Imaging farnesyl protein transferase using a topologically activated probe

We report on the development and application of a "smart" activatable peptide-based probe for detection of Ras-related farnesyl protein transferase (FPT). Upon farnesylation by FPT, the probe was brought close to a hydrophobic milieu and as a consequence emitted fluorescent light that could be detected by several media, such as fluorescence microscopy, a plate reader, and an optical imaging system. A FPT activity assay confirmed the specificity of the probe (IC50 = 1.2 muM) for FPT compared to that of the native peptide (IC50 = 0.17 muM). In addition, the probe has remarkable binding constant, Kd = 26 nM. The specificity of enzyme activation was proved in pure enzyme assays as well as in cell-based assays. Furthermore, the fluorescent enhancement of the probe was 30-fold stronger than the control peptide in a live cell assay.