title: Binding of BOBO-3 intercalative dye to DNA homo-oligonucleotides with different base compositions.
abstract: The interactions between trimethine cyanine homodimer dye, BOBO-3 (1,1'-(4,4,7,7-tetramethyl-4,7-diazaundecamethylene)-bis-4-[3-methyl-2,3-dihydro-(benzo-1,3-thiazole)-2-methylidene]-pyridinium tetraiodide), and single-stranded homo-oligonucleotides, double-stranded complementary homo-oligonucleotides, and high-molecular-weight double-stranded polyhomonucleotides have been investigated in detail using absorption and both steady-state and time-resolved fluorescence spectroscopy. In this work, we describe the differences in the binding behavior of BOBO-3 with double-stranded DNA (dsDNA) having different base contents. The fluorescence intensity of BOBO-3 interacting with deoxyadenosine-deoxythymidine (dAdT) dsDNA was higher than with the deoxyguanosine-deoxycytidine (dGdC) double helix. However, the BOBO-3 lifetime was longer in dGdC-rich dsDNA than in dsDNA with many dAdT sites. This result was detected at both the ensemble level and the single-molecule level. This behavior is a consequence of the dye's interacting with dsDNA on two kinds of binding sites. This phenomenon also occurs in natural dsDNA (Ruedas-Rama, M. J.; Orte, A.; Crovetto, L.; Talavera, E. M.; Alvarez-Pez, J. M. J. Phys. Chem. B 2010, 114, 1094-1103). By using a time-resolved fluorescence methodology and the McGhee-von Hippel theory for two overlapping, noncooperative binding modes, we obtained the equilibrium binding constants and the number of occupied sites for each binding mode of BOBO-3 in dAdT and dGdC binding sites. BOBO-3 has a higher affinity for dAdT sites and occupies 4.0 +/- 1.0 sites in its primary binding mode, whereas in dGdC-rich double strands, BOBO-3 covers 6.2 +/- 1.1 sites and has a lower affinity. These differences in the binding features and spectral properties of BOBO-3 may be used to develop approaches to identify GC- or AT-rich regions within large strands of dsDNA.
authors.affiliation: Department of Physical Chemistry, Faculty of Pharmacy, University of Granada, Campus Cartuja, 18071 Granada, Spain.
authors.forename: Maria J
authors.initials: MJ
authors.lastname: Ruedas-Rama
authors.forename: Jose M
authors.initials: JM
authors.lastname: Alvarez-Pez
authors.forename: Jose M
authors.initials: JM
authors.lastname: Paredes
authors.forename: Eva M
authors.initials: EM
authors.lastname: Talavera
authors.forename: Angel
authors.initials: A
authors.lastname: Orte
mesh_terms: D001665:Binding Sites; D002232:Carbocyanines / Q000737:chemistry*; D004247:DNA / Q000737:chemistry*; D007364:Intercalating Agents / Q000737:chemistry*; D009841:Oligonucleotides / Q000737:chemistry*; D013050:Spectrometry, Fluorescence
chemical_list: C098829:BOBO 3; D002232:Carbocyanines; D007364:Intercalating Agents; D009841:Oligonucleotides; D004247:DNA