Observations of biomolecular dynamics using improved spectroscopic technique

Ultraviolet synchrotron radiation circular dichroism (SRCD) spectroscopy is a technique that has helped scientists better understand the structure and behavior of biological molecules and processes. Now, Auvray et al. have developed a time-resolved approach for SRCD measurements which will give access to increased temporal and spatial ranges, opening the door to observations of biomolecular dynamics such as protein folding.

The time-resolved SRCD approach provides the ability to study biological reactions in real-time, allowing scientists to see the temporal evolution and structural changes of a biomolecular system in a physiological solution.

To achieve this, the researchers focused a synchrotron pulsed white beam onto the sample and used a series of optical instruments to obtain the required spectral and time resolution. By using two beam portions of opposite polarization, the entire UV circular dichroism spectrum, which represents the difference in absorption between left- and right-handed circularly polarized light, can be obtained in a single measurement.

“The real novelty of this method is the instant acquisition of the full spectral band for a circular dichroism spectrum in the ultraviolet,” said author Matthieu Réfrégiers. “This includes the energy region of interest in which proteins absorb.”

They used a camera coupled with an optional intensifier to overcome limitations caused by insufficient exposure and acquired images of the sample at a wider wavelength range. The data acquisition frequency is determined by the camera frame rate, which can be adjusted to study kinetics at timescales ranging from microseconds to minutes.

“The temporal evolution of biomolecules spans a wide range of timescales,” said Réfrégiers.

Looking ahead, the authors plan to use the new time-resolved technique to better understand the regulation of gene expression and protein folding.

Source: “Time resolved transient circular dichroism spectroscopy using synchrotron natural polarization,” by François Auvray, David Dennetiere, Alexandre Giuliani, Frédéric Jamme, Frank Wien, Bastien Nay, Séverine Zirah, François Polack, Claude Menneglier, Bruno Lagarde, Jonathan D. Hirst, and Matthieu Réfrégiers, Structural Dynamics (2019). The article can be accessed at https://doi.org/10.1063/1.5120346 .