So far, thousands of PROTAC molecule have been reported and the PROTAC-DB database curated more than 2000 published PROTAC molecules. Compared with the chemical space of traditional drug-like small molecule, the PROTAC space is largely different due to their relatively large molecular size and still under-represented. So far, up to 60 E3 ligases have been found, but existing E3 ligands of PROTAC are mainly focused on the ligand set of von Hippel-Lindau (VHL) and cereblon (CRBN) ligases .