title: Synthesis and characterization of monomolecular DNA G-quadruplexes formed by tetra-end-linked oligonucleotides.
abstract: Guanine-rich DNA sequences are widely dispersed in the eukaryotic genome and are abundant in regions with relevant biological significance. They can form quadruplex structures stabilized by guanine quartets. These structures differ for number and strand polarity, loop composition, and conformation. We report here the syntheses and the structural studies of a set of interconnected d(TG(4)T) fragments which are tethered, with different orientations, to a tetra-end-linker in an attempt to force the formation of specific four-stranded DNA quadruplex structures. Two synthetic strategies have been used to obtain oligodeoxyribonucleotide (ODN) strands linked with their 3'- or 5'-ends to each of the four arms of the linker. The first approach allowed the synthesis of tetra-end-linked ODN (TEL-ODN) containing the four ODN strands with a parallel orientation, while the latter synthetic pathway led to the synthesis of TEL-ODNs each containing antiparallel ODN pairs. The influence of the linker at 3'- or 5'-ODN, on the quadruplex typology and stability, in the presence of sodium or potassium ions, has been investigated by circular dichroism (CD), CD thermal denaturation, (1)H NMR experiments at variable temperature, and molecular modeling. All synthesized TEL-ODNs formed parallel G-quadruplex structures. Particularly, the TEL-ODN containing all parallel ODN tracts formed very stable parallel G-quadruplex complexes, whereas the TEL-ODNs containing antiparallel ODN pairs led to relatively less stable parallel G-quadruplexes. The molecular modeling data suggested that the above antiparallel TEL-ODNs can adopt parallel G-quadruplex structures thanks to a considerable folding of the tetra-end-linker around the whole quadruplex scaffold.
authors.affiliation: Dipartimento di Chimica delle Sostanze Naturali, Università degli Studi di Napoli Federico II, Via D. Montesano 49, I-80131 Napoli, Italy.
authors.forename: Giorgia
authors.initials: G
authors.lastname: Oliviero
authors.forename: Jussara
authors.initials: J
authors.lastname: Amato
authors.forename: Nicola
authors.initials: N
authors.lastname: Borbone
authors.forename: Aldo
authors.initials: A
authors.lastname: Galeone
authors.forename: Luigi
authors.initials: L
authors.lastname: Petraccone
authors.forename: Michela
authors.initials: M
authors.lastname: Varra
authors.forename: Gennaro
authors.initials: G
authors.lastname: Piccialli
authors.forename: Luciano
authors.initials: L
authors.lastname: Mayol
mesh_terms: D002851:Chromatography, High Pressure Liquid; D002942:Circular Dichroism; D004247:DNA / Q000138:chemical synthesis / Q000737:chemistry*; D008958:Models, Molecular; D019906:Nuclear Magnetic Resonance, Biomolecular; D009841:Oligonucleotides / Q000737:chemistry*; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization
chemical_list: D009841:Oligonucleotides; D004247:DNA