Selective labeling of proteins by using protein farnesyltransferase

The challenging task of identifying and studying protein function has been greatly aided by labelling proteins with reporter groups. Here, we present a strategy that utilizes an enzyme that labels a four-residue sequence appended onto the C terminus of a protein, with an alkyne-containing substrate. By using a bio-orthoganal cycloaddition reaction, a fluorophore that carried an azide moiety was then covalently coupled to the alkyne appended on the protein. FRET was used to calculate a Forster (R) distance of 40 angstrom between the eGFP chromophore and the newly appended Texas Red flurophore. This experimental value is in good agreement with the predicted R value determined by using molecular modeling. The small recognition tag, the high specificity of the enzyme, and the orthogonal nature of the derivatization reaction will make this approach highly useful in protein chemistry.