title: NMR based structural studies decipher stacking of the alkaloid coralyne to terminal guanines at two different sites in parallel G-quadruplex DNA, [d(TTGGGGT)]4and [d(TTAGGGT)]4.
abstract: Telomere elongation by telomerase gets inhibited by G-quadruplex DNA found in its guanine rich region. Stabilization of G-quadruplex DNA upon ligand binding has evolved as a promising strategy to target cancer cells in which telomerase is over expressed.
  
  
  
  Interaction of anti-leukemic alkaloid, coralyne, to tetrameric parallel [d(TTGGGGT)]4(Ttel7), [d(TTAGGGT)]4(Htel7) and monomeric anti-parallel [dGGGG(TTGGGG)3] (Ttel22) G-quadruplex DNA has been studied using Circular Dichroism (CD) spectroscopy. Titrations of coralyne with Ttel7 and Htel7 were monitored by1H and31P NMR spectroscopy. Solution structure of coralyne-Ttel7 complex was obtained by restrained Molecular Dynamics (rMD) simulations using distance restraints from 2D NOESY spectra. Thermal stabilization of DNA was determined by absorption, CD and1H NMR.
  
  
  
  Binding of coralyne to Ttel7/Htel7 induces negative CD band at 315/300nm. A significant upfield shift in all GNH, downfield shift in T2/T7 base protons and upfield shift (1.8ppm) in coralyne protons indicates stacking interactions.31P chemical shifts and NOE contacts of G3, G6, T2, T7 protons with methoxy protons reveal proximity of coralyne to T2pG3 and G6pT7 sites. Solution structure reveals stacking of coralyne at G6pT7 and T2pG3 steps with two methoxy groups of coralyne located in the grooves along with formation of a hydrogen bond. Binding stabilizes Ttel7/Htel7 by ~25-35°C in 2:1 coralyne-Ttel7/Htel7 complex.
  
  
  
  The present study is the first report on solution structure of coralyne-Ttel7 complex showing stacking of coralyne with terminal guanine tetrads leading to significant thermal stabilization, which may be responsible for telomerase inhibition.
authors.affiliation: Department of Biotechnology, Indian Institute of Technology Roorkee, Roorkee 247667, India.
authors.forename: Kumar
authors.initials: K
authors.lastname: Padmapriya
authors.affiliation: Department of Biotechnology, Indian Institute of Technology Roorkee, Roorkee 247667, India. Electronic address: ritubfbs@iitr.ac.in.
authors.forename: Ritu
authors.initials: R
authors.lastname: Barthwal
mesh_terms: D000470:Alkaloids / Q000737:chemistry*; D001600:Berberine Alkaloids / Q000737:chemistry*; D002942:Circular Dichroism; D004247:DNA / Q000737:chemistry*; D054856:G-Quadruplexes; D006147:Guanine / Q000737:chemistry*; D006860:Hydrogen Bonding; D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D056004:Molecular Dynamics Simulation; D011522:Protons; D019098:Telomerase / Q000737:chemistry; D016615:Telomere / Q000737:chemistry
chemical_list: D000470:Alkaloids; D001600:Berberine Alkaloids; D011522:Protons; D006147:Guanine; C000666:coralyne; D004247:DNA; D019098:Telomerase
keywords: Alkaloid coralyne; Circular dichroism; Nuclear magnetic resonance; Restrained molecular dynamics; Telomeric G-quadruplex DNA; Thermal stabilization