THE 2.0 ANGSTROM CRYSTAL-STRUCTURE OF A HETEROTRIMERIC G-PROTEIN

The structure of a heterotrimeric G protein reveals the mechanism of t he nucleotide-dependent engagement of the alpha and beta gamma subunit s that regulates their interaction with receptor and effector molecule s. The interaction involves two distinct interfaces and dramatically a lters the conformation of the alpha but not of the beta gamma subunits . The location of the known sites for post-translational modification and receptor coupling suggest a plausible orientation with respect to the membrane surface and an activated heptahelical receptor.