A heterotrimeric G protein. (A) A ribbon diagram shows the relation between the three subunits. In this complex, the α subunit (gray and purple) is bound to GDP. Notice that GDP is bound in a pocket close to the surface at which the α subunit interacts with the βγ dimer. (B) A schematic representation of the heterotrimeric G protein.

[Drawn from 1GOT.pdb.]