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Genetically Encoded Electron Acceptor Enables Photoinduced Electron Transfer in Green Fluorescent Protein

Jun 01, 2015

Electron transfer (ET) plays a central role in many biological processes, such as photosynthesis and respiration. Photoinduced electron transfer (PET) is a fundamental biological process in photosynthesis which initiates the process to harvest light energy in plants and cyanobacteria. Construction of the PET in a small model protein would provide a useful tool for understanding and mimic the biological electron transfer and rational design of reductases. However, the limitation of the imitation in proteins and design redox enzymes is lacking in methods to genetically encoded electron acceptors into proteins in vivo since all nature amino acids act as electron donor.

WANG Jiangyun's group from Institute of Biophysics of Chinese Academy of Sciences, in collaboration with Dr. XIA Andong from Institute of Chemistry of Chinese Academy of Sciences realized PET in a small model protein, green fluorescent protein (GFP) with the help of an unnatural amino acid. They developed a system to incorporate 4-fluoro-3-nitrophenylalanine (FNO2Phe) into protein through genetic codon expansion. The unnatural amino acid has similar reduction potentials to reduced form of the electron acceptor nicotinamide adenine dinucleotide phosphate and ferredoxin, the most important biological reductants.

By measuring femtosecond transient absorption spectra of GFP variants containing FNO2Phe, they showed that PET from the GFP chromophore to FNO2Phe occurs very fast (within 11 picoseconds), comparable to that of the first electron transfer step in photosystem I, from P700* to A0. This genetically encoded, low-reduction potential unnatural amino acid (UAA) can significantly improve the ability to investigate electron transfer mechanisms in complex reductases, and facilitate the design of miniature proteins which mimic their functions.

This work entitled “Ultrafast Photo-induced Electron Transfer in Green Fluorescent Protein Bearing a Genetically Encoded Electron Acceptor” was published online in Journal of the American Chemical Society.

This work was supported by the Major State Basic Research Program of China, the National Natural Science Foundation of China and the Chinese Academy of Sciences.

 

Figure: Genetically encoded electron acceptor (Image by WANG Jiangyun's group) 

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