title: Role of locked nucleic acid modified complementary strand in quadruplex/Watson-Crick duplex equilibrium.
abstract: In the human genome, the G-rich sequences that form quadruplexes are present along with their C-rich complementary strands; this suggests the existence of equilibrium between a quadruplex and a Watson-Crick duplex which allows the execution of their respective biological functions. We have investigated the sensitivity of this equilibrium to pharmacological agents by employing locked nucleic acid (LNA) modified complementary strands, and demonstrated successful invasion of the stable telomeric quadruplex d[(G(3)TTA)(3)G(3)]. Fluorescence, UV, ITC, and SPR studies were performed to understand the binding process involving the preformed quadruplex and LNA-modified complementary strands compared with that involving the unmodified complementary strand. Our data indicate that LNA modifications in the complementary strand shift the equilibrium toward the duplex state. These modifications confer increased thermodynamic stability to the duplex and increase the magnitude of relative free energy (DeltaDeltaG degrees) difference between duplex and quadruplex, thus favoring the predominance of duplex population over quadruplex. This superior ability of LNA-modified complementary strand can be exploited to pave an exploratory approach in which it hybridizes to a telomeric quadruplex and drives duplex formation, and inhibits the recognition of 3' G-rich overhang by RNA template of telomerase which guides telomere extension.
authors.affiliation: Proteomics and Structural Biology Unit, Institute of Genomics and Integrative Biology, CSIR, Mall Road, New Delhi 110 007, India.
authors.forename: Niti
authors.initials: N
authors.lastname: Kumar
authors.forename: Souvik
authors.initials: S
authors.lastname: Maiti
mesh_terms: D020029:Base Pairing; D002942:Circular Dichroism; D004247:DNA / Q000737:chemistry*; D054856:G-Quadruplexes; D009841:Oligonucleotides / Q000737:chemistry*; D014466:Ultraviolet Rays
chemical_list: D009841:Oligonucleotides; C477371:locked nucleic acid; D004247:DNA