Identification of the translation start site of the human melanocortin 3 receptor

The melanocortin-3-receptor (MC3R) is a G-protein coupled receptor participating in hypothalamic energy metabolism. So far, it was assumed that the translation of the human MC3R starts at the non-conserved first ATG, however, a second evolutionary conserved ATG is located 37 amino acids downstream. One frequent polymorphism, T6K, is located between these two ATGs.

For characterization of the two potential start ATGs, COS-7 cells were transfected with plasmids encoding the longer and the shorter form of the human MC3R. For signal transduction properties, cAMP was measured. Cell surface expression was determined by using an ELISA method. The translational start point of the MC3R was investigated by a GFP-based method.

Signal transduction was comparable for the long and the short receptor form. Cell surface expression via aminoterminal hemagglutinin tag could only be detected in the shorter form, but not in the longer one. In our study we show that the translation of the human MC3R protein starts at the evolutionary conserved ATG codon which results in a shorter protein than previously assumed.

The polymorphism T6K is not located in the coding region of the human MC3R and has no influence on translation initiation which makes an impact on body weight unlikely.