title: Luminescence study of G-quadruplex formation in the presence of Tb3+ ion.
abstract: The interactions of Tb3+ with the quadruplex-forming oligonucleotide bearing human telomeric repeat sequence d(G(3)T(2)AG(3)T(2)AG(3)T(2)AG(3)), (htel21), have been studied using luminescence spectroscopy and circular dichroism (CD). Enhanced luminescence of Tb3+, resulting from energy transfer from guanines, indicated encapsulation of Tb3+ ion in the central cavity of quadruplex core. The ability of lanthanide ions (Eu3+ and Tb3+) to mediate formation of quadruplex structure has been further evidenced by the fluorescence energy transfer measurements with the use of oligonucleotide probe labeled with fluorescein and rhodamine FRET partners, FAM-htel21-TAMRA. The CD spectra revealed that Tb3+/htel21 quadruplex possesses antiparallel strand orientation, similarly as sodium quadruplex. Tb3+ binding equilibria have been investigated in the absence and the presence of competing metal cations. At low Tb3+ concentration (8 microM) Tb3+/htel21 quadruplex stability is very high (5 x 10(6) M(-1)) and stoichiometry of 5-7 Tb3+ ions per one quadruplex molecule is observed. Luminescence and CD titration experiments suggested that the cavity of quadruplex accommodates two Tb3+ ions and the remaining Tb3+ ions bind probably to TTA loops of quadruplex. Higher concentration of Tb3+ (above 10 microM) results in the excessive binding of Tb3+ ions that finally destabilizes quadruplex, which undergoes transformation into differently organized assemblies. Such assemblies (probably possessing multiple positive charge) exhibit kinetic stability, which is manifested by a very slow kinetics of displacement of Tb3+ ion by competing cations (Li+, Na+, K+).
authors.affiliation: Department of Analytical Chemistry, Faculty of Chemistry, A. Mickiewicz University, 60-780 Poznan, Poland.
authors.forename: Elzbieta
authors.initials: E
authors.lastname: Galezowska
authors.forename: Agata
authors.initials: A
authors.lastname: Gluszynska
authors.forename: Bernard
authors.initials: B
authors.lastname: Juskowiak
mesh_terms: D002412:Cations / Q000737:chemistry; D002942:Circular Dichroism; D031541:Fluorescence Resonance Energy Transfer; D006147:Guanine / Q000737:chemistry*; D006801:Humans; D049449:Luminescence; D009690:Nucleic Acid Conformation; D009838:Oligodeoxyribonucleotides / Q000737:chemistry* / Q000235:genetics; D016615:Telomere / Q000235:genetics; D013725:Terbium / Q000737:chemistry*
chemical_list: D002412:Cations; D009838:Oligodeoxyribonucleotides; D013725:Terbium; D006147:Guanine