Abstract:We have investigated the interaction of the intramolecular human telomeric DNA G-quadruplex with a hemicyanine-peptide ligand, by studying the rate of quadruplex opening with a complementary DNA oligonucleotide. By employing a minimal kinetic model, the relationship between the observed rate of quadruplex opening and the ligand concentration has enabled estimation of the dissociation constant. A van't Hoff analysis revealed the enthalpy and entropy changes of binding to be −77 ± 22 kJ mol −1 and −163 ± 75 J mo… Show more
“…an increase in the lifetime and thermal stability of the complex). This is in agreement with other studies demonstrating that a quadruplex ligand affects the dissociation of a quadruplex (64,65). Several questions remain unanswered, and two main questions are the purpose of our ongoing studies: (i) Do these observations hold for different ligands?…”
G-quadruplexes are a family of four-stranded DNA structures, stabilized by G-quartets, that form in the presence of monovalent cations. Efforts are currently being made to identify ligands that selectively bind to G-quadruplex motifs as these compounds may interfere with the telomere structure, telomere elongation/replication and proliferation of cancer cells. The kinetics of quadruplex–ligands interactions are poorly understood: it is not clear whether quadruplex ligands lock into the preformed structure (i.e. increase the lifetime of the structure by lowering the dissociation constant, koff) or whether ligands actively promote the formation of the complex and act as quadruplex chaperones by increasing the association constant, kon. We studied the effect of a selective quadruplex ligand, a bisquinolinium pyridine dicarboxamide compound called 360A, to distinguish these two possibilities. We demonstrated that, in addition to binding to and locking into preformed quadruplexes, this molecule acted as a chaperone for tetramolecular complexes by acting on kon. This observation has implications for in vitro and in vivo applications of quadruplexes and should be taken into account when evaluating the cellular responses to these agents.
“…an increase in the lifetime and thermal stability of the complex). This is in agreement with other studies demonstrating that a quadruplex ligand affects the dissociation of a quadruplex (64,65). Several questions remain unanswered, and two main questions are the purpose of our ongoing studies: (i) Do these observations hold for different ligands?…”
G-quadruplexes are a family of four-stranded DNA structures, stabilized by G-quartets, that form in the presence of monovalent cations. Efforts are currently being made to identify ligands that selectively bind to G-quadruplex motifs as these compounds may interfere with the telomere structure, telomere elongation/replication and proliferation of cancer cells. The kinetics of quadruplex–ligands interactions are poorly understood: it is not clear whether quadruplex ligands lock into the preformed structure (i.e. increase the lifetime of the structure by lowering the dissociation constant, koff) or whether ligands actively promote the formation of the complex and act as quadruplex chaperones by increasing the association constant, kon. We studied the effect of a selective quadruplex ligand, a bisquinolinium pyridine dicarboxamide compound called 360A, to distinguish these two possibilities. We demonstrated that, in addition to binding to and locking into preformed quadruplexes, this molecule acted as a chaperone for tetramolecular complexes by acting on kon. This observation has implications for in vitro and in vivo applications of quadruplexes and should be taken into account when evaluating the cellular responses to these agents.
“…This implies that the kinetic stability of the different species varies over at least a 10-fold range. As for other such intramolecular quadruplexes (42,51,53), the AS1411 quadruplexes are extremely kinetically stable, but not especially thermodynamically stable. Figure 8.Dissociation kinetics of AS1411.…”
The remarkable structural polymorphism of quadruplex-forming sequences has been a considerable impediment in the elucidation of quadruplex folds. Sequence modifications have commonly been used to perturb and purportedly select a particular form out of the ensemble of folds for nuclear magnetic resonance (NMR) or X-ray crystallographic analysis. Here we report a simple chromatographic technique that separates the individual folds without need for sequence modification. The sequence d(GGTGGTGGTGGTTGTGGTGGTGGTGG) forms a compact quadruplex according to a variety of common biophysical techniques. However, NMR and chromatography showed that this oligonucleotide produces at least eight monomeric quadruplex species that interconvert very slowly at room temperature. We have used a combination of spectroscopic, hydrodynamic and thermodynamic techniques to evaluate the physicochemical properties of the mixture and the individual species. These species have almost identical thermodynamic, hydrodynamic and electrophoretic properties, but significantly different NMR and circular dichroism (CD) spectra, as well as kinetic stability. These results demonstrate that simple standard low-resolution techniques cannot always be used for quadruplex fold determination or quality control purposes, and that simple thermodynamic analysis does not directly provide interpretable thermodynamic parameters.
“…[9][10][11][12][13][14] Fluorescence resonance electron transfer (FRET) in molecular beacons has been exploited in the detection of folded and unfolded states of oligonucleotides. [15][16][17] These changes have been coupled with sensing capabilities to detect a variety of analytes. FRET also has been used to detect movements of nanomachines.…”
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