Advances in 2D infrared spectroscopy provide new tools for characterizing protein functions

2D infrared spectroscopy offers the fast timescale and spatial resolution needed to characterize proteins. Most prior IR spectroscopy has focused on vibrations of the amide backbone, but they are inherently delocalized and suffer from spectral congestion. A new review takes stock of the history and future of using “transparent windows” on protein spectra.

Researcher Megan Thielges has published a perspective piece highlighting the progress and future hurdles for using amino acid side chains with vibrational groups that can be studied in the 2D transparent window of protein spectra. With a foundation of the approach established, the paper discusses advances in synthesizing molecules and boosting sensitivity that provide a way forward for the approach.

“Just like, say a tractor in the macroscopic world, one could take a picture of a protein, but that would be just a first step toward understanding how it works,” Thielges said. “Until one can view each of the moving parts, one could not fully understand how a tractor works.”

Several molecules have shown promise for use as local IR probes within proteins, including increasing the vibrational lifetime of probes by isotopic labeling and adding heavy atoms to detune vibrations from accepting modes.

Challenges remain, however, in achieving adequate sensitivity to detect 2D IR signals when low protein concentrations are used. Ongoing work on spectrally narrowing excitation pulses has looked to mitigate these issues.

Thielges hopes the review stokes further interest in solving issues of scalability in the growing field of 2D protein IR spectroscopy and that it will further complement other modalities in spectroscopy.

Source: “Transparent window 2D IR spectroscopy of proteins,” by Megan C. Thielges, Journal of Chemical Physics (2021). The article can be accessed at https://doi.org/10.1063/5.0052628 .