Mechanism of receptor assembly via the pleiotropic adipokine Leptin

The adipokine Leptin activates its type I cytokine receptor (LEP-R) in the hypothalamus to regulate body weight and exerts additional pleiotropic functions in immunity, fertility, and cancer. However, the structure and mechanism of Leptin-mediated LEP-R assemblies has remained unclear. Here, we show that Leptin:LEP-R assemblies adopt an unprecedented structure within the type I cytokine receptor family featuring 3:3 stoichiometry. We validate Leptin-induced trimerization of LEP-R in the plasma membrane of living cells via multicolor single molecule microscopy. In mediating such assemblies Leptin undergoes drastic restructuring that activates its site III for binding to the Ig-domain of an adjacent LEP-R molecule in the complex. These interactions are abolished by pathological mutations linked to obesity. Collectively, our study uncovers an evolutionarily conserved Leptin:LEP-R assembly as a new mechanistic blueprint for Leptin-mediated signaling in physiology and disease, including insights into how the lowly abundant signaling-competent isoforms of LEP-R can productively participate in signaling.