Deletions of the N-terminal regions of the human melanocortin receptors.

The non-homologous N-terminal regions of four human melanocortin (MC) receptors were truncated in order to investigate their putative participation in ligand binding. Eleven constructs were made, where different numbers of residues from the N terminus were deleted. These constructs were used for transient expression experiments in COS cells and analysed by ligand binding. The results show that 27, 25, 28, and 20 amino acids could be deleted from the N terminus of the human MC1, MC3, MC4 and MC5 receptors, respectively, including all potential N-terminal glycosylation sites in the MC1 and the MC4 receptors, without affecting ligand binding or expression levels. The results indicate that the N-terminal regions of the human MC1, MC3, MC4 and MC5 receptors, do not play an important role for the ligand binding properties of these receptors.