A PROTAC (Proteolysis-Targeting Chimera) molecule is a bifunctional small molecule or biomolecule composed of three key components: 1. Target protein ligand: Specifically binds to the protein of interest (e.g., kinases, transcription factors). 2. E3 ubiquitin ligase ligand: Recruits an E3 ligase (e.g., VHL, CRBN). 3. Linker: Covalently connects the two ligands, modulating molecular conformation and activity. PROTACs induce ubiquitination of the target protein, leading to its degradation via the proteasome.