Large ribosomal subunit A-site (50S A-site) (50S A-site)

The Large ribosomal subunit A-site (aminoacyl site) is a critical functional region within the ribosome responsible for receiving incoming aminoacyl-tRNA molecules during the elongation phase of protein synthesis [1, 5]. In bacteria, this site is located on the 50S subunit and is positioned adjacent to the peptidyl transferase center (PTC), where the actual formation of peptide bonds occurs [2]. It serves as a major target for several classes of clinically important antibiotics, including oxazolidinones like linezolid and pleuromutilins like lefamulin, which bind to the A-site to physically block tRNA entry or disrupt the catalytic environment [1, 3]. Because human mitochondrial ribosomes share structural homology with bacterial 50S subunits, drugs targeting the A-site can lead to off-target inhibition of mitochondrial translation, resulting in side effects such as myelosuppression and neuropathy [3, 5]. Resistance to these drugs often arises through point mutations in the 23S rRNA or through the action of methyltransferases like Cfr, which modify the binding site to reduce drug affinity [1, 2]. Consequently, the A-site remains a focal point for the development of next-generation antimicrobials designed to bypass these resistance mechanisms while maintaining high selectivity over eukaryotic and mitochondrial counterparts [5]. The site's structural complexity, involving both ribosomal RNA and proteins, provides multiple interaction points for small molecule inhibitors [2]. Monitoring for resistance mutations in the 23S rRNA is a common strategy for assessing the efficacy and longevity of drugs targeting this region [1].

Other names

Aminoacyl-tRNA binding site50S A-site60S A-siteAcceptor siteRibosomal A-site

Inhibition of bacterial protein synthesis by binding to the A-site of the 50S ribosomal subunit, which prevents the proper positioning of aminoacyl-tRNA and inhibits peptide bond formation at the peptidyl transferase center.