title: Binding interaction of phenothiazinium dyes with double stranded RNAs: Spectroscopic and calorimetric investigation.
abstract: RNA targeting through small molecules is an emerging and promising therapeutic route that necessitates identification of small molecules that can selectively target specific RNA structures. In this context a comparative study of the interaction of two phenothiazinium dyes thionine (THN) and toluidine blue O (TBO) with three double stranded RNA polynucleotides (ds RNAs) viz. poly(I).poly(C), poly(A).poly(U) and poly(C).poly(G) was conducted by various biophysical techniques. A higher binding of THN with poly(I).poly(C) over poly(A).poly(U) and poly(C).poly(G) was observed. The intercalative binding and RNA induced fluorescence quenching of the dyes through a static mechanism was confirmed by viscosity studies and steady state polarization anisotropy experiments. Binding induced structural perturbation in the RNA polynucleotides was confirmed from circular dichroism spectroscopy. DSC and thermal melting experiments confirmed that the binding resulted in strong thermal stabilization. The binding affinity of THN with poly(I).poly(C) was the highest followed by that to poly(A).poly(U) and poly(C).poly(G). The trend was the same for TBO also, but THN bound stronger than TBO. The binding of the dyes was characterized by strong negative enthalpy changes with minimum positive entropy changes indicating typical intercalative interaction. The results presented here may be useful to design new types of RNA binding antitumor, antibacterial and anticancer agents.
authors.affiliation: Biophysical Chemistry Laboratory, Organic and Medicinal Chemistry Division, CSIR-Indian Institute of Chemical Biology, Kolkata 700 032, India.
authors.forename: Baishakhi
authors.initials: B
authors.lastname: Saha
authors.affiliation: Biophysical Chemistry Laboratory, Organic and Medicinal Chemistry Division, CSIR-Indian Institute of Chemical Biology, Kolkata 700 032, India. Electronic address: gskumar@iicb.res.in.
authors.forename: Gopinatha Suresh
authors.initials: GS
authors.lastname: Kumar
mesh_terms: D002152:Calorimetry, Differential Scanning; D002942:Circular Dichroism; D004396:Coloring Agents / Q000737:chemistry*; D005454:Fluorescence Polarization; D009690:Nucleic Acid Conformation; D009994:Osmolar Concentration; D010640:Phenothiazines / Q000737:chemistry*; D012330:RNA, Double-Stranded / Q000737:chemistry*; D013050:Spectrometry, Fluorescence; D013816:Thermodynamics; D014783:Viscosity
chemical_list: D004396:Coloring Agents; D010640:Phenothiazines; D012330:RNA, Double-Stranded
keywords: Calorimetry; Ds RNAs; Hydrodynamic study; Phenothiazinium dyes; Spectroscopic interaction; Thionine; Toluidine blue O