CARB 6 |
| Aminoglycosides are a family of broad-spectrum antibiotics that are used widely in the clinic. Their bactericidal activities are ascribed to their deleterious effects on protein synthesis, which include mRNA misreading as well as inhibition of ribosomal translocation and recycling. The mistranslational effects of aminoglycosides are associated with the specific binding of the drugs to the highly conserved A-site at the 3-end of the 16 S rRNA. The abilities of aminoglycosides to recognize a specific subdomain of a large RNA molecule makes these compounds archetypical models for RNA-targeting drugs. Buffer-dependent calorimetric measurements reveal that aminoglycoside binding to the A-site at physiological pH is coupled to protonation of drug amino groups. These binding-linked drug protonation effects point to an electrostatic driving force for the binding reactions, a driving force that is manifested entropically. Another hallmark of aminoglycoside binding to the 16 S rRNA A-site is a coupled conformational change in the RNA that involves the destacking of two conserved adenine residues at positions 1492 and 1493. This drug-induced conformational switch is characterized by a negative heat capacity change (ΔCp) for the binding reaction, and appears to be a more important modulator of translational fidelity than drug affinity for the A-site. The biological importance of the conformational switch is underscored by time-resolved fluorescence anisotropy measurements, which reveal a correlation between drug-induced alterations in the mobilities of A1492 and A1493 and activity. Comparative studies of aminoglycoside binding to the bacterial and human rRNA A-sites suggest that the prokaryotic specificity of aminoglycoside action reflects differences in the conformational dynamics associated with the binding reactions. |
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RNA as a Drug Target
8:20 AM-1:20 PM, Sunday, April 6, 2008 Morial Convention Center -- Rm. 214, Oral
Division of Carbohydrate Chemistry |