16S ribosomal RNA aminoacyl-tRNA site (16S rRNA A-site)

The 16S ribosomal RNA (rRNA) A-site is a critical functional region within the 30S small subunit of the bacterial ribosome, specifically located in helix 44 (Source: https://www.nature.com/articles/35030019). It serves as the decoding center where the codon of the messenger RNA (mRNA) is matched with the anticodon of the incoming aminoacyl-transfer RNA (tRNA) (Source: https://pubmed.ncbi.nlm.nih.gov/11130711/). This site ensures the high fidelity of protein synthesis by facilitating the selection of the correct tRNA through specific conformational changes, notably the flipping of residues A1492 and A1493 (Source: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3103295/). Because of its essential role in bacterial translation, it is a primary target for several classes of antibiotics, most notably aminoglycosides and tetracyclines (Source: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4112220/). Aminoglycosides bind to this site and induce conformational changes that lead to mistranslation or premature termination of protein synthesis, while tetracyclines physically block tRNA entry (Source: https://pubmed.ncbi.nlm.nih.gov/11130711/). The specificity of these drugs for the bacterial A-site over the eukaryotic version is the basis for their therapeutic index, although similarities with human mitochondrial 12S rRNA can lead to side effects such as ototoxicity and nephrotoxicity (Source: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4112220/). Resistance to drugs targeting this site often arises through enzymatic modification of the rRNA, such as methylation by RmtB or ArmA enzymes (Source: https://pubmed.ncbi.nlm.nih.gov/17307767/).

Other names

16S rRNA decoding site30S A-siteHelix 44 of 16S rRNABacterial decoding centerA-site of the 30S ribosomal subunit

Aminoglycosides bind to the 16S rRNA A-site, inducing a conformational change in residues A1492 and A1493 that stabilizes near-cognate tRNA binding, leading to mistranslation and protein synthesis inhibition. Tetracyclines bind to the A-site to sterically block the binding of aminoacyl-tRNA to the mRNA-ribosome complex, preventing peptide chain elongation.