Multiscale dynamics of photo-induced Chirality changes in biomolecules probed by Arbitrary Detuning ASynchronous OPtical Sampling – ChirADASOPS

Conformational dynamics of biomolecules are intimately related to their function. However, the monitoring of these multiscale dynamics, which can range from a few hundreds of femtoseconds to a few milliseconds, still remains an experimental challenge. In this respect, ultrafast pump-probe spectroscopy offers a tool of choice to follow these dynamics in real time with a "virtually" unlimited temporal resolution. However, conventional femtosecond pump-probe setups do not generally allow access to dynamics beyond a few nanoseconds. Moreover, few setups allow to combine both structural sensitivity and high temporal resolution. ChirADASOPS proposes to overcome these two technological barriers by combining the unique pump-probe methods developed by our team at the Laboratoire d’Optique et Biosciences at Ecole Polytechnique, for multiscale detection and time-resolved circular dichroism (TRCD), to follow the structural changes of biomolecules over an observation window of more than 10 orders of magnitude, ranging from picoseconds to milliseconds.
Circular dichroism, which is the difference in the absorption of a chiral sample between a left- and right-handed circularly polarized light, is a very sensitive probe of biomolecule secondary structures. However, TRCD measurements usually require the introduction of a modulation or a variable phase delay on the probe polarization combined with the detection of very small signal variations. To circumvent these time-consuming detection procedures and to improve the signal-to-noise ratio, the first objective of the project will be to develop single-shot TRCD measurements with a balanced detection, for which we already established the proof of principle. The second objective will aim at the development of a new approach to multi-timescale pump-probe spectroscopy by combining the ADASOPS (Arbitrary Detuning ASynchronous OPtical Sampling) method developed in our team with a diode-pumped high-repetition rate femtosecond amplifier for generating the probe. The combination of the single-shot TRCD detection and the use of a high-repetition rate laser for the probe will achieve an accuracy in the measurements of ca. 0.1 mdeg (<3 µOD). In the third step of ChirADASOPS, we will take advantage of our new experimental setup to investigate the conformational dynamics of two hemoproteins of interest to the team, the bacterial CO transcription regulator, CooA, and the human NO receptor, guanylate cyclase. We will also address the folding/unfolding mechanisms of a G-quadruplex (G4) DNA structure known to play an important role in cellular regulation, with the study of a complex made of an azobenzene-derived photoswitch and the G4 sequence, 5'-GGTTGGTGTGGTTGG-3'.
To achieve its three objectives, this PRME project at the interface of physics and biology will greatly benefit from the remarkable complementarity of the skills of all the team members, which will allow the development of a robust and user-friendly tool for TRCD spectroscopy in a table-top pump-probe configuration. The broad community can benefit significantly from this new experimental development which can fulfill the need to observe the movements of complex molecular architectures in real time. The scientific results obtained could also clearly contribute to popularize this new method of pump-probe spectroscopy and to broaden the scope of its applications to provide new insights into the structure-function relationship of biomolecules, opening the door to applications for the development of innovative therapies.