Table 2.
Ligand binding and agonist-stimulated cAMP response of the WT and naturally occurring mutant hMC4Rs
| hMC4R | n | NDP-MSH binding | NDP-MSH-stimulated cAMP | n | AgRP binding IC50 (nM) | ||
|---|---|---|---|---|---|---|---|
| IC50 (nM) | Bmax (% WT) | EC50 (nM) | Rmax (% WT) | ||||
| WT | 9 | 13.16 ± 1.91 | 100 | 1.22 ± 0.19 | 100 | 4 | 4.16 ± 0.70 |
| R7C | 3 | 12.32 ± 0.99 | 99 ± 3 | 3.06 ± 0.06‡ | 102 ± 4 | 3 | 3.60 ± 0.36 |
| C84R | 3 | N/A | N/A | 8.73 ± 0.43‡ | 20 ± 1‡ | 3 | N/A |
| S127L | 3 | 14.99 ± 2.57 | 32 ± 2‡ | 1.78 ± 1.07 | 57 ± 3† | 3 | 18.25 ± 4.85‡ |
| S136F | 3 | 3.72 ± 0.77† | 101 ± 9 | 7.61 ± 0.23‡ | 11 ± 1‡ | 3 | 0.41 ± 0.05‡ |
| W174C | 3 | N/A | N/A | 14.80 ± 0.35‡ | 31 ± 1‡ | 3 | N/A |
| A219V | 3 | 20.11 ± 3.55 | 40 ± 3† | 24.19 ± 1.27‡ | 56 ± 3† | 3 | 12.83 ± 0.33† |
| P230L | 3 | 12.82 ± 1.31 | 62 ± 6* | 12.31 ± 0.67‡ | 122 ± 4* | 3 | 4.01 ± 1.09 |
| F261S | 3 | 2.49 ± 0.94† | 15 ± 1‡ | 1.48 ± 0.12 | 49 ± 1‡ | 3 | 1.33 ± 0.59* |
| I317V | 3 | 18.44 ± 2.53 | 94 ± 8 | 3.60 ± 0.14‡ | 100 ± 2 | 3 | 3.56 ± 0.19 |
| L325F | 3 | 5.12 ± 0.42† | 92 ± 6 | 2.62 ± 0.06† | 94 ± 4 | 3 | 6.17 ± 0.12 |
*
Significantly different from WT hMC4R, P < 0.05.
†
Significantly different from WT hMC4R, P < 0.01.
‡
Significantly different from WT hMC4R, P < 0.001.
Data shown are the mean ± S.E.M. of the number of experiments indicated. The Rmax of WT hMC4R was 948 ± 86 pmol cAMP/106 cells (mean ± S.E.M. of nine experiments). IC50 is the concentration of NDP-MSH that is needed to cause 50% inhibition in the binding assay. EC50 is the concentration of NDP-MSH that results in 50% stimulation of the maximal response.