Fig. 4.

Theoretical model of MC4R dimer activation. R represents the MC4R monomer, RR the MC4R dimer and RR* the activated state of the dimer. A In case of MC4R-WT homo-dimerization or dimerization of WT-MC4R with a mutant MC4R that does not cause a dominant negative effect ligand stimulation result in a shift of the equilibrium to the activated state RR* that allows efficient coupling to the Gs/adenylyl cyclase pathway. B In case of MC4R dimerization with a dominant negative mutant receptor (Rm) the receptor dimer is trapped in the inactive state in which a shift to the activated state is alterated.