title: Fast gas-phase hydrogen/deuterium exchange observed for a DNA G-quadruplex.
abstract: The gas-phase hydrogen/deuterium (H/D) exchange kinetics of DNA G-quadruplexes has been investigated using Fourier transform ion cyclotron resonance mass spectrometry (FTICRMS). The quadruplex [(TGGGGT)4 . 3NH4+] undergoes very fast H/D exchange, in both the positive and in the negative ion modes, compared to DNA duplexes and other quadruplexes tested, and compared to the corresponding single-stranded TGGGGT. Substitution of NH4+ for K+ did not alter this fast H/D exchange, indicating that the hydrogens of the ammonium ions are not those exchanged. However, stripping of the interior cations of the quadruplex by source collision-induced dissociation (CID) in the positive ion mode showed that the presence of the inner cations is essential for the fast exchange to be possible. Molecular dynamics simulations show that the G-quadruplex is very rigid in the gas phase with NH4+ ions inside the tetrads. We suggest that the fast H/D exchange is favored by this rigid quadruplex conformation. This example illustrates that the concept that compact DNA structures exchange H for D slower than unfolded ones is a misconception.
authors.affiliation: Mass Spectrometry Laboratory, University of Liège, Belgium. v.gabelica@ulg.ac.be
authors.forename: Valérie
authors.initials: V
authors.lastname: Gabelica
authors.forename: Frederic
authors.initials: F
authors.lastname: Rosu
authors.forename: Matthias
authors.initials: M
authors.lastname: Witt
authors.forename: Gökhan
authors.initials: G
authors.lastname: Baykut
authors.forename: Edwin
authors.initials: E
authors.lastname: De Pauw
mesh_terms: D004247:DNA / Q000737:chemistry*; D003903:Deuterium / Q000737:chemistry*; D054856:G-Quadruplexes; D005740:Gases; D006151:Guanosine / Q000737:chemistry*; D006859:Hydrogen / Q000737:chemistry*; D009690:Nucleic Acid Conformation; D017550:Spectroscopy, Fourier Transform Infrared / Q000379:methods*
chemical_list: D005740:Gases; D006151:Guanosine; D006859:Hydrogen; D004247:DNA; D003903:Deuterium