Czech Society for Mass Spectrometry

(13^th Czech Mass Spectrometry Conference and 11^th Informal Proteomic Meeting - WeO-04)
G-quadruplex – ligand interaction biophysics explored by native mass spectrometry and trapped ion mobility spectrometry

Aleksandr Melikov ^1 *, Frédéric Rosu ¹, Anton Granzhan ¹, Valérie Gabelica ¹

1. University of Geneva

Abstract

Guanine-rich nucleic acid sequences are able to form G-quadruplexes (G4), both in vivo and in vitro. Due to their involvement in many important biological processes, such as gene expression and telomere maintenance, G-quadruplexes became a prominent target for anticancer therapy by small G4-binding molecules, or G4 ligands. Mass spectrometry combined with electrospray ionization source (ESI-MS) provides a great tool to relatively quickly asses the in-solution binding properties of G4 ligands, as was determined by previous studies . Coupling ESI-MS with the trapped ion mobility (timsTOF SCP) and the in-house made variable-temperature nano-electrospray source (vt-nESI) allows to obtain a detailed biophysical characterization of G4-ligand interactions.
In native conditions (room temperature), all the tested compounds showed very high affinity for parallel folds (both intra and intermolecular), as well as telomeric variants. For the telomeric hybrid topologies, the displacement of 1 of the 2 ammonium cations initially complexed by the G4 by the ligand suggests a similar binding mode as PhenDC3, that is, intercalation between G-quartets. The melting experiments conducted with the vt-nESI source allowed us to monitor temperature-dependent G4 unfolding, extrapolate binding constants to room temperature, as well as to estimate thermodynamic parameters of ligand binding by van’t Hoff equation fit. In addition, the effect of coordinated cation (ammonium vs potassium) and the annealing of G4 in the temperature-controlled environment was tackled by these techniques for several human telomeric sequence variants. Future work will be devoted to the influence of ligands on protein binding to G-quadruplexes.

* Corresponding author: aleksandr.melikov@unige.ch

Acknowledgement:

We would like to acknowledge Bruker Daltonics for provided instrument upgrades and University of Geneva for funding this research.