INSR, or Insulin Receptor, is a transmembrane receptor protein that plays a crucial role in mediating the biological effects of insulin, a hormone involved in regulating glucose metabolism, lipid metabolism, and cellular growth. INSR is predominantly found on the surface of target cells, such as adipocytes, hepatocytes, and skeletal muscle cells. Its primary function lies in insulin signalling pathways — when insulin binds to the extracellular domain of INSR, the receptor undergoes conformational changes that initiate autophosphorylation of tyrosine residues in its intracellular domain, thereby activating its tyrosine kinase activity.