Table 1.
Functional characterization of S136F MC4R in comparison to wild type receptor, the wild type receptor co-expressed with the S136F mutant and the wild type receptor co-expressed with MCT8 as negative control based on ligand-induced cAMP production and cell surface expressiona
| NDP-α-MSH |
α-MSH |
β-MSH |
Cell surface expression, % wild type | ||||
|---|---|---|---|---|---|---|---|
| EC50, nmol/l | Emax/Emax wild type | EC50, nmol/l | Emax/Emax wild type | EC50, nmol/l | Emax/Emax wild type | ||
| MC4R wild type | 0.59 ± 0.04 | 1 | 5.67 ± 3.00 | 1 | 6.21 ± 4.35 | 1 | 99.4 ± 17 |
| S136F | * | 0.14 ± 0.01 | * | 0.18 ± 0.02 | * | 0.23 ± 0.02 | 86.8 ± 12 |
| Wild type + S136F | 2.13 ± 1.04 | 0.77 ± 0.11 | 13.37 ± 6.93 | 0.76 ± 0.08 | 92.18 ± 51.7 | 1.09 ± 0.26 | 102 ± 17 |
| Wild type + MCT8 | 0.44 ± 0.08 | 0.87 ± 0.21 | 5.29 ± ±2.51 | 0.80 ± 0.05 | 16.86 ± 11.0 | 0.92 ± 0.04 | 104 ± 10 |
a
EC50 and Emax values were obtained using the computer program GraphPadPrism. Data represent means ± S.E.M derived from at least three independent experiments each performed in duplicates in cAMP assays or hexplicates in case of cell surface ELISA. Range of wild type Emax was between 1,807 and 5,706 cpm. Optical density of wild type MC4R in ELISA studies ranged between 0.53 and 0.86.
*
Not determinable due to low maximal stimulation.