Binding of aminoglycoside antibiotics to helix 69 of 23S rRNA

Abstract

Aminoglycosides antibiotics negate dissociation and recycling of the bacterial ribosome's subunits by binding to Helix 69 (H69) of 23S rRNA. Aminoglycoside binding to the chemically synthesized terminal domains of the E. coli and human H69 was detected and quantified using UV‐monitored thermal denaturation, circular dichroism spectrapolarimetry, and isothermal titration calorimetry. The unmodified E. coli H69 hairpin exhibited a significantly higher affinity for neomycin and tobramycin than for paromomycin, while the binding of streptomycin was too weak to assess. The three conserved pseudouridine modifications (Ψ1911, Ψ1915, Ψ1917) occurring in the loop of the E. coli H69 did not significantly effect the dissociation constant or stoichiometry for the binding of paromomycin. In contrast, the human 28S rRNA H69 had a considerably decreased affinity for the antibiotics. The higher affinity of the bacterial 23S rRNA H69 for aminoglycosides is an important validation of the antibiotic target. The higher affinity of the E. coli H69 for neomycin and tobramycin as compared to paromomycin and streptomycin indicates differences in the efficacy of the aminoglycosides as anti‐microbial agents.