Incorporation of an Unnatural Amino Acid as a Domain-Specific Fluorescence Probe in a Two-Domain Protein.

The biophysical analysis of multidomain proteins often is difficult because of overlapping signals from the individual domains. Previously, the fluorescent unnatural amino add p-cyanophenylalanine has been used to study the folding of small single-domain proteins. Here we extend its use to a two-domain protein to selectively analyze the folding of a specific domain within a multidomain protein.