Figure 6.

Differences in the dynamic character of rhodopsin and β₂AR.

(A) The β₂AR is conformationally dynamic in the inactive state, and agonists induce further dynamics to varying degree. The active state is only stabilized in the presence of either G protein or a G protein mimetic. Inverse agonists increase the rate of exchange between ionic lock intact (S1) and broken (S2) states, thereby reducing the lifetime of both states.

(B) Dark rhodopsin is minimally dynamic due to the highly efficacious inverse agonist 11-cis-retinal. Illumination by light induces a conformational change to Metarhodopsin II and an accompanying outward displacement of TM6. This active state is then recognized by the G protein transducin (G_t).