Figure 3

Experimentally determined increase in α-MSH affinity by mutations in segment S4. Experimentally determined increase in affinity (pK) afforded by mutations N240G/M241L/I245V (indicated in green), and V253I/V255F/V256L (indicated in blue) (i.e., exchanging amino acid residues in the MC₄ receptor with the corresponding residues in the MC₁ receptor), and swapping intracellular loop 3 (IL3, indicated in dark yellow) in the MC₄ receptor with the corresponding in the MC₁ receptor. Also shown is the increase in affinity for the whole S4 segment (S4, indicated in pale yellow). Significance (nonparametric Wilcoxon Rank Sum statistical test [29]) denoted as indicated in the legend to Fig. 2.