Jiangyun Wang’s group at the Institute of Biophysics, CAS published a ‘VIP” and “inside cover” article on Angewandte Chemie International Edition, titled “Genetic Incorporation of a Metal Chelating Amino Acid as a Probe for Protein Electron Transfer” in September, 2012.

This paper describes a novel and innovative approach to study electron transfer (ET) through proteins. The authors describe a method to incorporate an unnatural metal-chelating amino acid (pyTyr) into specific sites in green fluorescent protein (GFP). The pyTyr residue may then be loaded with copper (Cu)(II). When Cu(II) is bound to pyTyr, the GFP fluorescence is quenched. Using this property, the authors measured photoinduced ET (PET). Careful control experiments were performed to ensure that both the bound copper and the GFP fluorophore changed their redox states during the reaction, confirming that the observed fluorescence quenching was associated with PET and not resonance energy transfer. Furthermore, a distance dependence of the rate of PET was demonstrated. Another interesting point, on which the authors did not elaborate, is that the very rapid rates of ET suggest that the activation energy is near zero (i.e. the driving force is approximately the same magnitude as the reorganization energy).
There are currently relatively few methods for introducing redox-active species at specific sites in proteins. It is possible to monitor PET by straightforward fluorescence techniques. A redox-active fluorophore, such as the GFP chromophore, is also required; however, there seems to be no reason why this technique should be limited to that particular chromophore, and many other possibilities exist. The requirement to introduce an unnatural amino acid into the protein of interest will pose a technical challenge to many wishing to use this approach. However, the overall approach is very interesting and may provide inspiration for similar approaches to elucidate mechanisms of protein ET and develop practical applications for redox proteins.

This article was recommended by F1000 biology. Prof. Brian Crane, a prestigious biophysical chemistry professor at the Cornell University, praise that this is an “important advance” and is currently using the new technology Prof. Wang has developed to further advance his study on protein electron transfer.

Prof. Jens Bredenbeck, a prestigious biophysical chemistry professor at the University of Frankfurt in Germany, adds: "To position a metal center in a protein at will - this goal has been achieved very elegantly by Dr. Wang and his team through genetic incorporation of an unnatural metal-chelating amino acid. The great flexibility of their site selective approach will allow to address various important problems in biophysics such as mapping electron transfer pathways or resolving protein dynamics by photoinduced electron transfer. The rational design of metalloproteins for fundamental research as well as technological applications will be greatly advanced by the unnatural amino acid approach." Prof. Jens Bredenbeck’s group is currently using this new technology to study protein electron transfer through infrared spectroscopy.