The complex between the activated β2-AR and a heterotrimeric G protein. (A) When the β2-AR (green) binds a receptor agonist, the cytoplasmic face of the receptor forms an interaction surface with the Gα subunit of a heterotrimeric G protein. (B) The interaction with the activated receptor leads to a substantial conformational change in the Gα protein, in which the GTP binding site is opened, enabling nucleotide exchange. In this figure, Gα in its GTP form is shown in red and in its receptor-bound form is shown in blue.
[Drawn from 3SN6.pdb and 1AZT.pdb.]