Selenomethionine, p-cyanophenylalanine pairs provide a convenient, sensitive, non-perturbing fluorescent probe of local helical structure.

The use of selenomethionine (MSe)-p-cyanophenylalanine (FCN) pairs to probe protein structure is demonstrated. MSe quenches FCN fluorescence via electron transfer. Both residues can be incorporated recombinantly or by peptide synthesis. Time-resolved and steady-state fluorescence measurements demonstrate that MSe-FCN pairs provide specific local probes of helical structure.