engleski

SERS spectra of urea disrupted G-quadruplexes on silver and gold nanoparticles

G-Quadruplexes (G4) are non-canonical nucleic acid structures formed by guanine-rich sequences of DNA or RNA. This four-chain spiral structures arise from tetrads of guanine bases cyclically linked through Hoogsteen hydrogen bonds, which stack on each other by means of π-π stacking interactions. The monovalent cations, such as Na+ or K+, are located between G-quartets, reducing the repulsion of O6 atoms and stabilizing the structure of G- quadruplexes. On the other hand, urea is a well known denaturing agent that affects the equilibrium between unfolded and folded structures of proteins. G4 have globular shape and are less charged compared to other nucleic acids, that makes them similar to globular proteins. Surface- enhanced Raman scattering (SERS) spectroscopy was applied to investigate the effect of urea on the structure of G4 using citrate stabilized silver and gold nanoparticles. SERS spectroscopy provides structural information about molecules in close vicinity to a nanostructured metal surface. SERS spectroscopy was used to investigate the structure of human telomeric sequence d[TTAGGG]4 (Tel24) in the absence and presence of stabilizing Na+ ions as well as after addition of urea. Characteristic marker bands originating from breathing vibrations of adenine and guanine rings of unfolded Tel24 structure were observed in the SERS spectra without Na+ ions. After heating Tel24 with Na+ ions the SERS spectra confirmed the presence of ordered G-quadruplex. The intensity ratios of the marker bands proved the presence of the folded telomeric sequence on the surface of metal nanoparticles. Addition of urea induces disruption of the ordered G4 structure, which was clearly visible from the SERS spectra that corresponded to the spectra of unfolded Tel24. Comparison of results based on varying the metal used in the SERS substrate was performed in order to determine how the choice of metal affects amplification of Raman scattering.

G-Quadruplex ; Urea ; SERS ; nanoparticles

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