Study Protein Folding and Aggregation Using Nonnatural Amino Acid p-Cyanophenylalanine as a Sensitive Optical Probe

Incorporation of nonnatural amino acids with a variety of special side groups into protein sequences has substantially expanded the experimental means of exploring protein structures and functions. Recently, p -cyanophenylalanine (Phe_CN ), the nitrile analogue of phenylalanine, has been used as a novel optical probe for protein binding and folding studies. The fluorescence emission of Phe_CN is sensitive to solvent and local environment of the residue, making it a useful fluorescent probe of protein structural change at residue-specific resolution. Moreover, the utility of Phe_CN is increased by its ability to excite tryptophan fluorescence via the mechanism of fluorescence resonance energy transfer. Phe_CN could be applied to study a variety of biological problems, e.g., protein folding/unfolding and protein aggregation.