Glutamine235 and arginine272 in human melanocortin 5 receptor determines its low affinity to MSH

The human melanocortin 5 receptor (hMC5R) in the melanocortin receptor family has been identified as the receptor with low affinity towards alpha-MSH. Here we show that the glutamine at position 235 and arginine at the position 272 in the hMC5R are contributing to the low affinity of this receptor. Glutamine235 and arginine272 in hMC5R were mutated to lysine (Q235K) and cysteine (R272C), respectively, residues which are conserved at these positions in other melanocortin receptor subtypes. Upon these mutations affinity of alpha-MSH for hMC5R was increased 10-fold for Q235K and 690-fold for R272C mutants, respectively. The results explain the unusually low affinity of the hMC5R to the melanocortic ligands and suggest the importance of these conserved residues in maintaining the high affinity form of melanocortin receptors.