title: Phenazinium dyes safranine O and phenosafranine induce self-structure in single stranded polyadenylic acid: structural and thermodynamic studies.
abstract: The interaction of phenazinium dyes, safranine O and phenosafranine with single stranded polyadenylic acid was studied using spectroscopic viscometric and calorimetric techniques. Both dyes bind to polyadenylic acid strongly with association constant of the order of 10(5)M(-1). Safranine O showed higher affinity over phenosafranine. The binding induced conformational changes in polyadenylic acid, but the extent of change was much higher with safranine O. The bound safranine O molecules acquired strong induced circular dichroism spectra compared to the weak induced circular dichroism of phenosafranine. Fluorescence polarization, iodide quenching, viscosity results and energy transfer from bases to bound dyes suggested intercalation of the dye molecules to polyadenylic acid structure. The binding was entropy driven in both the cases. Circular dichroism and optical melting studies revealed cooperative melting profiles for dye-polyadenylic acid complexes that provided evidence for the formation of self-structured polyadenylic acid on dye binding. This structural reorganization was further confirmed by differential scanning calorimetry results.
authors.affiliation: Biophysical Chemistry Laboratory, Chemistry Division, CSIR-Indian Institute of Chemical Biology, Kolkata 700 032, India.
authors.forename: Asma Yasmeen
authors.initials: AY
authors.lastname: Khan
authors.affiliation: Biophysical Chemistry Laboratory, 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, Chemistry Division, CSIR-Indian Institute of Chemical Biology, Kolkata 700 032, India. Electronic address: gskumar@iicb.res.in.
authors.forename: Gopinatha
authors.initials: G
authors.lastname: Suresh Kumar
mesh_terms: D002152:Calorimetry, Differential Scanning; D002942:Circular Dichroism; D005454:Fluorescence Polarization; D031541:Fluorescence Resonance Energy Transfer; D005456:Fluorescent Dyes / Q000737:chemistry*; D007364:Intercalating Agents / Q000737:chemistry; D009690:Nucleic Acid Conformation; D010619:Phenazines / Q000737:chemistry*; D011061:Poly A / Q000737:chemistry*; D013053:Spectrophotometry; D014783:Viscosity
chemical_list: D005456:Fluorescent Dyes; D007364:Intercalating Agents; D010619:Phenazines; D011061:Poly A; C011977:phenosafranine; C009195:safranine T
keywords: Phenazinium dyes; Poly(A) binding; Self-structure induction