One of the unsolved key questions in structural biology is how a protein's primary sequence encodes its structure and function. This is due, in part, to the fact that the structural and functional energy landscapes of proteins are intrinsically complex and that it is exceedingly difficult, if not impossible, to directly visualize/observe with atomic-level resolution all of the conformational motions and/or molecular interactions that are required for a protein to fold or function. Therefore, many spectroscopic techniques have been used to provide important, albeit indirect, information about the biological process in question. However, in many cases spectroscopic signals arising from natural amino acids are insufficient toreveal the underlying dynamics and mechanism and unnatural amino acids (UAAs) with specific spectroscopic propertiescan be used to help extract the needed chemical and/or physical information. In this regard, in the past two decades significant effort has been made in the development of UAA-based probes for various spectroscopic and imaging applications in biological science.
In order for a UAA to be useful as a spectroscopic probe, it needs to meet the following requirements: (1) it should be a simple derivative of one of the natural amino acids, (2) it should possess unique spectroscopic characteristics, (3) its signal should be easily measurable, distinguishable, and interpretable, (4) it should be chemically stable(for being used as a fluorescence reporter, it should be also photostable), (5) it can be incorporated into proteins via either a chemical or biological method. In comparison to other commonly used probes in biological spectroscopy and microscopy, UAA-based probes enjoy the advantage of being less perturbative towards the native property of the protein in question, due to their relatively small size.
In the May 22nd issue of Chemical Reviews, Dr. Ran-ran Feng, PhD student Manxi Wang, and Prof. Feng Gai from College of Chemistry and Molecular Engineering of Peking University and Prof. Wenkai Zhang from School of Physics and Astronomy of Beijing Normal University published a comprehensive review about the recent progress of this very active research area, with a focus on UAAs that can be used as site-specific vibrational, fluorescence, electron paramagnetic resonance (EPR), or nuclear magnetic resonance (NMR) probes. They also provided insights intofuture directions for the further development of UAA-based spectroscopic probesand their applications in studying various biological processes, such as protein folding and enzymatic reactions.
This work was funded by the National Natural Science Foundation of China and the full citation of the articleis: Chemical Reviews 2024, 124, 10, 6501-6542 (https://pubs.acs.org/doi/10.1021/acs.chemrev.3c00944).
