Abstract
The hierarchical process of guanosine (G) self-assembly, leading in aqueous solution and in the presence of metal cations to the formation of G-quadruplexes, represents an intriguing topic both for the biological correlation with telomerase activity and for the nano-technological applications, as demonstrated by the current measured in a quadruplex wire 100 nm long. Similar to G-rich DNA sequences and G-oligonucleotides, the guanosine 5′-monophosphate (GMP) self-aggregates in water to form quadruplexes. However, due to the absence of a covalent axial backbone, this system can be very useful to understand the chemical-physical conditions that govern the guanosine supramolecular aggregation. We have then investigated by in-solution Synchrotron Small Angle X-ray Scattering technique the role of different cations in promoting the quadruplex formation as a function of concentration and temperature. Results show how potassium, with its peculiar biological traits, favours the G-quadruplex elongation process in respect to other cations (Na, but also NH and Li), determining the longest particles in solution. Moreover, the formation and the elongation of G-quadruplexes have been demonstrated to be controlled by both GMP concentration and excess cation content, even if they specifically contribute to these processes in different ways. The occurrence of condensed liquid crystalline phases was also detected, proving that excess cations play also unspecific effects on the effective charges on the G-quadruplex surface.
Highlights
Guanine (G) has gained considerable interest in the last years because of the four DNA bases is the only one able to give rise to supramolecular aggregation phenomena in solution, leading to complex structures ranging from G-quartets to G-quadruplexes and G-ribbons [1,2,3,4,5,6,7]
Quadruplexes can be formed via intramolecular assembly or by association of two or four filaments, according to different geometries [11]: even if such guanosine-rich sequences have focused the attention of the scientific community due to the potential applications in the fields of medicine and chemistry, the role of G-quadruplexes in vivo is still not satisfactory resolved, possible because most of the published studies refer to synthetic oligomers, restriction fragments, or recombinant plasmids in cell-free systems
The interest around G-quadruplexes has been gradually increasing in the last years [17,18,23], with special emphasis to those obtained by low-molecular weight derivatives, as guanosine 5’-monophosphate (GMP)
Summary
Guanine (G) has gained considerable interest in the last years because of the four DNA bases is the only one able to give rise to supramolecular aggregation phenomena in solution, leading to complex structures ranging from G-quartets to G-quadruplexes and G-ribbons [1,2,3,4,5,6,7]. A possible idea is that these two cations may regulate a switch process between two DNA forms in the cells: linear and G-quadruplexes, as described by Sen and Gilbert [22] For all these reasons, the interest around G-quadruplexes has been gradually increasing in the last years [17,18,23], with special emphasis to those obtained by low-molecular weight derivatives, as GMP. It should be clear that GMP can be considered a very suitable model to extract information on the guanosine self-assembly process and on G-quadruplex structure, elongation and stability The study of such a system has always been complex, owing to three main factors: the very intricate phenomenon of hierarchical aggregation, the large number of parameters controlling the G-quadruplex nucleation (GMP concentration, temperature, counterions effect) and the concomitant elongation/fragmentation processes [10]. In the case of K+, G-quadruplex melting curves were obtained by SAXS and validated by FTIR spectroscopy measurements
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