When light encourages team-work...

To begin with

Scientists discovered that guanines (G), which are DNA building blocks, under light irradiation they work as a team. But this happens if guanines are linked together in column-like structures called quadruplexes. 

Keywords

Guanine, Guanine quadruplexes, DNA bases, Cancer, Light absorption, Optoelectronics, Molecular electronics

About

Guanine quadruplexes (or G-quadruplexes) are nano-structures which have recently attracted the attention of the scientists. G-quadruplexes are four-stranded helices made of tetrads of guanines (G), which are building blocks of the DNA molecule. (watch Dr. Markovitsi talking about guanines and their four-stranded structures) These nano-structures may be engineered in the laboratory but can also be produced in natural DNA. Besides their biological significance, G-quadruplexes have such qualities that make them promising candidates for applications in the field of molecular electronics and optoelectronics. As part of the effort to understand better the properties of G-quadruplexes, photochemists at the Francis Perrin Laboratory (FPL) have started exploring their interaction with light.

Links with society

More and more research projects are devoted to studying the stability, geometry and function of the guanine quadruplexes (or G-quadruplexes). G-quadruplexes are of great biological interest because they play an important role in the expression of genes in an organism. They are also associated with potential applications of cancer therapy.
Besides their biological significance, G-quadruplexes are considered as promising candidates for numerous applications in the field of molecular electronics and optoelectronics. They could behave as nano-wires allowing, for example, the flow of electric charges or that of the energy deposited by photons. (watch Dr. Markovitsi explaining why G-quadruplexes are important for research)

Research innovation

A group of scientists at the Francis Perrin Laboratory (FPL) have contributed to better understanding the interaction of different types of guanine quadruplexes (or G-quadruplexes) with light. (watch Dr. Markovitsi explaining the research methodology) Their experimental data brought evidence that the guanine bases, when embedded within the four-stranded helices of G-quadruplexes, have a collective behaviour if irradiated with ultraviolet (UV) light. It has been shown that the energy of a UV photon is not absorbed by one single guanine but by a group of them. Besides guanines when in G-quadruplexes, such a collective behaviour has already been observed by FPL researchers for all four types of bases (adenine, thymine, guanine, cytosine) within the DNA double helices. However, it is significantly increased in the quadruplexes due to their higher structural firmness ensuring efficient coupling. As a result, one photon is not absorbed individually by a single guanine, but simultaneously by a group of them within the quadruplex. Another finding is that the energy deposited by the photon is very rapidly exchanged among the guanines composing the quadruplex.


Relevant scientific publications

1. Francois Alexandre Miannay, Akos Banyasz, Thomas Gustavsson, Dimitra Markovitsi (2009), Excited states and energy transfer in G quadruplexes, Journal of Physical Chemistry, C 113, 11760-11765.
2. Pascale Changenet-Barret, Emanuela Emanuele, Thomas Gustavsson, Roberto Improta, Alexander B. Kotlyar, Dimitra Markovitsi, Ignacio Vaya, Krystyna Zakrzewska and Dragoslav Zikich, Optical properties of guanine nanowires: experimental and theoretical study, Journal of Physical Chemistry C, August 11, 2010.

Description of the method

Researchers at the Francis Perrin Laboratory (FPL) studied how guanine quadruplexes (or G-quadruplexes) dissolved in water absorb and subsequently emit light. The emitted light (fluorescence) has a different wavelength from that absorbed. The researchers compared the photon absorption and emission by quadruplexes with those observed for isolated guanines.
In particular, they followed the way fluorescence evolves with time. To achieve the rapid irradiation of the G-quadruplexes samples with photons, researchers used a very fast laser (femtosecond laser). Sophisticated spectroscopic techniques allowed the scientists to detect the photons emitted by the G-quadruplexes over time. The tools used helped them to observe the evolution of fluorescence until it fades. The observation period ranges from 100 femtoseconds (10^-13 of a second) through to 100 nanoseconds (10^-7 of a second).

This work required collaboration with other research groups; one of them at Tel Aviv University (Alexander B. Kotlyar, Department of Biochemistry) prepared especially long guanine quadruplexes called G4 wires (G4 refers to the guanine tetrad). Other groups, located at Lyon (Krystyna Zakrzewska, Institut de Biologie et Chimie des Protéines) and in Naples (Roberto Improta, Institute for Biostructures and Bioimaging) made theoretical calculations, which helped to interpret the experimental results. In a more general way, the research groups interested in the properties of G-quadruplexes are part of a European network called G4 net.

The "face" of Science: Let's meet the scientists!

Who are the people working behind the scenes?

The "face" of Science: Dr. Pascale Changenet-Barret, CNRS research scientist moved to Francis Perrin Laboratory on 2010 in order to work on guanine quadruplexes.

Editing team

Editing Team for the Digital Exhibit “When light encourages team-work...”

Scientific editors: Pascale Changenet-Barret (CNRS research scientist), Dimitra Markovitsi (CNRS research Director),  Ignacio Vaya (young researcher) 

Content Coordination: Glykeria Anyfandi
Science Communication Editors: Evlalia Amygdalaki, Glykeria Anyfandi
Content Administration: Christina Troumpetari, John Stoitsis
Technical Development: John Stoitsis
Photographs, videos & web material: Evlalia Amygdalaki
e-Knownet Live experiments: Interactive Science & Technology Exhibition, Eugenides Foundation