A non-natural amino acid for efficient incorporation into proteins as a sensitive fluorescent probe

A small and highly fluorescent non-natural amino acid that contains an anth raniloyl group (atnDap) was incorporated into various positions of streptav idin. The positions were directed by a CGGG/CCCG four-base codon/anticodon pair. The non-natural mutants were obtained in excellent yields and some of them retained strong biotin-binding activity. The fluorescence wavelength as well as the intensity of the anthraniloyl group at position 120 were sen sitive to biotin binding. These unique properties indicate that the atnDap is the most suitable non-natural amino acid for a position-specific fluores cent labeling of proteins that is highly sensitive to microenvironmental ch anges. (C) 2001 Federation of European Biochemical Societies. Published by Elsevier Science B.V. All rights reserved.