDA-approved drug Omacetaxine mepesuccinate binds specifically to the A-site cleft to inhibit protein synthesis in leukemic cells, particularly those overexpressing short-lived pro-survival proteins like MCL1 (Gandhi et al., 2014; Blood). Additionally, the A-site is the target of various potent toxins like ricin, which depurinates a specific adenine residue in the sarcin-ricin loop adjacent to the PTC, effectively inactivating the ribosome (Walsh et al., 2013; Toxins). Because the 60S subunit is essential for all eukaryotic life, drugs targeting this site must be carefully managed to avoid systemic toxicity, often manifesting as myelosuppression or gastrointestinal distress.

Other names

Eukaryotic large ribosomal subunit A-site28S rRNA peptidyl-transferase centerRibosomal A-site60S A-site cleftPeptidyl transferase center A-site

Inhibition of the elongation phase of protein translation by competitively occupying the A-site cleft of the peptidyl-transferase center, thereby preventing the binding of aminoacyl-tRNA and subsequent peptide bond formation (Gandhi et al., 2014; PubMed CID 24901544).