Controlling PROTACs with Light

Proteolysis targeting chimeras, PROTACs, are emerging as a powerful strategy for exerting exogenous control over protein levels, allowing small molecules to exploit the ubiquitin-proteasome pathway for targeted protein degradation. This highlight focuses on the fusion of photochemistry with these bifunctional compounds, which has provided a novel pathway for spatiotemporally tuning the activation of PROTACs in the form of their photocaged and photoswitchable versions. Photocaged PROTACs consist of a hindered optolabile group that detaches only upon irradiation at a specific wavelength, releasing the active PROTAC. These modified PROTACs are inactive in the dark. Photoswitchable PROTACs are photoisomerizable molecules with azobenzene linkages that are active in either the cis or trans form and inactive in the other. The isomers interconvert upon irradiation with an appropriate wavelength of light and relax to the thermodynamically stable isomer in the dark or with another wavelength of light. Although photocaged PROTACs only permit activation control for protein degradation, photoswitching PROTACs offer reversible activation and deactivation by using suitable wavelengths of light.