Bert Willis

Triple recognition of B-DNA by a neomycin-Hoechst 33258-pyrene conjugate.

Recent developments have indicated that aminoglycoside binding is not limited to RNA, but to nucleic acids that, like RNA, adopt conformations similar to its A-form. We further sought to expand the utility of aminoglycoside binding to B-DNA structures by conjugating neomycin, an aminoglycoside antibiotic, with the B-DNA minor groove binding ligand Hoechst 33258. Envisioning a dual groove binding mode, we have extended the potential recognition process to include a third, intercalative moiety. Similar conjugates, which vary in the number of binding moieties but maintain identical linkages to allow direct comparisons to be made, have also been prepared. We report herein novel neomycin- and Hoechst 33258-based conjugates developed in our laboratories for exploring the recognition potential with B-DNA. Spectroscopic studies such as UV melting, differential scanning calorimetry, isothermal fluorescence titrations, and circular dichroism together illustrate the triple recognition of the novel conjugate containing neomycin, Hoechst 33258, and pyrene. This study represents the first example of DNA molecular recognition capable of minor versus major groove recognition in conjunction with intercalation.

An Expanding View of Aminoglycoside–Nucleic Acid Recognition

Publisher Summary This chapter discusses the applications of aminoglycosides in the field of medicine. The origin of aminoglycoside antibiotics began with streptomycin 60 years ago. Isolated from Actinomyces griseus, streptomycin immediately found applications for the treatment against the tuberculosis-causing microorganism—Mycobacterium tuberculosis. This was the second antibiotic after penicillin to be used clinically. Throughout the coming years, a number of aminoglycosides were discovered with varying potencies for treating infections. However, therapeutic applications were diminished by the emergence of resistance to aminoglycosides by bacteria. Though widely known for binding to prokaryotic ribosomal RNA, aminoglycosides have more recently shown affinity for other nucleic acid targets. This opens door to a new area of therapeutic applications. This chapter outlines the history of aminoglycosides, from their discovery, structural elucidation, and mechanism of action to the current knowledge of mechanisms of action and resistance, toxicity, and novel nucleic acid targets. Owing to a number of recent reviews pertaining to some of these areas, particular emphasis is placed on the recently discovered aminoglycoside targets and their potential therapeutic applications.

Triple recognition of B-DNA.

A novel conjugate of Hoechst 33258, pyrene and neomycin was synthesized and examined for its binding and stabilization of A-T rich DNA duplexes using spectroscopic and viscometric techniques. The conjugate, containing three well known ligands that bind nucleic acids albeit in different binding modes, was found to significantly stabilize DNA over parent conjugates containing only one or both of the other recognition elements. The study represents the first example of DNA molecular recognition capable of minor/major groove recognition in conjunction with intercalation.

Recognition of RNA duplex by a neomycin-Hoechst 33258 conjugate.

DNA minor groove binding drugs such as Hoechst 33258 have been shown to bind to a number of RNA structures. Similarly, RNA binding ligands such as neomycin have been shown by us to bind to a number of A-form DNA structures. A neomycin-Hoechst 33258 conjugate was recently shown to bind B-DNA, where Hoechst exhibits high affinity for the minor groove of A/T tract DNA and neomycin docks into the major groove. Further studies now indicate that the Hoechst moiety of the conjugate can be driven to bind RNA duplex as a consequence of neomycin binding in the RNA major groove. This is the first example of Hoechst 33258 binding to RNA duplex not containing bulges or loop motifs.