Functional Characterization of Naturally Occurring Pathogenic Mutations in the Human Leptin Receptor

We have recently reported the first naturally occurring missense mutations in the leptin receptor (LR) in patients with severe obesity. We have examined the molecular mechanisms by which these extracellular domain mutations disrupt LR signaling. The Ala409Glu mutant receptor is expressed at the cell surface, binds leptin normally but fails to signal to downstream pathways. A409 is present on the surface-exposed region of the Ig-like domain that forms the binding site III for interaction with leptin. This binding site does not appear to contribute to the binding affinity of leptin to its receptor but is critical for receptor activation in response to ligand binding. The Trp664Arg and His684Pro mutations are predicted to impair receptor folding. Both mutants result in a complete inability to signal to downstream pathways despite evidence for some residual cell surface expression and ligand binding. The Arg612His mutant falls in the second subdomain of the high-affinity binding site for leptin, and results i...