Targeted Protein Degradation

Targeted protein degradation (TPD) encompasses a variety of strategies designed to eliminate specific proteins from cells. Here are the main types of TPD methods:

• PROTACs (PROteolysis TArgeting Chimeras):
  PROTACs are heterobifunctional linker molecules that link the target protein to an E3 ubiquitin ligase. This facilitates the ubiquitination and subsequent proteasomal degradation of the target protein. PROTACs are particularly notable for their ability to degrade intracellular proteins. There are trivalent PROTACs, which are advanced protein degradation molecules that utilize three binding components—two for the target protein and one for an E3 ubiquitin ligase—to form a highly specific and potent ternary complex, leading to enhanced degradation of the target protein compared to traditional bivalent designs.
• Molecular Glues:
  Molecular glues are small molecules that induce protein-protein interactions between an E3 ubiquitin ligase and the target protein, leading to its ubiquitination and degradation. Unlike PROTACs, molecular glues do not require a linker and are generally smaller in size.
• LYTACs (Lysosome-Targeting Chimeras):
  LYTACs are designed to target extracellular and membrane proteins for degradation via the lysosomal pathway. They function by binding to the target protein and directing it to lysosomes for degradation through endocytosis.
• AbTACs (Antibody-based PROTACs):
  AbTACs use antibodies to target proteins for degradation. These antibodies are conjugated to ligands that recruit E3 ubiquitin ligases, facilitating the ubiquitination and degradation of the target protein.
• AUTACs (Autophagy-TArgeting Chimeras):
  AUTACs utilize the autophagy pathway to degrade target proteins. These molecules tag the target protein with a degradation signal recognized by the autophagy machinery, leading to its encapsulation in autophagosomes and subsequent lysosomal degradation.
• ATTECs (Autophagosome-Tethering Compounds):
  ATTECs are small molecules that promote the tethering of target proteins to autophagosomes, facilitating their degradation via the autophagy-lysosomal pathway. This method is particularly useful for degrading protein aggregates and damaged organelles.
• dTAGs (Degradation Tags):
  dTAGs are small molecules that bind to a tagged protein of interest and recruit an E3 ubiquitin ligase, leading to the ubiquitination and proteasomal degradation of the tagged protein. This approach is often used in research to study protein function.
• Hydrophobic Tagging (HyT):
  HyT involves attaching hydrophobic tags to target proteins, which induces their misfolding and recognition by the proteasome for degradation. This method is particularly useful for degrading proteins that are otherwise difficult to target.
• SNIPERs (Specific and Non-genetic Inhibitors of Apoptosis Protein Degradation):
  SNIPERs are small molecules that induce the degradation of inhibitor of apoptosis proteins (IAPs) by recruiting them to E3 ubiquitin ligases. This promotes the ubiquitination and degradation of IAPs, which can trigger apoptosis in cancer cells.
• MADTACs (Macroautophagy Degradation Targeting Chimeras):
  MADTACs are designed to target proteins for degradation via macroautophagy. They use a ligand to bind the target protein and a macroautophagy-inducing component to direct the protein to autophagosomes for degradation.
• GlueTACs:
  GlueTACs are similar to molecular glues but specifically designed to enhance the interaction between a target protein and lysosomal targeting receptors, directing the target protein to lysosomes for degradation.
• Bispecific Aptamer Chimeras:
  These chimeras use aptamers (nucleic acid molecules) to bind both the target protein and lysosomal targeting receptors, facilitating the lysosomal degradation of the target protein.
• Degron Tags:
  Genetic methods that involve tagging proteins with degrons (degradation signals) to direct them for proteasomal or lysosomal degradation.
• IMiDs (Immunomodulatory Drugs):
  Small molecules that modify the substrate specificity of E3 ubiquitin ligases, promoting the degradation of specific proteins.
• Covalent Inhibitors:
  Molecules that form a covalent bond with the target protein, causing its misfolding or aggregation and subsequent degradation.