FIGURE 6.

Olfr57 is activated by monoterpenes. (A) Olfr57 was expressed in HEK293T cells under conditions of maximal surface expression (Figure 4) along with two luciferase reporter constructs, Firefly and Renilla. Cells were incubated with the identified compounds to elicit an activated cAMP response indicated by an increase in the ratio of Firefly to Renilla. A representative activation graph is shown for 2 concentrations of compounds (300 and 3,000 μM) with *p > 0.05 deemed significant activation over baseline. To confirm specificity, the identified ligands were also screened against another OR (Olfr16, Olfr99, or Olfr78) at the highest dose. No responses were detected. The numbers shown in (A) correspond to the chemical names listed in (B). (B) All 5 monoterpene agonists were tested at multiple concentrations to generate a dose-response curve and to calculate the EC₅₀ values. Activation graphs are plotted as means ± SEM. (C) The chemical structures of all activators and some notable ‘non-activators’ are shown relative to their potency. The inner circle indicates the best activators as determined by their EC₅₀ values, while those compounds in the middle ring represent the remaining activators. Those compounds that are structurally similar but did not elicit a response are shown in the outermost ring. (Agonists: 1 – camphor; 2 – borneol; 3 – eucalyptol; 4 – fenchyl alcohol; 5 – fenchone. Notable non-activators: 6 – camphene; 7 – pinene; 8 – thujone; 9 – camphorsulfonic acid; 10 – norcamphor).