Proteins with beta-(thienopyrrolyl)alanines as alternative chromophores and pharmaceutically active amino acids

L-beta-(Thieno[3,2-b]pyrrolyl)alanine and L-beta-(thieno[2,3-b]pyrrolyl)ala nine are mutually isosteric and pharmaceutically active amino acids that mi mic tryptophan with the benzene ring in the indole moiety replaced by thiop hene. Sulfur as a heteroatom causes physicochemical changes in these trypto phan surrogates that bring about completely new properties not found in the indole moiety. These synthetic amino acids were incorporated into recombin ant proteins in response to the Trp UGG codons by fermentation in a Trp-aux otrophic Escherichia coli host strain using the selective pressure incorpor ation method. Related protein mutants expectedly retain the secondary struc ture of the native proteins but show significantly changed optical and ther modynamic properties. In this way, new spectral windows, fluorescence, pola rity, thermodynamics, or pharmacological properties are inserted into prote ins. Such an engineering approach by translational integration of synthetic amino acids with a priori defined properties, as shown in this study, prov ed to be a novel and useful tool for protein rational design.