Effects of pH, salt and time on ligand binding properties of overexpressed melanocortin 4 receptor

The G-protein coupled melanocortin 4 receptor (MC4r) plays an important role in the energy metabolism. We overexpressed the MC4r in CHO cells and performed characterisation studies on the cell membranes to determine functional stability and ligand binding properties of the receptor. The affinity for the ligands Nle4, d-Phe7]-alphaMSH and MTII was lost below pH 6 but could be restored by returning to physiological pH. Increasing NaCl concentration up to 1 M had little influence on the binding of either ligand. At neutral pH, physiological salt concentration and 4 degrees C the ligand affinity of the receptor was stable for up to 6 days. These findings will facilitate design of purification methods for the receptor.