Researchers at the University of Sheffield have defined the structure of a key part of the human obesity receptor, which has an essential role in the regulation of body fat. This understanding will greatly enhance the ability to generate drugs which could moderate complications caused by obesity and malnutrition. Researchers solved the challenging crystal structure of the leptin-binding domain of the obesity receptor using state of the art X-ray crystallography. Leptin, the obesity hormone, is produced by fat. Excess leptin contributes to conditions such as multiple sclerosis, cancer and heart disease while a deficiency in leptin, as occurs in malnutrition, results in infertility and immunodeficiency. Blocking the receptor, and therefore the excessive actions of leptin, could prevent the complications of obesity and stimulating the receptor may improve fertility and the immune response.