Enabling Protein Degradation Drug Discovery

A shift in both the excitation and the emission toward longer wavelength helps overcome problems of compound autofluorescence in screening assays. One such substrate is the rhodamine based ubiquitin-eN-(aN-tetramethyl-rhodamine)lysine (Ubiquitin-Lys-TAMRA), which mimics the naturally occurring isopeptide bond Between the C-terminus of ubiquitin and the e-amino group of a lysine residue of an ubiquitinated protein (Tirat et al., 2005). Cleavage of the isopeptide bond results in a decrease of fluorescence polarization, which makes Ubiquitin-Lys-TAMRA suitable  for high-throughput screening applications (Hassiepen et al., 2007). Fluorescence polarization, in contrast to fluorescence intensity, allows a ratiometric read-out of the activity and is thus less sensitive to autofluorescing or quenching caused by test compounds (Tirat et al.,2005).